School Science Lessons
Please send comments to:

Chemistry L
Table of Contents
Labile substances are unstable and liable to change to another form or to move away.
See: Label Maker (Commercial)
See: Laboratory Equipment (Commercial)
See: Laboratory Suppliers (Commercial)
Labware (Commercial)
Lactase: 7.1.3
Lactic acid, C3H6O3
Lacto-alcohol, Prepare lacto-alcohol, insect-fixing solution: 4.12
Lactometer test (Milk testing and quality control): 16.1.8
Lactophenol, Prepare lactophenol solution: 3.17
Lactucin, C15H16O5,
Lactucopicrin, C23H22O7
Lager, Yeast, fermentation, brewing, beer: 16.7.11
Lamiidoside, C26H32O14, iridoid glucoside
Laminaribiose, Oligosaccharides
Laminarin, laminaran, β-1, 3- and β-1, 6-glucan, in brown algae, Laminaria digitata, oarweed
Lamotrigine, C9H7Cl2N5, Lamictal, drug for treating epilepsy, causes skin rashes
Lampblack, Prepare lampblack: 8.1.2b
Lanatoside C, C49H76O20
Langbeinite, K2Mg2(SO4)3, may be in in "potash" fertilizers (Mineral)
Langelier saturation index: 18.7.43 (swimming pools)
Lanolin, wool wax
Lanoxicaps, C41H64O14
Lanthanides, Rare earth elements, lanthanides: 2.11.0
Lanthanum, La
Lapachol, C15H14O3
Lapis lazuli: 35.20.55 (Mineral)
LAS (linear alkylbenzene sulfonic acid), Ionic surfactants in washing powders powders:
Latex, rubber: 3.85.0
Laudanum, opium, diluted in wine with cloves and other spices, former common medicine, e.g."poppy-head tea"
Laughing gas, N2O, Nitrous oxide: 13.1.27
Laundry detergents, Ionic surfactants in washing powders:
Lauric acid C12H24O2
Lauryl, C12H25-
Lauryl alcohol, CH3(CH2)11OH
Lauryl peroxide, C24H46O4
Lauryl sulfate, Sodium laurel sulfate.
Lavandulol, C10H18O
Lavandulyl acetate, C12H20O2
Lavender oil
Lavoisier, Antoine, Prepare verdigris with copper and vinegar: 12.11.1
Law, First law of thermodynamics, Chemical potential energy, enthalpy:
Law of mass action
Lawrencium, Lw
LDPE, Plastics recycling code: 3.5.3
Lead, Pb, lead metal
Leavening agents:
Leaves, Distil essences from leaves and flowers: 10.5.4
LeBlanc process, Prepare sodium carbonate: 12.16.8
Leclanché cell, dry cell
Lectins: 16.3.17
Leishmann's stain, Prepare Leishman's stain, Wright's stain: 3.19
Length, metre:
Lepidimoide, Oligosaccharides
Leucine, C6H13NO2, (Table of amino acids)
Leucine, DNA codons
Leucine, Separate amino acids with paper chromatography:
Leuco dyes, Thermochromism, Colour Changing Ducks (Child's toy)
Leurosine, C46H56N4O9
Levodopa, C9H11NO4
Lichenin, β-1, 3- and β-1, 4-glucan, in lichen reindeer food
Licorice, liquorice
10.01.10 (JPG)
24.1.2 Lift ice cube with salt
12.3.23 Lifting power of balloons containing different gases
Ligands: 1.0
Lignans, type of polyphenol, in flax, pumpkin seed, sesame, sunflower
Light bulb, Incandescence, electric light bulb, filament lamp: 33.4.0
Light oil, sewing machine oil, e.g. WD-40 penetrating oil to prevent corrosion
Light stick, chemical light stick, Chemiluminescence, bioluminescence: 14.3.0
Lighted splint tests for: Tests
See: Lighters, Matches, (Commercial)
Ligroin, Petroleum spirit:
Lime, CaO
Lime sulfur, CaSx: 16.6.12 (agricultural fungicide)
Lime water, Tests for carbon dioxide with lime water:
Limonene, C10H15
Limonin lactone:
Limonite, Geothite, FeO(OH) (Mineral)
Linalool, C10H18O
Linalyl acetate, C12H20O2
Linamarin, C10H17NO6
Lindane, C6Cl6: 16.3.3
Linoleic acid, C18H32O2
Linolenic acid, C18H30O2
Linseed oil
Lip balm:
Lipase, Tests for lipase: 9.3.14
Lipitor: CPY3A4
Lipitor, Bergamottin: 16.9.20
Lipoprotein, fat with protein, in cell membranes, α-Lipoprotein, HDL, High density lipoprotein in human plasma
Lipstick: 19.7.2
Liquid broth media, Prepare: 9.2.12, (Microbiology)
Liquid crystals, Thermochromism, Colour Changing Ducks (Child's toy)
Liquid paraffin
Liquid, states of matter, solid (s), liquid (l), gas (g), aqueous solution, (dissolved in water) (aq)
Lists of chemicals, e.g. Acids, Bases: 5.0
Lithage, PbO, lead (II) oxide
Lithium, Li
15.6.15 Lithium-ion battery
See: Lithium (Commercial)
Litmus: 15 (indicator)
See: Litmus (Commercial)
Live animals, Biological experiments and use of live animals: 3.2.5
Liver of sulfur, K2S, potassium sulfide
Lobeline, C22H27NO2
Locant, organic chemistry term for numbering carbon atoms in a carbon chain
Loeffler serum medium: 6.13 (Microbiology)
Loss of substance on heating indicates:
Lost volume, Shrinking mixture of liquids: 10.3.1
Lotaustrain, C11H19NO6
Lotion, Solutions for herbal remedies: 5.04
Low-cost chemicals and common substancs: 15.0.4
Low-cost equipment, simple equipment: 1.12.0
LPG (Liquefied Petroleum Gas, LP gas)
LSD, C20H25N3O
Lubricating oil:
Lucite (C5O2H8)n (Perspex): 3.7.24
Lugol's iodine solution, Prepare: 3.15
Lupanine, C15H24N2O
Lupeol, C30H50O
Lupinine, C10H19NO
35.6 Lustre (metallic lustre, non-metallic lustre) (Geology)
Lutein, C40H56O2
Luteolin, C15H10O6
Lutetium, Lu
Lychnose, Oligosaccharides
Lycopene, C40H56
Lycopersene, C40H66
Lycopodium species, fine yellow powder, Highly flammable
Lyophilic sols, Sols:
Lyophobic sols, Sols:
L-lysine monohydrochloride, H2N(CH2)4CH(NH2)CO2H·HCl0, pure L-lysine, for ruminants, swine, poultry
Lysine, C6H14N2O2, (Table of amino acids)
Lysine, DNA codon
Lyxose, C5H10O5, sold as: [D-Lyxose, D-Lyxopyranose], [L-(+)-Lyxose, L-Lyxopyranose]

Laboratory equipment, Laboratory ware
See: Laboratory (Commercial)
Lab Grade, chemicals standards
Laboratory coat, Safety coats
Laboratory equipment: 22.8.0
Laboratory gas, piped gas, "lab gas", Household gas
Laboratory organization: 3.1.5
Laboratory safety, physics: 7.0.0
Laboratory Safety: 3.0
Laboratory safety and hazardous chemicals: 3.0
Toxicity: 4.0.

