Introduction to Salts
28 Grade 10 Chemistry questions on Introduction to Salts, with worked marking schemes. 28 questions are available on this topic in full.
Question 1
3 marksA learner followed the correct procedure for preparing zinc sulphate crystals but obtained a much smaller mass of crystals than expected. Suggest three reasons for the low yield.
(3 marks)
Marking scheme
Any three, 1 mark each: - Some of the salt remained dissolved in the mother liquor filtered off from the crystals. - Solution or solid was lost during transfer and filtration (left on the beaker, rod or filter paper). - The crystals were washed with too much water, so part of them dissolved away. - The solution was not evaporated far enough, so it was not saturated and little crystallised on cooling.
Question 2
4 marksState four general rules about the solubility of salts in water.
(4 marks)
Marking scheme
Any four, 1 mark each: - All nitrates are soluble. - All sodium, potassium and ammonium salts are soluble. - All chlorides are soluble except lead(II) chloride and silver chloride. - All sulphates are soluble except barium sulphate, lead(II) sulphate and calcium sulphate (slightly soluble). - All carbonates are insoluble except those of sodium, potassium and ammonium.
Question 3
2 marksName the acid and the base from which each of the following salts may be regarded as having been formed: (a) ammonium sulphate; (b) calcium nitrate.
(2 marks)
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1 markTrona harvested at Lake Magadi is processed into sodium carbonate. The largest industrial use of this salt is in:
A. hardening water for domestic use
B. the manufacture of glass
C. the manufacture of ammonium nitrate fertiliser
D. the galvanising of iron sheets
(1 mark)
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4 marksSuggest a salt that could be used in each of the following situations, giving a reason in each case: (a) lowering the acidity of soil on a tea farm in Kericho; (b) preserving omena landed at Lake Victoria; (c) supplying nitrogen to a maize crop in Trans Nzoia; (d) removing suspended clay from river water before treatment.
(4 marks)
Marking scheme
1 mark each (salt + reason both needed): (a) Calcium carbonate (agricultural lime) – it is basic and neutralises the acid in the soil, raising the pH. (b) Sodium chloride – it draws water out of the fish so that bacteria cannot grow. (c) Ammonium sulphate or calcium ammonium nitrate – it dissolves in soil water and supplies nitrogen for leaf growth. (d) Potassium aluminium sulphate (alum) – it coagulates the fine clay particles so that they settle out.
Question 6
4 marksDescribe what is observed when (a) lead(II) nitrate and (b) sodium nitrate are each heated strongly in a dry test-tube.
(4 marks)
Marking scheme
(a) 1 mark – The crystals crackle and melt, and brown fumes (nitrogen dioxide) are given off together with a colourless gas that relights a glowing splint (oxygen). (a) 1 mark – A residue of lead(II) oxide remains; brown when hot and yellow on cooling. (b) 1 mark – The solid melts and gives off a colourless gas only, which relights a glowing splint (oxygen). (b) 1 mark – No brown fumes are produced; a white solid (sodium nitrite) remains.
Question 7
3 marksA farmer is advised not to apply agricultural lime and ammonium sulphate fertiliser to the same field on the same day. Explain this advice.
(3 marks)
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1 markWhich one of the following salts can only be prepared by mixing two solutions and filtering off the solid product?
A. Sodium nitrate
B. Lead(II) sulphate
C. Zinc chloride
D. Magnesium sulphate
(1 mark)
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3 marksIn preparing potassium chloride, a learner first titrated potassium hydroxide solution against dilute hydrochloric acid using an indicator, and then repeated the experiment with the same volumes but without the indicator. Explain why the second run is necessary.
(3 marks)
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1 markWhich one of the following is a normal salt?
A. Sodium sulphate, Na₂SO₄
B. Potassium hydrogensulphate, KHSO₄
C. Calcium hydrogencarbonate, Ca(HCO₃)₂
D. Sodium hydrogencarbonate, NaHCO₃
(1 mark)
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1 markCrystals of hydrated sodium carbonate left in an open dish in a warm laboratory slowly change into a dry white powder. The crystals are said to be:
A. efflorescent
B. deliquescent
C. hygroscopic
D. saturated
(1 mark)
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1 markA learner shakes a spatulaful of each of the following salts with cold water in separate test-tubes. In which test-tube does most of the solid remain undissolved?
A. Magnesium chloride
B. Barium sulphate
C. Potassium carbonate
D. Ammonium nitrate
(1 mark)
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1 markWhich metal will NOT give hydrogen gas when added to dilute hydrochloric acid?
A. Zinc
B. Iron
C. Copper
D. Magnesium
(1 mark)
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3 marksA learner wished to prepare barium nitrate from barium carbonate. Explain why dilute nitric acid is used and not dilute sulphuric acid.
(3 marks)
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1 markBlue crystals of hydrated copper(II) sulphate are heated gently in a dry test-tube. Which observation is correct?
