School Science Lessons
Topic 07b
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7b Chemistry terminology, physical changes, forms of sulfur

Table of contents

See: Chemicals (Commercial)

See: Laboratory Equipment (Commercial)

7.1.6 Chemical changes & physical changes

7.9.0 Chemistry terminology

7.1.5 Prepare forms of sulfur

7.2.0 Pure substances & impure substances

7.2.1 Classify substances

7.1.6 Chemical changes and physical changes
7.1.0 Chemical changes and physical changes
Experiments Burn magnesium and weigh the products Burn steel wool and weigh the products Derive empirical formula of magnesium oxide
7.1.2 Chemical changes, heat organic substances
7.1.3 Chemical changes, heat metals in chlorine
7.1.4 Physical changes, magnetize and demagnetize iron wire

7.1.5 Prepare forms of sulfur, allotropes of sulfur
See: Sulfur Elements, Compounds, (Commercial)
Experiments Physical changes, prepare forms of sulfur, allotropes of sulfur Prepare monoclinic sulfur from powdered sulfur (flowers of sulfur) Prepare monoclinic crystals from roll sulfur Prepare plastic sulfur then rhombic sulfur
12.18.1 Prepare forms of sulfur Reactions between two elements, Heat iron with sulfur

7.9.0 Chemistry terminology Acid, acids
7.9.2 Aerobic
7.9.3 Aliquot
5.5.0 Alloys
12.7.0 Alkali, Bases, properties of bases, strong bases Allotropes, sulfur, carbon
5.5.2 Amalgams
7.9.6 Amphoteric
7.9.12 Anti-bumping granules, boiling chips Aqueous solutions, states of matter
3.0.0 Atoms
7.9.7 Azeotrope
7.9.8 Base
7.9.9 Bessemer process
7.9.10 Borosilicate glass, Pyrex
7.9.11 Buffers
Catalyst, catalytic Catalytic converter in a motor vehicle
7.0.0 Chemical compounds Chemical potential energy, enthalpy Chloramphenicol Clathrate
7.9.15 Continuous phase / outer phase
Cracking, Thermal cracking, Catalytic cracking
7.9.16 Detergent, SYNDET, Synthetic Detergent
8.0.0 Direct union of elements to form compounds
2.0.0 Elements
14.0 Electrophiles and nucleophiles, hydrogen chloride Elements and compounds, Properties of elements
7.9.19 Enzymes
7.9.20 Equilibrium Etchants
7.9.22 Flammable
7.9.24 Flocculent
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 Heavy metals safety Heavy metals recycling
7.9.32 Hydronium ion (hydroxonium ion, oxonium ion)
7.9.33 Hydrophilic, hydrophobic
Hygroscopic, deliquescent and efflorescent substances
7.9.35 Inhibit
5.0.0 Ions
7.9.36 Labile
7.9.37 Martensite
1.0.0 Matter
1.1.0 Micronization
4.0.0 Molecules
5.1.0 Mole, amount of substance
7.9.39 Molecular mass
7.9.40 Napalm
7.9.41 Petroleum fraction Petroleum spirit Petroleum ether
7.9.42 Photolysis
7.9.46 Radical
7.9.47 Sequester
7.9.48 Solute
7.9.49 Solvent
7.9.50 Spontaneous
7.9.51 Substrate Sulfates, battery sulfation Sulfides Sulfites
7.9.52 Surfactants
7.9.53 Synergism
7.9.54 Tempering Urethane Waste chemical bottles
7.9.56 Water glass Xanthene dyes
7.9.57 Zymase

1.0.0 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 Caffeine, extraction 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 following:
RESS process (Rapid Expansion of Supercritical Solutions), where the solution is expanded through a nozzle,
SAS method (Supercritical Anti-Solvent), where the material precipitates out of the solution as a solid with a very small
particle diameter,
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.

2.0.0 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.

3.0.0 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.

4.0.0 Molecules
Molecules have 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.
Molecular formula represents the number of atoms of each element in the molecule.
The molecular formula of water is H2O, so water contains two H atoms and one O atom.
The empirical formula of a compound shows the ratio of elements present in the compound.
Glucose has a molecular formula of C6H12O6, so it contains 2 moles of hydrogen for every mole of carbon and oxygen.
The empirical formula for glucose is C6H12O6/6 = CH2O.
2CH Empirical formula - Equipment for senior chemistry practicals (Commercial).

5.0.0 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.

7.0.0 Chemical 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.

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 (chemical change takes place in air causing a gain in weight).
4. Chew food (physical change for biting and masticating, and chemical change for the reactions of starch with
salivary amylase). Burn magnesium and weigh the products
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). Burn steel wool and weigh the products
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. Derive empirical formula of magnesium oxide
To obtain useful data when burning magnesium, problems may occur with igniting the Mg, keeping the Mg burning
and recording very little or no mass gain.
Using only 3 cm is not enough so coil it up and use about 25cm in a crucible over a Bunsen burner to oobtain
reasonable results.
Use sandpaper on the magnesium before experimenting tp remove the oxide layer, then place the magnesium in the
crucible, leaving the lid open until it was just about to react.
Make sure that as much of as possible of the coiled longer piece is in contact with the crucible.
Leave the lid off until it ignites, then, while still heating, keep raising the crucible lid with tongs to let in
more oxygen, without releasing too much ash. until the reaction appears complete.

