4 Useful Rocks The rock cycle Extraction and electrolysis of salt ContentsUseful RocksThe rock cycleExtraction and electrolysis of saltUses of the products of saltUses of limestoneSummary activities
5 Three-quarters of the salt we use comes from rock salt. As the earth’s surface changed stretches of sea-water became landlocked.Evaporation of this water along with further geological changes led to deposits of rock salt in many countries including the UK.
6 Electrolysis of salt (1) Negative ionsSalt consists of sodium ions (Na+) and chloride ions (Cl-).Chloride ions go to the anode where they lose an electronThe neutral chlorine atoms produced join up into pairsChlorine gas is formed2Cl e-Cl2
7 Electrolysis of salt (2) Positive ionsNa+ are not the only + ions present.There are also H+ ions because some water molecules split up into H+ and OH- ions.H+ accepts electrons more easily than Na+ does.This has important consequences at the cathode.Na+Cl-HO-H+HO
8 Electrolysis of salt (3) Na+ ions move to the cathode but do not accept electrons.It is the hydrogen ions that gain electronsAs a result hydrogen gas is formed at the cathode.2H e- H2
9 Electrolysis of salt (4) What happens to the various ions?No change “Spectator ion”Na+Cl-HO-H+Changed into chlorine gas at anodeChanged into hydrogen gas at cathodeNo change “Spectator ion”
10 Electrolysis of salt (5) Sodium hydroxide is what is left in the solution at the end of electrolysisNa+Cl-HO-H+Na+HO-ClHSolutionElectrodes
11 Questions about saltSome salt is dug out of underground deposits of rock salt but most salt is obtained by pumping river water into the salt deposits which may be about 2000m below ground. The salt dissolves to form a solution called brine which travels up a second pipe to the surface. It is then stored in a brine reservoir prior to being used for various purposes.Name one important winter use of solid rock-salt.Draw a diagram illustrating the production of brine and its subsequent electrolysis.Draw a diagram showing how you could remove the gritty impurities in rock-salt in the laboratory.
12 Answers about salt (1)An important winter use of solid rock-salt is to treat icy roads.Diagram of brine production to electrolysis.pumpBrineRiverRock Saltdissolves2000m+-Electrolysis CellDissolved salt.up to surfaceHydrogengasChlorine gasSodium Hydroxide
13 Removal of gritty impurities from Rock Salt Answers about salt (2)Removal of gritty impurities from Rock SaltResidue:Gritty impuritiesFilter paperFilter funnelFiltrate:brineConical flask
14 Useful Rocks The rock cycle Extraction and electrolysis of salt ContentsUseful RocksThe rock cycleExtraction and electrolysis of saltUses of the products of saltUses of limestoneSummary activities
15 Uses of chlorine (1) Sterilisation of water e.g. swimming pools and drinking waterSodiumchloride‘rock salt’solutionelectrolysisChlorinegasBleaching agent,e.g. paper industry
16 Uses of chlorine (2) Sterilisation of water e.g. swimming pools and drinking waterSodiumchloride‘rock salt’solutionelectrolysisBleaching agent,e.g. paper industryChlorinegasManufacture of HClcontinuedManufacture ofCl-containingorganic chemicals
17 Uses of chlorine (3) Manufacture of PVC and Manufacture of HCl other plasticsManufacture of HCl
18 Uses of chlorine (4) Manufacture of PVC and Manufacture of HCl other plasticsManufacture of HClPesticidesManufacture ofCl-containingorganic chemicalsSolvents, e.g. solvent fortippex, & ‘dry cleaning’dyes
19 Uses of sodium hydroxide (1) Extraction of aluminiumSodiumchloride‘rock salt’solutionManufacture of soapelectrolysisSodiumhydroxideManufacture of Paper
20 Uses of sodium hydroxide (2) Extraction ofaluminiumSodiumchloride‘rock salt’solutionManufacture of soapSodiumhydroxidesolutionelectrolysisManufacture of PaperTextiles (wool,cotton)
21 Uses of sodium hydroxide (3) Extraction ofaluminiumSodiumchloride‘rock salt’solutionManufacture of soapSodiumhydroxidesolutionelectrolysisManufacture of paperTextiles (wool,cotton)Neutralizationof acid effluents
22 Uses of products from salt Join the appropriate substances with arrows.chlorinehydrogenSodium hydroxidesaltHydrochloric acidpvcsoapbleachOrganic chloridesAluminium extractiondyesAcid neutralization
23 Useful Rocks The rock cycle Extraction and electrolysis of salt ContentsUseful RocksThe rock cycleExtraction and electrolysis of saltUses of the products of saltUses of limestoneSummary activities
24 Limestone Limestone is a sedimentary rock. It comes from the shells of sea creatures or from solids formed in the oceans long ago.It is mostly made of calcium carbonate - CaCO3.It is an important raw material for both the chemical and the construction industries.
