School Science Lessons
Topic 7 Chemical changes and physical changes, elements and compounds
2012-05-17 SPwp
Please send comments to: J.Elfick@uq.edu.au
Table of contents
7.2.2 Elements and compounds
7.2.2.1 Elements and compounds, descriptions
of common elements and their chemical reactions
9.4.0
Levels of organization
7.2.2 Elements and compounds
3.0 Atoms
6.0 Chemical bonds
7.0 Compounds
8.0 Direct union of elements to form compounds
2.0 Elements
7.2.2a Elements experiment
5.0 Ions
1.0 Matter
1.1.0 Micronization
4.0 Molecules
7.2.2.1 Elements and compounds,
descriptions of common elements and their chemical reactions
[The properties listed below are based on information from IUPAC,
International Union of Pure and Applied Chemistry.]
Al, Aluminium properties: 7.2.2.1
Alums: 7.2.2.1a
Aluminium chemical reactions: 12.1
Sb, Antimony properties: 7.2.2.2
Antimony chemical reactions: 12.2.1
Ar, Argon properties: 7.2.2.3
As, Arsenic properties: 7.2.2.4
Arsenic, Reactions of arsenic and arsenic compounds: 12.2.2
Ba, Barium properties: 7.2.2.5
Barium chemical reactions: 12.2.3
Bi, Bismuth properties: 7.2.2.6
Bismuth chemical reactions: 12.2.4
B, Boron properties: 7.2.2.7
Br, Bromine properties: 7.2.2.8
Bromine experiments: 12.19.9
Cd, Cadmium properties: 7.2.2.9
Cadmium chemical reactions: 12.3.1
Ca, Calcium properties: 7.2.2.10
Calcium chemical reactions: 12.4.1
C, Carbon properties: 7.2.2.11
C, Charcoal blocks: 7.2.2.11a
Carbon chemical reactions: 16.1.0
Cl, Chlorine properties: 7.2.2.12
Chlorine experiments: 12.19.8
Cr, Chromium properties: 7.2.2.13
Chromium chemical reactions: 12.5
Cobalt
Cu, Copper properties: 7.2.2.15
Copper chemical reactions: 12.7
F, Fluorine properties: 7.2.2.16
Fluorine experiments: 12.19.7
Au, Gold properties: 7.2.2.17
He, Helium properties: 7.2.2.18
H, Hydrogen gas properties: 7.2.2.19
I, Iodine properties: 7.2.2.20
Iodine experiments: 12.19.6
Fe, Iron properties: 7.2.2.21
Iron chemical reactions: 12.8.0
Kr, Krypton properties: 7.2.2.22
Pb, Lead properties: 7.2.2.23
Lead chemical reactions: 12.9
Lead paint: 7.2.2.23a
Tetraethyl lead: 7.2.2.23b
Li, Lithium properties: 7.2.2.24
Lithium chemical reactions: 12.9A.1
Mg, Magnesium properties: 7.2.2.25
Magnesium chemical reactions: 12.10.1
Mn, Manganese properties: 7.2.2.26
Manganese chemical reactions: 12.17
Hg, Mercury properties: 7.2.2.27
Mercury, Reactions of mercury compounds: 12.8.4
Mercury and dental amalgam
Mo, Molybdenum properties: 7.2.2.28
Ne, Neon properties: 7.2.2.29
Ni, Nickel properties: 7.2.2.30
Nickel, Reactions of nickel compounds, Ni: 12.9.4
N, Nitrogen properties: 7.2.2.31
Nitrogen experiments: 12.11
Reactions of nitrates,
NO3-: 12.11.2
Reactions
of nitrites, NO2-: 12.11.1
Ammonia and the ammonium ion, NH3,NH4+:
12.11.3
O, Oxygen gas properties: 7.2.2.32
Oxygen experiments, hydrogen peroxide: 12.12.0
Ozone, O3, Prepare ozone: 3.50
P, Phosphorus properties: 7.2.2.33
Red phosphorus: 7.2.2.33a
White phosphorus: 7.2.2.33b
Phosphorus chemical reactions: 12.13
Phosphorescence, luminescence, chemiluminescence, fluorescence:
7.2.2.33.1
Detergent phosphates: 7.2.2.33.2
Pt, Platinum properties: 7.2.2.34
K, Potassium properties: 7.2.2.35
Potassium chemical reactions: 12.14
Ra, Radium properties: 7.2.2.36
Rn, Radon properties: 7.2.2.37
Se, Selenium properties: 7.2.2.38
Si, Silicon properties: 7.2.2.39
Silicon chemical reactions: 12.15
Silicon solar panel: 7.2.2.39.1
Ag, Silver properties: 7.2.2.40
Silver chemical reactions: 12.16
Na, Sodium properties: 7.2.2.41
Sodium chemical reactions: 3.73
Sr, Strontium properties: 7.2.2.42