Laboratory gas
In a laboratory, the pilot light should burn with a 90% blue flame.
If the flame is yellow, the gas may be contaminated with condensates.
Do not use such a gas but immediately inform the local gas authority.
The heating values of fuels: town gas 88 MJ / kg, natural gas 55.6 MJ / kg, LPG gas 49 MJ / kg, diesel fuel oil 38 MJ / L,
kerosene 36.7 MJ / L, coke or coal 27 MJ / kg, dry split wood 12.5 MJ/ kg.

Lactic acid
Lactic acid, C3H6O3, CH3CHOHCOOH
Lactic acid,   85%, 2-hydroxypropanoic acid, an α-hydroxy acid, skin irritant
Lactic acid, L-(+)-Lactic acid, Sarcolactic acid
16.1.2 Clot on boiling test (C.O.B test) (milk)
16.1.3 Alcohol test (milk)
16.1.5 Acidity test (milk)
16.1.10 Inhibitor test (milk)
16.2.4 Cheese
Anatomy and physiology of meat: 19.3.2
Baking powder
Candidiasis (Thrush) Candida albicans: 10.10.2
E270 Lactic acid, Food acids, food additives)
E472b Lactic acid esters of monoglycerides
E326 Potassium lactate (Humectant, bulking agent, acidity regulator)
E328 Ammonium lactate (Humectant, bulking agent)
E329 Magnesium lactate (Humectant, bulking agent)
Prepare carbon dioxide, heat hydrogen carbonates: 13.7.7
Lactase: 7.1.3
Lactic acid, 2-hydroxypropanoic acid, C3H6O3:
Lactic acid with potassium carbonate:
Leavening agents:
Make yoghurt, a report from Turkey: 4.2.1a
Make yoghurt, test milk quality: 4.3.17
Prepare lactic acid with sourdough: 4.2.3
Prepare lactic acid with milk: 12.7.10
Prepare yoghurt: 4.2.1
Tests for lactic acid solution: 12.7.11
Yoghurt and lactic acid bacteria, "Yakult": 9.3.0.

Lactose, Oligosaccharides
Lactose, C12H22O11.H2O, milk sugar lactitol, food additive E966, sweetener, texturizer, humectant, E279
Lactose, disaccharides:
Lactose intolerance: 19.2.4
Ice cream:
Tests for glucose, urine test:

, La (Greek lanthanein lie hidden), phosphorescent in energy saving light bulbs
Lanthanum with Cerium, Ce, in mischmetal: negative electrode NiH battery, cigarette lighter ignition element
Lanthanum chloride
Lanthanum chloride AAS
Lanthanum nitrate
Lanthanum oxide
Lanthanum perchlorate
2.11.0 Rare earth elements,lanthanides.

3.85.0 Rubber, latex
23.6.4 Heat and cool rubber bands, rubber band heat engine
23.6.2 Latex plants
23.6.1 Natural rubber
23.6.3 Negative thermal expansion (NTE) of rubber, entropy Polyterpenes (many isoprene units)
23.6.5 Stretch rubber bands.

Lauric acid
Lauric acid, C12H24O2, CH3(CH2)10COOH, dodecanoic acid, , medium chain, saturated fatty acid in milk (human, cow, goat) laurel
oil, palm oil, coconut oil, high melting point 43.2oC, increases high density lipoprotein (HDL), the "good" cholesterol
Fatty acids in coconut oil and other oils: 17.2 (Table)
Fats in food: 3.90.

Lauryl, C12H25-, Laurel oil from bay laurel, Laurus nobilis.

Lauryl alcohol
Lauryl alcohol, dodecanol, dodecam-1-ol, n-dodecanol, CH3(CH2)11OH, Irritant (detergent manufacture)
Fatty alcohols, lauryl alcohol: 3.8.0.

Lauryl peroxide
Lauryl peroxide, C24H46O4,   di(docecanoyl) peroxide, dilauroyl peroxide, Toxic by ingestion and inhalation, skin irritant
White solid, soapy odour, floats on water, melting point 49oC, bleaching and drying agent for fats
Lauryl peroxide, Solution <20%, Not dangerous.

Lavender oil
Lavender products (Lavendula angustifolia), Lamiaceae.
Lavender flower oil, mainly linalyl acetate and linalool, from Lavandula latifolia (insect repellent, dog inhibitor, air freshener, pain relief).

Law of mass action
Chemical equilibrium, law of chemical equilibrium: 17.5.0
Heat nitrogen tetroxide (dinitrogen tetroxide, N2O4):
Reversible reactions, effect of alteration of concentration:
Reversible reactions, hydrolysis of bismuth chloride:

Lawrencium, Lw
, Lw, Table of the elements (Earnest O. Lawrence, 1901-1958, USA).

Lead, Pb
See: Lead Elements, Compounds, (Commercial)
Lead, Table of Elements
Lead compounds
"Lead pencil": 35.41.4
Lead properties:
Aquadag: 35.41.5
Graphite: 35.41.3 (See: 4.)
Lead paint
Lead tetra-ethyl, tetraethyl lead
Lead-acid battery, Motor vehicle battery: 32.7.0
Lead, group 1 tests for Ag+, Pb2+:
Lead occurrence, galena: 35.20.22, (Mineral)
Lead residues: (Laboratory disposal)
Prepare lead-acid battery electrolyte:
Prepare lead-tin alloys in a casting mould: 3.61
Reactions of lead (II) salts, Pb2+: 12.9.1
Reactions of lead (IV) salts, Pb4+: 12.9.2
Separate sand and lead powder by panning: 10.8.1
Tests for lead: Tests for lead.

Tests for lead
Tests for hardness of lead, tin: 3.62
Tests for lead: (See: 6.)
Tests for lead, potassium iodide:
Tests for lead ions: 15.8.3
Tests for lead, melting point of lead, tin, and lead-tin alloys: 3.63.

