School Science Lessons
Topic 7b Chemistry terminology, physical changes, forms of sulfur
2012-05-10 SPwp
Please send comments to: J.Elfick@uq.edu.au
Table of contents
7.9.0 Chemistry terminology
7.1.5 Prepare forms of sulfur, allotropes of sulfur
7.2.0 Pure substances and impure substances, elements and compounds
7.2.1 Classify substances, pure substances, mixtures, solutions
7.9.0 Chemistry terminology
7.9.1 Acid
7.9.2 Aerobic
7.9.3 Aliquot
5.5.0 Alloys
7.9.4 Alkali
7.9.4.1 Alkaloid
7.9.4.1 Allotropes, sulfur, carbon
7.9.6 Amphoteric
7.9.6.1 Anodize
7.9.6.2 Aqueous solutions, states of matter
7.9.7 Azeotrope
7.9.8 Base
7.9.8.1 Benzoic acid
7.9.9 Bessemer process
7.9.10 Borosilicate glass, Pyrex
7.9.11 Buffer
7.9.12 Bumping, boiling chips
7.9.12.1 Catalase
7.9.13 Catalyst
7.9.13.1 Catalytic converter in a car
7.9.14 Caustic
7.9.14.1 Chemical potential energy, enthalpy
7.9.14.2 Chloramphenicol
7.9.14.3 Clathrate
7.9.15 Continuous phase / outer phase
7.9.15.1 Cracking
7.9.16 Detergent, SYNDET, Synthetic Detergent
7.9.21 Electrochemical cell
7.2.2 Elements and compounds
7.9.19 Enzyme
7.9.20 Equilibrium
7.9.20.1 Etchants
7.9.22 Flammable
7.9.23 Flashpoint
7.9.24 Flocculent
7.9.25 Fluorescence
7.9.26 Flux
7.9.27 Froth flotation
7.9.28 Fuel cell
7.9.29 Galvanize
7.9.30 Group formula
7.9.31 Heavy metals
7.9.31.1 Recycle heavy metals
7.9.32 Hydronium ion (hydroxonium ion, oxonium ion)
7.9.33 Hydrophilic, hydrophobic
3.31.01 Hygroscopic substances
7.9.35 Inhibit
7.9.36 Labile
7.9.37 Martensite
5.1.0 Mole, amount of substance
7.9.39 Molecular mass
7.9.40 Napalm
7.9.41 Petroleum fraction
7.9.41.1 Petroleum spirit
7.9.42 Photolysis
7.9.44 pK
7.9.46 Radical
7.9.47 Sequester
7.9.48 Solute
7.9.49 Solvent
7.9.50 Spontaneous
7.9.51 Substrate
7.9.51.1 Sulfates
7.9.51.2 Sulfides
7.9.51.3 Sulfites
7.9.52 Surfactant
7.9.53 Synergism
7.9.54 Tempering
7.9.54.2 Urethane
7.9.55.1 Waste bottles
7.9.56 Water glass
7.9.56.1 Xanthene dyes
7.1.5 Prepare forms of sulfur, allotropes of sulfur
7.1.5.0 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
12.2.2.1 Reactions between two elements, Heat iron with sulfur
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. In this document the expression used is as follows: "hydrogen gas with oxygen gas forms water". The new substances, the products, have properties different from the original substances, 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. Do 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.
7.1.5.0 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, sulfur 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
When heated to the melting point, sulfur usually ignites and forms sulfur dioxide gas that may distress people suffering from asthma.
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, elements and compounds
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. An element cannot be broken down into simpler substances by a chemical reaction and all the atoms in it have the same atomic number, the number of protons and electrons is the same, but the number of neutrons may vary. Ninety two naturally occurring elements exist..
3. A compound is composed of two or more elements combined in fixed proportions as a result of a chemical reaction and which cannot be separated into simpler substances by any physical process, e.g. shaking. 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
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.
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 mixture +
6. Brass alloys -
 + or mixture +
7.9.1 Acid
(Latin: acidus, sour tasting) An acid is a good electrolyte, reacts with active metals, turns blue litmus red and has a sour taste. Acids with water produce hydrogen ions, H+. An acid is a proton donor (H+) (Bronsted-Lowry definition). The "acid test" was originally the nitric acid test for gold because only gold would not dissolve in it.
