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A LevelChemistryEdexcelExam Questions1. Physical Chemistry1.7 Reaction Calculations

Reaction Calculations (Edexcel A Level Chemistry)

Exam Questions

3 hours12 questions
Medium
Hard
1a5 marks

This question is about sodium carbonate.

Sodium carbonate forms a number of hydrates with the general formula Na2CO3.xH2O.

A 250 cm3 standard solution of one of these hydrates contained 10.0 g of the compound.

Describe, including the names of any relevant apparatus, how to make this standard solution when provided with 10.0 g of the hydrate in a beaker.

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1b
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25.0 cm3 portions of the standard solution described in (a) are titrated with hydrochloric acid solution of concentration 0.300 mol dm–3, using methyl orange as an indicator.

The table shows the results for this titration.

  Titration 1 Titration 2 Titration 3
Final volume / cm3 30.25 29.75 31.25
Initial volume / cm3 0.30 0.90 2.60
Total titre / cm3 29.95 28.85 28.65

i)
What is the colour change at the end-point of the reaction?

(1)
      From To
  ☐ A red orange
  ☐ B red yellow
  ☐ C yellow orange
  ☐ D yellow red

ii)
State why the value for the total titre in Titration 1 should not be used to calculate the mean titre.

(1)

iii)
Calculate the mean titre.

(1)

iv)

Calculate the relative formula mass, Mr, of the hydrated sodium carbonate, Na2CO3.xH2O.

The equation for the reaction in the titration is

Na2CO3 + 2HCl → 2NaCl + H2O + CO2

(4)

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1c
Sme Calculator2 marks

In an experiment, the Mr of a different hydrated sodium carbonate was found to be 286 g mol–1.

i)
Calculate the relative formula mass of anhydrous sodium carbonate, Na2CO3.

(1)

ii)
Calculate the number of molecules of water of crystallisation, x, for this hydrated sodium carbonate, Na2CO3.xH2O.

(1)

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1d3 marks

Sodium carbonate is manufactured from sodium chloride in a two-stage process.

NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl
                                  2NaHCO3 → Na2CO3 + H2O + CO2

Calculate the maximum mass of sodium carbonate, Na2CO3, which could be obtained from 500 kg of sodium chloride.

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2
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The equation for the complete combustion of butane is

2C4H10 (g) + 13O2 (g) → 8CO2 (g) + 10H2O (l)

What is the minimum volume of oxygen, at room temperature and pressure (r.t.p.), needed for the complete combustion of 0.200 mol of butane?

[Molar volume of a gas at r.t.p. = 24.0 dm3 mol−1]

  ☐ A 4.8 dm3
  ☐ B 9.6 dm3
  ☐ C 31.2 dm3
  ☐ D 62.4 dm3

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3a
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This question is about the molar volume of gases.

i)
Calculate the volume of one mole of an ideal gas, A, at 60 °C and 500 kPa pressure.
Give your answer to two significant figures and include units.
 
[The ideal gas equation is pV = nRT. Gas constant (R) = 8.31 J K−1 mol−1] 
(3)
 
ii)
At room temperature and pressure (r.t.p) another gas B, with formula XH3 , has a density of 1.42 g dm−3.
 
Calculate the molar mass of the gas XH3 and deduce the identity of the element X.
 
[The molar volume of gas B = 24000 cm3 mol−1 at r.t.p.]
(2)

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3b
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The apparatus shown was used to measure the volume of gas evolved when a weighed mass of sodium carbonate reacted with dilute hydrochloric acid.

 
screenshot-2022-11-22-225125
 

The following procedure was used.

  1. Solid sodium carbonate was placed in a container and weighed accurately.
  2. The delivery tube and rubber bung were removed and the sodium carbonate was transferred to the test tube.
  3. The container was then reweighed.
  4. The syringe plunger was pushed in, to zero the syringe.
  5. 10.0 cm3 of 0.400 mol dm−3 hydrochloric acid was then added to the sodium carbonate and the rubber bung and delivery tube rapidly replaced.
  6. The mixture was shaken and, when the reaction had finished, the reading of the syringe was noted.
 