Lead compounds
Lead compounds
Lead (II) acetate
Lead (II) acetylacetonate, C10H14O4Pb
Lead antimonate
Lead (II) bromide
Lead (II) bromide, PbBr2, Electrolysis of melted lead (II) bromide: 3.68.0
Lead (II) bromide, Solution < 1% Not hazardous
Lead (II) carbonate
Lead (II) chloride
Lead (II) chromate
Lead (II) fluoride, PbF2
Lead (II) iodide, PbI2, lead iodide, lead diiodide, Highly toxic, cumulative poison
Lead (II) iodide, Solution < 1%, Not hazardous
See: Lead (II) Iodide LR, (Serrata)
Lead magnesium niobate, MgNb2Pb3O9
Lead (II) methanesulfonate, C2H6O6PbS2
Lead (II) molybdate, PbMoO4
Lead (II) nitrate, Pb(NO3)2
Lead (II) oxide
Lead subacetate, C4H10O8Pb3
Lead (II) sulfate
Lead (II) sulfide, PbS, lead sulfide, lead glance, blue lead, Toxic, cumulative poison, galena: 35.20.15
Lead (II) sulfide, Solid mixture < 1%, Not hazardous
Lead (II) thiocyanate
Lead (II/IV) oxide
Lead (IV) acetate, lead (IV) ethanoate, Pb(CH3COO)4, lead tetraacetate
Lead (IV) oxide
Lead (IV) tetraethyl, Pb(C2H5)4: Lead tetraethyl
Lead antimonate, Naples yellow for craft, antimonate of lead
Lead azide, Pb(N3)2, contact explosive, in detonators
Lead hydroxide, amphoteric
Lead manganese oxide, coronadite, Pb2Mn8O16: 35.20.12 (Mineral)
Lead residues: (Laboratory disposal)
Minium, Pb3O4, red oxide of lead, red lead
Pyromorphite, Pb5(PO4)3Cl (lead phosphate): 35.20.33 (Mineral)
Tetraethyl lead.

Lead acetate, Lead (II) acetate, Pb(CH3COO)2, lead (II) ethanoate
See: Lead Acetate Trihydrate AR, (Serrata)
See: Test Strips Lead acetate, (Commercial)
Lead (II) acetate, Toxic by all routes, cumulative poison
Lead (II) ethanoate, Solution < 0.5%, Not hazardous
Lead (II) acetate, m.p. 75oC, white to colourless, monoclinic crystals or granules, slowly efflorescent, absorbs CO2 from air and
becomes insoluble
Lead (II) acetate dissociation: Pb(CH3COO)2 (aq) <--> Pb2+ + 3CH3COO-
Lead (II) acetate, "sugar of lead" (HARM 1616),
Lead (II) acetate trihydrate crystals, Pb(CH3COO)2.3H2O
Lead (II) acetate trihydrate, C4H6O4Pb.3H2O
Lead (II) acetate, For 0.1 M solution, 38 g in 1 L water + dilute ethanoic acid to clear
Lead (II) acetate test paper for H2S (for testing anions),
Lead (II) acetate basic, anhydrous, Pb(CH3COO)2, 72% for sugar analysis.

Lead antimonate
Lead antimonate, Pb3Sb4O3, Pb(SbO3).Pb3(SbO4)2, "Naples yellow", antimony yellow, ancient mineral pigment, for craft,
antimonate of lead, toxic.

Lead (II) carbonate, PbCO3
See: Lead (II) Carbonate (Serrata)
Lead (II) carbonate, PbCO3, cerussite, basic lead carbonate, (PbCO3 + Pb(OH)2), white lead
Lead (II) carbonate, PbCO3, lead carbonate, lead carbonate basic, white lead flux, paint pigment, Toxic
Lead (II) carbonate, cerussite, ceruse: 35.20.8, (Mineral)
Lead (II) carbonate Solution / mixture < 1%, Not hazardous
Lead (II) carbonate hydroxide, PbCO3.Pb(OH)2, white lead, basic lead carbonate, flux, paint pigment, Low cost: pottery supply stores.

Lead (II) chloride
See: Lead (II) Chloride LR, (Serrata)
Lead (II) chloride, PbCl2, lead chloride, Highly toxic by allroutes
Lead (II) chloride, Solution < 1%, Not hazardous.

Lead (II) chromate
Lead (II) chromate, PbCrO4, lead chromate, very insoluble in water, Highly toxic by all routes, highly corrosive, strong oxidizing agent
Lead chromate, orange-yellow powder, crystalline, S.G. 6.3, insoluble in water, acetic acid, and ammonia, but soluble in acid and
alkalis, possibly most insoluble salt in water.
If heated to decomposition emits toxic chromium fumes which affect the lungs, possibly lung cancer.
Lead chromate pigment (Naples yellow), is a highly toxic cumulative poison
Lead (II) chromate, Solution < 1%, Not hazardous
Chrome red, PbO.PbCrO4, basic lead chromate pigment
Chrome yellow, PbCrO4, lead chromate pigment
Use in printing inks, paints, to colour vinyl and rubber.

Lead (II) nitrate
See: Lead Nitrate AR, (Serrata)
See: Lead Nitrate LR, (Serrata)
Lead (II) nitrate, Pb(NO3)2, zinc displaces lead from lead (II) nitrate solution: 12.14.1
Lead (II) nitrate, For 0.1 M solution, 33 g in 1 L water
Lead (II) nitrate, Prepare nitrogen dioxide, [nitrogen (IV) oxide, NO2]: 3.47 (See 2.)
Lead (II) nitrate, Tests for hydrogen sulfide solution, ionization of hydrogen sulfide: 3.43.1 (See 2.)
Coloured precipitates: 12.2.1c (See 1., 3.)

Lead (II) nitrate, white to colourless large crystals, reactivity series, lead (II) nitrate, Toxic, cumulative poison
Lead (II) nitrate (HARM 1469), Pb(NO3)2, lead (II) nitrate, Oxidizing, Environment dangers
Lead (II) nitrate, lead (II) nitrate, Pb(NO3)2, Toxic, cumulative poison, Oxidizing, Environment danger
Lead (II) nitrate, Solution < 1%, Not hazardous
Lead (II) nitrate, Pb(NO3)2, lead dinitrate, lead nitrate, white to colourless, translucent cubic or monoclinic crystals, decomposes at
470oC, the only common soluble lead compound, forms explosive mixture with combustible materials, e.g. S, P, metal powders,
heated solid forms highly toxic nitrogen dioxide, test for anions: forms bright yellow precipitate of lead iodide, with sodium or
potassium iodide.

Lead (II) sulfate
See: Lead Sulfate LR, (Serrata)
Lead (II) sulfate, PbSO4, lead sulfate, green vitriol, blue lead, white lead, Toxic, cumulative poison
Lead (II) sulfate (previously in white lead paint)
Lead (II) sulfate, Solution < 1%, Not hazardous
Lead sulfate, sulfation, Prepare lead acid battery electrolyte: (See: 4.)
Lead sulfate, PbSO4, lead (II) sulfate, basic lead (II) sulfate, Toxic, anglesite: 35.20.1 (Mineral).