7.9.2 Aerobic
(Greek: aēr air, bios live) A bacterial processes that occurs only in the presence of oxygen is an aerobic process, the opposite is an anaerobic process.
7.9.3 Aliquot
An aliquot is a portion, a known fraction of the whole sample.
7.9.4 Alkali
(Arabic: al-kalī, calcined ashes) An alkali is water-soluble base yielding a caustic solution, pH > 7.
7.9.4.1 Alkaloid
Basic organic nitrogen compounds in plants with powerful action on animals, e.g. nicotine, morphine, quinine, strychnine
7.9.4.1 Allotropes, sulfur, carbon
If the same element may have different bonding structure and crystal structure and so has different properties within, each variation of structure and properties is called an allotrope. Sulfur has 3 allotropes, rhombic or α sulfur, monoclinic or β sulfur, and plastic sulfur.
Carbon has different bonding and crystal structure in the allotropes graphite and diamond. Graphite is slippery because weak van der Waals' forces between the flat layers allow them to slide over each other. So graphite is used as a dry lubricant in machinery and in "lead" pencils. Diamond has very high melting point and is extremely hard because of strong chemical bonds holding the carbon atoms into a rigid three-dimensional structure, a network solid with a tetrahedral arrangement, making it chemically unreactive. However, diamond is a poor conductor of electricity because the electrons are held in relatively fixed positions around the carbon atoms.
7.9.6 Amphoteric
Can act as an acid or a base, e.g. water, bicarbonate ion. Amphoteric oxides react with both acids and bases, e.g. Al2O3, PbO, SnO ZnO. Their hydroxides are also amphoteric.
7.9.6.1 Anodize
To anodize is to give a metal a positive coating, usually aluminium, by an electrolytic process where the metal is the anode.
7.9.6.2 Aqueous solutions, states of matter
An aqueous solution is a solution in water. In this document "solution" is always an aqueous solution unless otherwise specified. So a sugar solution contains sugar dissolved in water but a solution of liquid sucrose contains no water. The states of matter are solid (s), liquid (l), gas (g), aqueous solution (dissolved in water) (aq).
7.9.7 Azeotrope
An azeotrope is a mixture of liquids that has a constant boiling point because the vapour has the same composition as the liquid mixture, so the components of the solution cannot be separated by distillation. The boiling point of an azeotropic mixture may be higher or lower than any component. An example of a constant boiling mixture is 4.37% water and 95.63%. The mixture boils at 78.2oC, but pure ethanol boils at 78.4oC and water boils at 100oC.
7.9.8 Base
A base or an alkali is a good electrolyte, that turns red litmus blue and has a slippery feel. Bases with water form hydroxide ions, OH-. Bases react with hydrogen ions, H+. A base is a proton acceptor (H+). (Bronsted-Lowry definition)
7.9.8.1 Benzoic acid
Benzene carboxylic acid, C6H5COOH, preservative, in creams for treating haemorrhoids
7.9.9 Bessemer process
The Bessemer process converts pig iron from a blast furnace into steel by blowing air or pure oxygen into the molten impure metal to convert impurities into a separating slag.
7.9.10 Borosilicate glass, Pyrex
Addition of borate allows the formation of a glass that melts at a lower temperate than silica, and expands less on heating than soda glass, as well as more plastic over a wider temperature range, e.g. Pyrex and glass wool. So borosilicate glass has a very low coefficient of thermal expansion and a softening temperature above 800oC. The composition may be 70% silica, 10% boron oxide and some sodium, potassium and calcium oxides. The chemical composition of the Pyrex used in laboratory glassware may
be different from the Pyrex used in kitchenware.
Commercial:
Mixing bowls, Pyrex, glass 1 litre
Casserole dish, freezer and dishwasher safe, 2 litre
7.9.11 Buffer
A mixture of substances that tend to hinder large changes in acid or basic properties of a solution. Used in a more general sense outside chemistry. The pH of a buffer solution is not greatly changed by the addition of an acid or an alkali. Most buffer solutions are a mixture of a weak acid or base with one of its salts. In body fluids, the buffers include H2CO3 with HCO3-.
