Acids, Bases & Salt Preparations (Edexcel IGCSE Chemistry)

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)

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.

(3)

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)

Solutions of silver nitrate and potassium chloride react together to make the insoluble salt, silver chloride. A student uses this method to prepare a sample of silver chloride.

Step 1     add 25 cm³ of silver nitrate solution to a conical flask

Step 2     add potassium chloride solution to the flask

Step 3     filter off the silver chloride

What term is used for this reaction?

Give two more steps that will produce a pure, dry sample of silver chloride.

Step 4 ........................................................................................................ Step 5 ........................................................................................................

Acidified silver nitrate solution is used to test for chloride ions.

Give a reason why hydrochloric acid is not used to acidify silver nitrate solution.

The chemical equation for the reaction between solutions of silver nitrate and potassium chloride is

AgNO₃(aq) + KCl(aq) → AgCl(s) + KNO₃(aq)

A student adds an excess of potassium chloride solution to 25.0 cm³ of 0.100 mol/dm³ silver nitrate solution

Calculate the maximum mass of silver chloride, in grams, that can be produced. [M_r of AgCl = 143.5]

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

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

A student wants to prepare sodium chloride crystals from sodium hydroxide solution and dilute hydrochloric acid.

He does a titration to find the volume of dilute hydrochloric acid needed to neutralise the sodium hydroxide solution.

This is his method.

• Add 25.0 cm³ of sodium hydroxide solution to a conical flask

• Add a few drops of phenolphthalein indicator to the conical flask

• Titrate the solution with the hydrochloric acid

Name a suitable piece of apparatus that the student should use to measure 25.0 cm³ of sodium hydroxide solution.

i) Give the colour of the phenolphthalein indicator in sodium hydroxide solution and in hydrochloric acid.

 (2)

 Colour in sodium hydroxide solution: .................................................

 Colour in hydrochloric acid: ....................................................................

 ii) Suggest why universal indicator is never used in a titration. 

(1)

The student finds that 21.50 cm³ of hydrochloric acid is needed to neutralise 25.0 cm³ of sodium hydroxide solution.

 i) Describe what the student should do next to prepare a pure solution of sodium chloride. 

(2)

 ii) Describe how the student could obtain dry crystals of sodium chloride from the pure sodium chloride solution.

(4)

The student needs 21.50 cm³ of hydrochloric acid to neutralise 25.0 cm³ of sodium hydroxide solution of concentration 0.800 mol / dm³. 

The equation for the reaction is 

NaOH + HCl → NaCl + H₂O 

Calculate the concentration, in mol / dm³, of the hydrochloric acid.

 concentration = .............................................................. mol / dm³

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 salts.

Soluble salts can be prepared by the reaction between a metal oxide and an acid.

The equation for this type of reaction is: 

metal oxide + acid → salt + water

i) State the name given to this type of reaction.

(1)

ii) State, in terms of protons, what happens in this reaction.

(1)

A student is given 50 cm³ of dilute sulfuric acid and a bottle of solid copper(II) carbonate.

i) Describe the method that the student should use to prepare a saturated solution of copper(II) sulfate.

In your answer, refer to the pieces of apparatus that the student should use.

(5)

ii) The student produces dry crystals of hydrated copper(II) sulfate from the saturated solution.

He calculates that 6.40 g of dry crystals should be formed.

The mass of dry crystals he actually obtains is 1.80 g less than he calculated.

Calculate the student’s percentage yield.

Give your answer to one decimal place.

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

(3)

i) Gypsum is hydrated calcium sulfate.

 A sample of gypsum contains 79% of calcium sulfate by mass.

 Calculate the value of x in CaSO₄.xH₂O

 [M_r of CaSO₄ = 136   M_r of H₂O = 18]

x = ..............................................

(3)

ii) Describe a test for calcium ions in the sample of gypsum.

(2)

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 = ............................................................... %

This question is about some Group 2 elements and their compounds.

Calcium reacts with water to produce calcium hydroxide and hydrogen gas.  

i) Give the word equation for this reaction.

(1)

ii) State two observations that would be made during this reaction.

(2)

i) Describe how a pure, dry sample of the insoluble salt, barium sulfate, could be made from the two solids sodium sulfate and barium chloride.

(5)

ii) Give an ionic equation for the reaction that occurs. Include state symbols in your equation.

(2)

When magnesium nitrate is heated, magnesium oxide, nitrogen dioxide and oxygen form. The equation for the reaction is

2Mg(NO₃)₂ (s) → 2MgO (s) + 4NO₂ (g) + O₂ (g)

i) What is the name for this type of reaction?

(1)

ii) Calculate the total volume, in dm³, of gas produced at rtp when 7.7 g of magnesium nitrate completely reacts.

[Assume that the molar volume of a gas at rtp is 24 dm³]

[M_r of Mg(NO₃)₂ = 148] Give your answer to two significant figures.

(4)

total volume of gas = ................................................ dm³

The hydroxides of the Group I metals are soluble in water. Most other metal hydroxides are insoluble in water.

 Crystals of lithium chloride can be prepared from lithium hydroxide by titration.

25.0 cm³ of aqueous lithium hydroxide is pipetted into the conical flask.

  A few drops of an indicator are added. Dilute hydrochloric acid is added slowly to the alkali until the indicator just changes colour. The volume of acid needed to neutralise the lithium hydroxide is noted.

  A neutral solution of lithium chloride, which still contains the indicator, is left. Describe how you could obtain a neutral solution of lithium chloride which does not contain an indicator.

The reaction between hydrochloric acid with lithium hydroxide solution is an example of a neutralisation reaction.

Write the ionic equation, including state symbols, for neutralisation.

Explain why a pipette is used to measure the lithium hydroxide solution but a burette is used to measure the hydrochloric acid.

The concentration of the hydrochloric acid was 2.20 mol / dm³. The volume of acid needed to neutralise the 25.0 cm³ of lithium hydroxide was 20.0 cm³. Calculate the concentration of the aqueous lithium hydroxide. 

LiOH + HCl → LiCl + H₂O

An insoluble solid and dilute nitric acid can react to produce soluble salts. 

Copper, copper carbonate and copper oxide are insoluble solids.  Which of these insoluble solids can be used to make a copper salt by reacting the solid with dilute nitric acid?

A student made crystals of magnesium nitrate using nitric acid and magnesium oxide. 

Write a balanced symbol equation for the reaction.

The method the student used to make magnesium nitrate crystals is below. 

Explain why each of the following steps were carried out:

Step b: ...........................................................................................................

Step e: ...........................................................................................................

Step f: ..........................................................................................................

A different student used magnesium carbonate and nitric acid to make magnesium nitrate. They wanted to make 11 g of magnesium nitrate.  The equation for the reaction is: 

MgCO₃ + 2HNO₃  →  Mg(NO₃)₂ + H₂O + CO₂

Calculate the mass of magnesium carbonate the student should react with dilute nitric acid to make 11.0 g of magnesium nitrate.

(A_r: H= 1; C = 12; O = 16; N = 14; Mg = 24)

The percentage yield of magnesium nitrate was 76.3%. 

Calculate the mass of magnesium nitrate the student actually produced.