Results 

Mass of container and sodium carbonate before transfer = 20.135 g
 
Mass of container after transfer of the sodium carbonate = 19.893 g
 
Mass of sodium carbonate used = 0.242 g
 
The equation for the reaction is
 
Na2CO3 (s) + 2HCl (aq) → 2NaCl (aq) + CO2 (g) + H2O (l)
 
i)
Calculate the moles of hydrochloric acid and the moles of sodium carbonate used in this experiment.
 
Use your answers to decide which reactant is in excess.
Calculate the maximum volume of carbon dioxide which could be produced.
 
Molar mass of Na2CO3 = 106.0 g mol−1
 
Molar volume of gas = 24000 cm3 mol−1 at r.t.p.
(5)
 
ii)
The actual volume of carbon dioxide collected was less than calculated.
Give two reasons for this.
 
(2)

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4a1 mark

The reaction of sulfuric acid with potassium hydroxide is a neutralisation.

The equation for this reaction is

H2SO4 (aq) + 2KOH (aq) → K2SO4 (aq) + 2H2O (l)

A titration was carried out using the following method.

  1. Potassium hydroxide solution of unknown concentration was placed in a burette and the initial reading was recorded.
  2. 25.0 cm3 of sulfuric acid solution, concentration 0.0800 mol dm−3, was transferred to a conical flask.
  3. Three drops of phenolphthalein indicator were added to the sulfuric acid.
  4. Potassium hydroxide was added from the burette until the solution just changed colour and then the burette reading was recorded.
  5. Repeat titrations were carried out until concordant titres were obtained.

Select the most appropriate piece of apparatus to measure the 25.0 cm3 of sulfuric acid.

  ☐ A burette
  ☐ B measuring cylinder
  ☐ C pipette
  ☐ D volumetric flask

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4b1 mark

What is the colour of the solution when neutralisation has just occurred? 

  ☐ A colourless
  ☐ B orange
  ☐ C pale pink
  ☐ D red

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4c
Sme Calculator6 marks
i)
Complete the table of results for titration number 1, using the diagrams to find the initial and final burette readings.
 
screenshot-2022-11-22-215722
 (2)
 
Table of results
 
Titration number Final reading / cm3  Initial reading / cm3  Titration volume / cm3 
1      
2 28.05 1.10 26.95
3 37.65 10.20 27.45
4 32.05 5.00 27.05
 
ii)
The best value for the mean titre of this reaction is 
(1)
  ☐ A 27.00 cm3
  ☐ B 27.15 cm3
  ☐ C 27.25 cm3
  ☐ D 27.30 cm3
 
iii)
Calculate the concentration, in mol dm−3, of the potassium hydroxide solution, giving your answer to an appropriate number of significant figures. 
(3)

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5a
Sme Calculator5 marks

Many vehicles are fitted with airbags which provide a gas-filled safety cushion to protect the occupant of the vehicle if there is a crash.

The first reaction in airbags is the thermal decomposition of sodium azide, NaN3, to form sodium and nitrogen gas.

i)
Write the equation for this decomposition of sodium azide.
State symbols are not required.
(1)
ii)
In the reaction in (a)(i), a typical airbag is inflated by about 67 dm3 of gas.
Calculate the minimum mass of sodium azide, in grams, needed to produce this volume of gas. Use the Ideal Gas Equation and give your answer to an appropriate number of significant figures.

For the purpose of this calculation, assume that the temperature is 300 °C and the pressure is 140000 Pa.
(4)

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5b3 marks

The second reaction in the airbag is between the sodium produced in the reaction (a)(i) and potassium nitrate.