Acidic buffer, e.g. sodium hydrogen carbonate with carbonic acid solutions, the salt of the weak acid is completely dissociated into ions but the weak acid is only partly dissociated.
Basic buffer, e.g. ammonium chloride in ammonia solutions
7.9.12 Bumping, boiling chips
Boiling chips, usually fused alumina, also flower pot bits, prevents large bubbles of gas forming that could cause explosive emissions from a beaker containing a heated solution. Sudden formation of a large amount of vapour from the bottom of a heated vessel of liquid, rather than the usual controlled boiling. So boiling chips (anti-bumping granules) are added to chemical reactions to keep the bubbles small and aid steady boiling. Hydrocarbons with longer chains will have higher boiling points than similar hydrocarbons
with branched chains because they have more van der Waals intermolecular bonds between one molecule and another molecule.
7.9.12.1 Catalase
A catalase is a common enzyme in animal and plant cells that catalyzes the decomposition of hydrogen peroxide to water and oxygen.
7.9.13 Catalyst
A catalyst is an agent that speeds up a chemical reaction without itself being used up in the process, e.g. the transition metals Co, Ni, Pt. Enzymes are catalysts for biological reactions.
7.9.13.1 Catalytic converter in a car
See 18.6.3: Danger of vehicle exhausts, tailpipe gases
A catalytic converter reduces emissions of carbon monoxide, nitrogen oxides and hydrocarbons from motor vehicles, usually with a three-way catalyst of platinum, palladium and rhodium on a ceramic base. Carbon monoxide is oxidized to carbon dioxide. Hydrocarbons are oxidized to carbon dioxide and water. Nitrogen oxides are reduced to nitrogen gas. If the catalytic converter uses an oxidation catalyst, it cannot reduce the oxides of nitrogen which must be lessened by engine design.
7.9.14 Caustic
A caustic substance is very alkaline, with pH approaching 14. It can dissolve skin and fat to form soap.
7.9.14.1 Chemical potential energy, enthalpy
The chemical potential energy stored in a substance is called the heat content or enthalpy. In a chemical reaction, chemical bonds are broken in the reactants (energy is absorbed) and formed in the products (energy is released). The energy is measured in joules, J or more commonly in kilojoules, kJ, where 1000 J = 1 kJ. In a chemical reaction energy is neither created nor destroyed, the law of
conservation of energy and the First Law of Thermodynamics. In an endothermic reaction, the amount of energy absorbed when chemical bonds are broken is greater than the amount of energy released when chemical bonds are formed. In an exothermic reaction, the amount of energy absorbed when chemical bonds are broken is less than the amount of energy released when chemical bonds are formed. The heat of reaction, δH, is the heat change for the reaction and is measured in a calorimeter. If δH is negative, the reaction is endothermic. The reaction releases heat energy and the container feels hotter. If δH is positive the reaction is endothermic. The reaction takes in heat energy and the container feels cooler.
7.9.14.2 Chloramphenicol
Broad acting powerful antibiotic, natural and synthetic, that may have severe side effects.
7.9.14.3 Clathrate
Inclusion compound where the "guest molecule" is in a lattice cage formed by the host molecule, e.g. Dianin's compound, 4-p-hydroxyphenyl-2,2,4-trimethylchroman.
7.9.15 Continuous phase / outer phase
The continuous phase is the continuous "outside" liquid that surrounds a second liquid, its droplets being discontinuous, in an emulsion.
7.9.15.1 Cracking
Thermal cracking is the use of heat and pressure for controlled breakdown of naphtha, C10, to form smaller hydrocarbon molecules and light olefins (alkenes), e.g. ethylene, propylene butylene. They can later be polymerized. The process increases the yield of petrol (gasoline), C6-10, from crude oil and increases the octane rating.
Catalytic cracking:
Use of silica or aluminium as a catalyst to lower the temperature needed to break down heavy hydrocarbons in crude petroleum, or liquefied petroleum gas and natural gas to form monomers, e.g. ethane. propane. The smaller molecules formed by cracking often have branch chains. For example:
CH3(CH2)8CH3 (thermal cracking) --> CH3
|
CH3-CH-(CH2)4-CH3 + CH2=CH2 (ethylene)
7.9.16 Detergent, SYNDET, Synthetic Detergent
A detergent is a synthetic surfactant, not a soap, the sodium salts of natural fats. A detergent has the cleansing properties of a soap but it does not combine with any salts present as soap does in hard water. So detergents holds dirt in suspension.