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, so a physical change has occurred.
Hammer the iron wire, the iron wire cannot attract the iron filings so strongly, so the physical change has been reversed. Physical changes, prepare forms of sulfur, allotropes of sulfur
See diagram 12.18.1: Sulfur crystals
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. 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. 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. 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.
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.

4. 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.
Table 7.2.1
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 + Acid, acids
(Latin: acidus, sour tasting)
An acid is a good electrolyte, reacts with active metals, turns blue litmus red and has a sour taste.
Acids contain hydrogen replaceable by metals.
Acids neutralize alkalis and alkalis neutralize acids.
Acids are sour corrosive, mainly liquids, that can dissolve metals.
Acids with water produce hydrogen ions, H+.
An acid is a proton donor (H+) (Bronsted-Lowry definition).
Acids an donate protons or accept pairs of electrons.
The "acid test" was originally the nitric acid test for gold because only gold would not dissolve in it.
To acidify is to add acid to usually a solution.
Acidic substance have pH < 7.
An acid salt is formed by an acid where incomplete exchange of replaceable hydrogen occurs.
An acid dye is a dye that is metallic salt of an acid and c an be applied in an acid medium.

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.
Bauxite digestion: 12.1.9
Chlorine levels in swimming pools: 18.7.12
Estimate aerobic mesophilic bacteria by the plate count method: Allotropes, sulfur, carbon
See diagram 12.18.1: Sulfur crystals
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

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. 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% ethanol.
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).

7.9.9 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.
Mixing bowls, Pyrex, glass 1 litre
Casserole dish, freezer and dishwasher safe, 2 litre.

7.9.11 Buffers
See: Buffer Solutions (Commercial)
A mixture of substances that tend to hinder large changes in acid or basic properties of a solution.
The term "buffer" is 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 Anti-bumping granules, boiling chips
Anti-bumping granules, boiling chips (- ceramic, silicon carbide, fused alumina)
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. 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. Chemical potential energy, enthalpy
1CH Enthalpy - Equipment for senior chemistry practicals (Commercial)
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
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.
Energy is usually measured at 100 kPa and 298 K. Chloramphenicol, C11H12Cl2N2O5
Chloramphenicol, amphicol, harmful if ingested, broad-acting natural and synthetic antibiotic, interferes with bacterial protein synthesis,
is used to treat eye infections, but may have severe side effects.
Chloramphenicol, the first broad-spectrum antibiotic manufactured synthetically, was isolated from Streptomyces venezuelae
a species of filamentous soil Gram-positive bacterium which produce spores above ground and in the soil.
9.2.32 DRBC (food spoilage medium). 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.

7.9.16 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.

7.9.19 Enzymes
Enzymes are biological catalysts that can speed up, and control, chemical reactions that would otherwise virtually never occur at
normal body temperature, 37oC.
Thousands of chemical reactions are occurring in the human body every moment of life, and each of these reactions is controlled by a
particular enzyme, e.g. catalase breaks down potentially poisonous hydrogen peroxide into water and oxygen.
Enzymes are proteins that are specific in their action, but are not altered by the reaction, so they can be used repeatedly.
An enzymes is neither a reactants nor a product of a chemical equation it influences.
As with all proteins, enzymes are destroyed by heat or by extreme values pH or salt concentration, denaturation.
So enzymes are sensitive to pH.

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.
The symbol for equilibrium in this document is <--> or <=>.
For example, if nitrogen dioxide is placed in a closed flask, some of it changes to dinitrgen tetroxide.
2NO2 (g) <=> N2O4 (g)
nitrogen dioxide <=> dinitrgen tetroxide. 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 construction of printed circuit boards 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

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,
7.7. 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.

7.9.24 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
In the mining industry, flocculation refers to coagulation of ore particles to form flocs and remove excess water.