............... Na space plus space............... KNO subscript 3 space rightwards arrow............... straight K subscript 2 straight O space plus space............... Na subscript 2 straight O space plus............... straight N subscript 2

Balance the above equation, justifying your answer in terms of the changes in oxidation numbers.

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5c3 marks

The third reaction in the airbag is between the metal oxides and silicon dioxide.

State the type of reaction taking place and justify why this reaction is necessary.

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5d1 mark

The Maxwell-Boltzmann distribution diagram shows the molecular energies for the gaseous system immediately after the airbag has been deployed.

q4d-9cho-al-2-june-2018-qp-edexcel-a-level-chem

What is the change in shape of the curve when the airbag cools?

  ☐ A the peak would shift to the left and be higher
  ☐ B the peak would shift to the left and be lower
  ☐ C the peak would shift to the right and be higher
  ☐ D the peak would shift to the right and be lower

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6a2 marks

This question is about the reaction of magnesium with dilute hydrochloric acid.

Write an equation for the reaction of magnesium with hydrochloric acid.

Include state symbols.

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6b
Sme Calculator9 marks

The apparatus shown in the diagram can be used to collect the gas produced during the reaction of magnesium with dilute hydrochloric acid.

q7b-8cho-as-1-june-2019-qp-edexcel-a-level-chem

The following procedure was used.

Step 1  The apparatus was set up as shown in the diagram. The test tube contained 10.0 cm3 of 0.20 mol dm–3hydrochloric acid.
Step 2 A piece of magnesium ribbon was weighed. It had a mass of 0.12 g.
Step 3  The delivery tube and bung were removed from the test tube, the magnesium ribbon was added and the delivery tube and bung quickly replaced.
Step 4 When the reaction was complete, the final volume of gas was recorded.

i)

A measuring cylinder was used to measure the 10.0 cm3 of dilute hydrochloric acid in Step 1. The uncertainty for a volume measurement is ± 0.5 cm3.
Calculate the percentage uncertainty in the volume of hydrochloric acid.

(1)

ii)
Determine which reactant is in excess by calculating the number of moles of magnesium and of hydrochloric acid used in the experiment.

(3)

iii)
Calculate the maximum number of moles of gas that could be produced, using your answers to (a) and (b)(ii).

(1)

iv)

Under the conditions of the experiment, the temperature was 23°C and the pressure 98 000 Pa.

Calculate the maximum volume of gas, in cm3, that could be produced using your answer in (b)(iii).
Give your answer to an appropriate number of significant figures.

[The ideal gas equation is pV = nRT.  Gas constant (R) = 8.31 J mol–1 K–1]   

(4)

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6c4 marks
i)
Deduce two possible reasons why the volume of gas collected in the experiment was smaller than that calculated in (b)(iv).

(2)

ii)
Describe two changes to the procedure that would enable the volume of gas collected to be closer to that calculated in (b)(iv).

(2)

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7a
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This question is about the titration of a weak acid with a strong base.

A standard solution of ethanedioic acid, which is a weak, diprotic acid, can be used to determine the concentration of a sodium hydroxide solution. 25.0 cm3 of the ethanedioic acid solution, with concentration 3.80 g dm−3, was pipetted into a conical flask. A few drops of indicator solution were added. The ethanedioic acid was titrated with the sodium hydroxide solution which was in the burette. The titration was repeated and the following results were obtained. 

[Molar mass of ethanedioic acid = 90.0 g mol−1]

 
  Titration 1 Titration 2 Titration 3 Titration 4
Final reading / cm3 18.00 17.60 35.30 27.70
Initial reading / cm3 0.00 0.00 17.60 10.05
Titre / cm3 18.00 17.60 17.70 17.65
Titre used to find the mean titre (✔)        
      Mean titre / cm3  
 
i)
In the appropriate row, tick (✔) those titre values that should be used to find the mean, and use these titres to calculate it.
Write the value of the mean titre in the box provided in the table of results.
(2)
 
ii)
Ethanedioic acid is a weak acid. Name a suitable indicator for this titration and state the colour change at the end-point.
(2)
 
Name of indicator ..................................................
 