Lead compounds
Lead compounds are cumulative poisons.
All lead salts are highly toxic if ingested or particles inhaled.
Wash hands after handling.
Use < 10 mL or g per activity.
Bright orange pottery glazes usually contain lead salts.
The pigments white 1, white 2, white 16, mixed white, chrome yellow, chrome green, and chrome orange are highly toxic cumulative
Chrome red, PbO.PbCrO4, basic lead chromate
Chrome yellow, PbCrO4, lead chromate pigment
Crocoite, PbCrO4, Red lead ore
Lead paint detection kit to detect lead in paint
Lead (II) acetate, Lead (II) ethanoate, lead acetate
Lead (II) bromide, PbBr2, lead bromide, Highly toxic by all routes.

Lead (II) oxide
Lead (II) oxide, PbO, lead oxide, lead monoxide, plumbous oxide, amphoteric, litharge, massicot, Toxic
See: Lead (II) Oxide (Monoxide) LR, (Serrata)
Lead (II) oxide mono, yellow lead oxide, litharge, massicot, flux, lead monoxide, lead protoxide,
yellow amorphous powder, fused and crystalline form called litharge, used as pigment in glass and enamels.
Lead monoxide pigment (yellow 46), is a highly toxic cumulative poison.
Solution < 1%, Not hazardous
Lithage, PbO, lead (II) oxide, lead monoxide, lead oxide, massicot (amphoteric)
Battery capacity:

Lead (II/IV) oxide
Lead (II/IV) oxide, Pb3O4, triplumbic tetroxide, lead tetroxide, red lead, minium, Toxic by all routes, cumulative poison
Lead (II/IV) oxide, red lead oxide, Pb3O4 (2PbO.PbO2), dilead (II) lead (IV) oxide (red lead, anticorrosive paint pigment)
Lead (II/IV) oxide, Reduce red lead to lead and oxygen: 10.10.1
Lead (II/IV) oxide, Solid mixture < 1%, Not hazardous.

Lead (IV) oxide
Lead (IV) oxide, PbO2, lead dioxide, lead peroxide, Highly toxic by all routes, cumulative poison
Lead (IV) oxide, Solid mixture < 1%, Not hazardous
Lead (IV) oxide, PbO2, lead dioxide, car battery plates, lead-acid accumulator (+ve accumulator electrode)
Lead (IV) oxide, lead tetroxide pigment (red 105), is a highly toxic cumulative poison.

Lead (II/ IV) oxide, Pb3O4, (2PbO.PbO2), minium, red lead oxide, trilead tetroxide, red lead, triplumbic tetroxide, lead tetroxide,
See: Lead (II, IV) Oxide (Red lead) LR, (Serrata)
Toxic by all routes, cumulative poison.
Two valence states: Pb2+ and Pb4+ (Pb4+)(Pb2+)2O4
It reacts violently with Al and Mg powders and some organic materials.
Do NOT heat lead (II, IV) oxide on a charcoal block.
Old paints may contain > 30% lead but nowadays may contain only < 1% lead, bright red or orange, pigment.
Lead (II/IV) oxide forms insoluble iron (II) plumbate and iron (III) plumbate with iron and iron oxides, so it is used in anti-corrosive
lead paints, especially rustproof primer paints.
However, lead tetroxide is soluble in dilute hydrochloric acid so it can dissolve in the hydrochloric acid in the stomach and act as a
lead poison.
Lead (II/IV) oxide is NOT soluble in water so it can be used in lead glass.
It is used to make lead cell accumulators (car batteries, lead-acid batteries), and flux.
Minium stone is used for craft and smelting.

Lead paint
Lead (II/IV) oxide, red lead, rust-proof primer paints
Lead paint formerly contained the white pigment "white lead", basic lead carbonate, Pb(OH)2PBCO3, nowadays 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-based paints deteriorate leaving lead in the dust that can be inhaled.
Children can be exposed by eating lead-based paint chips, chewing on objects painted with lead-based paint, or swallowing house dust
or soil that contains lead.

"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, and also 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."

Lead tetra-ethyl, tetraethyl lead
| Octane (C8H18), Octane number
| Spark plugs, operating temperature, pre ignition, spark plug gap
| 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.

Lead metal
Lead Plate Electrodes 100 x 50 x 1.5 mm, (Scientrific)
Lead Plate Electrodes 100 x 50 x 3 mm, (Scientrific)
Lead Plate Electrodes 75 x 25 x 1.5 mm, (Scientrific)
Lead electrode circuit board pencil (Scientrific)
Lead cube, 10 mm (Scientrific)
Lead cube, 25 mm (Scientrific)
Lead cube, 20 mm (Scientrific)
Lead shield, for radioactive sources (Scientrific)
Lead metallic lead, (Scientrific)
Lead Foil AR, (Serrata)
Lead Foil TG, (Serrata)
Lead Shot (95% lead), (Serrata)
Leads, Lead electrical "leads", metallic "lead", (Serrata)

Lemons, lemon juice, 5-8% citric acid
Lemon (Citrus x limon), Rutaceae.
Acid-base indicators in the home: 19.1.5, (lemonade)
Catalysts and rate of reaction: 3.94, (lemonade)
Citric acid, C6H8O7
Citric acid with sodium hydrogen carbonate solution: 12.6.6
Citrus species, Rutaceae.
Extraction of caffeine and benzoic acid from soft drinks, e.g. cola and lemonade: 16.8.3
Lemon cells: 33.3.4 (electricity)
Lemon juice, lemon oil
Lemon juice, invisible ink:
Isolation of benzoic acid in lemonade:
Prepare citric acid crystals with lemon juice: 12.6.1
Prepare mayonnaise and salad dressing emulsions: 16.7.12
Soft drinks: 15.8.6 (lemonade)
Tests for lemon juice on apple browning: (Cooking)
Tests for pH of water in the laboratory: 18.1.2 (lemonade)

Lemon juice, lemon oil
Lemon juice is rich in vitamin C (50-60  mg per 100 g of raw lemon pulp), pH 2-3 because of citric acid content, but it can break down
the amines in fish into non-volatile ammonium salts to neutralize the fishy odour and it can hydrolyse the tough collagen fibres in meat to
tenderise it.
Lemon juice does not dissolve fat.
Use lemon juice to treat dandruff, blackheads, facial blemishes, rough hands, sore feet, constipation, itches, minor wounds, with honey
and olive oil relieve coughing, unclog ketchup bottles, write with invisible ink, blonde hair, deodorize cooked fish, cutting boards, fish
cooking utensils, microwave ovens and refrigerators, remove fruit stains, rust, mineral discoloration, ink spots from clothing, whiten
fingernails, with salt clean brass and stainless steel sink.
Use lemon juice to prepare bathtub rust stains cleaner.
Lemon oil is oil from lemon peel, D-limonene, a terpene, used for furniture polish, inhibits spiders and insects, stain remover.

