Answers Chapter 11

Summary Questions 11.1 p1331 insoluble; neutralised; oxide; limiting; filter; filtrate2a iron(III) oxide / iron oxide + hydrochloric acid → iron(III) chloride / iron chloride + water b magnesium + sulfuric acid → magnesium sulfate + hydrogen3 add excess calcium oxide very slowly to hydrochloric acid; filter off excess calcium oxide; evaporate some of the water from the filtrate; leave in a warm place to crystallise

Summary Questions 11.2 p1351 soluble; alkali; burette; indicator; repeated2a ammonia + hydrochloric acid b sodium hydroxide + hydrochloric acid c ammonia + nitric acid3a sodium nitrate b ammonium sulfate c lithium nitrate

Summary Questions 11.3 p1371 insoluble; precipitation; ion; attracted; lattice; spectator2a soluble b insoluble c soluble d insoluble e insoluble3a Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq) b FeCl2(aq) + 2NaOH(aq) → Fe(OH)2(s) + 2NaCl(aq) allow: IONIC EQUATIONS

Summary Questions 11.4 p1391 collecting; heavier; displacement; insoluble; water2 hold piece of damp red litmus paper / universal indicator paper in the ammonia – the litmus turns blue because ammonia is alkaline 3 oxygen relights a glowing splint hydrogen pops/ gives a small explosion with a lighted splint

Summary Questions 11.5 p1411 cations; hydroxide; ammonia; precipitate; distinctive; white; zinc2a reddish-brown b white c light blue3 zinc ions and calcium ions both give a white precipitate with sodium hydroxide But with excess sodium hydroxide the zinc hydroxide precipitate redissolves but the calcium hydroxide precipitate does not. If we use ammonia the calcium ions do not usually form a precipitate but a precipitate is obtained with zinc ions which redissolves in excess ammonia solution

Summary Questions 11.6 p1431a silver ions and iodide ions b barium ions and sulfate ions2a add aqueous sodium hydroxide; add aluminium foil / Devarda’s alloy and warm; test the gas given off with damp red litmus paper; if the litmus paper turns blue a nitrate is present. b add (hydrochloric) acid to the suspected carbonate; bubble the gas produced through limewater; if a carbonate is present the limewater turns milky

c to the suspected chloride add nitric acid then aqueous silver nitrate; if a white precipitate is formed which turns grey rapidly in the light, then chloride ions are present3 copper iodide / copper(II) iodide

Chapter 11 Summary Questions p1441 iron(II) sodium hydroxide iodide silver nitrate sulfate barium chloride carbon dioxide limewater nitrate aluminium + sodium hydroxide2 salt; excess; sulfuric; filtered; filtrate; evaporating; water; crystallise3a/b oxygen relights a glowing splint hydrogen pops/ gives a small explosion with a lighted splint4 put sodium hydroxide into a flask and hydrochloric acid into a burette ↓ put a few drops of acid base indicator solution into the flask ↓ drip the hydrochloric acid from the burette into the flask until the indicator changes colour ↓ note the volume of hydrochloric acid added ↓ repeat the experiment without the indicator by adding the volume of hydrochloric acid recorded previously ↓ take the solution in the flask, put it in an evaporating basin and evaporate off some of the water ↓ leave the filtrate to crystallise in a warm place ↓ filter off the crystals and dry them on filter paper5 1. calcium hydroxide + hydrochloric acid (titration method – neither reagent in excess) 2. calcium oxide + hydrochloric acid (calcium oxide in excess so filtered off) 3. calcium + hydrochloric acid (either calcium or HCl in excess) – this method is less good because of the violent reaction of calcium with the acid6a insoluble b soluble c insoluble d soluble e insoluble f soluble g soluble h insoluble7a method ii b method i c method ii d method iii

Chapter 11 Exam Questions p144-1451 B [1]2 D [1]3a sulfuric acid [1] 3 of the following = 2 marks . 2 of the following 1 mark, 0 or 1 of the following 0 marks [2] evaporate of some of the water / leave in warm place to crystallise; filter off crystals / pick out crystals; wash crystal with minimum amount of water; dry crystals on filter paper / leave to dry / allow warm in oven below 100oC b to make sure that all the acid had reacted [1] ci (acidify with nitric acid) add (aqueous) barium chloride / nitrate; [1] ii white precipitate [1]4a turns its red [1] b bubble through limewater; [1]

limewater turns cloudy / white precipitate [1] c add aqueous sodium hydroxide; [1] white precipitate; [1] insoluble in excess sodium hydroxide [1] d calcium carbonate; [1] carbonates give off carbon dioxide with acids; [1] M is an acid because it turns blue litmus red [1]5a hydrochloric acid [1] b burette (with acid); [1] flask (with alkali) under the burette; [1] indicator in flask [1] c drip acid into flask (containing alkali); [1] until indicator in flask changes colour; [1] record initial and final volume of acid added / record volume of acid delivered [1] d repeat titration without indicator adding the same amount of acid as before; [1] put solution from flask in evaporating basin; [1] evaporate of some of the water / leave in warm place to crystallise; [1] filter off crystals / pick out crystals; [1] e make a solution of the crystals / dissolve crystals in dilute nitric acid; [1] add aqueous silver nitrate; [1] white precipitate indicate presence of Cl- ions [1]6a lead nitrate / any soluble lead salt; [1] potassium iodide/ any soluble iodide [1] b Pb2+(aq) + 2I-(aq) → PbI2(s) [3] 1 mark for correct formula for reactants; 1 mark for correct formula of lead iodide and correct balance; 1 mark for correct state symbols c add the solutions containing lead ions and iodide ions; (no mark) filter the precipitate; [1] wash precipitate with water; [1] dry the precipitate below 100oC in an oven / allow the water to evaporate [1] d partly solubilise crystals in nitric acid; [1] add aqueous silver nitrate; [1] light yellow precipitate indicates presence of I- ions [1] ALLOW: for 1st mark allow references to making saturated lead iodide solution (since silver iodide is much less soluble than lead iodide) ei Ba2+(aq) + SO4

2-(aq) → BaSO4(s) [2] 1 mark for formulae of the two reactant ions if two marks not scored ii add aqueous sodium hydroxide and aluminium / Devarda’s alloy; [1] heat gently and test gas with (damp) red litmus paper; [1] litmus paper turns blue [1]7ai iron(II) salts give grey-green/ green precipitate; [1] iron(III) salts give a red-brown precipitate [1] IF: word precipitate not seen at all maximum of 1 mark ii ammonia is an alkali; [1] forms hydroxide ions in water [1] bi iron(II) has been oxidised by oxygen in the air/ reacted with the oxygen in the air; [1] ii Fe2+ + e- → Fe3+ [1] c add sodium hydroxide / ammonia to each solution; [1] iron(II) gives a grey-green colour; [1] iron(III) gives a red-brown colour; [1] mention of precipitates / specks in solution formed in both [1] NOTE: it is wise to include the word ‘precipitate’ when answering this type of question since there is often only one mark for the colour + the precipitate di react excess iron with sulfuric acid; [1] filter off the iron; [1] put the filtrate in an evaporating basin; [1] evaporate some of the water from the filtrate and leave to crystallise/ leave filtrate in warm place to crystallise [1] ii Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g) [3]

3 marks for equation correct with all state symbols correct 2 marks for equation correct but 1 or more state symbols incorrect 1 mark for correct formulae of hydrogen and iron(II) sulfate on right hand side of equation