Colour change at the end-point from .............................. to ..............................
 
iii)
The equation for the reaction of ethanedioic acid with sodium hydroxide is
 
C2H2O4 + 2NaOH → C2O4Na2 + 2H2O
 
Calculate the concentration of the sodium hydroxide solution, in mol dm−3.
Give your answer to three significant figures.
(4)

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7b
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The uncertainty in each burette reading is ± 0.05 cm3. The uncertainty in the pipette volume is ± 0.06 cm3. 

i)
Calculate the percentage uncertainties for titre 4, and the pipette volume.
(2) 
ii)
Which of the following changes would halve the percentage uncertainty in the volume of liquid measured by the burette?
(1)
  ☐ A halve the acid concentration and halve the acid volume
  ☐ B double the acid concentration and leave the acid volume unchanged
  ☐ C double the acid concentration and halve the acid volume
  ☐ D halve the acid concentration and leave the acid volume unchanged

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8
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A group of students analysed a hydrated salt with the formula KH3(C2O4)y.zH2O where y and z are whole numbers.

The students carried out experiments to determine the values of y and z.

Experiment 1 – to determine the value of y

One student was provided with a 0.0235 mol dm-3 solution of the salt.

25.0 cm3 portions of the salt solution were acidified with excess dilute sulfuric acid and heated to about 60 °C.

Each portion was titrated with 0.0203 mol dm-3 potassium manganate(VII).

The results of four titrations are shown in the table.

Titration number 1 2 3 4
Final burette reading / cm3 23.85 47.20 24.05 48.10
Initial burette reading / cm3 0.00 24.00 0.50 25.00
Titre / cm3 23.85 23.20 23.55 23.10

i)
Complete the diagram to show the final burette reading in Titration 1.

(2)

q7ai-9cho-al-3-june-2019-qp-edexcel-a-level-chem

ii)
Explain why this student should use a mean titre of 23.15 cm3 and not 23.43 cm3 in the calculation.
(2)
iii)
The uncertainty in each burette reading is ±0.05 cm3.

Calculate the percentage uncertainty in the titre volume of potassium manganate(VII) solution used in Titration 2.
(1)
iv)
The equation for the reaction is

2MnO4– + 5C2O42– + 16H+ → 2Mn2+ + 10CO2 + 8H2O

Deduce, by calculation, the value of y, to the nearest whole number, in the formula KH3(C2O4)y.zH2O.

Use the mean titre of 23.15 cm3 and other data from Experiment 1.

You must show your working.
(4)

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1a3 marks

This question is about a titration experiment carried out by a group of students to determine the concentration of a solution of ethanoic acid using sodium hydroxide.

A student weighed about 4.00 g of sodium hydroxide pellets and added them to a beaker containing 50 cm3 of deionised water.

The mixture was stirred with a glass rod to dissolve the pellets and to give a homogenous solution.

The solution was poured through a funnel into a 250.0 cm3 volumetric flask and deionised water was added up to the mark and then the flask was shaken.

i)
Describe how you would ensure that all the sodium hydroxide was transferred to the volumetric flask.

(2)

ii)
A student adds deionised water above the mark and shakes the flask.

State why the procedure has to be restarted rather than using a teat pipette to remove the excess water.

(1)

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1b3 marks

Two students each cleaned a burette, then poured sodium hydroxide solution into their burettes.

i)
Student 1 used a funnel to pour sodium hydroxide solution into the burette.

Give two steps needed before the student takes the initial burette reading.

(2)

ii)
Student 2 cleaned the burette by rinsing it with deionised water immediately before filling it with the sodium hydroxide solution.

Give the effect, if any, on the value of the first titre. Justify your answer.

