School Science Lessons
2024-06-23
Chemistry, L
Contents
Labile substances
Laboratory safety
Lactams
Lactase
Lactic acid, (Experiments)
Lacto-alcohol Prepare
Lactometer test, (Experiments)
Lactones
Lactophenol solution, Prepare
Lactose
Lactucin
Lactucopicrin
Lager beer, (Experiments)
Lamiidoside
Laminaribiose
Laminarin, Lanthanum, La
Lamotrigine
Lampblack, Prepare
Lanatoside C
Langbeinite, (See:Kaolinite), (Geology)
Langelier saturation index
Lannaconitine
Lanolin
Lanoxicaps
Lanthanum, La
Lapachol
Lapis lazuli, (Geology)
LAS, Linear Alkylbenzene Sulfonic acid, Ionic sulfactants
Lasers
Lasiocarpine
Latex, (Experiments)
Latin Square
Laudanidine
Laudanosine
Laudanum
Laughing gas, N2O, (Experiments)
Laundry detergents
Laundry starch
Lauric acid, (Experiments)
Lauryl
Lavandulol
Lavandulyl acetate
Lavender oil
Law of mass action
Lawrencium Lawsone
Lindane
LDPE, Low density polyethylene
Lead, Pb, lead metal, (Experiments)
Leavening agents
Leaves, essences
LeBlanc process, sodium carbonate, Prepare
Leclanché cell, dry cell
Leclanché cell, Dry cell battery
Lectins
Legheamoglobin
Leishman's stain, Wright's stain, Prepare
Lemon grass, citronella oil
Lemons, (Experiments)
Length, metre
Lepidimoide
Lepidine
Leucine
Leurosine, alkaloid
Levodopa
Licorice, (Glycyrrhiza glabra), Fabaceae
See diagram: Liebig condenser
Lift ice cube with salt, (Experiments)
Lifting power of balloons containing different gases
Ligands
Light bulb, incandescence
Light stick, Chemiluminescence, bioluminescence
Lighted splint tests, (Experiments)
Lighters, Matches, (Commercial)
Legheamoglobin
Lignans
Lignin, (Experiments)
Ligroin, Petroleum spirit
Lilaline, alkaloid
Lime, CaO, (Experiments)
Limestone, tests for limestone, (Geology)
Lime sulfur, CaSx, (Agriculture)
Limewater, Ca(OH)2
Limonene
Limonin
Limonite, Geothite, (Geology)
Linagliptin, (Medicine)
Linalool
Linalyl acetate
Linamarin, (Cassava)
Lindane, (Agriculture)
Linoleic acid
Linolenic acid
Linseed oil
Linustatin
Lotoaustralin
Lip balm
Lipase, Tests
Lipids
Lipitor, (Medicine)
Lipoprotein
Lipstick
Liquid broth media, microbiology, Prepare
Liquid paraffin, (See: 3.)
Liquid pressure, fluid pressure, hydrostatics
Liquids with different viscosity, hydrogen bonds
Lists of chemicals
Lithage, Lead (II) oxide
Lithium, Li, (Experiments)
Lithium-ion battery, Li-ion battery
Lithospermic acid
Litmus, acid-base indicator
Littorine, alkaloid
Liver of sulfur, Potassium sulfide
Lobelanidine, alkaloid
Lobelanine, alkaloid
Lobeline, alkaloid
Loeffler serum, Microbiology, Prepare
Loganin
Loss on heating, (Experiments)
Lost volume, (Experiments)
Lost volume, Shrinking volume, Shrinking mixture of liquids
Lotaustrain
Lovastatin, Benzofuranoids, benzopyranoids
Low-cost, chemicals, equipment
LPG (Liquefied Petroleum Gas, LP gas)
LSD, Lysergic acid diethylamide
Lubricating oil
Lucite, Polymethyl methacrylate, (Experiments)
Lugol's iodine solution, Prepare
Luminescence
Lunarine, alkaloid
Lupanine, alkaloid
Lupeol
Lupinine, alkaloid
Lupulone
Lustre, (Geology)
Lutein
Luteolin
Lutetium
Lycoctonine, alkaloid
Lycopene
Lycopersene
Lycopodine, alkaloid
Lycorine, alkaloid
Lycopodium flammable "flash powder", (Safety)
Lycopsamine, alkaloid
Lynchnose
Lyophilic sols, (See: Sols)
Lysine, (Table of amino acids)
Lysine, DNA codons
Labile
Labile substances are unstable and liable to change to another form or to move away.
Laboratory equipment
Laboratory (Commercial)
Lab Grade, chemicals standards
Laboratory coat, Safety coats
Laboratory equipment
Laboratory gas, piped gas, "lab gas", Household gas
Laboratory organization: 3.1.5
Laboratory safety, physics teaching: 7.0
Laboratory safety: 4.0
Laboratory Safety: appendix C
Toxicity: 4.6.01
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, C3H6O3, CH3CHOHCOOH
Lactic acid
L-(+)-Lactic acid, 2-Hydroxypropionic acid, Sarcolactic acid, in sour milk, an α-hydroxy acid, skin irritant
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 making
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: 4.7.1.3
Lactobacillus
Lactones
Leavening agents: 19.1.6.0
Prepare lactic acid with milk: 12.7.10
Prepare lactic acid with sourdough: 4.2.3
Prepare yoghurt: 4.2.1a
Prepare yoghurt, test milk quality: 4.3.17
Tests for lactic acid solution: 12.7.11
Yoghurt and lactic acid bacteria, "Yakult": 4.3.0
12.7.11 Tests for lactic acid solution
1. Add lactic acid solution to the solution to sodium hydrogen carbonate (baking soda) in a test-tube.
Note the effervescence, because of the formation of carbon dioxide gas.
Test for carbon dioxide with limewater.
2. Heat lactic acid solution with iron filings.
Note the effervescence, because of the formation of hydrogen gas.
Increase the reaction by adding drops of copper sulfate solution.
However, it is difficult to obtain sufficient hydrogen to test by explosion with a glowing splint.
3. Boil 5 ml of lactic acid solution with two drops of dilute sulfuric acid.
Leave the solution to cool, then add it to a copper hydroxide precipitate from the reaction of copper sulfate with sodium hydroxide.
Heat the solution and observe a yellow precipitate, which turns red as copper (I) oxide (cuprous oxide) forms.
Laminarin
Laminarin, C18H32O16, laminaran, β-1,3- and β-1,6-glucan
It occurs in brown algae, Laminaria digitata, Chorda filum, Pleurotus ostreatus.
Lanthanum, La
See: Lanthanum, Table of the Elements
See: Lanthanum, RSC
Lanthanum, 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 nitrate | Lanthanum oxide | Lanthanum perchlorate
2.11.0 Rare earth elements, Lanthanides
Lamotrigine
Lamotrigine, C9H7Cl2N5, lamictal, a phenyltriazine
It is used as an anticonvulsant, antidepressant, mood stabilizer, drug for treating epilepsy, causes skin rashes
Latex, rubber
Latex, rubber, caoutchouc
Condom, male latex condom
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
3.6.11, Vulcanization
Laudanum
Laudanum, opium, diluted in wine with cloves and other spices, former common medicine, e.g."poppy-head tea" given to noisy babies
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 MP 43.2oC, increases high density lipoprotein (HDL), the "good" cholesterol
Fatty acids in oils of natural products: 17.6 (Table)
Fats in food: 3.90
Lauryl
Lauryl, C12H25-, Laurel oil from bay laurel: Bay tree
Lauryl sulfate, Sodium laurel sulfate
Lauryl alcohol
Lauryl alcohol, C12H26O, CH3(CH2)10CH2OH, dodecanol, 1-dodecanol, irritant
It is prduced from coconut oil fatty acids, is tasteless and colourless, but has a flowery smell, and is used in detergent manufacture.