25 Limestone is a base with the formula CaCO3. Limestone as a baseLimestone is a base with the formula CaCO3.It is capable of neutralising acids but because it is insoluble in water it does so without ever making the solution strongly alkaline.Carbonates fizz (effervesce) when they react with acids.1214131211109876543Neutralizes acid - without the need for strong alkali
26 Limestone for stomachs! Limestone is a base with the formula CaCO3.During indigestion the stomach may produce too much (excess) acid.Indigestion tablets neutralise some of this acid.These tablets often contain purified calcium carbonate.2HCl + CaCO3 CaCl2 +H2O +CO2
27 Limestone is used in agriculture. Limestone for soilLimestone is used in agriculture.Acidity can build up in soils.This can inhibit the growth of many crops. Consequently farmers need to adjust the pH back towards neutral.Limestone provides a cheap way of neutralising soil acidity.pH567
28 Limestone – extraction of iron In the blast furnace limestone removes acidic earthy impurities that would ruin the quality of iron.Limestone is one of three major raw materials used to extract iron from its ores.It reacts with acidic impurities changing them into a slag that separates from the iron.CaCO SiO2CaSiO3 + CO2
29 Quicklime – the limekiln Limestone is heated in huge ovens known as lime kilns.The calcium carbonate decomposes into calcium oxide (quicklime) and carbon dioxide.Quicklime is a vital ingredient of cement, concrete and of most types of glass.CaCO3CaO+ CO2
30 Limekiln Calcium oxide is made industrially in a limekiln. calcium carbonate (limestone)waste air and carbon dioxide1,500 °Chot airhot aircalcium oxide (lime)
31 CaO + H2O Ca(OH)2 Slaked lime If water is added to quicklime the calcium oxide changes into calcium hydroxide (slaked lime).Slaked lime is a vital ingredient of various building materials.CaO H2O Ca(OH)2A solution of calcium hydroxide (limewater) is also used to test for carbon dioxide gas (it goes cloudy).
32 The main raw materials for cement are limestone and clay. Manufacture of cementThe main raw materials for cement are limestone and clay.A small amount of gypsum is also added to help the cement set at the right speed.Clay or shaleLimestoneor chalkheatCementGypsum(calcium sulphate)
33 Cement, concrete and mortar To make concrete cement is mixed with small stones or gravel.Mortar consists of cement mixed with calcium hydroxide. This makes a smooth slow setting mixture suitable for bricklayingCement, concrete and mortar all set when interlocking crystals grow between cement particles joining them together.
34 Manufacture of glassLimestone, sand and sodium carbonate are the raw materials used to make most glass.SodiumcarbonateGlassLimestoneheatwaterLime(calciumhydroxide)heatSand (silicondioxide)
35 Limestone for indigestion Manufacture of quicklime Uses of limestoneJoin matching pairs with arrows.Limestone for indigestionIron ManufactureSlaking of limeManufacture of quicklimeCaCO3 CaO + CO2CaO + H2O Ca(OH)2CaCO HCl CaCl2 + H2O +CO2CaCO3 + SiO2 CaSiO3 + CO2
36 Useful Rocks The rock cycle Extraction and electrolysis of salt ContentsUseful RocksThe rock cycleExtraction and electrolysis of saltUses of the products of saltUses of limestoneSummary activities
37 Glossarybrine – A strong solution of salt, especially sodium chloride.electrolysis – The process in which an electric current is passed through sodium chloride solution to produce chlorine, hydrogen and sodium hydroxide.limestone – A sedimentary rock containing mainly calcium carbonate.quicklime – Calcium oxide. Produced by heating limestone in a limekiln.rock cycle – A series of processes that cause rocks to change from one type to another.rock salt – Naturally-occurring crystalized sodium chloride.