(1)

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1c5 marks

The sketch shows the pH changes during a titration of 25.0 cm3 of ethanoic acid with sodium hydroxide of the same concentration.

q3c-9cho-al-3-nov-2020-qp-edexcel-a-level-chem

The ideal indicator for this titration will change colour on the addition of a very small volume of sodium hydroxide solution at a titre value very close to the equivalence point of the reaction.

i)
Assess the suitability of methyl red as an indicator for this titration. Make use of the Data Booklet in answering this question.

(4)

ii)
Complete the table, with a tick (✓) or a cross (✗), to show whether or not the indicator would be suitable for use in this titration.

(1)

Indicator pH range Tick or Cross
Bromocresol purple 5.2 – 6.8  
Thymol blue 8.0 – 9.6  
Thymolphthalein 8.3 – 10.6  
Alizarin yellow R 10.1 – 13.0  

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1d
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Each student used a pipette to measure 25.0 cm3 of the ethanoic acid solution into four separate conical flasks and added an indicator.

The results of one student’s titrations are shown in the table.

Titration number 1 2 3 4
Final burette reading / cm3 13.00 25.50 37.90 50.00
Initial burette reading / cm3 0.25 13.00 25.50 37.90
Titre / cm3        
Concordant titres (✓)        

i)
Complete the table.

(1)

ii)
The low titre for titration 4 was queried by the teacher. The student had wanted to refill the burette and continue the titration but had been told the measurement uncertainty would increase if this was done.

Calculate the total percentage measurement uncertainty if the burette had been refilled to 0.00, and then a further 0.30 cm3 had been added from the burette, to the conical flask.

The measurement uncertainty for each burette reading is ±0.05 cm3.

(1)

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1e
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The teacher carried out the experiment and obtained the following results.

Mass of sodium hydroxide used to make 250.0 cm3  solution = 3.80 g

Volume of ethanoic acid solution = 25.00 cm3

Mean titre of sodium hydroxide = 11.90 cm3

CH3COOH (aq) + NaOH (aq) → CH3COONa (aq) + H2O (l)

Calculate the concentration of the ethanoic acid solution in g dm−3.

Give your answer to an appropriate number of significant figures.

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2a5 marks

A student made crystals of a metal chloride, JCl2.6H2O, by reacting the metal carbonate, JCO3 , with hydrochloric acid, HCl(aq). The product was purified.

Procedure

  1. 150 cm3 of hydrochloric acid, concentration 0.80 mol dm−3, was transferred to a 400 cm3 conical flask. The flask was warmed gently using a Bunsen burner. A spatula measure (about 1.0 g) of metal carbonate was added to the acid.
  2. When the reaction in Step 1 was finished, more metal carbonate was added until the metal carbonate was in excess.
  3. The resulting mixture was filtered into an evaporating basin.
  4. The evaporating basin was heated using a Bunsen burner to concentrate the solution. The concentrated solution was allowed to cool and crystallise.
  5. Once crystal formation was complete, the resulting mixture was filtered for a second time.
  6. The resulting white crystals were rinsed with a small volume of ice-cold water.

The equation for the reaction between the metal carbonate and hydrochloric acid is

JCO3 (s) + 2HCl (aq) → JCl2 (aq) + H2O (l) + CO2 (g)

i)
Describe two observations that the student might make which show that the reaction in Step 1 has finished. 
(2)
 
ii)
State the purpose of the filtration in Step 3. 
(1)
 
iii)
Explain the use of a small volume of ice-cold water in Step 6. 
(2)

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2b
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The student obtained a mass of 14.26 g of hydrated crystals.

Assuming that the percentage yield is 100%, use the information in the procedure to give a possible identity of J. 

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2c
Sme Calculator5 marks

The student was surprised by the white colour of the crystals of JCl2.6H2O in Step 6.

This did not agree with the possible identity for J from the calculation in (b).