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
Power supply, Fuel cell, (Commercial)
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.
A fuel cell is like a battery, except that fuels, e.g. methanol, rather than metals are consumed, and the reaction is not reversible.
Fuel cells need a continuous source of fuel and oxygen from the air. However, in a battery the energy comes from chemicals already stored in the battery.
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,

7.9.31 Heavy metals
Heavy metals, metals of high density, specific gravity > 5, high relative atomic weight (atomic mass), especially if poisonous.
The term "heavy metals" is used in legislation related to chemical hazards and safe use of chemicals with the legal regulations
in specifying a list of heavy metals to which they apply.
Heavy metals defined as elements commonly used in industry and toxic to animals and to aerobic and anaerobic processes
may include As, Cd, Cr, Cu, Pb, Hg, Ni, Se, Zn.
The following are called "heavy metals", if they cause pollution:
| Copper
| Lead
| Mercury
| Zinc, The term "heavy metal" is not exact, for example, Aluminium and Beryllium are toxic, but they are not called "heavy metals". Heavy metals safety
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.
Heavy metals 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
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. Heavy metals recycling
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
"Magic Sand" (Hydrophobic Sand), invisible in water, absorbent hydrophilic polymer (toy product)
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 form 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:
A fraction of oil selected in a refinery distillation process on the basis of boiling point. Petroleum spirit
Petroleum spirit, Do NOT use in school laboratories
Petroleum spirit, 60 / 80, 80 / 100, flammable liquids: 3.5.8
Petroleum ether, Toxicity, Poisons and First Aid: 3.10.0 (Table)
Petroleum spirit, petroleum ether ACS reagent, ligroin, benzine (not "benzene"), petroleum fraction 60-150oC,
mixture of mostly pentanes and hexanes, petroleum benzine, petroleum solvent, 40oC-60oC,
light petroleum, petroleum solvent, Highly flammable, Toxic by all routes, so do not inhale vapour.
Petroleum spirit, use higher boiling point fractions to avoid benzene, thinner, solvent in non-polar chromatography.
Highly flammable liquid and vapour, may be fatal if swallowed and enters airways, and may cause genetic defects and cancer.
Low cost but substitute toluene or xylene from hardware store.
("benzine", in some countries = petrol).

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.

7.9.46 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. Sulfates, battery sulfation
Salt or ester of sulfuric acid, sulfuric (IV) acid, contain ion SO42-, normal and acid salts, organic sulfates R2SO4.
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.

Battery sulfation
Sulfation on plates of a lead-acid battery, secondary cell, causes reduced efficiency because PbSO4 forms.
Sulfation is the effect of overcharging or other environmental conditions in lead acid batteries that leads to permanent capacity loss.
Flakes of lead sulfate break away from the plates and fall to the bottom of the cell, where they can no longer react and produce energy. 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, 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. 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
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. Urethane
Urethane, ethyl carbamate ester, carbamic acid ethyl ester, C3H7NO2, NH2COOC2H5, CO(NH2)OC2H5, toxic, suspected carcinogen,
veterinary anaesthetic, colourless, odourless, emits toxic fumes of nitrogen oxides when heated, used to make pesticides and
pharmaceuticals, prepare polyurethane plastic, contaminant of fermented alcoholic beverages. 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. Xanthene dyes
See diagram Fluorescein
From condensation of phthalic anhydride with resorcinol, have xanthene nucleus, e.g. fluorescein.

7.9.57 Zymase
Zymase is the mixture of enzymes, enzyme complex, in yeasts that catalyzes the breakdown of sugar in alcoholic fermentation into
alcohol and carbon dioxide.

8.0.0 Direct union of elements to form compounds
To form acids
H2 + Cl2 --> 2HCl
H2 + S --> H2S.

To form salts
2Na + Cl2 --> 2NaCl
Fe + S --> FeS
8Fe + S8 --> 8FeS (ferrimagnetic iron (II) sulfide) Heat iron with sulfur, Synthesis reaction.

14.0 Electrophiles and nucleophiles, hydrogen chloride
In the reaction of hydroxide ion with hydrogen chloride, the oxygen of hydroxide ion has -1 charge and the hydrogen of hydrogen
chloride has δ+ charge because chlorine is more electronegative than hydrogen, so the H-Cl bonding electron pair is unequally shared.
The oxygen atom of hydroxide ion shares a lone electron pair with the hydrogen atom of hydrogen chloride.
In most organic chemistry reactions, one species in the reaction shares an electron pair (a Lewis base), with another species (a Lewis
acid), to form a covalent bond.
An electrophile (Greek: electron loving) (Lewis acid), is a molecule or ion that accepts a pair of electrons to make a covalent bond.
So a molecule, ion or atom that is electron deficient can be an electrophile, e.g. CH3+ methyl, HCl (Hδ+ ), NH4+ ammonium.
A nucleophile (Greek: nucleus loving) (Lewis base) is a molecule or ion that donates a pair of electrons to form a covalent bond.
So a molecule, ion or atom that has electrons that can be shared can be a nucleophile, e.g. I- iodide, NH3 ammonia.
Electrons always move from nucleophile to electrophile.
However, the oxygen atom of water has two lone pairs and a δ- charge because oxygen is more electronegative than hydrogen, so
water can behave an a nucleophile, but each hydrogen atom has a δ+ charge, so the water molecule can also behave as an electrophile.
If water reacts with an electrophile, it behaves as a nucleophile.
In organic chemistry, electrophiles are + ve charged reagents attracted to electron rich areas of molecules.

Nucleophilic reactions
Prepare esters: 16.5.3
Reactions of 2-bromopropane with hydroxide ions: