School Science Lessons
Topic 7 Chemical substances, chemical properties, chemical changes, suspensions, solutions, colloids
Updated: 2009-08-29
Please send comments to: J.Elfick@uq.edu.au
See: Interesting websites
Table of contents
7.1.0 Chemical changes and physical changes
7.2.0 Pure substances and impure substances
7.2.1 Classify substances, pure substances, mixtures, solutions
7.2.2 Elements and chemical reactions
7.2.3 Silicon compounds, glass
7.3.0 Metals and non-metals
7.4.0 Melting point, m.p. of solids
7.5.0 Boiling point, b.p. of liquids
7.6.0 Suspensions and precipitates
7.7.0 Solutions, solubility equilibrium, solubility rules
7.8.0 Colloids, sols, emulsions, gels, aerosols, foams, types of colloids
7.9.0 Chemistry terminology
7.10.0 Prefixes and suffixes
19.2.0 Composition of food, vitamins, minerals
7.1.0 Chemical changes and physical changes
7.1.1 Chemical changes, burn magnesium
7.1.1.1 Chemical changes, burn steel wool, combustion of iron wool
7.1.2 Chemical changes, heat organic substances
7.1.3 Chemical changes, heat metals in chlorine
7.1.4 Physical changes, magnetize and demagnetize iron wire
7.1.5 Physical changes, prepare forms of sulfur, allotropes of sulfur
3.70 Reactions between two elements, iron with sulfur
7.1.5 Physical changes, prepare forms of sulfur, allotropes of sulfur
7.1.5.1 Prepare monoclinic sulfur from powdered sulfur (flowers of sulfur)
7.1.5.2 Prepare monoclinic crystals from roll sulfur
7.1.5.3 Prepare plastic sulfur then rhombic sulfur
12.18.1 Prepare forms of sulfur
7.3.0 Metals and non-metals
7.3.1 Properties of metals
7.3.2 Properties of non-metals
2.43 metals (Primary)
12.11.3 Flame tests to identify metals and their compounds
12.11.3.1 Borax bead test to identify metals in metallic salts and minerals
7.4.0 Melting point, m. p., of solids
3.2 Melting point of naphthalene
3.3 Melting point of naphthalene with a capillary tube
3.4 Impurities affect the melting point of a substance
7.4.1 Melting point and cooling curve of stearic acid
7.4.2 Melting point of substances
7.4.3 Melting point of ice and freezing point, f.p., of water, antifreeze
7.4.3.1 Temperature at which ice melts
7.4.3.2 Temperature at which ice and salt mixture freezes
7.4.3.3 Lift ice cube with match stick
2.9 Melt substances (Primary)
7.5.0 Boiling point, b.p. of liquids
3.5 Boiling point of water
3.5.1 Boiling point of sodium chloride solution
3.6 Boiling point of inflammable liquids
3.7 Volatility of liquids
3.8 Pressure affects the boiling point
7.5.0.1 Elevation of boiling points, ebullioscopic constant, kB
7.5.3 Boiling point of mixture of two liquids, water and alcohol
7.5.4 Boiling points of inflammable liquids, alcohol
7.5.4.1 Boiling points of inflammable liquids, acetone
13.7.13 Simulated boiling
7.2.2 Elements and chemical reactions
Descriptions of common elements
[The properties listed below are based on information from IUPAC, International Union of Pure and Applied Chemistry.]
7.2.2.1 Al Aluminium | Reactions 12.1
7.2.2.2 Sb Antimony | Reactions 12.2.1
7.2.2.3 Ar Argon
7.2.2.4 As Arsenic | Reactions 12.2.2
7.2.2.5 Ba Barium | Reactions 12.2.3
7.2.2.6 Bi Bismuth | Reactions 12.2.4
7.2.2.7 B Boron
7.2.2.8 Br Bromine | Reactions 12.19.9
7.2.2.9 Cd Cadmium | Reactions 12.3.1
7.2.2.10 Ca Calcium | Reactions 12.4.1
7.2.2.11 C Carbon | Reactions 16.1.0
7.2.2.12 Cl Chlorine | Reactions 12.19.8
7.2.2.13 Cr Chromium | Reactions 12.5
7.2.2.14 Co Cobalt | Reactions 12.6
7.2.2.15 Cu Copper | Reactions 12.7
7.2.2.16 F Fluorine | Reactions 12.19.7
7.2.2.17 Au Gold
7.2.2.18 He Helium
7.2.2.19 H Hydrogen gas
7.2.2.20 I Iodine | Reactions 12.19.6
7.2.2.21 Fe Iron | Reactions 12.8
7.2.2.22 Kr Krypton
7.2.2.23 Pb Lead | Reactions 12.9
7.2.2.23a Lead paint
7.2.2.23b Tetraethyl lead
7.2.2.24 Li Lithium | Reactions 12.9A.
7.2.2.25 Mg Magnesium | Reactions 12.10.1
7.2.2.26 Mn Manganese | Reactions 12.17
7.2.2.27 Hg Mercury | Reactions 12.17a.1
7.2.2.27.1 Mercury (I) nitrate
Mercury and dental amalgam
7.2.2.28 Mo Molybdenum
7.2.2.29 Ne Neon
7.2.2.30 Ni Nickel | Reactions 12.17b.1
7.2.2.31 N Nitrogen | Reactions 12.11
12.11.1 Reactions of the nitrites, NO2-
12.11.2 Reactions of the nitrates, NO3-
12.11.3 Ammonia and the ammonium ion, NH3,NH4+
7.2.2.32 O oxygen gas | Reactions 12.12 | Ozone, O3 3.50
7.2.2.33 P Phosphorus | Reactions 12.13
7.2.2.33.1 Phosphorescence
7.2.2.33.2 Detergent phosphates
7.2.2.34 Pt Platinum
7.2.2.35 K Potassium | Reactions 12.14
7.2.2.36 Ra Radium
7.2.2.37 Rn Radon
7.2.2.38 Se Selenium
7.2.2.39 Si Silicon | Reactions 12.15
7.2.2.39.1 Solar panel
7.2.2.40 Ag Silver | Reactions 12.16
7.2.2.41 Na Sodium | Reactions 3.73
7.2.2.42 Sr Strontium | Reactions 12.16a.1
7.2.2.43 S Sulfur | Reactions 12.18
7.2.2.44 Sn Tin | Reactions 12.20
7.2.2.45 W Tungsten
7.2.2.46 U Uranium
7.2.2.47 Xe Xenon
7.2.2.48 Zn Zinc | Reactions 12.21
7.2.2.49 Zr, Zirconium
7.1.0 Chemical changes and physical changes
1. In a chemical change, one or more substances changes into one or more new substances, e.g. hydrogen gas combines with oxygen gas to form water. The product(s) has properties from the reactants. For example burning wood forms black ash containing carbon, white ash containing mineral salts, carbon dioxide gas and water vapour. New substances form and the change cannot be reversed. The arrow symbol " --->" represents this type of change.
2H2 (g) + O2 (g) ---> 2H2O (l)
2. In a physical change, the properties of a substance change, but the substance is still the same. The change can be reversed. The physical properties of water change when water freezes to ice. However, the ice is composed of water molecules and the change can be reversed. When electricity passes through a tungsten filament in a light bulb, the filament becomes hot and emits light. It is still tungsten. When you turn off the light, the tungsten filament is the same as before. Physical or chemical changes may be fast or slow, e.g. hammering iron, wearing away rock by wind erosion, an explosion when hydrogen gas burns, rusting of iron.
Classify common examples of changes into chemical change or physical change.
Do the following activities and in each case say whether it is a chemical or physical change: 1. Light a match. (chemical change) 2. Turn on the light. (physical change)
3. Let a nail rust. (a chemical change takes place in air causing a gain in weight) 4. Chew food. (physical change for biting and masticating, and a chemical change for the reactions of starch with salivary amylase)
7.1.1 Chemical changes, burn magnesium
Put a piece of magnesium ribbon in a crucible. Weigh the crucible and lid and magnesium ribbon. Burn the magnesium in the nearly closed crucible so that the ash is not lost. Weigh the crucible and lid and ash. The weight of the ash is greater than the weight of the magnesium. The reaction forms a new substance, magnesium oxide. Mg, density 1.74 g / cm3 oxidizes to MgO, density 3.58 g / cm3, so when oxygen attaches to magnesium the volume decreases because of the strength of the (Mg2+-- O2-) bond.
2Mg (s) + O2 (g) ---> 2MgO (s)
7.1.1.1 Chemical changes, burn steel wool, combustion of iron wool
Cover the end of a wooden ruler with aluminium foil then note where the ruler balances as a first order lever, see-saw, over a fulcrum. Put the ruler balance on a sink bench. Put 5 g loose steel wool on the aluminium foil end of the ruler then put a weight on the other end of the ruler so that this end is just down. Heat the steel wool with a Bunsen burner flame. The steel wool glows and its side of the balance moves down as the iron becomes iron oxide.
7.1.2 Chemical changes, heat organic substances
1. Often one product is black because carbon forms. Heat the following substances in a hard glass or Pyrex test-tube. Observe any decomposition of the substances. When smoke appears, leave the test-tube to cool. No chemical change occurs when you heat charcoal. For the following substances, a chemical change occurs and the residue in the test-tube is carbon:
1.1 Wood or saw dust, note the brown substances that stick to the sides of the test-tube and the black substance that remain in the bottom, 1.2 sugar, 1.3 bread, 1.4 fruit, 1.5 fat or oil, 1.6 starch or potato or rice, 1.7 paper, 1.8 wool or hair or nail clippings, 1.9 meat.
2. Put a small piece of wood in a Pyrex test-tube. Heat the tube gently then more strongly. The wood decomposes into a black solid and brown liquids and vapours. Stop heating when you see no more dense smoke. Let the test-tube and observe the substances on the sides of the tube. Put any remaining solid substance in another clean test-tube. Heat it gently and then more strongly. You produce no further liquids or gases from this substance. Compare the black substance with a sample of the original wood for colour and can be bent. Place the end of each in a Bunsen flame for a few seconds. Remove and observe them. The black substance does not decompose or burn with a flame but glows red-hot. The black substance is charcoal, i.e. carbon. Heat small quantities of sugar, paper, wool, meat and compare the residue in the test-tubes with the original substance.
7.1.3 Chemical changes, heat metals in chlorine
Be Careful! Chlorine is poisonous. These experiment may not be allowed on your school system. D the experiments in a fume cupboard.
1. Use tongs to heat steel wool in a Bunsen burner flame, then place it in a test-tube containing chlorine gas. Observe whether any heat is given out during the reaction. Iron and chlorine react together to form a brown yellow iron chloride.
2. Using a wire gauze, scrape some powdered antimony from a lump of the element so that it falls into a test-tube of chlorine. The sparks and burning show that a chemical change is taking place. The new white substance is antimony chloride.
7.1.4 Physical changes, magnetize and demagnetize iron wire
When physical changes occur, no new substance forms.
Pull a thick iron wire (fencing wire) through iron filings. The iron does not attract the iron filings. Magnetize the iron by stroking it with a bar magnet. Hold the iron wire in the iron filings. The iron wire now attracts the iron filings. A physical change has occurred. Hammer the iron wire. The iron wire cannot attract the iron filings so strongly. The physical change has been reversed.
7.1.5 Physical changes, prepare forms of sulfur, allotropes of sulfur
Sulfur is a non-metallic element that occurs in several allotropic forms. Allotropes are variations of the same element with bonding and crystal structure. Sulfur occurs in three forms: Form 1: Rhombic sulfur is a light yellow powder. At 100oC it changes to: Form 2: Monoclinic sulfur with a deeper colour. The monoclinic and rhombic forms differ in the arrangement of the S8 molecules. At 160oC, it melts to form a sticky dark brown liquid that can be cooled quickly to form red brown plastic sulfur. Form 3: Plastic sulfur contains long chains of S atoms.
Put sulfur powder in a test-tube. Heat the sulfur extremely gently until it slowly melts to a golden yellow liquid. Continue to heat more strongly until a red gas appears above the liquid. Leave the test-tube to cool. Sulfur forms deposits on the sides of the tube and in the bottom of the tube.
7.1.5.1 Prepare monoclinic sulfur from powdered sulfur (flowers of sulfur)
Monoclinic sulfur has a deep yellow colour, m.p. = 119oC, and density = 1.96.
Heat powdered sulfur extremely gently in an evaporating dish. The sulfur changes to liquid. Add more powdered sulfur. The colour should stay pale yellow. If the sulfur turns dark, you have overheated it. Repeat the experiment with gentler heating. Leave the sulfur to cool, without moving the evaporating dish. Monoclinic crystals form between 96oC and 114oC. After a thin crust forms, punch two holes through the crust with a nail. Pour out the hot sulfur through one hole. Remove the crust and note the monoclinic sulfur crystals on the underside.
7.1.5.2 Prepare monoclinic crystals from roll sulfur
Put small pieces of roll sulfur in a test-tube. Heat the test-tube extremely gently until the sulfur melts, m.p. = 114.5oC. The liquid is lemon yellow. Pour the liquid sulfur into a folded filter paper. A crust forms on the surface. When the crust forms, open the filter paper. Needle-shaped crystals remain on the filter paper.
7.1.5.3 Prepare plastic sulfur then rhombic sulfur
Rhombic sulfur is a yellow powder, m.p. = 119oC, and density = 1.96.
Put roll sulfur in a test-tube. Heat the test-tube slowly. Note the changes at the melting point from a light yellow colour to a red liquid. The red brown sulfur becomes viscous and it does not flow out if you hold the test-tube upside down. Continue heating until the reaction forms a brown black liquid. Continue to heat until the sulfur boils at 445oC. BE CAREFUL! Pour the melted sulfur into a beaker of cold water. The reaction forms strands of amorphous sulfur. When the strands are cool, twist them to show that they are elastic. Later the sulfur hardens because it returns to the rhombic form of sulfur as a ring of eight sulfur atoms in tiny crystals. When heated, the ring breaks open to form long chains.
7.2.0 Pure substances and impure substances
1. Pure substances contains only one kind of atom or molecule, e.g. iron, sulfur, water, and oxygen. It can consist of elements or compounds. Elements may be metals or non-metals.
Impure substances contain more than one kind of substance. They may be mixtures, e.g. sulfur and iron filings, or air, or solutions, e.g. sea water. Mixtures in the home include flour, milk, ink, face powder, and tooth paste. Solutions in the home include fruit drinks (although often an emulsion) lemonade, mineral water. You make toffee or candy with a supersaturated sugar solution. French polish is shellac with methylated spirit solution.
2. Most compounds are ionic, e.g. common salt (NaCl) or covalent molecular, e.g. CO2 or H2O, or covalent network, e.g. SiO2. Each compound has a name or formula. Compounds with names ending in "-ide" contains two elements. Compounds with names ending in "-ate" or "-ite" contain oxygen, with more oxygen in the "-ate". Compounds found at home include water, sugar, starch, baking soda, cream of tartar (potassium hydrogen tartrate)
3. Inorganic chemistry is the chemistry of the elements and their compounds, including CO2, CO and carbonates. Organic chemistry is the chemistry of carbon and its compounds.
7.2.1 Classify substances, pure substances, mixtures, solutions
1. Describe materials at home and in the classroom from their observable physical properties: 1. colour (shiny or dull) 2. opaque (or transparent or translucent) 3. shape (or shape of crystals) 4. odour, 5. state (solid, liquid, gas) (change in state when heated or cooled) 6. mass (heavy, light) more dense or less dense than water, 7. taste (sweet, sour, bitter, other) 8. can be magnetized, 9. can conduct heat, 10. can conduct electricity, 11. can absorb liquids, 12. flexibility (can be bent, fragile). Describe the materials used to make items in the classroom and in the home.
2. Describe materials as pure substance, or solution or mixture
If a solution is a homogeneous mixture of a liquid with a gas or a solid, then you would not classify air as a solution, nor brass as an alloy, unless they were in liquid form. However, if a solution is a homogeneous mixture of two or more components in a single phase, and usually refers to a solution in water (aqueous solution) then perhaps you can classify air and solid alloys as solutions.
Substances Pure substance Solution Mixture
1. Ice floats in water + . .
2. Tincture of iodine . + .
3. Washing powder . . +
4. Tap water . + .
5. Air . + or +
6. Brass alloys . + or +
7.2.2 Elements and compounds, descriptions of common elements
Matter is composed of atoms which, in turn, contain protons and neutrons in a nucleus, and electrons outside the nucleus. The number of positively charged protons is equal to the number of negatively charged electrons in a neutral atom, and determines all the chemical properties of an atom.
An element is a substance in which all atoms have the same number of protons. Atoms of an element may contain different numbers of neutrons, and are known as isotopes. Every element is assigned a unique chemical symbol.
The atomic mass of an atom is arbitrarily defined relative to the mass of the isotope carbon.
Pairs of atoms may be bound together by the sharing of electrons between them in a covalent bond.
Two or more atoms bound together by one or more covalent bonds form a molecule, with definite size, shape and arrangement of bonds.
An atom or group of atoms covalently bound together may gain or lose one or more electrons to form ions.
Ionic bonding occurs when positive and negative ions are held together in a crystal lattice by electrostatic forces.
When chemical bonds, whether ionic or covalent, are formed between different elements, a chemical compound is obtained, which can be represented by a chemical formula. Forces weaker than covalent bonding exist between molecules.
The structure of  metals involves positive ions embedded in a sea of electrons. Materials may be elements, compounds or mixtures.
In compounds containing carbon-hydrogen bonds, organic compounds, the carbon atoms bind to one another through single, double or triple covalent bonds to form chains or rings.
1. An element is a substance that cannot be broken down into simpler substances by a chemical change.
At room temperature and atmospheric pressure, eleven elements are gases: H2, He, N2, O2, F2, Ne, Cl2, Ar, Kr, Xe, Rn.