7.9.21 Electrochemical cell
An electrochemical cells (Voltaic cell) forms electricity from chemical reactions. The cell is made up of two half cells. Each half cell consists of an electrode in contact with an electrolyte. It is usually a metal in contact with one of the metal salt solutions.
In an electrochemical cell:
1. Cations, (positive ions, e.g. Fe2+), flow to the cathode where they are reduced, i.e. gain electrons, from the cathode,
2. Anions, (negative ions, e.g. SO42-), flow to the anode where they are oxidized, i.e. lose electrons, by depositing electrons onto the anode.
The anode is usually labelled as the positive terminal with "+" sign on it and painted red.
The cathode is usually labelled as the negative terminal, with "-" sign on it and painted black.
When electrochemical cells are part of a circuit, electrons carry electric current through the external electrical circuit and ions carry current through the solutions in the cell.
Oxidation at the anode and reduction at the cathode occur in both electrochemical and electrolytic cells. However, an electrochemical cell can react spontaneously, but an electrolytic cell needs external electrical energy to force electrons around the circuit.
7.9.19 Enzyme
An enzyme is a biological molecule that can promote or catalyse a particular reaction.
7.9.20 Equilibrium
An equilibrium occurs in reactions in which the forward and reverse rates are matched so that the composition of the mixture appears unchanging in time.
7.9.20.1 Etchants
Etching may be done in schools to prepare printed circuit boards, metal specimens for examination, etchings and lithographic plates. However, many etchants are hazardous.
1. Ammonium persulfate, (NH4)2S2O8, a strong oxidizing agent, is used as an etchant for copper plates as a 20% solution (w / v), (20 g in 100 mL of water), and 5% solution (w / v), (5g in 100 mL of water), prepared before the lesson, and used at 80oC, to prepare copper and alloys for microscopic examination, etch copper in PCB construction and prepare tin coating on steel for microscopic examination.
2. Copper ammonium chloride solution, [Cu(NH3)3Cl2], 10% solution (w /v), (10 g per 100 mL of water), to prepare steels for macroscopic examination.
3. Iron (III) chloride, (ferric chloride), 20% solution (w / v), (20 g in 100 mL of water), prepared before the lesson, is an etchant for most metals and alloys, and is used etch copper in PCB construction, and etch aluminium zinc and copper plates, but it may leave persistent stains.
4. Nitric acid, 25% solution (approximately 4M), is an etchant for copper plates.
5. Sodium hydroxide solution, 1% solution (w / v), (1 g per 100 mL of water), to prepare aluminium and alloys for microscopic examination.
6. Sulfuric acid with concentration < 2M, may be used with care.
7. The following etchant chemicals or mixtures containing them are not permitted in schools because of high corrosive risk and in some cases potential fire hazard: 7.1. Ammonium hydroxide + hydrogen peroxide, 7.2. Chromic acid, 7.3. Hydrofluoric acid.
7.4. Nitric acid + potassium dichromate + water which can produce nitric acid, 7.5 Nitric acid + methanol, 7.6 (Nital), Nitric acid + glycerol + acetic acid, 7.5. Picric acid
7.9.22 Flammable
1. The word "flammable" means "easily set on fire". Also, you can use "non-flammable", but in chemistry do not use "inflammable". Flammability, explosion, limits: outer limits for the ratio of fuel to air within which the mixture will burn. The mishandling of flammable solvents has probably caused fires and personal injuries in chemical laboratories, especially the burning of loose long hair. Staff and students must have securely fixed and contained hair by tying back the hair or using caps or hair nets. Flammable solvents become more difficult to ignite as their boiling points rise, so use the highest boiling point solvent possible. Do not use water baths to heat volatile flammable solvents. Solvents should only be used by staff with students after assessment of the risks, which include not only flammability but their toxicity including possible allergic reactions.
2. Carbon disulfide has a greater flammability than ether and forms more dense vapours, with a low ignition temperature < 100oC. Carbon disulfide is not permitted in schools.