Lauryl peroxide, br> Lauryl peroxide, C24H50O2<, 1-dodecylperoxydodecane, dilauroyl peroxide, Toxic by ingestion and inhalation, skin irritant
It has a white solid, soapy odour, floats on water, melting point 49oC, is used as a bleaching and drying agent for fats
Lauryl peroxide, Solution <20%, Not dangerous
Lavender oil
Lavendula angustifolia, Lamiaceae
Lavender flower oil, | linalyl acetate | 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: 17.5.6.2
Reversible reactions, effect of alteration of concentration: 17.5.5.0
Reversible reactions, hydrolysis of bismuth chloride: 17.5.5.1
Lawrencium, Lw
Lawrencium, Table of the Elements
Lawrencium, RSC
Lawrencium, Lw, (Earnest O. Lawrence, 1901-1958, USA)
Lead, Pb
See: Lead Table of Elements
See: Lead, RSC
Lead Elements, Compounds, (Commercial).
Commercial:
Lead, element, Lead foil, Lead shot, Lead Plate Electrodes 100 x 50 x 1.5 mm, 100 x 50 x 3 mm, 75 x 25 x 1.5 mm, Lead cube, 10 mm, 20 mm
Lead, Pb (plumbum) (Old English leād), metal foil 0.3 mm, powder, filings, strip, sheet, grain, lead AAS std, lead cell test kit, (0.5-5 mg / L), lead shot, fishing sinkers, roof guttering, Harmful, chronic poison if long-term exposure from pipe work, pottery glazes, containers, dusts.
Lead poisoning kills more than half a million people every year from long-term effects such as kidney failure, high blood pressure, heart disease, stroke and it can cause brain damage.
Lead type (lead, tin, antimony alloy), invented by Johannes Gutenberg (1395-1468, Germany), first printed Bible using moveable lead type, lead shot, fishing sinkers, roof guttering, foil, powder, filings, strip, is a soft, dense, and unreactive metal, available as lead foil, powder and lead shot, extracted from the ore galena (PbS), used in fishing sinkers, solder, lead glazes and X-ray protective shields, holds the pieces of glass together in stained glass windows, used in bullets, lead shot, building construction, lead cell accumulators, pewter, bearings and alloys.
Formerly, ladies used lead carbonate to whiten their laces and some may have died from such use.
Reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2.
No reaction with dilute HCl or H2SO4or with water.
Heated powder forms oxide.
Inorganic Pb2+is an accumulated poison and can replace calcium in bone.
A "lead pencil" contains graphite, not lead.
Lead is a metal with a silvery appearance that is resistant to attack by acids, because of the formation of a protective oxidized layer on its surface.
The metal melts at low temperature and is a good conductor of electricity, so it is used in solders.
The vapours of molten lead are extremely toxic and the effect of inhaling them is cumulative.
Lead salts are toxic by inhalation and can be absorbed through the skin, so should be handled with great care.
Wash laboratory areas where lead salts have been used with a dilute detergent solution to prevent exposure to any residual dust containing lead.
Do not heat lead oxide on a charcoal block.
Lead is used in the production of batteries, ammunition, metal products (solder and pipes), and devices to shield X-rays.
Lead was present in petroleum, paints and ceramic products, caulking and pipe solder, however, because of health concerns, it is now prohibited to include lead in these products.
Water pipes in some older buildings may contain lead solder.
Atomic number: 82, Relative atomic mass: 207.2, RD 11.3 g cm-3 MP = 327oC, BP = 1744oC.
Specific heat capacity: 130 J kg-1 K-1.
Lead compounds
Lead, Pb
Lead-acid battery
"Lead pencils": 35.3.5, (Geology)
Lead properties: 7.2.2.23
Aquadag: 35.41.5, (Geology)
Graphite: 35.41.3 (See: 4.), (Geology)
Lead paint
Lead paint
Lead tetra-ethyl, tetraethyl lead
Lead tetra-ethyl
Lead, group 1 tests for Ag+, Pb2+: 12.11.4.1
Lead occurrence, galena: 35.20.22, (Geology)
Lead residues: 3.5.3 (Disposal)
Prepare lead-acid battery electrolyte: 32.5.3.6
Prepare lead-tin alloys in a casting mould: 3.61.0
Prepare lead dioxide and lead (II) nitrate: 12.9.4
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 hardness of lead, tin: 3.62
Tests for lead: 12.11.3.8 (See: 6.)
Tests for lead, potassium iodide: 12.11.3.21
Tests for lead ions: 15.8.3
Tests for lead, melting point of lead, tin, and lead-tin alloys: 3.63.0
Lead compounds
Lead (II) acetate
Lead (II) acetylacetonate, C10H14O4Pb
Lead antimonate
Lead azide, Pb(N3)2, contact explosive, in detonators
Lead (II) bromide
Lead (II) carbonate
Lead (II) chloride
Lead (II) chromate
Lead (II) fluoride, PbF2
Lead hydroxide, Pb(OH)2, amphoteric
Lead (II) iodide, PbI2, lead iodide, lead diiodide, highly toxic, cumulative poison
Lead (II) iodide, Solution < 1%, Not hazardous
Lead magnesium niobate, MgNb2Pb3O9
Lead (II) methanesulfonate, C2H6O6PbS2
Lead (II) molybdate, PbMoO4
Lead (II) nitrate
Lead (II) oxide
Lead (II) sulfate
Lead (II) sulfide
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 manganese oxide, coronadite, Pb2Mn8O16: 35.20.12, (Geology)
Lead residues: 3.5.3 (Laboratory disposal)
Lead subacetate, C4H10O8Pb3
Pyromorphite: 35.20.33, Pb5(PO4)3Cl (lead phosphate), (Geology)
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 poisons.
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 acetate
Lead (II) acetate, Pb(CH3COO)2, lead (II) ethanoate
Lead Acetate AR, (Modern Teaching Aids)
Lead acetate Elements, Compounds, (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) bromide
Lead (II) bromide, PbBr2, Solution < 1% Not hazardous
Electrolysis of lead (II) bromide melt: 3.68.0
Lead (II) carbonate
Lead (II) carbonate, PbCO3
Lead (II) Carbonate (Modern Teaching Aids), (Commercial)
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, (Geology)
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 supplies
Lead (II) chloride
Lead chloride, (Modern Teaching Aids) (Commercial)
Lead (II) chloride, PbCl2, lead chloride, highly toxic by all routes
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, SG 6.3, insoluble in water, acetic acid, and ammonia, but soluble in acid and alkalis.
It is possibly the 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
Lead (II) nitrate, Pb(NO3)2, white to colourless large crystals, reactivity series, lead (II) nitrate, Toxic, cumulative poison
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.
It is the only common soluble lead compound, forms explosive mixture with combustible materials, e.g. S, P, metal powders
The heated solid forms highly toxic nitrogen dioxide, test for anions: forms bright yellow precipitate of lead iodide, with sodium or potassium iodide
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, Tests for hydrogen sulfide solution, ionization of hydrogen sulfide: 3.43.1 (See 2.)
Coloured precipitates: 12.2.1c (See 1, 3.)
Lead (II) sulfate
Lead Sulfate, (Modern Teaching Aids), (Commercial)
Lead (II) sulfate, PbSO4, lead sulfate, green vitriol, blue lead, white lead, Toxic, cumulative poison
Lead (II) sulfate was previously in white lead paint.
Lead (II) sulfate, Solution < 1%, Not hazardous
Prepare lead acid battery electrolyte: 32.5.3.6
Lead sulfate, PbSO4, lead (II) sulfate, basic lead (II) sulfate, Toxic, anglesite: 35.20.1, (Geology)
Lead (II) sulfide
Lead (II) sulfide, PbS, lead sulfide, lead glance, blue lead, Toxic, cumulative poison
Galena: 35.20.15, (Geology)
Lead (II) sulfide, Solid mixture < 1%, Not hazardous
Lead (II) oxide
Lead (II) oxide, PbO, lead oxide, lead monoxide, plumbous oxide, amphoteric, litharge, massicot, Toxic
Lead Oxide (Modern Teaching Aids)
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: 32.5.3.7
Lead (II/IV) oxide
Lead Oxide (Modern Teaching Aids), (Commercial)
Lead (II/IV) oxide, Pb3O4, triplumbic tetroxide, red oxide of lead, 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, Solid mixture < 1%, Not hazardous, trilead tetroxide, red, lead, triplumbic tetroxide, lead tetroxide
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.
It is used in anti-corrosive lead paints, especially rustproof primer paints.
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 (II/IV) oxide, Reduce red lead to lead and oxygen: 10.10.1
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 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 caused "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
Lead tetra-ethyl, tetraethyl lead, tetraethylplumbane, Pb(C2H5)4 or C8H20Pb, lead tetra-ethyl (in "leaded" gasoline)
| 16.6.8.0: Octane C8H18, Octane number
| 32.5.5.5.1: 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.
Lemons
Lemons, lemon juice, 5-8% citric acid
Lemon, (Citrus x limon), (lemon citrus fruit), 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, (Citrus species), Rutaceae
Extraction of caffeine and benzoic acid from soft drinks, e.g. cola and lemonade: 9.8.3
Lemon cell, (electricity from lemons)
Lemon juice, lemon oil
Lemon juice, invisible ink: 3.2.5.14
Isolation of benzoic acid in lemonade: 9.8.3.2
Prepare citric acid crystals with lemon juice: 12.6.1
Prepare mayonnaise and salad dressing emulsions: 16.4.7
Soft drinks: 15.8.6 (lemonade)
Tests for lemon juice on apple browning: 19.3.4.2.2 (Cooking)
Tests for pH of water in the laboratory: 18.1.2 (lemonade)
19.3.4.2.1
Lemon juice
Lemon juice is rich in vitamin C (100g of lemon juice contains 38 mg of vitamin C), pH 2-3, because of citric acid content.
It can break down the amines in fish into non-volatile ammonium salts to neutralize the fishy odour.
It can hydrolyse the tough collagen fibres in meat to tenderize it.
Lemon juice does not dissolve fat.
Use lemon juice to treat dandruff, blackheads, facial blemishes, rough hands, sore feet, constipation, itches, minor wounds, Use with honey and olive oil relieve coughing, unclog ketchup bottles, write with invisible ink, blonde hair, deodorize cooked fish, fish cooking utensils.
Use it on microwave ovens and refrigerators, remove fruit stains, rust, mineral discoloration, ink spots from clothing, whiten fingernails.
Use it with salt to clean brass and stainless steel sink.
Use lemon juice to prepare bathtub rust stains cleaner.
Lemon oil
Lemon oil is oil from lemon peel, D-limonene, a terpene, used for furniture polish, inhibits spiders and insects, stain remover.
Lighted splint tests
Carbon dioxide: 3.34.1.0
Dinitrogen oxide (nitrous oxide): 3.45.1
Hydrogen chloride: 3.42.1.4
Hydrogen gas: 3.41.1
Linseed oil
Linseed oil, from seeds of flax Linum usitatissimum, contains glycerides of oleic acid and other unsaturated acids
Linseed oil, conditions and seals 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
Lignin is an organic polymer in wood fibres and grass cell walls of vascular plants and is composed of coniferyl, p-coumaryl, and sinapyl alcohols in varying ratios
Lignin, cellulose, hemicellulose, are copolymers of phenyl propane units with side chains.
Copper is involved in the formation of lignin for strong shoots and stems.
Filter paper contains lignin, but cigarette paper does not contain lignin.
Lignans, polyphenols from degradation of lignin, e.g. Sesamin.
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
Lime, CaO, Ca(OH)2, CaCO3, 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: 4.4.12 (Agriculture)
Limestone, stone dust, carving stones: 35.22.7. (Geology)
Marble: 35.23.3, (Geology)
Experiments
Cellulose digestion: 9.214
Chalk (lime) content of the soil: 6.9.02, (Agriculture)
Heat calcium metal to form calcium oxide: 8.2.14
Limewater
See diagram: 9.154 Limewater test for carbon dioxide in the breath.
Limewater, saturated calcium hydroxide solution
Calcium hydroxide, Ca(OH)2, limewater, 10 g in 1 L water, shake, allow it to settle, decant clear liquid.
Weaker bases, e.g. calcium hydroxide (limewater, slaked lime), can cause burns if they are left in contact with the skin.
If poison ingested = Ammonium oxalate, Buffer solution tablets pH 2, Oxalic acid, Potassium hydrogen oxalate, Sodium oxalate, give milk or water, weak limewater, chalk solution
Experiments
Candle flame forms carbon dioxide: 8.1.4
Dilute acids with carbonates, common carbonates: 12.3.9.0, See: 4.
Dilute hydrochloric acid with calcium carbonate: 12.3.9.1
Dilute hydrochloric acid with sodium carbonate: 12.3.9.2
Dilute tartaric acid with sodium carbonate: 12.3.9.3
Dilute tartaric acid with egg shell, soil, wood ash: 12.3.9.4
Dilute sulfuric acid with calcium carbonate: 12.3.9.6
Effervescent tablets, health salts, sodium bicarbonate, (baking soda): 11.1.1 See: 1.
Elements in food: 19.3.0, See: 2.
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
Hydrogen peroxide with potassium sodium tartrate, cobalt (II) chloride catalyst: 17.7.6.3
Precipitation: 10.11.01
Prepare ethyl acetate, (ethyl ethanoate): 16.4.2
Prepare hard water: 12.13.2
Prepare limewater: 5.4.5
Reactions of metals with water, Cu, Zn, Fe, Mg, Al: 12.15.1
Respiration, limewater tests for carbon dioxide: 9.155
Sodium carbonate with calcium hydroxide: 12.2.4.2
Tea with limewater: 12.10.4
Tests for acetates: 12.11.5.1
Tests for carbon dioxide in the breath with limewater : 9.6.10
Tests for carbon dioxide through calcium hydroxide solution, limewater: 12.16.1.1
Tests for gases from burning hydrocarbons: 16.4.6.0
Tests for lactic acid solution: 12.7.11
Tests for respiration of soaked peas with limewater, respiration apparatus: 9.155
Tests for soap: 12.9.2 (See: 3.)
Lithium, Li
See: Lithium Elements, Compounds, (Commercial)
See: Lithium Li, Table of the Elements
See: Lithium, RSC
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 it 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.
Lithium reacts with oxygen gas and water, and, 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, RD 0.53 g cm-3 MP = 180oC, BP = 1330oC.
Specific heat capacity: 3.39 × 103 J kg-1 K-1.
Lithium compounds
Heat lithium metal to form lithium oxide: 8.2.10
Reactions of lithium with water: 12.9.3
Lithium-ion battery
Lithium compounds, (very toxic)
Lithium-ion battery, Li-ion battery: 33.6.15
Lithium aluminium hydride, LiAlH, lithium tetrahydroaluminate, Toxic by all routes, Not permitted in schools
Lithium aluminium silicate, LiAlSi2O6, spodumene, forms 6 m crystals, grey-white ash when ignited
Lithium carbonate, Li2CO3 for craft, flux, glaze, tranquillizer for mental disorders, white solid, Toxic, Irritant
Lithium carbonate, Low cost: from pottery supplies stores
Lithium hydride, Toxic by all routes, fine particles mixed with air is explosive, reacts violently with water to form dangerous hydrogen
Lithium chloride
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
Lithium nitrate, LiNO3, Toxic if ingested, explosive mixture with combustibles or organic compounds
Lithium oxide, Li2O, lithia
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, but do NOT use a scalpel with a disposable blade!
Lithium is toxic if ingested and corrosive to the skin.
2Li (s) + 2H2O (l) --> 2LiOH (aq) + H2 (g)
8.2.10 Heat lithium metal to form lithium oxide, prepare lithium oxide
Heat pieces of lithium metal shot on a metal spoon (deflagrating spoon).
Note the violet glow when it starts to burn, then put the burning lithium in oxygen gas.
4Li + O2 --> 2LiO2
Lithium oxide is used in some ceramic glazes as a flux and colorant.
LPG, Liquefied Petroleum Gas
LPG, Liquefied Petroleum Gas, LP gas, LPG gas, LP-gas, compressed gas, bottled gas
Bottled gas
Ethyl mercaptan: 16.1.3.3.3, (odorant in LPG)
LPG, LP-gas (bottled gas), hazards: 3.8.8
Petroleum gas: 16.1.12.1
Propane: 16.6.2.0
Thiophene: 16.1.3.3.4, (odorant in LPG)
Liquefied petroleum gas, LPG
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. but use a soap solution.
LP Gas is 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
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.
28.101 Candoluminescence
14.3.0 Chemiluminescence, bioluminescence:
Fluorescence
14.3.0a Fluorophores, (fluorescent chemical compounds
28.104 Luminance and illuminance
14.3.1 Luminol tests for blood, Cu, Fe, Cn-
7.33.3 Phosphorescence
Triboluminescence
Thermoluminescence
Lutetium, Lu
See: Lutetium, Table of the Elements
See: Lutetium, RSC
Lutetium, Lu (Latin Lutetia ancient Paris), heaviest lanthanide, rare earth
3.61.0 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.
3.62.0 Tests for hardness
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.
3.63.0 Tests for melting point of lead, tin, and lead-tin alloys
See diagram 3.63: 3.63 Melting point apparatus: A metal plate, B suspended metal plate
Cut 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 size.
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, rubber
Natural rubber, latex, 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 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
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
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
12.9.4 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, Sapotaceae.
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, 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.
A rubber band contracts on heating, because when long polymer chains in rubber absorb energy, adopt a more contorted configuration, reducing the volume.
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 system.
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.
Lepidine
Lepidine C, C21H20N4O2, diphenylether, solid, almost insoluble in water, in cell membranes, brassicas and garden cress, used as a biomarker.
Leucine
Leucine, (Table of amino acids)
Leucine, DNA codons
Leucine, (See: a3), (Experiments)
Linagliptin,
Linagliptin, C25H28N8O2, a dipeptidyl peptidase4 inhibitor, a xanthine, used in combination with diet and exercise for type 2 diabetes and to lower blood sugars.
Prescription medicine: Trajenta
Lipoprotein
Lipoprotein, fat with protein, in cell membranes, α-Lipoprotein, HDL, high density lipoprotein, in human plasma.
Linoleic acid
See diagram: 19.2.1: cis and trans, linoleic acid
19.2.1.7.2 Trans fats, Omega-fatty acids
Linoleic acid
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, 2 on one side and 2 on the other.
The more stable trans configuration may be produced from the cis configuration during 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)
These actions may result in changes in cholesterol levels that may increase the risk of the heart disease atherosclerosis.
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, α-linolenic acid
Alpha linolenic acid, C18H30O2, (ALA), polyunsaturated fatty acid (PUFA), essential fatty acid in diet because not synthesized by mammals.
It occurs 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 in vegetable oils:
1. Alpha-linolenic acid (ALA), C18H30O2, is a polyunsaturated omega-3-fatty acid, essential fatty acid not produced in the human body.
High concentration occurs in lants, nuts, vegetable oils, including:
| Chia, (Salvia hispanica) | Kiwi fruit, (Actinidia deliciosa)
| Perilla, (Perilla frutescens)
| Flaxseed, (Linum usitatissimum)
2. Gamma-linolenic acid (GLA), C18H30O2, a polyunsaturated omega-6-fatty acid.
High concentration in and seed oils of blackcurrent and borage and Evening primrose,.
Linustatin
Linustatin, C16H27NO11, cyanogenic glycoside, diglucoside of acetone cyanohydrin, methylpropanenitrile, toxic, in flaxSeed meal, in Passiflora
Lipitor,
Lipitor, C33H34CaFN2O5+, a pyrrole (from: Atorvastatin)
It is used to reduce serum levels of LDL-cholesterol, apolipoprotein and triglycerides, for the prevention of cardiovascular diseases
Heptanoic acid, C7H14O2, oenanthic acid, colourless liquid, pungent odour, floats on water, very corrosive, toxic, in rancid oils.
Used in fragrance industry, and in cigarettes..
It is occurs in Artemisia macrocephala, and Ajania fastigiata.
Lotoaustralin
Lotoaustralin, C116H19NO6, methyl-linamarin, a cyanogenic glycoside, toxic, protects the plant against insects and herbivores.
Enzymatic degradation may produce lethal hydrocyanic acid HCN
It occurs in Lotus australis, Trifolium repens, Linum, Passiflora, Tritium monococcum, and in Cassava tubers and leaves
Low-cost, chemicals, equipment
Low-cost chemicals and common substances: 16.0.0
Low-cost equipment, simple equipment: 1.12.0, (Experiments)
Consumable low cost equipment
Lupeol,
Lupeol, C30H50O, fagasterol, clerodol, monogyrol B, beta-viscol, lupane, a pentacyclic triterpenoid, secondary alcohol
It is antitumour, antihypoglycaemic, anti-hypotensive, and anti-inflammatory It occurs in Phyllanthus emblica, lupin Lupinus luteus seeds skin, mango, Acacia visco, Abronia villosa, and in dandelion coffee
It occurs in lupin seeds and skin, in fig trees latex, in rubber plants latex, in fruits and vegetables.
Lupulone
Lupulone, , C26H38O4, lupulon, beta-lupulic acid, beta-bitter acid, antineoplastic agent, antibiotic, antimicrobial, apoptosis inducer, angiogenesis inhibitor
It is used for bitter taste of beer, and it occurs in hops, Humulus lupinus.
Luteolin,
Luteolin, C15H10O6, a flavone, yellow crystalline, anti-inflammatory, anti-tumour, strong antioxidant, radical scavenger, possible anti-cancer
It is used in expectorants, hypoglycaemic agent, withstands radiation and chemotherapy It occurs in parsley, thyme, peppermint, basil, celery, artichoke, broccoli, dandelion, perilla), Aiphanes aculetat palm, Salvia tomentosa, and Ambrosia
Hypolaetin, (8-Hydroxyluteolin), C15H10O7, a pentahydroxyflavone, (derived from a luteolin), antioxidant, plant metabolite
Potassium sulfide
Not permitted in schools
Potassium sulfide, K2S, highly toxic if ingested, releases hydrogen sulfide gas: E225, preservative, antioxidant.
Potassium sulfide, liver of sulfur, sulfurated potash, red-yellow to brown-red, deliquescent, analytical reagent and epilatory, dusts may explode
It is used as a depilatory, hair removing.
Potassium sulfide, liver of sulfur: Alkaline mixture of mainly potassium polysulfides turns silver black.
16.8.4 Lubricating oil, motor oil, grease
Mix of C16H34 to C24H50, 20 to 50 carbon atoms, alkanes and cycloalkanes and aromatics, boiling range 300oC to 370oC.