Lighted splint tests for:
Carbon dioxide:
Chlorine: 3.40.1
Dinitrogen oxide (nitrous oxide): 3.45.1
Hydrogen chloride:
Hydrogen gas: 3.41.1.

Linseed oil
Linseed oil, seeds of flax Linum usitatissimum, glycerides of oleic acid and other unsaturated acids
Linseed oil, condition and seal bare wood in putty, paints, varnishes, for cricket bats, linoleum, outdoor furniture
Use linseed oil to stop splitting in chopping boards, wooden bowls, and cricket bats
Use linseed oil, boiled with ground resin, to make sticky flypaper paste.

Lignin, cellulose, hemicellulose, copolymer of phenyl propane units with side chains
Filter paper contains lignin but cigarette paper does not contain lignin.
Copper is involved in the formation of lignin for strong shoots and stems.
Lignans, polyphenols from degradation of lignin, e.g. sesamin, C20H18O6.
Cellulose digestion: 9.214
Characteristics and functions of plant tissue types: 9.0.1 (See: Xylem.)
Lignotuber, Banksia, Eucalyptus:
Microbial decomposition of thin paper, cigarette paper: 4.2.7 (See 2.)
Tests for lignin: 9.145
Tests for lignin, Microscope staining techniques: 9.61 (See: 3.)
Tests for starch, iodine solution: 1.6
Tests for wood, hemicellulose, lignin: 9.144

Lime, CaO
Lime, ambiguous name, usually CaO, lump, lime, quicklime, powder, Toxic if ingested or by skin contact
"Lime" may be also Ca(OH)2 or CaCO3.
Chalk: 35.22.3 (Geology)
Lime, quicklime and slaked lime: 34.3.1
Lime sulfur, CaSx: 16.6.12, (Agriculture)
Limestone, stone dust, carving stones: 35.22.7 (Geology)
Marble: 35.23.3 (Geology).

Chalk (lime) content of the soil: 6.43, (Agriculture)
Heat calcium metal to form calcium oxide: 8.2.14
Lime water, tests for carbon dioxide
Prepare quicklime, CaO: 34.3.2
Tests for limestone: 35.31 (Geology)
Test for quicklime by slaking, prepare quicklime: 34.3.3

Lime water, saturated calcium hydroxide solution, Ca(OH)2
Dilute hydrochloric acid with calcium carbonate, lime water tests for carbon dioxide:
Heat a hydrogen carbonate, sodium hydrogen carbonate (sodium bicarbonate): 12.16.4
Heat different carbonates, carbonates of Cu, Mg, Na, Pb and Zn: 12.16.3
Lime water test for carbon dioxide:
Respiration, lime water tests for carbon dioxide: 6.6.1
Prepare lime water, ionization of calcium hydroxide: 5.3.5
Reactions of metals with water, Cu, Zn, Fe, Mg, Al: 12.15.1
Tests for carbon dioxide, carbon dioxide through calcium hydroxide solution, lime water:
Tests for respiration of soaked peas with lime water, respiration apparatus: 9.155.

Lithium, Li
See: Lithium Elements, Compounds, (Commercial)
Lithium, Table of Elements
Lithium, properties:
Lithium compounds
Heat lithium metal to form lithium oxide: 8.2.10
Reactions of lithium with water: 12.9.312.9.3.

Lithium, Li (Greek lithos stone), lithium metal, lithium ribbon, lithium in paraffin liquid
Lithium 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
pegmatite, used in Al and Mg alloys, batteries and anti-depressant medicines.
Reacts with oxygen gas and water.
On heating, it 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.

Lithium compounds
Lithium compounds (very toxic)
Lithium-ion battery, Li-ion battery: 15.6.15
Lithium acetate
Lithium acetate dihydrate
Lithium aluminium hydride, LiAlH
Lithium aluminium silicate, LiAlSi2O6, spodumene, forms 6 m crystals, grey-white ash when ignited
Lithium amide
Lithium benzoate
Lithium bromide
Lithium carbonate, Li2CO3 for craft, flux, glaze, tranquillizer for mental disorders, white solid, Toxic, Irritant
Lithium carbonate, Low cost: from pottery supplies stores
Lithium chloride, LiCl, lithium chloride anhydrous, very hygroscopic, lithium chloride hydrated, Toxic
Lithium hydride, LiH
Lithium hydroxide, LiOH, white crystals, strong alkali, absorbs CO2, Toxic if ingested, corrosive to skin
Lithium hydrogen carbonate, LiHCO3, tranquillizer for mental disorders
Lithium hypochlorite: 18.7.45 (swimming pools)
Lithium iodide
Lithium iodide hydrate
Lithium metaborate
Lithium niobate
Lithium nitrate, Toxic if ingested, explosive mixture with combustibles or organic compounds
Lithium oxide, Li2O, lithia
Lithium perchlorate
Lithium manganese dioxide primary battery
Lithium rechargeable cells for extreme temperatures
Lithium sulfate, Li2SO4, lithium sulfate hydrate, lithium sulfate monohydrate, Li2SO4.H2O, Harmful
Lithium sulfur dioxide (Li / SO2) primary battery
Lithium sulfur (metal) rechargeable battery
Lithium titanate (LTO) rechargeable battery
Lithium thionyl chloride primary battery.

12.9.3 Reactions of lithium with water
Lithium reacts violently with water to form corrosive lithium hydroxide and hydrogen gas that, if mixed with air, may explode if ignited.
Lithium reacts vigorously with water and acids and so is usually stored under oil.
Lithium floats on paraffin oil so when returning a piece of lithium to the storage container shake the container to recoat the surface with
the oil.
Handle lithium in the same way as you would handle sodium metal.
However, lithium is harder to cut than sodium so used a single piece strong scalpel, not a scalpel with a disposable blade.
Lithium is toxic if ingested and corrosive to the skin.
2Li (s) + 2H2O (l) --> 2LiOH (aq) + H2 (g).

LPG (Liquefied Petroleum Gas, LP gas)
LPG gas, LP-gas, compressed gas, bottled gas
LPG, liquefied petroleum gas (methane, ethane, propane, butane)
Bottled gas
Ethyl mercaptan, ethanethiol, CH3CH2SH: (odorant in LPG)
Petroleum gas:
LPG (Liquefied Petroleum Gas, LP gas):
LPG, LP-gas (bottled gas), hazards: 3.8.8
Propane (C3H8):
Thiophene, thiolane, THT (CH2)4S: (odorant in LPG).

Liquefied petroleum gas
LPG, LP Gas, Liquefied Petroleum gas, is a clean burning fuel and is stored in gas cylinders as bottled gas.
LPG is a simple asphyxiant.
LPG consists of propane (about 95%), together with varying proportions of butane, propylene and butylene.
A rank smelling compound, odorant, e.g. ethyl mercaptan, is added so that the presence of the gas can be easily detected.
Incomplete combustion forms carbon monoxide.
Do not search for a gas leak with a lighted match or lighted taper.
Use a soap solution.
Highly flammable, violently explosive mixture with air, toxic if inhaled, purchased as cylinders containing the liquefied gas.
Fill cylinders by weight only.
Hazchem Code 2YE.
UN number 1075. Keep container upright in a well-ventilated place away from sources of ignition.

Bottled gas
Bottled gas, compressed gas, is gas in metal cylinders under pressure e.g. O2 and N2 , and gas liquefied under pressure e.g. C4H10.
UK standard colours on cylinder shoulders (EN 1089-3): black (N2), blue (N2O), brown (He), dark green (Ar), grey (CO2), light
blue (oxidizing gas), maroon (C2H2), red (flammable gas), white (O2), yellow (toxic gas and corrosive gas).
See the internet for colours in your country e.g. EU Compressed Gas Cylinder colour codes.

Luminescence is the property of substances that can emit light without any heat being applied and they include fluorescent and
phosphorescent substances.
Luminescence means emitting light from an object without its being heated and may refer to the glow from that object.
Luminescence is emission of light for any reason other than a rise in temperature, e.g. excited photons returning to a ground state.
However, thermoluminescence and candoluminescence refers to a substance emitting light when heated.

4.101: Candoluminescence
14.3.0 Chemiluminescence, bioluminescence
, fluorescein, fluorescence microscopy
14.3.0a Fluorophores (fluorescent chemical compounds.
4.104 Luminance and illuminance, candela, candlepower, lumen, lux
14.3.1 Luminol tests for blood, Cu, Fe, Cn- Luminous intensity, candelaa, cp

Lutetium, Lu
, Lu (Latin Lutetia ancient Paris), heaviest lanthanide, rare earth.

3.61 Prepare lead-tin alloys in a casting mould
See diagram 3.61: Casting mould from a nut and bolt
Make a casting mould by drilling out the thread of a nut to leave a smooth hole of about 0.6 cm diameter.
Then cut the nut into two halves with a hacksaw.
Use wire to bind the two halves together for casting, then put this caste on sand.
Pure tin melts at 232oC and pure lead melts at 327oC.
Weigh out pieces of lead and tin to make four alloys so that the percentage of tin by weight is 20% tin, 40% tin, 60% tin and 80% tin.
Put each mixture of lead and tin in a crucible or Pyrex test-tube.
Cover each mixture with powdered charcoal to prevent oxidation of the metals, then heat with a Bunsen burner until they melt.
Stir the melt with a wood splint to help the metals dissolve.
Pour each mixture of molten metal into the mould until it is full.
Be careful! Hold back the carbon from the charcoal with a wooden splint while pouring.
When the cast alloy is cool, knock away the two halves of the nut.

3.62 Tests for hardness of lead, tin, and lead-tin alloys
See diagram 3.62: Hardness test apparatus
Test the hardness of the four lead-tin alloys and two pure metals, lead and tin.
Use a metal punch with a pointed end and a 1 metre plastic tube to guide the punch as it falls on to the alloy and makes a small hole.
The softer the alloy the larger the hole.
Measure the diameters of the holes with vernier calipers and a magnifying glass.
The pure metals should be less hard than the alloys.
The 60% tin alloy should be the hardest alloy.
This test is a kind of dynamic hardness test, e.g. Vickers hardness test.
Geologists test the hardness of minerals with a scratch hardness test, Mohs' test.

3.63 Tests for melting point of lead, tin, and lead-tin alloys
See diagram 3.63: Melting point apparatus: A metal plate, B suspended metal plate
Prepare a metal plate from a 12 cm X 12 cm piece of iron, 0.2 to 0.4 cm thick.
Draw a hexagon on the metal plate, then drill a small equal depth depressions at each corner of the hexagon.
Drill holes through the four corners of the metal plate.
Thread wire through the four holes and suspend the metal plate horizontally.
Pour a few globules of four alloys and the two pure metals into separate porcelain bowls.
Be careful! Put one pellet of each alloy or metal into a depression on the metal plate.
Heat the middle of the metal plate with a Bunsen burner.
Touch the pellets with a wood splint to check when they melt.
When all the pellets are all molten, use the wooden splint to remove excess molten metal from bigger pellets so that they are all the same
Remove the Bunsen burner flame, leave the metal plate to cool and note the time to form crystals.
Make a table of time to crystallize and plot the results on graph paper.
Pure lead solidifies first, then 20% tin, then 40% tin, then 60% tin.
The alloy that takes the longest time to solidify has the lowest melting point.
The 60% tin alloy should have the lowest melting point.

23.6.1 Natural rubber, latex
Natural rubber (C5H8)n, [n = 4, 0005, 000] (Hevea brasiliensis), and (Ficus elastica)
Polyisoprene, elastomer, diene polymer, natural rubber is mainly cis-1, 4-polyisprene, from Hevea brasiliensis, main monomer isoprene,
-CH2=C(CH3)CH=CH2-, 2-methyl-1, 3-butadiene, also made synthetically, cis polyisoprene, isoprene rubber.
Gutta-percha is mainly trans-1, 4-polyisprene.
1. Natural polymers occur as brittle glassy gums and resins in plants, e.g. conifers, and as polysaccharides, e.g. starch.
Natural rubber, para rubber, hevea rubber obtained from the milky latex sap of Hevea braziliensis, Euphorbiaceae, contains
polyterpenes with linked isoprene units CH2=C(CH3)CH=CH2, [cis-1, 4-polyisoprene], in which all the -CH=CH-= groups are cis.

2. The polymer chains in natural rubber are elastic in the sense that the chains can be unravelled without coming apart, i.e. the rubber
can stretch.
Elasticity was improved by cross-linking with sulfur, using the Goodyear process to produce vulcanized rubber.
Stretching aligns the random chains, and temporarily crystallizes and toughens rubber, so that rubber tyres do not form cracks.
Natural rubber is not very elastic in the Hooke's law sense of stress being proportional to strain.
The transisoprene polymer, trans-1, 4-polyisoprene, occurs in tropical trees in the latex of Palaquium oblongifolium, Sapotaceae
family, the same chemical as natural rubber, polyisoprene, but with trans not cis bonding.