A. The crystals turn white and brown fumes are given off
B. The crystals melt to a blue liquid whose colour does not change
C. The crystals turn white and colourless droplets collect on the cooler part of the tube
D. The crystals turn black and a gas that turns limewater milky is given off
(1 mark)
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3 marksA shopkeeper in Kitale stored bags of a nitrogenous fertiliser salt in a damp room. After some weeks the fertiliser was wet and sticky. Distinguish between deliquescence and hygroscopy, and state which of the two has taken place.
(3 marks)
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2 marksExplain what is meant by water of crystallisation and give one example of a salt that contains it.
(2 marks)
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1 markWhich carbonate remains unchanged when heated strongly in a Bunsen flame?
A. Magnesium carbonate
B. Copper(II) carbonate
C. Sodium carbonate
D. Lead(II) carbonate
(1 mark)
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1 markA green solid is heated strongly. It turns black and gives off a gas that forms a white precipitate with limewater. The black residue is:
A. copper(II) carbonate
B. copper metal
C. copper(II) oxide
D. copper(II) sulphate
(1 mark)
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6 marksZinc carbonate is insoluble in water. Describe how you would prepare a dry sample of zinc carbonate starting from zinc metal, dilute sulphuric acid and sodium carbonate solution.
(6 marks)
Marking scheme
1 mark – Add excess zinc to warm dilute sulphuric acid; effervescence occurs as hydrogen is given off until all the acid has reacted. 1 mark – Filter the mixture to remove the unreacted zinc and keep the zinc sulphate filtrate. 1 mark – Add sodium carbonate solution to the zinc sulphate solution until no further change. 1 mark – A white precipitate of zinc carbonate is formed. 1 mark – Filter off the precipitate and wash it with a little distilled water to remove the soluble sodium sulphate. 1 mark – Dry the solid between filter papers or in a warm oven.
Question 21
1 markLead(II) nitrate solution is added to potassium iodide solution in a boiling tube. What is observed?
A. A white precipitate forms
B. No change occurs because both salts are soluble
C. A colourless gas is given off
D. A yellow precipitate forms
(1 mark)
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4 marksDistinguish between an acid salt and a double salt, and give one example of each.
(4 marks)
Marking scheme
1 mark – An acid salt still contains one or more replaceable hydrogen ions from the parent acid, i.e. only part of the acid's hydrogen has been replaced by a metal ion. 1 mark – Example of an acid salt: sodium hydrogencarbonate, NaHCO₃ (accept potassium hydrogensulphate, KHSO₄). 1 mark – A double salt contains two different cations with a common anion and is formed when two simple salts crystallise together from the same solution. 1 mark – Example of a double salt: potassium aluminium sulphate (alum).
Question 23
1 markWhen dilute sulphuric acid reacts with sodium hydroxide solution, either sodium sulphate or sodium hydrogensulphate can be formed, but dilute hydrochloric acid forms only sodium chloride. This is because:
A. hydrochloric acid is a gas dissolved in water and so cannot form crystals
B. sulphuric acid is a stronger acid than hydrochloric acid
C. sulphuric acid contains oxygen atoms which it can give away to the metal
D. sulphuric acid has two replaceable hydrogen ions per molecule while hydrochloric acid has one
(1 mark)
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4 marksDescribe how you would obtain a dry sample of lead(II) chloride starting from lead(II) nitrate solution and sodium chloride solution.
(4 marks)
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1 markA learner evaporated magnesium sulphate solution to complete dryness over a strong flame instead of stopping at the point of crystallisation. The most likely result is:
A. a larger mass of pure crystals
B. a white powder rather than crystals, because the water of crystallisation is driven off
C. crystals containing more water of crystallisation
D. a solution that will crystallise on cooling
(1 mark)
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1 markWhich one of the following pairs of substances reacts to give a salt and water only?
A. Zinc and dilute sulphuric acid
B. Sodium carbonate and dilute nitric acid
C. Copper(II) oxide and dilute hydrochloric acid
D. Lead(II) nitrate solution and sodium chloride solution
(1 mark)
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1 markDry chlorine gas is passed over iron wire heated in a combustion tube. The salt formed is:
A. iron(II) chloride
B. iron(III) oxide
C. iron(III) chloride
D. iron(II) chloride together with hydrogen gas
(1 mark)
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5 marksA Grade 10 class was asked to prepare dry crystals of magnesium sulphate from magnesium carbonate and dilute sulphuric acid. Describe how they would carry out the preparation.
(5 marks)
Marking scheme
1 mark – Warm some dilute sulphuric acid in a beaker and add magnesium carbonate a little at a time while stirring. 1 mark – Continue adding until effervescence stops and some solid remains undissolved, showing that all the acid has reacted. 1 mark – Filter the mixture to remove the excess magnesium carbonate; keep the filtrate. 1 mark – Evaporate the filtrate until it is saturated (point of crystallisation) and allow it to cool slowly. 1 mark – Filter off the crystals formed and dry them between filter papers.
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