3. Diethyl ether evaporates readily to form a heavy vapour in air, which can travel along the bench or floor in an air current. Diethyl ether is not permitted in schools.
4. Hydrogen forms violently explosive mixtures with air in almost any proportions and spontaneously combusts at concentrations greater than 4% in air. Use this gas for demonstration purposes only in extremely small quantities or use soap bubble techniques.
5. Natural gas forms explosive mixtures with air so turn off heaters, Bunsen burners, and other equipment using natural gas and other flammable gases, e.g. acetylene.
6. Methylated spirit, ethanol and hydrocarbon solvents, e.g. petroleum spirit, hexane, pose the greatest risk in schools. Mixtures of air with any of these materials are highly flammable, and ignition of vapour is usually followed by a fire in or around the solvent container.
7.9.23 Flashpoint
The flashpoint is the temperature at which a chemical produces enough vapour to catch fire in the presence of flame.
7.9.24 Flocculent
A flocculent is usually a precipitate in cloud-like tufts, flocs. In bacteriology, flocculation refers to the formation of floccules (agglutinated bacteria) in a precipitin test, especially for antigens of Salmonella. In mining, flocculation refers to coagulation of ore particles to form flocs and remove excess water.
7.9.25 Fluorescence
The rapid emission of light at longer wavelengths than that which is absorbed, e.g. adsorption of ultraviolet light can yield blue fluorescence. Use a 1:500 alcoholic solution of eosin to demonstrate fluorescence.
7.9.26 Flux
A flux is a substance added to lower the melting temperature in metallurgy and soldering. The fusion of metals to form alloys is often done under a flux that may promote liquefaction, prevent volatilization and unnecessary exposure to the air.
7.9.27 Froth flotation
The mining industry uses froth flotation to adsorb chemicals on solid particles along with a foam to preferentially float off certain minerals and leave others behind.
7.9.28 Fuel cell
A fuel cell is a device with a cathode and anode, which converts a fuel directly into electricity without burning. The simplest case is hydrogen gas bubbled over a porous sintered nickel anode in alkali solution, while oxygen is bubbled over a similar cathode separated by a porous membrane. An electric current is produced in an external circuit. Like a battery, except that fuels, e.g. methanol, rather than metals are consumed, and the reaction is not reversible.
7.9.29 Galvanize
(Luigi Galvani 1737-1798)
To galvanize to cover metal by electrodeposition of zinc. A common roofing material is galvanized iron.
7.9.30 Group formula
A group formula places atoms together in groups that correspond to the grouping in the actual molecule, e.g. aspirin, CH3CO.O.C6H4COOH.
7.9.31 Heavy metals
See 1.14: List of heavy metal compounds
Heavy metals are higher atomic mass metals. They tend to form more poisonous compounds, e.g. Hg, Cd, Pb.
From New South Wales Department of Education publication "Chemical safety in schools":
Not all heavy metal salts are toxic, but most are, i.e. arsenic, lead, cadmium and mercury compounds are extremely hazardous. They are toxic mainly by ingestion and by inhalation of dusts or fumes, and skin contact especially with chromates, which can cause severe dermatitis. It is important to use safe working practices to prevent student contact with heavy metal salts. Some heavy metal salts are powerful oxidants and may also present a reactive hazard. Avoid or control contact of heavy metals with reducing agents. Collect solution wastes of heavy metals, and reduce volume by allowing solvent (usually water) to evaporate. Solid wastes of heavy metals should be recycled if practicable. Insoluble heavy metal salts (such as barium sulfate) may be placed in garbage. Very often chemical disposal can be incorporated into student activity to demonstrate a chemical process. For example, recrystallization of copper sulfate or displacement of copper from solution using steel wool.
7.9.31.1 Recycle heavy metals
Solutions of the following heavy metals may be treated for recycling: antimony, barium, beryllium, chromium, cobalt, lead, manganese, molybdenum, nickel, selenium, strontium, tellurium, tin, vanadium, zinc, Precipitate insoluble metal salts with sodium carbonate, sodium hydroxide or sodium sulfide. Decant the clear solution above the precipitate and wash it down the sink. Store the dried precipitate in a waste disposal bottle or use a displacement reaction to recover the elemental metal. For example copper may be displaced from solution by adding steel wool to precipitate the copper. Decant the clear solution above the precipitate and wash it down the sink. Store the dried precipitate.