3. Test for strength of cross-linkages, add toluene then measure the increase in volume.
Rubber bands are made mostly of natural rubber cured by heat.
Petrol can dissolve the cross-linkages between the polyisoprene molecules to allow water molecules to move in between them and swell
the rubber band.

4. Hard rubber was made by Charles Goodyear and shown at the 1851 exhibition at Crystal Palace, London.
During the vulcanization process, 30-40% sulfur is added to the natural rubber to form a compound with high dielectric power,
high resistance to chemical products, hardness and rigidity up to 50C, and a bright shiny appearance.
It is processed with extruders then worked on machines or compression moulds to make battery separators, telephone receivers, tyres.

12.9.1 Reactions of lead (II) salts, Pb2+
1. Add dilute hydrochloric to lead (II) nitrate solution.
Note the white precipitate of lead chloride.
Wash the precipitate, add four times its volume of water and heat.
The precipitate dissolves and precipitates again cooling.
Pb2+ + 2Cl- --> PbCl2 (s).

2. Add dilute sulfuric acid to lead (II) nitrate solution.
Note the white precipitate of lead sulfate.
Wash the precipitate, concentrated ammonium acetate solution and heat.
The lead sulfate dissolves.
Pb2+ + SO42- --> PbSO4 (s).

3. Add potassium chromate solution to 3 mL of lead nitrate solution.
Note the yellow precipitate of lead chromate.
Pb2+ + CrO42- --> PbCrO4 (s).

4. Add potassium iodide solution to 3 mL of lead nitrate solution.
Note the yellow precipitate of lead iodide that is soluble in hot water.
Pb2+ + 2I- --> PbI2.

5. Add drops of sodium hydroxide solution to lead nitrate solution.
Note the white precipitate of lead hydroxide that is soluble in excess sodium hydroxide solution.
Pb2+ + 2OH- --> Pb(OH)2 (s)
2 Pb(OH)2 + 2OH- --> PbO22- + 2HO
(Note: PbO22- = plumbite ion).

6. Pass hydrogen sulfide through lead (II) nitrate solution.
Note the black precipitate of lead sulfide.
Wash the precipitate, transfer to an evaporating dish, add dilute nitric acid and heat the solution until it boils.
Some lead sulfide dissolves forming lead (II) nitrate solution, and some lead sulfide is oxidized to lead sulfate.
Pb2+ + S2- ---> PbS (s).

7. Add drops of dilute sodium hydroxide solution to lead acetate solution until a precipitate forms, then disappears.
Add hydrogen peroxide solution and heat the solution.
Note the brown precipitate of lead dioxide.

8. Add sodium carbonate solution to lead (II) nitrate solution.
Note the white precipitate of basic lead carbonate, Pb(OH)2.2PbCO3.
3Pb2+ + 3CO32- + H2O --> Pb(OH)2.2PbCO3 (s) + CO2 (g)
Add sodium hydrogen carbonate solution to lead (II) nitrate solution.
Note the white precipitate of lead carbonate.
Pb2+ + 2HCO3- --> PbCO3 (s) + CO2 (g) + H2O.

12.9.2 Reactions of lead (IV) salts, Pb4+
1. Add 2 cc of red lead to 2 cm with glacial acetic acid.
Heat the mixture and the red lead dissolves.
If a brown precipitate occurs repeat the experiment using less red lead.
Cool under the tap to precipitate white crystals of lead tetraacetate, lead(IV) acetate.
Pb3O4 + 8CH3COOH --> Pb(CH3COO)4 + 2Pb(CH3COO)2 + 4H2O
Add three times the volume of water to the mixture and heat it to hydrolyse the lead tetraacetate, lead(IV) acetate.
Note the brown precipitate of lead dioxide.
Pb(CH3COO)4 + 2H2O --> PbO2 (s) + 4CH3COOH.

2. Add 2 cc of lead dioxide to 2 cm of concentrated hydrochloric acid and cool under the tap.
Filter the mixture and note the golden yellow solution containing lead (IV) chloride.
Divide the solution into 3 parts.
PbO2 + 4HCl --> PbCl4 + 2H2O
Heat part A of the yellow lead (IV) chloride solution and test for chlorine.
Cool the remaining solution under the tap and leave to crystallize.
Note the white crystals of lead (II) chloride.
PbCl4 --> PbCl2 + Cl2 (g)
Add drops of part B of the yellow lead (IV) chloride solution to 880 ammonia solution, NH3 (aq) ("ammonium hydroxide").
Note the fine yellow crystals of ammonium chloroplumbate.
PbCl4 + 2NH3 + 2HCl --> (NH4)2PbCl6 (ammonium chloroplumbate)
Add drops of sodium hydroxide solution part B of the yellow lead (IV) chloride solution.
Note the red gelatinous precipitate that on heating forms lead dioxide as a brown powder.
PbCl4 + 2H2O ---> PbO2 (s) + 4HCl.

3. Prepare lead dioxide and lead (II) nitrate.
Slowly add 20 g of red lead to 50 mL of dilute nitric acid and boil for 1 minute.
Be careful! Filter the solution while hot.
Leave the filtrate to cool and form lead (II) nitrate crystals.
Wash the residue of lead dioxide twice with hot water and dry it by gentle heating in an evaporating basin.
Pb3O4 + 4HNO3 --> PbO2 + 2Pb(NO3)2 + 2H2O.

15.8.3 Tests for lead ions
Prepare separate solutions of lead (II) nitrate, iron (III) chloride and barium chloride.
Test a small portion of each solution in turn with dilute hydrochloric acid, dilute sulfuric acid and sodium hydroxide solution.
Tabulate your results.
Note that lead (II) nitrate solution always produces a precipitate.
Also, iron (III) chloride solution gives a precipitate only when sodium hydroxide solution is added.
Barium chloride solution gives a precipitate with both sulfuric acid and sodium hydroxide solutions.

23.6.2 Latex plants
Latex is an emulsion of rubber globules in water, found in latex paints, male latex condom, and latex tubing.
1. Ficus elastica, Indian rubber plant, India rubber tree, [polyterpenes in milky latex sap], Moraceae
2. Hevea braziliensis, natural rubber, para rubber, hevea rubber, [polyterpenes with linked isoprene units, cis-1, 4-polyisoprene,
[in milky latex sap], Euphorbiaceae
3. Manilkara achras, sapodilla, chiku, chicle polyterpene, Mexico, South America, desert fruit, latex chicle used, chewing gum,
4. Manilkara bidentata, balata, latex used for non-elastic rubber, sticky pulp eaten, Sapotaceae
5. Palaquium oblongifolium, latex called gutta-percha, polymer, natural trans-1.4-polyisoprene, the same chemical as natural rubber,
polyisoprene, but with trans not cis bonding, Sapotaceae.

