Acids, Bases & Salt Preparations (Edexcel IGCSE Science (Double Award): Chemistry)

A neutralisation reaction occurs between ammonia and sulfuric acid. 

How does the sulfuric acid act in this reaction?

A student makes some magnesium nitrate crystals from magnesium oxide and dilute nitric acid. The equation for the reaction is

MgO (s) + 2HNO₃ (aq) → Mg(NO₃)₂ (aq) + H₂O (l)

i) Give the formula of each ion in magnesium nitrate.

......................................... and ......................................

(2)

ii) A student has a beaker containing dilute nitric acid. Describe a method that she could use to prepare a pure, dry sample of magnesium nitrate crystals from magnesium oxide.

(6)

Magnesium nitrate crystals contain water of crystallisation with the formula Mg(NO₃)₂.6H₂O

i) Show by calculation that the relative formula mass of Mg(NO₃)₂.6H₂O is 256.

(1)

ii) Show that the maximum mass of Mg(NO₃)₂.6H₂O that could be made from 0.050 mol of nitric acid is about 6 g.

(3)

iii) The actual mass of crystals that the student obtains is 4.8 g. Calculate the percentage yield of Mg(NO₃)₂.6H₂O in this experiment.

(2)

The chemical equation for the preparation of lead(II) sulfate is written below. 

Pb(NO₃)₂  (___) + Na₂SO₄ (___) → PbSO₄ (___) + 2NaNO₃ (___)

What are the state symbols for each substance in this reaction? 

A student investigates the neutralisation reaction between sodium hydroxide and nitric acid. This is her method.

• pour 20 cm³ of sodium hydroxide solution into a polystyrene cup

• record the temperature of the sodium hydroxide solution

• add 5 cm³ of dilute nitric acid to the cup

• stir the mixture and record the highest temperature reached

• add further 5 cm³ portions of dilute nitric acid, recording the highest temperature reached each time, until a total of 40 cm³ of acid has been added

i) Give a word equation for this neutralisation reaction.

(1)

ii) Explain why a polystyrene cup is used rather than a beaker.

(2)

iii) Give a safety precaution that the student should take when using sodium hydroxide solution.

(1)

The table shows the student’s results.

i) Plot the results on the grid. Draw a straight line of best fit through the first five points and another straight line of best fit through the last four points. Make sure that the two lines cross.

ii) The point where the lines cross shows

• the volume of acid needed to exactly neutralise the alkali

• the maximum temperature reached

Use your graph to determine these values.

volume of acid = ...................................................................... cm³ maximum temperature = ............................................... °C

[2]

A student making copper sulfate crystals used the method below. 

Unreacted copper carbonate was left over as it had been added in excess.

What is the reason for adding it in excess and what would step 3 be of this method?

Which equation does not show the correct reaction of an acid? 

A student was preparing the insoluble salt lead(II) sulfate from solutions of lead(II) nitrate and potassium sulfate.

Why could the student not use lead(II) carbonate to prepare this salt?

This question is about the insoluble salt silver chloride (AgCl). Silver chloride can be made by the reaction between copper(II) chloride and silver nitrate.

Describe how a student could prepare a pure, dry sample of silver chloride starting with copper(II) chloride solution and silver nitrate solution.

A student investigates the quantity of silver chloride produced when different volumes of silver nitrate solution are added to copper(II) chloride solution. This is the student’s method.

• pour 5.0 cm³ of copper(II) chloride solution into a test tube

• add 1.0 cm³ of silver nitrate solution to the test tube

• allow the silver chloride precipitate to settle

• measure the height of the precipitate

The student repeats the method using different volumes of silver nitrate solution. The table shows the student’s results.

i) Plot the student’s results.

(2)

ii) Draw two straight lines of best fit, ignoring the anomalous result.

(1)

iii) Suggest a mistake the student made to cause the anomalous result.

(1)

iv) Give a reason why the last three heights are the same.

(1)

The equation for the reaction between copper(II) chloride and silver nitrate is

CuCl₂ (aq) + 2AgNO₃ (aq) → 2AgCl (s) + Cu(NO₃)₂ (aq)

A student measures 25.0 cm³ of 0.500 mol / dm³ copper(II) chloride solution and reacts it with silver nitrate solution.

i) Name a piece of apparatus suitable for measuring 25.0 cm³ of copper(II) chloride solution.

(1)

ii) Calculate the maximum mass, in grams, of silver chloride that could be produced.

[M_r of AgCl = 143.5]

(3)

maximum mass = ............................................................... g

iii) In an experiment using different solutions, the mass of silver chloride produced is 0.744 g.

The maximum mass of silver chloride that could be produced is 0.850 g. Calculate the percentage yield.

(2)

percentage yield = ............................................................... %