7.9.32 Hydronium ion (hydroxonium ion, oxonium ion)
An hydronium ion H3O+ is formed when acids dissociate in water.
7.9.33 Hydrophilic, hydrophobic
The hydrophilic substances are water-loving, polar molecule materials that mix with water, are attracted to water and may dissolve in water to form hydrogen bonds, e.g. glucose, sugars. They have an affinity for water and are readily absorbed or wetted by water. Hydrophilic colloids readily for hydrosols or remain as hydrosols.
The hydrophobic substances are water-hating, non-polar molecule materials, often oily, that do not mix with water or repel water, e.g. oils. proteins, greases, clays. Hydrophobic colloids do not form or remain as hydrosols. Hydrophobia is the aversion to water of a person suffering from the disease rabies. Soap molecules have one end polar and the other end non-polar so they can attach to oils yet dissolve in water.
7.9.35 Inhibit
To inhibit is to slow down a chemical reaction by blocking a part of the mechanism.
7.9.36 Labile
A labile substance is unstable and liable to change to another form or to move away.
7.9.37 Martensite
A martensite forms when a solid solution of carbon in iron forms on rapid cooling. It is responsible for the hardness of quenched steel.
7.9.39 Molecular mass
The molecular mass, formerly molecular weight, is the mass of one mole of that material.
7.9.40 Napalm
Petrol gelled with the aluminium salts of naphthalene acids and palmitic acids, used for warfare in flame throwers and napalm bombs.
7.9.41 Petroleum fraction
Petroleum fraction, petroleum gas: 16.1.12.1
A fraction of oil selected in a refinery distillation process on the basis of boiling point.
7.9.41.1 Petroleum spirit, 60 / 80, 80 / 100, flammable liquids: 3.5.8
Petroleum spirit, petroleum ether, benzine, petroleum benzin, petroleum solvent, 40oC-60oC, pet ether, igroine, light petroleum, petroleum solvent, Highly flammable, Toxic by all routes, Do not inhale vapour. Petroleum spirit, use higher boiling point fractions to avoid benzene, chromatography solvent thinner
7.9.42 Photolysis
A photolysis is chemical reaction brought about by light including ultra-violet light. A radiolysis is the equivalent when radioactive emissions are involved.
7.9.44 pK
A measure of the degree to which an acid or base will dissociate in water. The negative logarithm of the acid dissociation constant K, When the pH of solution is at the value of pKa for a dissolved acid, that acid will be 50% dissociated.
7.9.46 Radical
A radical is a group of atoms that behaves like a single atom in a chemical reaction, e.g. the ammonium radical, NH4+. A free radical has an unpaired single electron, e.g. the methyl radical, CH3-.
7.9.47 Sequester
To sequester is to take out of circulation, to tie up metal ions so that they do not interfere, to form a stable chelate complex or biochemical complex with an ion to remove it from solution or otherwise make it unreactive, e.g. by precipitating soaps. A sequestering agent is a chemical that ties up metallic ions in solution.
7.9.48 Solute
The solute is the dissolved material in a solution or the material to be dissolved. The solute is the minor component in a solution.
7.9.49 Solvent
The solvent, usually a liquid, is the dissolving material in a solution or the liquid to dissolve the solute. The solvent is the main component of a solution.
7.9.50 Spontaneous
A spontaneous process that has the potential to occur on its own without further input. However, it may occur so slowly it is not measurable.
7.9.51 Substrate
A substrate basis on which something else is placed, a starting material. It is usually the underlying layer on which another substance reacts with and / or is deposited. Also, an enzyme act on a substrate to facilitate a chemical change in it.
7.9.51.1 Sulfates
Salt or ester of sulfuric acid, sulfuric (IV) acid, contain ion SO42-, normal and acid salts, organic sulfates R2SO4. Sulfation on plates of lead acid battery, secondary cell, causes reduced efficiency because PbSO4 forms. Sulfate ion is not toxic. Toxicity depends on the cation present, especially heavy metals, e.g. leads in lead sulfate. When sulfates are heated to decomposition, toxic sulfur dioxide gas forms.