Strontium, Reactions of strontium compounds: 12.17.1
Strontium chemical reactions: 12.16a.1
S, Sulfur properties: 7.2.2.43
Sulfur chemical reactions: 12.18
Sn, Tin properties: 7.2.2.44
Tin chemical reactions: 12.20
W, Tungsten properties: 7.2.2.45
U, Uranium properties: 7.2.2.46
Xe, Xenon properties: 7.2.2.47
Zn, Zinc properties: 7.2.2.48
Zinc, Reactions of zinc and
zinc compounds: 12.21.1
Zr, Zirconium properties: 7.2.2.49
1.0 Matter
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. Materials may be elements, compounds or mixtures.
1.1.0 Micronization
See 19.4.2.3.0: Extraction of caffeine with supercritical carbon dioxide, critical point
Size reduction mills are used in the pharmaceutical industry to increase
surface area, improve formulation dissolution and maintain a consistent average
particle size distribution for tablets and capsules. Impact size reduction
is usually by mechanical impact and impact via fluid energy using hammer mills
and liquidized bed jet mills. Micronization that uses supercritical fluids
to cause the small diameter of the solid particles by the supersaturation
at the time of the particle formation, includes the RESS process (Rapid Expansion
of
Supercritical Solutions), where the solution is expanded through a nozzle,
the SAS method (Supercritical Anti-Solvent) where the material precipitates
out of the solution as a solid with a very small particle diameter, and the
PGSS method (Particles from Gas Saturated Solutions), where the solid is
melted and the supercritical fluid is dissolved in it as in the SAS method
but the solution is forced to expand through a nozzle. The PGSS method is
used for pharmaceuticals and foodstuffs.
2.0 Elements
Elements cannot be broken down into simpler substances by a chemical
change. 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. 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. 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.
3.0 Atoms
Atom is the smallest division of an element that can chemically
exist alone and have the characteristics of the element. Atomic mass
(atomic weight) of an atom is arbitrarily defined relative to the mass
of the isotope carbon. The relative atomic mass of an element is the ratio
of average mass of atoms of the element to 1 / 12 of the mass of one atom
of the isotope C-12. Atomic mass unit, (a.m.u.) is a unit of mass used
to express the relative atomic mass. So 1 atomic mass unit = 1 / 12 of
the mass of the carbon-12 isotope, i.e. 1.66 × 10-27 kg.
The mass of 1 atom of oxygen = 16 a.m.u. The atomic theory dates from the 5th century B.C. when Greek
philosophers, e.g. Democritus, said that matter consists of indivisible
indestructible particles. The modern atomic theory started with the
hypothetical thinking of John Dalton, England, (1766 - 1844). However,
he did not envisage the structure of atoms, i.e. nucleus, electrons
and other particles.
4.0 Molecule
Molecule contains two or more atoms joined chemically to form
the simplest stable structure of that element or compound. So a hydrogen
molecule must contain 2 atoms, H2, because the hydrogen atom,
H, cannot exist by itself. A molecule of water, H2O, contains
2 atoms of hydrogen, H, and 1 atom of oxygen, O.
5.0 Ions
Ions form when an atom or group of atoms covalently bound together
may gain or lose one or more electrons. Ionic bonding occurs when positive
and negative ions are held together in a crystal lattice by electrostatic
forces. The structure of metals involves positive ions embedded in a
sea of electrons.
6.0 Chemical bonds
Chemical bonds are forces of attraction that the atoms together
in a molecule or a crystal. Ionic, electrovalent, bonds form by transfer
of electrons and covalent bonds form by sharing of electrons. Hydrogen
bonds are weak intermolecular forces of attraction between polar molecules
that contain hydrogen, i.e. between the H atom of one molecule and the
negative charged atoms in another molecule.
In water, there is weak attraction
between the hydrogen in a water molecule with the oxygen (in the OH) of
another water molecule. 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.
7.0 Compounds
Compounds are composed of two or more elements that are chemically
united in fixed proportion. Compounds can be broken down to simple
substances. Chemical compounds form when chemical bonds, whether ionic
or covalent, are formed between different elements. A chemical compound
can be represented by a chemical formula. Forces weaker than covalent
bonding exist between molecules. 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. 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 to do this.
4. Will the element
conduct electricity? Place the element between two electrical contacts
in a circuit.
8.0 Direct union of elements
to form compounds
Salts
2Na + Cl2 --> 2NaCl
Fe + S --> FeS
8Fe + S8 --> 8FeS (ferrimagnetic iron (II)
sulfide)
12.2.2.1 Heat iron with sulfur
Acids
H2 + Cl2 --> 2HCl
H2 + S --> H2S
7.2.2.1 Aluminium
Aluminium, Al, is not safe for school use so it is not supplied
as powder. Aluminium reagent test kit, No. 1 tablets, No. 2 tablets,
AAS Std, leaf, flakes, sheet, "Alfoil" cooking foil, drink-can, ingot,
wire, aluminium foil, 300 width × 150 m roll, "Alfoil" disposable
containers, rectangular 120 mm × 175 mm, round 120 mm diameter
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, and wire. The aluminium foil used in home kitchens
from grocery stores and the aluminium wire and aluminium sheeting from
hardware stores are all pure aluminium. Aluminium is 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.
2. Aluminium 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. are accustomed to use the spelling
"aluminum".
3. Finely-divided aluminium particles (powder or fine turnings)
burn in air with an intense white flame if ignited. A significant amount
of ultraviolet radiation is emitted, and the flame should not be watched
with the naked eye. Unoxidized aluminium powder reacts vigorously with
both concentrated acids or alkalis to yield hydrogen gas, which is explosive
when mixed with air. The reaction may occur with such vigour that the
aluminium particles and acid or alkali may be ejected from the container.
Most reactions of aluminium
are inhibited by a surface coating of aluminium
oxide. This is the reason that such an active metal as aluminium can be
used widely for construction and for containers. Aluminium metal reacts
violently with halogens (chlorine, bromine, iodine). The reaction of aluminium
with liquid bromine is hazardous and should not be attempted.
Atomic number: 13, Relative atomic mass: 26.9815, r.d. 2.70,
m.p.: 660oC, b.p.: 2470oC, E 173
Specific heat capacity:
900 J kg-1 K-1
7.2.2.1a Alums
The original "alum" was the hydrated double salt of aluminium
and potassium with colourless octahedral crystals and an astringent
taste. Later the term "alum" was used to describe similar double sulfates
where other elements or radicals replaced aluminium or potassium. Some
plants with astringent roots are called alum roots. So an alum is a hydrated
aluminium potassium sulfate and related minerals. 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. Aluminium potassium sulfate is a buffer and firming agent, E522.
Alums:
Ammonium alum, AlNH4(SO4)2.12H2O
Chrome alum, chromium (III) potassium sulfate, potassium chromium
sulfate, KCr(SO4)2.12H2O or K2SO4.Cr2(SO4)3.24H2O
Potassium alum, potash alum, hydrated potassium aluminium sulfate,
"common alum", Al2(SO4)3.K2(SO4).24H2O,
or AlK(SO4)2.12H2O or KAl(SO4)2.12H2O
7.2.2.2 Antimony
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
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
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
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 ethanol. Barium sulfate is used for a contrast medium
for X-ray examination of intestines. Surface coating of barium hydroxide
corrosive to the eyes. The reaction of barium with water produces flammable hydrogen
gas. Barium is very difficult to cut.
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
Bismuth, Bi, white metallic crystals, from bismuthinite mineral
Bi2S3 and niccolite, cobaltite, 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
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 × 103 J kg-1 K-1
7.2.2.8 Bromine
Bromine, Br, (Greek: bromos, stench), 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)
Bromine is a dense red-brown liquid with a powerfully irritant
vapour. Bromine water, a solution of bromine in water, is usually available
commercially. Handle pure liquid bromine in small quantities in a
fume cupboard. The liquid is unexpectedly dense, so increasing the chance
of containers being dropped by inexperienced people. Breakage of a bottle
of bromine outside a fume
cupboard will require evacuation of the area
until the vapour dissipates. Bromine reacts violently with active metals
such as aluminium / magnesium and sodium. Do not allow active metals to
contact liquid bromine. Always store the bromine in a cool secure store
area.
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
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
Calcium, Ca, 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. Calcium 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
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)
7.2.2.11a Charcoal blocks,
C
Charcoal blocks are hazardous in one way only: they smoulder
and burn for a long time after ignition and may cause fires if put away
before they have been properly extinguished. They have caused fires in
schools. If charcoal blocks are hastily collected and put in a drawer
or cupboard after a laboratory class, they may smoulder for hours or
days before either extinguishing themselves or flaring up. At the end of
a laboratory class, leave the blocks totally immersed in a bucket of water.
An alternative to using charcoal
blocks is to mix equal volumes of metal
oxide and charcoal powder in a test-tube and heat with a Bunsen burner
while the tube is held horizontally. Charcoal can be produced by charring
bread with a Bunsen burner in a fume cupboard.
7.2.2.12 Chlorine
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. For the reactions of chlorine with metals, solid non-metals, and hydrocarbons, 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
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
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. Cobalt, (German: kobold,
goblin of the mines) was associated by miners 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
12.6.1 Properties of cobalt
salts
[Co(H2O)6]2+ = pink hexa aqua
cobalt (II) ion, hexaaquacobalt (II) ion
1. Heat cobalt carbonate in a small hard glass tube. The brown
residue is cobalt (II) oxide.
CoCO3 --> CoO + CO2
Transfer the oxide to a crucible and heat to redness. The black
residue is cobalt (II) cobalt (III) oxide, Co2O4.
2. Add excess of hot sodium hydroxide solution to 3 cm of a cobalt
salt solution. Note the pink precipitate of cobalt (II) hydroxide. Note
the change to brown cobalt (III) oxide, Co2O3
on exposure to air. Cobalt (II) hydroxide is soluble in ammonia solution,
NH3 (aq) ("ammonium hydroxide") because of the formation of
the complex ion [Co(NH)6]2+
Co2+ + 2OH- --> Co(OH)2 (s)
3. Add a suspension of bleaching powder to a test-tube containing
a cobalt (II) salt solution. Note the black precipitate of cobalt (II)
hydroxide. The bleaching powder acts as an alkaline hydroxide and an
oxidizer. Divide the precipitate into two parts. Add excess hydrochloric
acid to one part to obtain a brown solution of the unstable cobalt (II)
chloride. Heat the second part to obtain oxygen gas and a residue containing
cobalt (II) oxide. Cobalt (II) hydroxide behaves as a weak base.
4. Evaporate cobalt (II) chloride solution to dryness and note
the blue colour of the anhydrous salt. Cobalt chloride is stable compare
to hydrated iron (II) chloride. Write on a piece of paper with dilute
cobalt chloride solution. Leave to dry and the writing becomes invisible.
Heat the paper from below and writing appears bright blue because of dehydration
of the salt. So cobalt chlorine solution is a kind of "invisible ink".
5. Put drops of pink cobalt chloride solution on filter paper
and hold it over a flame to se the brilliant blue colour of the anhydrous
salt. A weather indicator can be made by soaking white paper in a concentrated
solution of cobalt chloride.
6. Cobalt ions with carbonate ions
Pink cobalt ions solution,[Co(H2O)6]2+,
reacts with carbonate ions solution to form gelatinous calcium carbonate
precipitate in a pink solution.
Co2+ (aq) + CO32- (aq) -->
CoCO3 (s)
7. Add a dilute solution of ammonia to a cobalt chloride solution
to form a green-blue precipitate. Add excess ammonia to dissolve the
precipitate to leave a light brown solution. Leave to stand to allow oxidation
in the air to form a deep red-brown solution. The same colour change occurs
if hydrogen peroxide is used.
[Co(H2O)6]2+ + 2NH3
-- > [Co(H2O)4(OH)2] + 2NH4+
( hydrogen ions detached form the complex ions to form a green-blue neutral
complex precipitate.
[Co(H2O)6]2++ 2NH3
-- > [Co(NH3)6]2+ + 6H2O
(with excess ammonia, the neutral complex dissolves to form a green solution
containing hexa amine cobalt (II) ions, hexaaminecobalt (II) ions)
[Co(NH3)6]2+ + O2
in the air --> Co(NH3)6]3+ (leave
to stand so that the hexaminecobalt (II) complex is oxidized to deep red-brown
hexaminecobalt (III) complex)
2[Co(NH3)6]2+ + H2O2
--> 2Co(NH3)6]3+ + 2OH-
(same colour change as the above reaction only faster)
8. Add lime water, (CaOH)2, or sodium hydroxide solution
to cobalt chloride solution. A light blue precipitate forms that on standing
the solution turns pink.
Co(H2O)6]2+ + lime water -->
[Co(H2O)4(OH)2] (neutral complex
9.Test for aluminium compounds. Put drops of red cobalt chloride
solution on filter paper. Add drops of aluminium sulfate solution. Dry
the filter paper over a flame then ignite it over a ceramic bowl. The
blue ash formed is a test for all aluminium compounds in solution.
7.2.2.15 Copper
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
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
Gold, Au (aurum) is a yellow, lowest metal in the reactivity 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
Helium, He, is a non-metal noble gas (inert gas) at room temperature
and pressure. Helium has no known compounds. Helium has 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 (in party
balloons but these balloons may travel over the oceans to fall and choke
sea animals), welding. large concentration can asphyxiate, change of
pitch of voice due to increased velocity of sound. Helium has the lowest
critical temperature,
-268oC. Packaging gas, propellant gas
E939.
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 × 103 J kg-1 K-1
7.2.2.19 Hydrogen
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 × 104 J kg-1 K-1
7.2.2.20 Iodine
Iodine, I, I2, 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
complex (PVD-iodine) in the antiseptic "Betadine". Iodine is used in
the muscles and in the thyroid gland as part of the chemicals thyroxine
and triiodothyronine.
Thyroxine is a hormone containing iodine, from thyroid gland,
controls metabolic rate. 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). Iodine poses fewer risks in school laboratories
than the other halogens, chlorine and bromine. Do not inhale the acrid iodine
vapour. Avoid skin contact with solid iodine. Iodine, whether as a solid,
in solution or a
vapour can temporarily stain the skin. Do not allow iodine
to react with concentrated ammonia solution because it forms nitrogen triiodide,
NI3NH3, (touch powder), which is violently explosive. Solid crystalline iodine is toxic by all routes of exposure
and a highly irritating vapour comes off from the crystals and iodine
solutions. Do not mix iodine with concentrated ammonia solution because
the highly explosive nitrogen triiodide may form. The reactions of
iodine with acetaldehyde or antimony metal are violently exothermic.
Use of solid iodine by students should be limited to 0.2 g, (the size
of about 2 rice grains), per experimental activity.
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
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. Iron is
a safe material.
However, both iron filings and iron powder (ferrum reductum) are hazardous
when mixed with either sulfur, chlorine or bromine, because of the highly
exothermic reactions that can occur. Iron is made into steel by mixing it (alloying) with carbon
(mild steel) or with metals, e.g. manganese (armour plating steel),
chromium (stainless steel).
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
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
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
aces 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.
Lead is a metal with a silvery appearance that is resistant
to attack by acids because of the formation of a protective oxidized
layer on its surface. The metal melts at low temperature and is a good
conductor of electricity so it is used in solders. The vapours of molten
lead are extremely toxic and the effect of inhaling them is cumulative.
Lead salts are toxic by inhalation and can be absorbed through the skin
so should be handled with great care. Wash laboratory areas where lead
salts have been used with a dilute detergent
solution to prevent exposure
to any residual dust containing lead. Do not heat lead oxide on a charcoal
block.
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. Products containing lead are 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.
7.2.2.2 Lithium
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 × 103 J kg-1 K-1
7.2.2.25 Magnesium
Magnesium, Mg, as powder, ribbon, turnings, wire, (photographers'
flash bulbs, light bulbs, fire starters, cars, aircraft bodies, alloyed
with aluminium), Toxic if ingested, silver white alkaline earth metal,
2% of the earth's crust, forms protective oxide layer in air that prevents
further oxidation. 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,
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 × 103 J kg-1 K-1
7.2.2.26 Manganese
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.
Manganese is a cofactor for many enzymes, but magnesium can usually substitute
for it.
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
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.
Use mercury in a well-ventilated area that does not have porous surfaces.
Do not heat mercury because more toxic mercury vapour is given off. Liquid
mercury boils violently at atmospheric pressure. Do not react mercury
with chlorine or bromine because
highly toxic salts are formed. Mercury
reacts with the gold in gold rings to form an amalgam and spoil the ring.
Mercury and mercury salts react with aluminium in a violently exothermic
reaction. Sodium amalgam, NaHg2, is formed by electrolysis of
sodium chloride solution with a mercury cathode. Mercury thermometer should
only be used by senior students. Junior students should use alcohol or
electronic thermometers. Most mercury compounds are highly toxic if ingested
or absorbed through the skin. Mercury vapour is highly toxic when inhaled and is a cumulative
poison. The main concern posed by liquid mercury is spillage, followed
by inadequate cleanup. Spilled mercury shatters into many tiny droplets
that lodge in cracks in the floor and around skirting boards. The droplets
have a large total surface area and the mercury can evaporate slowly,
over months or years. Any person working in the area may regularly inhale
the mercury vapour, with adverse effects. Liquid mercury is extremely dense
so the weight of even a small container may surprise some people who may
then drop it. If the pressure measured with a mercury-in-glass manometer
suddenly changes because of the careless opening of a tap, the moving column
of mercury may break the walls of the manometer and mercury spills everywhere.
Avoid the use of mercury by using solid state electronic devices for measuring
pressure. Use less dense liquids, even water, in a manometer, to demonstrate
changes in pressure. Do not place mercury thermometers in a dish washer
for cleaning. Drains in laboratories often contain significant amounts of
mercury in the S-bends. Before disposal of broken thermometer debris or
mercury-contaminated rubbish from S-bends, mix them with an equal volume
of sulfur powder. Fit a tray containing a centimetre of sulfur powder beneath
the apparatus because mercury spilled on sulfur powder will not shatter into
fine droplets and the sulfur will inactivate the mercury. Pour mercury over
a plastic tray containing water so that any spilled mercury will not shatter
into droplets, but form a lower layer that can be recovered easily. Periodically
check the waste water filter of a laboratory dishwasher for liquid mercury.
Store mercury in a sealed container on a plastic tray to catch any spilt
mercury.
Mercury spills
Mercury metal gives off a highly toxic vapour that acts as a
cumulative poison. Spilt mercury shatters into droplets, which lodge
in cracks and crevices to evaporate slowly for years causing long-term
exposure to low levels of mercury vapour in the air. So spilt mercury must
be immediately treated with sulfur powder or mercury decontaminant, a
mixture of calcium hydroxide and sulfur, to form mercury (II) sulfide
that is stable and harmless. Then sweep up the mercury and sulfur together.
Always keep available 2 kg of
sulfur or 2 kg of mercury decontaminant in
the laboratory near any equipment containing mercury.
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
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
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 × 103 J kg-1 K-1
7.2.2.30 Nickel
Nickel, Ni, as foil, powder, is a transition metal that resists
corrosion. It is obtained from ores containing NiS and is available
as sheet. It is used in shiny coin alloys, nickel plating, and in "silver"
cutlery stamped "EPNS" (electroplated nickel silver) that has a shiny
metal protective coating. It reacts with dilute HCl or H2SO4
to form H2 and metal ion and reacts with concentrated oxidizing
acids, HNO3 or H2SO4 to produce high
oxidation number ions, and sulfur dioxide SO2 or nitrogen
dioxide, NO2. It reacts with steam to give the oxide and hydrogen
gas. Heated powder forms oxide. The name nickel 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
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 × 103 J kg-1 K-1
7.2.2.32 Oxygen
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
Phosphorus, P, Phosphorus is a non-metal network solid, occurs
mainly as phosphates and in many minerals, e.g. apatite, has two main
allotropes, Phosphorus has 2 main allotropes: 1. white phosphorus,
(yellow phosphorus) and 2. red phosphorus, see below. 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. Phosphoric
acid, H3PO4, behaves as a tribasic acid although
the normal salts are much hydrolysed in solution.
7.2.2.33a Red phosphorus
Red phosphorus, brown phosphorus, P4, 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 "safety match" striking surfaces that contain red phosphorus,
powdered glass, carbon black, a binder and a neutralizer, e.g. calcium
carbonate. Used for "doping" semiconductors. Red phosphorus is relatively
harmless compared with the white phosphorus allotrope. However, some
school systems do not allow red phosphorus to be used in school science
experiments. It is not poisonous when pure. It is deliquescent so keep
it in a sealed container. Do not heat red phosphorus in a test-tube because
it produces phosphorus vapour that condenses to form white phosphorus.
Re phosphorus form violently explosive mixtures with oxidizing agents,
e.g. metal nitrates (potassium nitrate, sodium nitrate, potassium permanganate),
nitric acid, chlorates, perchlorates, peroxides, peroxy salts. Do not heat
phosphorus on a platinum wire because it corrodes the platinum.
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
7.2.2.33b White phosphorus
White phosphorus (yellow phosphorus), P4, is too reactive
to be used in school science teaching so it is not permitted in schools,
White phosphorus is waxy, poisonous, spontaneously flammable, reacts
with oxygen gas in the air to form P2O5, so it
is stored under water. White phosphorus is extremely toxic. On contact
with iodine it ignites, with bromine it explodes, and it can be ignited
with a hot glass rod. Cover spilt white phosphorus with 0.2 M copper sulfate
solution that converts it to harmless copper sulfide.
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
7.2.2.33.1 Phosphorescence
Phosphorescence is the green glow from the slow oxidation of
white phosphorus. Luminescence is emission of light for any reason
other than a rise in temperature, e.g. excited photons returning to
a ground state. Chemiluminescence is luminescence resulting from a
chemical change. However, the term phosphorescence is also used to
describe a situation when the luminescence persists even though the
exciting cause has been removed. Luminescence that does not persist when
the exciting cause is removed is called fluorescence, e.g. a fluorescent
light.
Order online: Fluorescence
Activity Kit, four fluorescent minerals
7.2.2.33.2 Detergent phosphates
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 authorized food ingredient.
Phosphates occur in sewage from detergents, human foods, (transferred
into human wastes) animal
manure and food industry wastes. These phosphates
can be recovered and recycled back into fertilizers 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
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 placer deposits 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
Potassium, K (kalium) is a soft and shiny white alkali metal, highest
metal in the reactivity 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. (in liquid paraffin). Potassium metal is banned in many school systems.
Potassium reacts violently with water to form hydrogen gas that
may ignite or explode. Destroy potassium safely with 2-methylpropan-2-ol.
Potassium forms a crust of yellow oxide that may explode when cut.
Use sodium or lithium instead of potassium.
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
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
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
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 µ g for males, and 55 µ 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
Silicon, Si, lump [powder] 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
Order online: Solar Racer,
toy car moved by solar energy
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). A concentrated
solar power system (CSP) use lenses or mirrors to concentrate solar thermal
energy, onto a small area to heat water in a steam turbine and generate
electricity. A concentrated photovoltaic system (CPV) focus sunlight
onto photovoltaic materials to generate electricity directly.
7.2.2.40 Silver
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"
used in wrapping paper or in chocolates 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
Sodium, Na (in liquid paraffin) (natrium), 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.
Sodium metal reacts violently with water to form highly corrosive
sodium hydroxide and hydrogen gas. The surface of the reacting sodium
may become sufficiently hot to ignite the hydrogen and explode the
air / hydrogen mixture. Reacts explosively with acids, bromides, iodine,
sulfur, polyhalogenated hydrocarbons, e.g. chloroform. The surface of
sodium metal is coated with a mixture of the oxide and hydroxide, both
of which hygroscopic, causing the surface of sodium metal to absorb moisture
from the air, and resulting in further reaction to form hydrogen and sodium
hydroxide. Sodium metal, unprotected in a container, may absorb sufficient
moisture to form an air / hydrogen mixture and then become hot enough
to ignite the mixture, resulting in an explosion. So store sodium under
paraffin oil or kerosene. Store sodium on a low shelf to reduce the chance
of dropping the container. Cut sodium on a clean dry
surface with a clean
dry blade, e.g. an all metal scalpel or small knife, not a scalpel with
detachable blade. Do not lose small pieces of cut sodium. Dispose of sodium
waste by reacting it with ethanol or methylated spirit in a beaker in
a fume cupboard. The reaction of sodium with an alcohol is less violent
than with water, so it is relatively slow and easy to control, but there
is still a risk of fire. The use of flammable solvents in the vicinity
of sodium is always a risk.
Atomic number: 11, Relative atomic mass: 22.9898, r.d. 0.97,
m.p.: 97.8oC, b.p.: 890oC,
Specific heat capacity:
1.23 × 103 J kg-1 K-1
7.2.2.42 Strontium
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", harder to cut than sodium, use calcium as cheaper alternative,
purchase only small quantity and store in tightly-sealed container, give
students only few grains per activity
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
See diagram 12.18.1: Sulphur crystals
Sulfur, S, brimstone, sublimed sulfur, flowers of sulfur, sulfur
sticks, roll sulfur, is a non-metal occurs as S8 molecule
rings. 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. Sulfur is not toxic, but can be dangerous
because of its flammability and hazardous because of the formation of
sulfur dioxide gas as a product of combustion. Used as example of a non-metal
element. The main allotropes are as follows:
1. α sulfur, rhombic sulfur, with yellow octahedral crystals
2. β sulfur with monoclinic prismatic pale yellow crystals. Do not mix sulfur with oxidizing agents, e.g. potassium nitrate
or potassium permanganate, or mercury (II) oxide, because the mixtures
are explosive. Do not prepare mixtures of sulfur with active metal powders,
e.g. aluminium and magnesium, because they are also violently reactive.
Sulfur usually ignites when it is heated, forming sulfur dioxide gas.
This gas is highly irritant to the lungs and should not be inhaled. Use
a fume cupboard for experiments that produce sulfur dioxide. Some asthmatics
are particularly sensitive to sulfur dioxide.
Atomic number: 16, Relative atomic mass: 32.06, r.d. 2.07 (α),
1.96 (β), m.p.: 113oC (α) 119oC (β), b.p.: 445oC
(α),
Specific heat capacity: 0.71
7.2.2.44 Tin
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) and aluminium drink-cans, and in 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" used 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
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
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
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
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. Zinc is dangerous only as a fine powder, zinc dust, that is
flammable and has been used in the past to make rocket fuel by mixing
it with finely-divided sulfur. This procedure is not permitted in schools.
Zinc / sulfur mixtures are extremely hazardous materials, liable to
combust violently on ignition and release large amounts of sulfur dioxide
from oxidation of unreacted sulfur. Zinc dust forms hazardous mixtures
with iodine and many oxidizing agents, e.g. manganese dioxide, potassium
nitrate and potassium permanganate.
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
7.2.2.49 Zirconium
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
7.2.2a Elements experiment
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.