23.6.3 Negative thermal expansion (NTE) of rubber, entropy
Negative thermal expansion (NTE) materials contract on heating within certain temperature ranges.
They are not called "thermal contraction" materials.
When the long polymer chains in rubber absorb energy, they adopt a more contorted configuration, reducing the volume of the material,
so a rubber band contracts on heating.
A cooled rubber band, becomes stretchier and expands slightly because the molecules become more organized into a more efficient
stretching shape.
A common explanation of this phenomenon is that the arrangement of long polymer chains in rubber is like a ball of mixed up threads
of string.
By grabbing hold of each end of the tangle and pulling it in opposite directions, the threads of string become more horizontal as the
ball of string is elongated.
So the arrangement of threads becomes more ordered and the entropy of the system becomes lower.
Reduced entropy, more orderly alignment of molecules, causes the rubber band to lose heat.
A stretched rubber band feels hotter as it expands with heat lost in an exothermic process.
A contracting rubber band feels cooler with heat gained in an endothermic process.
The particles making up rubber in its natural state are more disordered than when the rubber is stretched and is under tension.
When tension is removed the rubber contracts back with the particles returning to their initial disordered state.
Entropy is a measure of the amount of disorder in a system, so the entropy of a rubber band increases when it changes from a stretched
state to a natural state.
The change of entropy of a system in a reversible process = the amount of heat absorbed or emitted / absolute temperature of the

23.6.4 Heat and cool rubber bands, rubber band heat engine
See diagram 23.6.4: Test heated rubber bands
1. To demonstrate the effect of heating rubber bands, stretch a rubber band around a wooden box.
Cut out an arrow shape from a piece of cardboard.
Mount the arrow on a pin and then push the pin under the middle of the elastic band.
If the elastic band is heated at the left of the pin, it contracts, pulling the pin towards it and the point of the arrow moves to the right.

2. Rubber band heat engine is a bicycle wheel with rubber bands instead of spokes.
Set up the bicycle wheel vertically.
Rubber contracts on heating so a lamp or a hair dryer placed on one side of the wheel shift the centre of gravity, resulting in rotation.
Cooler rubber spokes move into the irradiated region to repeat the process.
To achieve a smoother rotation the wheel is balanced using small pieces of Plasticine placed around the rim.

3. To make more space in a freezer, you might collect scattered items, e.g. ice lollies,
and put an elastic band around them .
However, after some time the originally stretched elastic band become loose and slacker, than when first applied to the ice lollies at
room temperature.

4. To observe the thermal properties of rubber, hang a 1 kg mass from four rubber bands, so it touches the table.
Heat with a radiant heater for 20 seconds and the mass will lift.
Enclose a rubber tube in a copper cylinder and heat with a Bunsen burner.
The rubber tubing contracts as it is heated.
Stretch and unstretch rubber bands on the lips to feel the changes in temperature.

23.6.5 Stretch rubber bands
Hooke's law does not apply to polymers or rubber.
1. Stretch a thick rubber bandit (> 0.5 cm wide) quickly against the forehead, lips, or wrist and note the increase in temperature.
Hold it stretched, allow it to cool back to room temperature.
Then let it suddenly contract against the lips to its original length and note the temperature drop.

2. Use a hair dryer to heat a stretched rubber band, e.g. 1 cm wide, with a weight on the end, e.g. 2 kg.

3. Stretch a wide rubber band between the index finger of your two hands.
Let the rubber band touch the lips.
Stretch the rubber band (not so far that it breaks!) then slowly release the tension.
Feel heat in your lips when the rubber band stretches because of friction between the rubber molecules.
The stretched rubber band feels cooler when the tension is released.

4. Hold each end of the rubber band with the fingers of your hands,
press your lips firmly to the middle of the rubber band,
and maintain contact as you quickly stretch the rubber band in opposite directions outward.
Your lips you will feel a sudden heat from the rubber band.

5. Suspend a 100 g weight from a rubber band attached to a clamp stand.
Adjust the height of the 100 g weight until it just touches the table.
Use a vertical ruler to measure the length of the suspended rubber band.
Bring a heat source, e.g. a lighted match or hair dryer close to the middle of the stretched rubber band.
Note that the heated rubber band contracts.

Linoleic acid, C18H32O2
See diagram 19.2.1: cis and trans, linoleic acid
See diagram 19.2.1: Glycerol, triglyceride, cis and trans, oleic acid, stearic acid, linoleic acid Trans fats, Omega-fatty acids
Linoleic acid, C18H32O2, CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH, polyunsaturated omega-6 fatty acid, has cis and trans forms
In the cis configuration, the four hydrogen atoms adjacent to the double bonds occur on the same side of the carbon axis.
In the trans configuration, the four hydrogen atoms adjacent to the double bonds occur on alternate sides of the main carbon axis with
two on one side and two on the other.
The more stable trans configuration may be produced from the cis configuration during partial hydrogenation of polyunsaturated
vegetable oils to improve their texture.
Trans fatty acids tend to raise the level of low density lipoproteins (bad LDLs) and lower the level of high density lipoproteins
(good HDLs) resulting in changes in cholesterol levels that may increase the risk of the heart disease atherosclerosis.
So mono-unsaturated, unhydrogenated oils, e.g. olive oil, are preferable to the trans fatty acids in french fries, chips, and doughnuts.
The first double bond is on carbon #6, counting from left to right so this is an omega-6 fatty acid, typical of the unsaturated fatty acids
in plant oils and seeds.
However, fish oils contain omega-3 fatty acids, i.e. the first double bond in on carbon #3.

Linolenic acid, C18H30O2
Linolenic acid, α-linolenic acid, CH3(CH2)CH=CH(CH2)CH=CH(CH2)CH=CH(CH2)7COOH
Alpha linolenic acid (ALA), polyunsaturated fatty acid (PUFA), essential fatty acid in diet not synthesized by mammals, in omega-3
fatty acids group, in plant oils, e.g. canola, soybean, linseed, olive, English walnut, may inhibit synthesis of prostaglandin so reducing
inflammation and some chronic health problems.
Linolenic acid, polyunsaturated omega-3 fatty acid
Two isomers in common invegetable oils.
1. Alpha-linolenic acid (ALA), C18H30O2, a polyunsaturated omega-3-fatty acid, essential fatty acid not produced in human body
High concentration in Chia | Kiwi fruitPerillaLinen flax | and other plants, nuts, vegetable oils
2. Gamma-linolenic acid (GLA), C18H30O2, a polyunsaturated omega-6-fatty acid
High concentration in Evening primrose, and seed oils of blackcurrent and borage.