Metal sulfates are used to study the following:
1. the reactivity series of metals,
2. the properties of the sulfate ion,
3. the heating to decomposition and
4. redox reactions, including the formation of precipitates.
Sulfate solutions, if not containing heavy metals, may be directly discharged to the sink if solution pH = 8-10.
7.9.51.2 Sulfides
Sulfur with more electropositive element to form an inorganic compound, sulfur with metal by direct combination, sulfur with nonmetals to form covalent compounds, e.g. hydrogen sulfide H2S, salts of hydrogen sulfide are ionic sulfides containing S2- ion, organic thioethers containing two hydrocarbon groups, RSR (R is not H), e.g. diallyl sulfide with garlic smell, and dimethyl sulfide CH3SCH3.
The sulfide zone of a sulfide mineral lode contains unaltered sulfide mineral and leached sulfides from above. Metal sulfides may react violently with oxidizing agents. When heated to decomposition they produce toxic fumes of sulfur compounds. They react with acid or water to produce toxic hydrogen sulfide gas.
Alkaline sulfides, i.e. calcium, sodium, ammonium and potassium sulfides, behave like alkalis, and may cause softening and irritation of the skin. Sulfides of heavy metals are usually insoluble and have low toxicity. However, they may react with acids to release hydrogen sulfide gas.
Metal sulfides are used to study the following:
1. reactivity series of metals,
2. properties of the sulfide ion,
3. reactions with acids,
4. reactions with water,
5. the heating to decomposition,
6. formation of precipitates in redox reactions.
Sulfide solutions, if not containing heavy metals, may be discharged down the sink after treatment to be made acidic in a fume cupboard to expel hydrogen sulfide gas. After completion of the reaction the solution should be made basic with sodium hydroxide to pH: 8-10, then discharged down the sink.
7.9.51.3 Sulfites
Salt or ester from sulfurous acid, sulfuric (IV) acid, with reducing properties, normal sulfites and acid sulfites, bisulfites, salts contain SO32-. Bisulfites are used to digest wood pulp. All sulfites are toxic if ingested. Most metal sulfites irritate the stomach by production of sulfurous acid. When sulfites are heated to decomposition, toxic sulfur dioxide forms. Sulfite solutions, if not containing heavy metals, may be discharged down the sink after treatment. Solutions should be made acidic in a fume cupboard to expel sulfur dioxide gas. At completion of the reaction the solution should be made basic with sodium hydroxide to pH: 8-10, then discharged down the sink.
7.9.52 Surfactants
A surfactant is molecule attracted to the surface of water and capable of changing the properties of the surface, generally by lowering the surface tension to make a solution more wettable.
7.9.53 Synergism
A synergism occurs when two or more substances together produce an effect that is greater than the sum of the individual separate effects. In pharmacology, the combined action a two drugs administered together may be greater than action of the combined action of the two drugs administered separately at different times.
7.9.54 Tempering
A tempering is a time temperature treatment for modifying the mechanical properties of complex materials such as steel and chocolate.
7.9.54.2 Urethane
Urethane, ethyl carbamate ester, CO(NH2)OC2H5, is toxic. Urethanes form when the isocyanate group (-NCO) reacts with (-OH) group to form a urethane, similar to amide bonds in nylon. Polyurethanes are synthetic resins containing the repeating group -NH-CO-O-.
7.9.55.1 Waste chemicals bottles
Recommended waste chemicals bottles include:
Waste copper residues
Waste halogenated organic chemicals
Waste heavy metal mixtures
Waste non-halogenated organic liquids
Waste lead residues
Waste mercury residues
Waste silver residues
Waste zinc residues
In some countries, waste chemicals bottles are collected periodically by government or contractors.
7.9.56 Water glass
Water glass is a colloidal solution of sodium or potassium silicate in water that solidifies on exposure to the air. It is used in chemical gardens, egg preserving, paper sizing, fire-resistant paint and fresco painting.
7.9.56.1 Xanthene dyes
From condensation of phthalic anhydride with resorcinol, have xanthene nucleus, e.g. fluorescein