Two elements are liquids at room temperature: Hg and Br.
Reactive elements have atoms weakly bound together and have electrons available for bonding, e.g. F.
2. A compound is a substance composed of two or more elements that are chemically united in fixed proportion. Compounds can be broken down to simple substances. For example the compound carbon dioxide can decompose to carbon and oxygen gas. [Comment: You can breakdown the carbon dioxide but you are likely to end with carbon and an oxide of something else.]
3. The periodic table has the elements arranged in groups. Some periodic tables using 1a, 2a to 0, suggest there are 18 groups. Other versions have only 8 or 9 groups. Elements in the same group in the periodic table have similar chemical properties because they have the same number of electrons in their outer shells. (This is not true if you group the transition elements together in the table.)
4. Group 1a elements include the alkali metals (Li, Na, K, Rb, Cs, Fr). The alkali metals are all soft, shiny and metallic when cut. They react easily with water, have low melting points and densities, and are good conductors of electricity. They all have one valence electron that they lose easily to form ions. (Some versions of the periodic table include hydrogen in group 1a also. However, today considering hydrogen separately is more usual as it has few of the properties of the alkali metals.)
5. Group 2a elements are the alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra). They are harder and have higher melting points and boiling points than the alkali metals. They easily lose two electrons to form ions, e.g. Mg2+.
6. Group 0 elements are the noble gases (inert gases or rare gases) He, Ne, Ar, Kr, Xe, Rn-222. They are colourless, odourless, monatomic gases and they form very few compounds. Unreactive elements have atoms joined by strong bonds, e.g. diamond. Elements that exist as separate small molecules have low boiling points and melting points, e.g. He, O2.
Observe samples of iron, carbon, copper, magnesium, mercury in a thermometer and solid sticks of sulfur. Classify each of them according to the following characteristics: 1. Is it a hard solid, a liquid or a gas at room temperature? 2. If the element is a solid, does it shine and have a lustre? If necessary scratch its surface. 3. Can the element be bent or twisted or does it fracture easily? You may require pliers or a vice to do this. 4. Will the element conduct electricity? Place the element between two electrical contacts in a circuit.
7.2.2.1 Aluminium, Al, is a silver white metal, with mechanical strength and forms protective oxide layer in air that prevents further oxidation, available as foil, sheet, wire and powder (1396) (FLAM, not safe for school use) extracted from the ore bauxite (Al2O3) 8% of the earth's crust so most abundant element in Earth's crust, extracted by electrolysis of bauxite dissolved in cryolite, protected by layer of oxide that can be thickened if an anode in electrolytic cell, i.e. anodized then can be coloured, malleable, low density, used in "Alfoil" cooking foil, drink-cans, saucepans, cars, duralumin, alloy of Al + Cu, Mg, for aircraft bodies and struts. Aluminium ions form alums that are complex hydrated metal sulfates that contain 12 or 24 H2O, e.g. aluminium potassium sulfate Al2(SO4)3.K2(SO4).24H2O, alum, potassium alum, used as mordants in dyeing. Reacts with dilute HCl or H2SO4 to form H2 and metal ion, with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, with steam to give the oxide and hydrogen gas. Heated powder forms oxide. Excess aluminium may cause short term toxicity, e.g. aluminium sulfate in drinking water, corroded cooking utensils used for cooking acidic foods, alum treatment of water. In 1990, The International Union of Pure and Applied Chemistry (IUPAC) confirmed the use of the spelling "aluminium" but people in the U.S.A. are accustomed to use the spelling "aluminum".
Atomic number: 13 | Relative atomic mass: 26.9815 | r.d. 2.70 | m.p.: 660oC | b.p.: 2470oC | Specific heat capacity: 900 J kg-1 K-1 | E 173
7.2.2.2 Antimony, Sb, blue white metal, burns in air but no reaction with water or dilute acids, attached by halogens and oxidizing acids, poor conductor of heat and electricity, used in alloys for cable covers, pewter and lead cell accumulator plates, donor impurity in silicon chips, radioactive isotopes to produce neutrons, from stibnite Sb2S3,
Atomic number: 51 | Relative atomic mass: 121.75 | r.d. 6.68 | m.p.: 630.5oC | b.p.: 1750oC | Specific heat capacity: 210 J kg-1 K-1
7.2.2.3 Argon, Ar, is a non-metal inert colourless odourless noble gas at room temperature and pressure Ar, 0.93% of the air, extracted from liquid air. Chemically inactive, no compounds, monatomic gaseous element, used in incandescent light bulbs, fluorescent tubes and lasers, and for welding. Most abundant noble gas, 0.9% of atmosphere by volume.
Atomic number: 18 | Relative atomic mass: 39.948 | r.d. 1.40 (87 K) | m.p.: -189oC | b.p.: -186oC | Specific heat capacity: 519 J kg-1 K-1
7.2.2.4 Arsenic, As, is a metalloid (or non-metal) poisonous found free and in combined many minerals, three allotropes are yellow, black and main allotrope grey arsenic sublimes at 613oC, and n-type dopant of silicon semiconductors, hardens lead alloys. White arsenic, arsenic (III) oxide, As4O6, common in sulfide ore deposits, very toxic, rodenticide. Salvarsan, Erlich's compound 606 (arsphenamine) was the first drug to treat syphilis. The most toxic form of arsenic is As3+ which reacts with enzymes in the body. Agricultural use of arsenic kills plants before concentration is toxic enough for humans.
Atomic number: 33 | Relative atomic mass: 74.9216 | r.d. 5.72 | m.p.: 814oC | b.p.: 613oC (sublimes) | Specific heat capacity: 326 J kg-1 K-1
7.2.2.5 Barium, Ba, is an alkaline earth metal, brittle and expensive, used to absorb high energy particles, in minerals barytes, BaSO4 and witherite, BaCO3, forms poisonous compounds, oxidizes in air and reacts with water and ethanol. Barium sulfate is used for a contrast medium for X-ray examination of intestines.
Atomic number: 56 | Relative atomic mass: 137.33 | r.d. 3.51 | m.p.: 725oC | b.p.: 1640oC | Specific heat capacity: 192 J kg-1 K-1
7.2.2.6 Bismuth, Bi, white metallic crystals, from bismuthinite mineral Bi2S3 but rare in the earth, very diamagnetic, low thermal conductivity, high electrical resistance, burns in air with blue flame, used in low melting point alloys for fire safety equipment, thermocouples, magnetic flux measurement, liquid metal coolant for nuclear reactors, cosmetics and medicines, e.g. bismuth carbonate for peptic ulcers.
Atomic number: 83 | Relative atomic mass: 208.98 | r.d. 9.78 | m.p.: 271.3oC | b.p.: 1560oC | Specific heat capacity: 123 J kg-1 K-1
7.2.2.7 Boron, B, is a non-metal or metalloid, yellow brown network solid, brown amorphous form and black metallic form, has metallic lustre, very hard (9.3 Mohs' scale) and strong semiconductor, found in minerals, e.g. tourmaline, and associated with volcanic activity as borates, used in control rods for nuclear reactors and in green flares.
Atomic number: 5 | Relative atomic mass: 10.81 | r.d. 2.34 (amorphous form) | m.p.: 2300oC | b.p.: 2550oC | Specific heat capacity: 123 X 103 J kg-1 K-1
7.2.2.8 Bromine, Br is a red-brown, fuming, volatile, poisonous, non-metal liquid between 19oC and 27oC, suffocation odour, vapour irritates eyes and throat, strong oxidizing agent, used for many chemical compounds including "anti-knock" petrol additive, 1,2-dibromoethane, scarce element extracted from sea water, 65 ppm, as bromide ion. Silver bromide import for photography. Bromoform, tribromomethane, CHBr3 used to separate minerals, bromothymol blue indicator, pH 6.0 to 7.6, potassium bromide formerly used as sedative and was supposed top be put in army tea to quieten soldiers' sexual urges, bromochlorodifluoromethane, CHBrClF2, low toxic fire extinguisher for confined spaces. The fat soluble fire retardant PBDE, polybromyldiphenyl ether, in the deca, octa and penta forms has been detected in mothers' milk, fish and the environment. (POISON COR 1744) Br2 (3.6% bromine) r.d. 3.12 gm cm-3, b.p. 58.7oC, solidifies -7oC (swimming pool sanitation, products from bromine, e.g. BCDMH)
Atomic number: 35 | Relative atomic mass: 79.904 | r.d. 3.12 | m.p.: -7.2oC | b.p.: 58.78oC | Specific heat capacity: 448 J kg-1 K-1
7.2.2.9 Cadmium, Cd is a soft blue white metal, toxic at low concentrations, a rare element that occurs in the mineral sphalerite, zinc sulfide, is used for cadmium plating against corrosion, in nuclear reactors and in films sensitive to ultraviolet light, reference voltage in a Western Standard cadmium cell, Cd/ Zn alloys in low melting point solders and aluminium solders, Ni-Cd batteries (Nicad) phosphorescent coating of TV tubes. Cadmium looks like zinc but make a crackling sound like tin when bent. Oysters in polluted water make accumulate cadmium. In former Communist countries that practised collection of "night soil" as a fertilizer, cadmium pollution of low lying agricultural soil has occurred. Cadmium is toxic because it competes with Zn and Ca. Large concentrations cause painful bone ailments. and bone porosity. Our body gets rid of excess Cd by deposition in the kidneys and liver.
Atomic number: 48 | Relative atomic mass: 112.41 | r.d. 8.64 | m.p.: 321oC | b.p.: 765oC | Specific heat capacity: 230 J kg-1 K-1
7.2.2.10 Calcium, Ca [FLAM 1401] is an alkaline earth metal, granules in liquid paraffin. Reacts with dilute HCl or H2SO4 to form H2 and metal ion, occurs mainly as carbonates, e.g. calcium carbonate, CaCO3, gypsum, CaSO4.2H2O, 3.5% of the earth's crust, essential nutrient element for bones, teeth and muscle contraction in animals and middle lamella of plan cells, extracted by electrolysis of fused calcium chloride. Reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide, SO2, or nitrogen dioxide, NO2. Reacts with cold water and reacts with air to form peroxides. Calcium is the most abundant mineral, and the fifth most abundant element mostly in bone tissue. About 1% is used in nerve transmission, muscle contraction and other functions
Atomic number: 20 | Relative atomic mass: 40.08 | r.d. 1.54 g cm-3| m.p.: 850oC | b.p.: 1487oC | Specific heat capacity: 653 J kg-1 K-1
7.2.2.11 Carbon, C, charcoal, lump, powder, lamp black, acetylene black, wood charcoal, activated carbon / charcoal (coke is left when coal is heated without air, for blowpipe work, charcoal may contain wood ash mainly potassium carbonate, soft "lead" pencils) non-metal network solid, has two natural crystalline forms, diamond and graphite. Diamond has strong covalent bonds in three dimensions to four other atoms, is the hardest substance known, transparent, brittle and non-conductor. It is used as gemstones, diamond dust abrasives and rock boring tools. Graphite has covalent bonds that are strong in one dimension but weak between layers, has density 3.5, and is soft and black. slippery with lustre and is good conductor only along its layers, available as graphite mineral, graphite powder and colloidal graphite "Aquadag", occurs as mineral deposits or is made from petroleum, used in the "lead" of soft "B" pencils, as a lubricant and electrical conductor, in cast iron and as coke for heating oildag, plumbago, "black lead", black-lead, graphite.
Atomic number: 6 | Relative atomic mass: 12.011 | r.d. 2.25 (graphite) | m.p.: 3730oC (sublimes) | b.p.: 4830oC | Specific heat capacity 711 J kg-1 K-1 (graphite) | 519 J kg-1K-1 (diamond)
7.2.2.12 Chlorine, Cl, is a non-metal green yellow, poisonous with irritating smell gas at room temperature and pressure Cl2, strong oxidizing agent and used in bleaching powder, disinfectant, 1.9% of sea water, produced from electrolysis of brine, used to make many organic products, e.g. chloroform trichloromethane CHCl3, chlorofluorocarbon refrigerant and aerosol now phased out because of damage to the ozone layer in atmosphere, chlorophenol red pH 4.8 to 6.4 indicator, chloral hydrate sedative, chloric (V) acid, HClO3 and its salts chlorates (V) powerful oxidizing agents and sometimes explosives. Chloride is a constituent of gastric juice which is about 0.03 M HCl. It is also used for controlling the transport of oxygen and carbon dioxide haemoglobin in red blood cells. Adults require a daily minimum, of 750 mg of chloride.
This gas is very toxic. It can react to cause fires or explosions upon contact with turpentine, ether, ammonia gas, illuminating gas, hydrocarbon, hydrogen gas and powdered metals. Dissolves readily in water forming highly corrosive solution. Do not prepare chlorine in open room. Use fume cupboard. Direct combination of chlorine and hydrogen gas in bright light or ignition of the mixture by lighted taper or electric spark. Reactions of chlorine with metals, solid non-metals, hydrocarbon. Use small quantities only.
Atomic number: 17 | Relative atomic mass: 35.453 | r.d. 1.56 (238 K) | m.p.: -101oC | b.p.: -34.7oC | Specific heat capacity: 477 J kg-1 K-1
7.2.2.13 Chromium, Cr, is a reactive transition metal but forms protective oxide layer in air that prevents further oxidation and forms hard alloys with Ni or Fe. Chromium is available as technical grade chromium, is extracted from chromite (Fe(CrO2)2) and is used for chromium plated metal, hard plating Cr2O3, catalysts, in stainless steel and in heat resistant steel. Strong reducing agent Cr2+ salts blue in aqueous solution, Cr3+ salts green in aqueous solution. CrO42- salts yellow, e.g. potassium chromate, K2CrO4, and strong oxidizing agent Cr2O72- orange, e.g. potassium dichromate K2Cr2O7. Chromium deficiency reduces tolerance to glucose.
Atomic number: 24 | Relative atomic mass: 51.996 | r.d. 7.19 | m.p.: 1890oC | b.p.: 2482oC | Specific heat capacity: 448 J kg-1 K-1
7.2.2.14 Cobalt, Co, is a transition hard, grey metal, forms complex ions, e.g. [Co(H2O)6]2+, magnetic below 1075oC, essential element but toxic in excess, used in alloys radiography, magnets, steel. Cobalt (II) oxide used to colour glass blue. Occurs in the body only as cyanocobalamin, vitamin B12.
(German: kobold, goblin of the mines, because associated with arsenic and sulfur health-damaging impurities)
Atomic number: 27 | Relative atomic mass: 58.9332 | r.d. 8.90 | m.p.: 1492oC | b.p.: 2900oC | Specific heat capacity: 435 J kg-1 K-1
7.2.2.15 Copper, Cu (cuprum) is a bright reddish orange, malleable and ductile transition metal, with high electrical and thermal conductivity, obtained form cuprite, Cu2S, available as filings, foil, powder, turnings, copper nails, copper wire, and copper turnings, is extracted from cuprite (Cu2S) and malachite (basic copper (II) carbonate, CuCO3.Cu(OH)2.H2O) and used for coin alloys, electrical wiring and heating vessels. Reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2. No reaction with dilute HCl or H2SO4. or with water. Heated powder forms oxide. Copper deficiency may occur in infants fed only on cow's milk. Copper bracelets my alleviate arthritis. A copper bowl may be preferable for beating cream. Copper poisoning may occur from water standing for a long time in copper pipes or in a copper hot water service. Copper is a cofactor for many enzymes and proteins, and is used in the development of nerve, bone, blood and connective tissue. Copper competes with zinc for entry from the intestines, so an increase in dietary zinc may result in copper deficiency. The recommended daily allowance (RDA) is 1.5 to 3.0 mg. Copper bracelets do not cure arthritis.
Atomic number: 29 | Relative atomic mass: 63.546 | r.d. 8.92 | m.p.: 1083oC | b.p.: 2595oC | Specific heat capacity: 385 J kg-1 K-1
7.2.2.16 Fluorine, F is a non-metal yellow poisonous gas at room temperature and pressure F2, most reactive element known, never found as free element but in many silicate minerals and fluorite, CaF2, most electronegative non-metallic element, strong oxidizing agent, combines with carbon to form low friction fluorocarbon polymers, e.g. PYFE, Teflon, used to make CFCs, chlorofluorocarbons, freon, that damages the ozone layer. Fluorine compounds are added to toothpaste and drinking water, e.g. tin (II) fluoride, sodium monofluorophosphate (MFP) sodium fluoride and amine fluorides. In Australia solid sodium silicofluoride is added to drinking water in some places. However, some natural water sources already contain the fluoride ion. The enamel of teeth are formed from the crystalline mineral hydroxyapatite, Ca10(PO4)6(OH)2. The fluoride ion F- replaces the OH- to form in the teeth Ca10(PO4)6F2. Fluoride is essential for teeth and bones.
Atomic number: 9 | Relative atomic mass: 18.9984 | r.d. 1.11 (85 K) | m.p.: -220oC | b.p.: -188oC | Specific heat capacity: 824 J kg-1 K-1
7.2.2.17 Gold, Au (aurum) is a yellow, lowest meal in activity series so most unreactive transition metal, is found in nature as free element form, available as gold leaf, occurs as the element and is used in coin alloys, electrical components, dentistry alloys, jewellery and as a monetary standard. No reaction with dilute HCl or H2SO4, air, water or concentrated oxidizing acids, e.g. HNO3 or H2SO4. Reacts with aqua regia, "royal water" that dissolves gold the "king of metals" (1 part concentrated HNO3 + 3 parts con. HCl) to form AuCl4. Atomic number: 79 | Relative atomic mass: 196.967 | r.d. 19.3 | m.p.: 1063oC | b.p.: 2970oC | Specific heat capacity: 130 J kg-1 K-1
7.2.2.18 Helium, He, is a non-metal noble gas at room temperature and pressure He, with separate small molecules, 0.0005% of the air, superfluid at 2.2 K, lowest boiling point, obtained from natural gas wells, using in diving gases, balloons, welding. Has no known compounds.
Atomic number: 2 | Relative atomic mass: 4.00260 | r.d. 0.147(4 K) | m.p.: -270oC | b.p.: -269oC | Specific heat capacity: 5.19 X 103 J kg-1 K-1
7.2.2.19 Hydrogen, H, is a colourless odourless gas at room temperature and pressure H2, lightest element, burns to form water, most common element in space, natural isotopes hydrogen and deuterium and manufactured isotope radioactive tritium, product of electrolysis of water, used to fix nitrogen and make ammonia in Haber process, reduction of ore oxides, manufacture of HCl, hydrogenation of oils, elemental gas in balloons and possible potential use as hydrogen gas fuel in motor cars.
Atomic number: 1 | Relative atomic mass: 1.0079 | r.d. 0.070 (20 K) | m.p.: -259oC | b.p.: -252oC | Specific heat capacity: 1.43 X 104 J kg-1 K-1
7.2.2.20 Iodine, I, resublimed [COR 1759] is a non-metal forms violet black solid poisonous scales with special smell, the least reactive of the halogens, most common as iodides, insoluble in water but dissolves in ethanol and a solution containing I-, 1% in KI, because it forms I3-, when heated sublimes to form vapour that irritates the eyes, important for function of the thyroid gland, intense blue colour is test for starch, extracted from unpurified Chile saltpetre (caliche) and seaweed, powerful disinfectant when dissolves in ethanol to form tincture of iodine, as radio iodine isotope Iodine-123 used in nuclear medicine, especially thyroid gland disorders. Strong oxidizing agent and antiseptic. As povidone-iodine in the antiseptic "Betadine". Iodine is used in the muscles and in the thyroid gland as part of the chemicals thyroxine and triiodothyronine. Iodine deficiency causes hyperthyroidism and an enlarged thyroid gland. The recommended daily allowance, RDA, is 150 pg. Radioactive labelled iodine used to measure percentage uptake of it by thyroid gland (RAI test).
Atomic number: 53 | Relative atomic mass: 126.905 | r.d. 4.93 | m.p.: 113.5oC | b.p.: 184oC | Specific heat capacity: 218 J kg-1 K-1
7.2.2.21 Iron, Fe (ferrum, ferrum reductum) as powder, iron nails, iron wire, iron filings, steel wool, is a magnetic and strong transition metal, 4.5% of the earth's crust, used for making iron and steel and is the most commonly used metal, available as filings, iron nails and wire, extracted from iron ores, e.g. haematite, Fe2O3, reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with steam to give the oxide and hydrogen gas. Heated powder forms oxide. The complex haemoglobin molecule has an iron atom in the centre. During rusting, metallic ion changes to Fe(OH)3.xH2O. Galvanized iron is Fe with Zn coating, e.g. "tin" roof. Iron is used in the haemoglobin protein that carries oxygen and carbon dioxide in the blood. Pig iron is cast iron, 2-4.3% carbon.
Atomic number: 26 | Relative atomic mass: 55.847 | r.d. 7.86 | m.p.: 1535oC | b.p.: 3000oC | Specific heat capacity: 448 J kg-1 K-1
7.2.2.22 Krypton, Kr, is a non-metal colourless odourless noble gas at room temperature and pressure Kr2, extracted from liquid air, 0.0001% of the air, mixed with other inert gases in fluorescent lamps. Forms few compounds.
Atomic number: 36 | Relative atomic mass: 83.80 | r.d. 2.16 (121 K) | m.p.: -157oC | b.p.: -152oC | Specific heat capacity: 247 J kg-1 K-1
7.2.2.23 Lead, Pb (plumbum) as lead shot, fishing sinkers, roof guttering, foil, powder, filings, strip, is a soft dense unreactive metal, available as lead foil, powder and lead shot, extracted from the ore galena (PbS) used in fishing sinkers, solder, lead glazes and X-ray protective shields, holds the pieces of glass together in stained glass windows, used in bullets, lead shot, fishing sinkers, building construction, lead cell accumulators, solder, pewter, bearings and alloys. Formerly, ladies used lead carbonate to whiten their faces and some may have died from such use. Reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2. No reaction with dilute HCl or H2SO4 or with water. Heated powder forms oxide. Inorganic Pb2+ is an accumulated poison and can replace calcium in bone. A "lead pencil" contains graphite, not lead.
Atomic number: 82 | Relative atomic mass: 207.2 | r.d. 11.3 g cm-3| m.p.: 327oC | b.p.: 1744oC | Specific heat capacity: 130 J kg-1 K-1
7.2.2.23a Lead paint
Lead paint formerly contained the white pigment "white lead", basic lead carbonate, Pb(OH)2PBCO3 that is now replaced by titanium dioxide, TiO2. Ingestion and skin absorption of lead causes lead poisoning, especially in young children sucking lead paint peeling off old walls.
"Lead in Paint" from the World Health Organization
No level of exposure to lead is considered safe. The poisonous properties of lead have been recognized since ancient times, and today it is recognized as one of the twenty leading risk factors contributing to the global burden of disease. Eliminating lead exposure from petrol has been one of the most significant environment health improvements in recent times.
Lead-containing products are however still widely made and sold across much of the developing world. It is very likely that most of the world's people live in countries where exposure to high lead levels in paint is frequent. Lead in paint is the second largest source of exposure to lead following exposure from petrol. Paint containing lead is used in infrastructure like bridges, industry (car parts) and for marine uses, as well as domestically.
The evidence of neurological damage, especially to children (whose intelligence can be impaired) and to workers in the lead industry is beyond doubt. Adults can suffer renal and cardiovascular damage. Some studies suggest a link to behavioural problems as well. Lead damage is irreversible, and its effects appear to persist into adolescence and adulthood. House dust is the commonest way in which children are harmed by lead in paint. The lead remains a risk for many years after the paint has been used.
7.2.2.23b Tetraethyl lead, lead tetra-ethyl
Octane (C8H18) Octane number 16.1.1h | See 32.5.5.5: Spark plugs, pre-ignition | See 11.11.2: Petrol-sniffing
The "anti-knock" additive to petroleum, the lead alkyl lead (IV) tetraethyl, Pb(C2H5)4, lessens pre-ignition, "knocking" by inhibiting combustion reactions and so improving its octane rating. This "leaded petrol" is no longer made or used in Australia and other countries because the compound causes lead poisoning and environmental pollution so is replaced by "unleaded petrol" that contains additional hydrocarbons to improve its octane rating, e.g. methanol and methyl tertiary butyl ether (MTBE). However, some pollution is still produced by unleaded petrol.
7.2.2.24 Lithium, L is a least dense, soft and shiny surface when cut by knife then tarnishes, very reactive alkali metal with acids so stored under oil because reacts with air and water, but least reactive element in group I, red flame test colour, rare element found in some granite pegmatites, used in Al and Mg alloys, batteries and anti-depressant medicines. Reacts with oxygen gas and water, on heating reacts with nitrogen and hydrogen gas. Lithium carbonate is used for a craft flux.
Atomic number: 3 | Relative atomic mass: 6.941 | r.d. 0.53 g cm-3| m.p.: 180oC | b.p.: 1330oC | Specific heat capacity: 3.39 X 103 J kg-1 K-1
7.2.2.25 Magnesium, Mg [FLAM 1418] as powder, ribbon, turnings, wire, photographers' flash bulbs, light bulbs and fire starters is a silver white alkaline earth metal, 2% of the earth's crust, forms protective oxide layer in air that prevents further oxidation. Magnesium burns in air with intense white light. It is available as powder (FLAM, dangerous), and ribbon (FLAM, safest form for school use) and as turnings (FLAM) low density. It is extracted from sea water, found in magnesite, MgCO3 and dolomite, MgCO3.CaCO3, used in aircraft bodies, cars, flashbulbs and alloyed with aluminium. Reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with hot water, reacts with halogens, sulfur and nitrogen. Heated powder forms oxide. Magnesium is stored in bones. It is used in many adenosine triphosphate, ATP, reactions. The recommended daily allowance, RDA, is 350 mg for adult males, and 280 mg for adult females. Manganese is a cofactor for many enzymes, but magnesium can usually substitute for it.
Atomic number: 12 | Relative atomic mass: 24.305 | r.d. 1.74 | m.p.: 650oC | b.p.: 1110oC | Specific heat capacity: 1.03 X 103 J kg-1 K-1
7.2.2.26 Manganese, Mn, is a white to reddish colour, hard, brittle transition metal, available as electrolytic flake and manganese (IV) oxide (manganese dioxide) extracted by electrolytic treatment of ores, e.g. pyrolusite (manganese (IV) oxide) used in ferromanganese for alloy steel manufacture.
Atomic number: 25 | Relative atomic mass: 54.9380 | r.d. 7.20 | m.p.: 1240oC | b.p.: 2100oC | Specific heat capacity: 477 J kg-1 K-1
7.2.2.27 Mercury, Hg (hydrargyrum, formerly "quicksilver") is a liquid metal between 19oC and 27oC, the lowest melting point of all substances, m.p. = -38.9oC, dissolves in most metals to produce amalgams, toxic when inhaled or taken internally or absorbed through the skin, free surface mercury not to be used in schools but can be examined in thermometers, extracted from cinnabar (mercury (II) sulfide) used in dentistry amalgams, mercury vapour lamps, electrical switches, interferometer lights and detonators, e.g. mercury fulminate (Hg(CNO)2). Reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2. No reaction with dilute HCl or H2SO4 or with water. Heated powder forms oxide.
7.2.2.27.1 Mercury (I) nitrate
Millon's Reagent contains mercury (I) nitrate in nitrous acid. Mercurous nitrate, mercury (I) nitrate, formerly used in the manufacture of felt hats, caused tremors in the workers and leading to the term "mad as a hatter", a character in Alice in wonderland by Lewis Carroll.
Atomic number: 80 | Relative atomic mass: 200.59 | r.d. 13.6 | m.p.: -38.9oC | b.p.: 357oC | Specific heat capacity: 138 J kg-1 K-1
7.2.2.28 Molybdenum, Mo, silvery solid, transition element, in molybdenite, MoS2, not affected by most acids, used in steel alloys, in two enzyme systems xanthine oxidase and aldehyde oxidase. Hard water can provide some of the daily intake of molybdenum.
7.2.2.29 Neon, Ne, is a non-metal inert noble gas at room temperature and pressure, 0.0018% of the air, with very low reactivity, used for high voltage display lighting, has bright orange colour, "neon" lights, strip lighting, high voltage display lighting and in pilot electrodes (starter electrodes to start up sodium vapour discharge lamps) cold cathode tubes, manufactured by recovery from atmosphere.
Atomic number: 10 | Relative atomic mass: 20.179 | r.d. 1.20 (27 K) | m.p.: -249oC | b.p.: -246oC | Specific heat capacity: 1.03 X 103 J kg-1 K-1
7.2.2.30 Nickel, Ni, as foil, powder, is a transition metal that resists corrosion, is obtained from ores containing NiS, is available as sheet, is extracted from NiS ores, isused in shiny coin alloys, nickel plating, and in "silver" cutlery stamped "EPNS" (electroplated nickel silver) that has a shiny metal protective coating, Reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with steam to give the oxide and hydrogen gas. Heated powder forms oxide.
The name comes from the German Kupfernickel, copper goblin. The nickel coin in U.S.A is made of a nickel copper alloy.
Atomic number: 28 | Relative atomic mass: 58.69 | r.d. 8.90 g cm-3| m.p.: 1453oC | b.p.: 2730oC | Specific heat capacity: 439 J kg-1 K-1
7.2.2.31 Nitrogen gas N2 is colourless, odourless, tasteless, neutral and unreactive. Nitrogen does not support combustion. Magnesium and calcium will continue to burn in nitrogen to form nitrides. Nitrogen is manufactured by fractional distillation of air. Air contains about 78.8% of nitrogen. Nitrogen, is a non-metal gas at room temperature and pressure, forms oxides: nitrous oxide N2O, nitric oxide NO, nitrogen dioxide NO2, dinitrogen tetroxide N2O4.
Atomic number: 7 | Relative atomic mass: 14.0067 | r.d. 0.808 (77 K) | m.p.: -210oC | b.p.: -196oC | Specific heat capacity: 1.04 X 103 J kg-1 K-1
7.2.2.32 Oxygen, O, oxygen gas, O2, is a non-metal colourless and odourless gas at room temperature and pressure, 20.95% of the air, 47% of the earth's crust, identified by lighting a glowing splint, supports combustion and is necessary for respiration, made in the laboratory by decomposition of hydrogen peroxide with MnO2 catalyst, manufactured by distillation of liquid air, most abundant element 50% of mass of rocks in earth's crust. Reacts with metals to form basic oxides, reacts with non-metals to form acidic oxides. Oxygen is carried by binding directly to the iron, in its 2+ oxidation state. Monthly loss of iron because of menstruation may average 28 mg. The recommended daily allowance, RDA, is 10 mg for adult males and 15 mg for adult females. Lecithin, diacylphosphatidylcholine is used in cell membranes. The lecithins are mixed esters of glycerol and choline with long chain fatty acids and phosphoric acid.
Atomic number: 8 | Relative atomic mass: 15.9994 | r.d. 1.15(90 K) | m.p.: -218oC | b.p.: -183oC | Specific heat capacity: 916 J kg-1 K-1
7.2.2.33 Phosphorus, P, Phosphorus is a non-metal network solid, occurs mainly as phosphates and in many minerals, e.g. apatite, has two main allotropes, white phosphorus, P4, is waxy, poisonous, very reactive, spontaneously flammable, reacts with oxygen gas in the air to form P2O5, so it is stored under water, red phosphorus red [FLAM 338] is not poisonous, ignites above 300oC, has phosphorus atoms bound in a covalent network so is less reactive than white phosphorus and can be stored in air, used in match heads and for "doping" semiconductors. Phosphates are important agricultural fertilizers, e.g. NPK. Phosphorus occurs as inorganic calcium phosphate in bones and teeth, in tissue and in the ATP molecule. The recommended daily allowance, RDA, is 1200 mg.
P (white) Atomic number: 15 | Relative atomic mass: 30.9738 | r.d. 1.82 | m.p.: 44.2oC | b.p.: 44oC | Specific heat capacity: 757 J kg-1 K-1
P (red) Atomic number: 15 | Relative atomic mass: 30.9738 | r.d. 2.34 | m.p.: 590oC | b.p.: 280oC | Specific heat capacity: 670 J kg-1 K-1
7.2.2.33.1 Phosphorescence is the green glow from the slow oxidation of white phosphorus. It is an example of chemiluminescence.
7.2.2.33.2 Detergent phosphates, as polyphosphates, mainly sodium tripolyphosphate (STPP), are used in detergents for different functions. Without using polyphosphates several different chemicals would be needed to replace them. There are also used in ceramics and are an authorised food ingredient. Phosphates occur in sewage from detergents, human foods, (transferred into human wastes) animal manures and food industry wastes. Thes phosphates can be recovered and recycled back into fertilisers and the detergent industry. Phosphates are the only recyclable ingredient of detergents.
See 8.1.0: Heat sources, light a match
7.2.2.34 Platinum, Pt, is a soft, ductile transition metal, resists most chemical agents and does not oxidize at high temperature, available as foil and wire, occurs in free elemental form or in alloys, used for electrical contacts, electrodes and jewellery. No reaction with dilute HCl or H2SO4, air, water or concentrated oxidizing acids, e.g. HNO3 or H2SO4, reacts with aqua regia (concentrated HNO3 + HCl) to form H2PtCl6.
Atomic number: 78 | Relative atomic mass: 195.08 | r.d. 21.4 | m.p.: 1769oC | b.p.: 4530oC | Specific heat capacity: 134 J kg-1 K-1
7.2.2.35 Potassium, K (kalium) is a soft and shiny white alkali metal, highest metal in activity series so does not occur in the free state, 2.5% of the earth's crust, available as the metal in liquid paraffin and is used widely in chemistry, is the " K" in the common fertilizer NPK, usually as K2O. Reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with cold water and reacts with air to form peroxides. Potassium has less concentration in extra cellular fluids than in intracellular fluids where it is the primary cation. Potassium ion is lost in sweat along with sodium ion. (FLAM 2257) (in liquid paraffin)
Atomic number: 19 | Relative atomic mass: 39.0983 | r.d. 0.86 | m.p.: 63.7oC | b.p.: 774oC | Specific heat capacity: 753 J kg-1 K-1
7.2.2.36 Radium, Ra, is a radioactive alkaline earth metal, used in some cancer therapy, extracted from pitchblende, uraninite, used as a radioactive resource.
Atomic number: 88 | Relative atomic mass: 226.025 | r.d. 5.0 | m.p.: 700oC | b.p.: 1140oC | Specific heat capacity: 121 J kg-1 K-1
7.2.2.37 Radon, Rn, is a non-metal noble colourless water-soluble gas at room temperature and pressure Rn2, formed by decay of radium-226, forms under granite where it may be a health habit to people living in granite houses, has few compounds, used in radiotherapy.
Atomic number: 86 | Relative atomic mass: (222) | r.d. 4.4 (211 K) | m.p.: -71oC | b.p.: -61.8oC | Specific heat capacity: 92 J kg-1 K-1
7.2.2.38 Selenium, Se, is a non-metal, obtained from sulfide ores, decolorizes glass, semiconductor that conducts electricity when e.m.f. applied, used in photoelectric cells and light meters. Similar properties to sulfur. The Kjeldahl catalyst is sodium sulfate + selenium. Selenium is a trace mineral used to destroy hydrogen peroxide. The recommended daily allowance, RDA, is 70 mu g for males, and 55 mu g for females.
Atomic number: 34 | Relative atomic mass: 78.96 | r.d. 4.81 | m.p.: 217oC | b.p.: 685oC | Specific heat capacity: 322 J kg-1 K-1
7.2.2.39 Silicon, Si, lump [powder FLAM 1346] is a non-metal network solid with many properties similar to carbon. occurs naturally as a brown powder or grey crystals, 28% of the earth's crust, forms a network solid similar to diamond and has valence 4, the second most abundant element mainly in silicates in rocks, prepared by reduction of silica SiO2 in an electric furnace, used as a semiconductor, conductivity can be increased by increasing its temperature or by adding small quantities of boron or phosphorus (doping). The common form of silicon dioxide is silica, SiO2 as in quartz. A major component of rocks is the silicate ion, SiO44- as in glass. Silicone greases have a polymer network of silicon and oxygen atoms attached to C and H atoms.
Atomic number: 14 | Relative atomic mass: 28.0855 | r.d. 2.33 | m.p.: 1410oC | b.p.: 2360oC | Specific heat capacity: 711 J kg-1 K-1
7.2.2.39.1 Solar panel
A crystalline silicon cell used in solar panels for solar power has an efficiency of about 22% for the conversion of light to electricity (16% for the cheaper cells in household solar panels).
7.2.2.40 Silver, Ag (argentum) is a silver white transition metal, does not oxidize in air and is the best electrical conductor, available as silver wire, occurs as the element and is used in coin alloys, electrical conductors, photographic emulsions, jewellery and ornaments. Reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with concentrated HNO3 and hot concentrated H2SO4. No reaction with dilute HCl or H2SO4, air, or water. The "silver paper" usind in wrapping is usually tin foil.
Atomic number: 47 | Relative atomic mass: 107.868 | r.d. 10.5 | m.p.: 961oC | b.p.: 2210oC | Specific heat capacity: 234 J kg-1 K-1
7.2.2.41 Sodium, Na (in liquid paraffin) (natrium) (FLAM COR 1428) is a very reactive, soft and shiny alkali metal with a silvery colour, 2.5% of the earth's crust, does not occur in the free state and soon becomes dull in air, available as sodium metal in liquid paraffin, extracted by electrolysis of fused sodium hydroxide, rock salt (halite) and evaporated sea water, used in sodium vapour discharge lamps. Reacts with dilute HCl or H2SO4 to form H2 and metal ion, with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with cold water and reacts with air to form peroxides. Sodium has greater concentration in extra cellular fluids than in intracellular fluids. The level of sodium ion in blood is 310 to 333 mg per 100 mL of serum.
Atomic number: 11 | Relative atomic mass: 22.9898 | r.d. 0.97 | m.p.: 97.8oC | b.p.: 890oC | Specific heat capacity: 1.23 X 103 J kg-1 K-1
7.2.2.42 Strontium, Sr, silver white metallic element, in minerals celestine SrSO4, strontianite SrCO3 and spring water, similar properties to calcium, salts used for crimson flame in fireworks, after nuclear explosion fallout contains 90Sr that can be absorbed in human bone, strontium chloride in toothpaste for sensitive teeth, e.g. "Sensodyne".
Atomic number: 38 | Relative atomic mass: 87.62 | r.d. 2.54 | m.p.: 800oC | b.p.: 1300oC | Specific heat capacity: 0.3 J kg-1 K-1
7.2.2.43 Sulfur, S [FLAM 1350] brimstone, sublimed, flowers of sulfur, sulfur sticks, brimstone, is a non-metal occurs as S8 molecule rings. The main allotropes are as follows: 1. Alpha sulfur, rhombic sulfur, with yellow octahedral crystals, and 2. Beta sulfur with monoclinic prismatic pale yellow crystals. Sulfur is insoluble in water, slightly soluble in ethanol, and soluble in benzene. Above 160o the S8 molecule rings break to form long chains of plastic sulfur, polymeric sulfur, that is not soluble in any solvents.
Atomic number: 16 | Relative atomic mass: 32.06 | r.d. 2.07 (Alpha) 1.96(Beta) | m.p.: 113oC (Alpha) 119oC (Beta) | b.p.: 445oC (Alpha) | Specific heat capacity: 0.71
7.2.2.44 Tin, Sn (stannum) (tin-plated jam tin) pewter is a ductile, malleable metal, resists corrosion, is available as granules, pellets, foil and powder, is extracted from the ore cassiterite (tin (IV) oxide, SnO2) and used in alloys and the shiny protective plating of tin cans (tin plate) alloys and solders. It reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2. No reaction with water. Heated powder forms oxide. The "silver paper" usind in wrapping is usually tin foil.
Atomic number: 50 | Relative atomic mass: 118.71 | r.d. 7.28 (white) 5.75(grey) | m.p.: 232oC | b.p.: 2270oC | Specific heat capacity: 218 J kg-1K-1
7.2.2.45 Tungsten, W, white-grey solid, transition element (formerly wolfram) light bulb filaments, from wolframite (MnFe)WO4, scheelite CaWO4, not affected by dilute acids, used in steels and lamp filaments, tungsten carbide, WC, black powder, used in cutting tools because has Mohs scale 9.5 The tungsten filament in a light bulb reaches about 2,300oC. It has the highest melting point of all metals.
Atomic number: 74 | Relative atomic mass: 183.85 | r.d. 19.3 | m.p.: 3,422oC | b.p.: 5,660oC | Specific heat capacity: 130 J kg-1 K-1
7.2.2.46 Uranium, U, is a radioactive hard grey metal obtained from pitchblende U3O8, 238U main isotope, 235U used as fuel in nuclear power stations and atomic bombs. Atomic number: 92 | Relative atomic mass: 238.029 | r.d. 19.1 | m.p.: 1130oC | b.p.: 3820oC | Specific heat capacity: 117 J kg-1 K-1
7.2.2.47 Xenon, Xe, is a non-metal noble gas at room temperature and pressure, 0.00001% of the air.
Atomic number: 54 | Relative atomic mass: 131.29 | r.d. 3.52(165 K) | m.p.: -112oC | b.p.: -108oC | Specific heat capacity: 159 J kg-1 K-1
7.2.2.48 Zinc, Zn, granulated, zinc foil, dry cell battery case, is a blue white metal, forms protective oxide layer in air that prevents further oxidation, is available as zinc granules, foil, filings and powder (FLAM) extracted from zinc blende (sphalerite, ZnS) used for dry cell battery casings and in the Daniell cell, galvanized iron, alloys and brass, a micronutrient (trace element) required in a very small quantity by living organisms as salts or compounds, not as the pure element. Reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with steam to give the oxide and hydrogen gas. Heated powder forms oxide. High level of zinc in the diet is undesirable, e.g. from oysters, and zinc deficiency symptoms occur where people live on unleavened bread made from highly extracted wheat flour and no meat or yeast products in the diet. Zinc is a cofactor for about 20 enzymes, e.g. alcohol dehydrogenase that breaks down ethanol and carboxypeptidase that catalyses the hydrolysis of proteins in the small intestine. The recommended daily allowance, RDA, is 15 mg for males and 12 mg for females.
Atomic number: 30 | Relative atomic mass: 65.39 | r.d. 7.14 | m.p.: 420oC | b.p.: 907oC | Specific heat capacity: 385 J kg-1 K-1
Describe each example.
1. Note the state of matter at room temperature, solid, liquid or gas.
2. Note whether the solid has a shiny surface or has a lustre when the surface is clean.
3. Note whether the metal can be bent or twisted with pliers, or whether it fractures.
4. Note whether the element conducts electricity when held between two alligator clips as electrical contacts.
5. Put a piece of the element on a combustion spoon and set it alight with a burner flame. Observe the burning element.
6. Shake the products of the combustion in a test-tube containing water. Test the solution with moist litmus paper.
7.2.2.49 Zirconium, Zr, grey-white solid, transition element, in zircon ZrSiO4, zirconium wire used in photography flash bulbs, camera flash cubes, e.g. "Magicube", nuclear reactor neutron absorber
7.3.0 Metals and non-metals
1. Metals are elements that form positive ions. Metals may also form complex ions with a non-metal, e.g. chromate ion, CrO4 2-.
2. Non-metals are elements that form negative ions. Non-metals may also combine with other non-metals, e.g. NO3-. The first 105 elements in the periodic table contain 84 metals and 21 non-metals (or metalloids). Metalloids have both metal and non-metal properties, e.g. B, Si, As, Te and Ge, Sb, Bi. 3. Transition elements include, first series: Cr, Mn, Fe, Co, Ni, Cu (and perhaps Zn), second series: Mo and Ag, and third series: Pt, Au (and perhaps Hg). Transition elements are hard, dense metals with high melting points and boiling points, form coloured ions and compounds and have more than one valence (oxidation number), e.g. copper (Cu1+ and Cu2+) and chromium (Cr2+ and Cr3+). The ion Cr2+ is a strong reducing agent and forms blue salts in solution. Cr3+ salts are green in solution. CrO42- salts are yellow and Cr2O72- is a strong oxidizing agent with orange salts, e.g. K2Cr2O7. Transition metals form complex ions and often have catalytic activity, e.g. Fe in the complex haemoglobin molecule, and Fe in the manufacture of ammonia
Observe common metals and non-metals, e.g. aluminium foil, calcium granules, carbon as charcoal, copper foil or wire, iodine crystals, lead foil or lead shot, magnesium ribbon, nickel sheets or plating, red phosphorus, potassium (in liquid paraffin) sodium (in liquid paraffin) sulfur powder or "flowers", tin foil or tin-plating, zinc foil or granulated zinc. List the metallic or non-metallic properties you can observe.
7.3.1 Properties of metals
1. Are usually opaque, hard solids with high density and have shiny, silvery lustre, when cut or scratched.
2. Have strong metallic bonds that make them malleable, ductile and easy to bend. They have high melting points, boiling points and density. You can hammer metals into new shapes because they are malleable. Metals can be drawn into a wire because they are ductile.
3. Have freely moving electrons and thus are good conductors of electricity and heat.
4. May form oxides that turn moist litmus blue. For example, calcium oxide dissolves in water to form the alkali calcium hydroxide. Some metals form a surface layer of oxide that prevents more oxidation, e.g. Al, Cr, Mg and Zn.
5. Reactive metals have stable compounds. Stable metals have compounds that easily decompose.
7.3.2 Properties of non-metals
1. May be monatomic, e.g. Ne, He, polyatomic, e.g. F2, white phosphorus P, or network solids, e.g. diamond, red phosphorus.
2. May be solids, liquids or gases.
3. Non-metals that are solids, they are usually dull and brittle, and have low density.
4. Are usually poor conductors of electricity and heat.
5. Usually form oxides that turn moist litmus red. For example, carbon dioxide dissolves in water to form the weak acid, carbonic acid (H2CO3).
H2O(l) <--> H+(aq) + OH-(aq)
2H+(aq) + CO32-(aq) <--> H2CO3(aq) carbonic acid
CO2 + H2O <--> H3O+ + HCO3-
HCO3- + H2O <--> H3O+ + CO32-
6. Exceptions to the properties of non-metals include graphite carbon that conducts electricity, silicon that has the physical properties of a metal.
7.4.0 Melting point of solids
See 3.2: Melting point of naphthalene
The melting point (m.p., fusing point) is the temperature at which a solid starts to liquefy. The melting point and freezing point of a pure substance are the same temperature. Melting (fusion) is the "solid to liquid" type of phase change. Other phase changes include change from liquid to solid (freezing), solid to gas (sublimation), liquid to gas (evaporation), gas to liquid (condensation). Pure substances melt at constant temperature. Impurities lower the melting point. Impure substances, e.g. alloys, melt over a range of temperature. The melting point graph for a pure substance is horizontal as the solid melts. The melting point graph for an impure substance has an inclined line as the solid melts. Melting points and melting behaviours can be used to identify a substance and decide if it is pure.
7.4.1 Melting point and cooling curve of stearic acid
See diagram 7.4.1
Stearic acid (octadecanoic acid) is a safer alternative to using naphthalene for the following experiments. Stearic acid melts at 69oC.
1. Put 2 cm of the acid in a test-tube with a thermometer. Put the test-tube in a beaker containing water. Heat the beaker tube gently until the acid just melts. Note the time and remove the test-tube from the beaker. Note the temperature every 30 seconds as the substance cools. The acid solidifies again at the same temperature. Heat the test-tube again to free thermometer. Draw the cooling curve of the acid. Plot temperature on the vertical axis and time on the horizontal axis. When the acid is changing from liquid to solid, the curve is horizontal.
2. A more accurate method to measure melting points. Heat one end of a 10 cm capillary tube to seal it. Put octadecanoic acid in the capillary tube. Attach the capillary tube to a thermometer with a rubber band. Put thermometer in a beaker of water. Heat the water while stirring with thermometer. Record the temperature at which the acid melts. Leave the capillary tube to cool. Record the temperature at which the acid solidifies.
7.4.2 Melting point of substances
Repeat the above experiments with substances, e.g. candle wax, m.p. = 45oC to 65oC, urea, m.p. = 133oC and hexadecan-1-ol (cetyl alcohol) [CH3(CH2)14CH2OH]. Cetyl alcohol forms the ester cetyl palmitate (C15H31.COO.C16H33) m.p. 42oC to 47oC, that is the main component of spermaceti, the white wax found in the head of the sperm whale. The wax was used to make cosmetics and ointments but nowadays we use other chemicals as substitutes to "Save the Whales"!
7.4.3 Melting point of ice and freezing point of water
For pure substances, the melting point, m.p. = freezing point, f.p. For water, m.p. and f.p. = 0oC. However, freezing mixtures of ice and salt have temperatures below 0oC. The freezing point of water in motor car radiators is lowered by adding antifreeze solutions, e.g. ethylene glycol (ethane-1,2-diol) that does not freeze above -20.6oC, also methanol. Freezing points can be used for detecting water in milk or other adulteration.
7.4.3.1 Temperature at which ice melts
Half fill a beaker with tap water. Note the temperature of the water after five minutes. Put pieces of ice in the water. Note the temperature every five minutes. The temperature drops to zero and remains at zero while ice remains floating in the water. Wait until all the ice melts. The temperature rises again until it reaches room temperature.
7.4.3.2 Temperature at which an ice and salt mixture freezes
See 19.1.16: Table salt and rock salt
At 0°C, the molecules in pure water form strong bonds to form ice. If sodium and chlorine are between water molecules, it is harder for these bonds to form. Seawater contains about 35 grams of salt per litre and freezes at -1.8°C. Mix crushed ice with salt. Note the temperature after five minutes. The temperature of the ice and salt mixture is below zero.
7.4.3.3 Lift an ice cube with a match stick
Float an ice cube in water. Put a match stick on the ice. Sprinkle a very small amount of salt on to the ice at each side of the match stick. After one minute, lift the ice cube by lifting the match stick. Salt water has a lower melting point or freezing point than pure water. The salt sprinkled on the ice dissolves in the ice lowering its freezing point. The ice around the matchstick melts and the matchstick floats in it. Some of the water may fall off the ice cube but also the salt keeps dissolving in the ice so lowering the concentration of salt around the matchstick and raising the freezing point back towards 0oC, when it freezes again trapping the matchstick in the ice. The layer of water between the match stick and the ice cube is now frozen so the match stick sticks to the ice.
7.5.0 Boiling point of liquids
See 3.8: Pressure affects the boiling point
When bubbles of vapour form in a boiling liquid, the vapour pressure of the gas in the bubbles is greater than atmospheric pressure. When the bonds between liquid molecules are strong, only a few molecules can break the bonds to become a vapour. The vapour pressure of that substance is low and the boiling point is high. The boiling point of a liquid is the temperature at which the liquid boils when exposed to the atmosphere. So the boiling point of a liquid is the temperature at which the vapour pressure of the liquid equals the pressure of the atmosphere, 1 atmosphere. At 100oC, the vapour pressure of pure water is one atmosphere (101.325 KPa, kNm-2). The boiling point varies with pressure. Boiling chips (anti-bumping granules) are added to chemical reactions to keep the bubbles small and aid steady boiling.
7.5.0.1 Elevation of boiling points, ebullioscopic constant, kB
See: 24.1.04: Depression of freezing point and elevation of boiling point
The boiling point of a liquid is raised if substances are dissolved in it. The elevation is proportional to the number of particles or molecules or ions dissolved in the liquid. The elevation in oC = the molal concentration of the solute in the liquid X a constant. The value of the constant (ebullioscopic constant, kB) depends on the solvent. So if kB is known, the molecular weight of the solute can be calculated.
Addition of substances to water used for cooking has little effect on cooking time because adding a tablespoon (20 g) of sodium chloride (common salt) to 5 litres of water increases the boiling point of pure water by only 0.04oC.
7.5.3 Boiling point of a mixture of two liquids, water and alcohol
Use the above method to compare the boiling points of mixtures of water and methylated spirit in proportions: BE CAREFUL! ALCOHOL IS HIGHLY FLAMMABLE!
Liquids Solution 1 Solution 2 Solution 3
1. Water 25% 50% 75%
2. methylated spirit 75% 50% 25%
7.5.4 Boiling point of inflammable liquids, ethanol
See 3.6.0: Boiling point of inflammable liquids
The boiling point of ethanol is 78oC. Heat water in a kettle. Turn off the gas or extinguish the flame. Pour 2 cm of methylated spirit into a test-tube. Put the test-tube in a beaker. Put a thermometer into the methylated spirit deep enough to cover the bulb. Pour hot water into the beaker so that the water level is higher than the level in the test-tube. Stir gently with thermometer. When boiling starts, record the temperature.
7.5.4.1 Boiling point of inflammable liquids, acetone
Repeat the experiment with propanone (acetone). BE CAREFUL! HIGHLY FLAMMABLE! THE FLASH POINT IS -20oC! Boil the propanone (acetone) by placing the test-tube in hot water. Do not allow flames in the room. The boiling range of 98% propanone (acetone) is 55.5oC to 56.5oC. Nail polish remover formerly contained propanone (acetone) but not in modern manufacture.