The student decided to perform a flame test on the crystals. 

i)
Explain why the student was surprised and decided to carry out a flame test. 
(2)
 
ii)
The flame test colour was crimson red. Identify J. 
(1)
  ☐ A barium
  ☐ B calcium
  ☐ C lithium
  ☐ D strontium
 
iii)
Calculate the actual percentage yield of the reaction, which produced 14.26 g of crystals.
 
Give your answer to two significant figures. 
(2)

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3a1 mark

Malachite is a green mineral with the formula Cu2CO3(OH)2 . It has a molar mass of 221 g mol–1.

What is the percentage by mass of copper in pure malachite?

  ☐ A 40.3%
  ☐ B 51.4%
  ☐ C 57.5%
  ☐ D 67.9%

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3b3 marks

Describe what you would expect to see when an excess of dilute hydrochloric acid is added to a sample of pure solid malachite.

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3c7 marks
i)
Describe how you would carry out a flame test on a sample of powdered malachite.
(3)

ii)
When the atoms of some elements are heated, they produce a characteristic flame colour. For example, the copper in malachite gives a blue-green colour. Explain how atoms of different elements can produce different characteristic flame colours when heated.
(4)

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3d
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i)
When malachite is heated to approximately 300 °C, water, carbon dioxide and copper(II) oxide are formed.

The equation for this decomposition is

Cu2CO3(OH)2 → 2CuO + CO2 + H2O

Calculate the maximum volume of carbon dioxide that could be produced when 0.810 g of malachite is thermally decomposed.

Assume that the gas is collected at a temperature of 25 °C and 101 kPa pressure.

Give your answer to an appropriate number of significant figures and state the units.[The ideal gas equation is pV = nRT. Gas constant (R) = 8.31 J mol–1K–1]

(5)

ii)
The gas was collected in a gas syringe with a stated accuracy of ±0.5 cm3.

Calculate the percentage uncertainty in the volume of gas collected.

(1)

iii)
Malachite ore is a mixture of malachite and rock. A 0.810g sample of malachite ore was thermally decomposed, producing 0.571g of copper(II) oxide.

Calculate the percentage purity of this malachite ore sample.
Give your answer to an appropriate number of significant figures.

(3)

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4a
Sme Calculator10 marks

Wine and gin are aqueous solutions of ethanol with traces of other organic
compounds which give these drinks their characteristic flavours and aromas.

When a bottle of wine is opened, oxidation of the ethanol in the wine produces ethanoic acid.

An experiment was carried out to determine the percentage of the ethanol that had been oxidised.

  • A bottle of white wine, with an ethanol concentration of 2.50 mol dm–3,was opened and left to stand at room temperature for three weeks.
  • A 25.0 cm3 sample of the wine was transferred to a conical flask and phenolphthalein indicator added.
  • Aqueous sodium hydroxide of concentration 0.235 mol dm–3 was added from a burette until the colour of the indicator permanently changed.
  • The titration was repeated and the titre values, in cm3, were 27.90, 26.75 and 26.85.

The equation for the neutralisation reaction is

CH3COOH + NaOH → CH3COO–Na+ + H2O

i)
Name the piece of apparatus used to measure 25.0 cm3 of wine.

(1)

ii)

To improve the accuracy, the burette should be rinsed.

State what should be used.

(1)

iii)
What is the colour change at the end-point?
(1)
  ☐ A from orange to yellow
  ☐ B from red to orange
  ☐ C from colourless to pink
  ☐ D from pink to colourless

iv)

State what is meant by the term ‘concordant results’ as applied to a titration experiment.

(1)

v)

Calculate the percentage of ethanol that has oxidised, given that one mole of ethanol forms one mole of ethanoic acid.

Give your answer to an appropriate number of significant figures.

(5)

vi)

Deduce why this method would not be effective for the analysis of the acid content of a red wine.

(1)

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4b
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The ethanol content of alcoholic drinks is usually measured as the percentage of alcohol by volume (ABV).

ABV = begin mathsize 16px style fraction numerator Volume space of space ethanol space in space a space solution over denominator Total space volume space of space the space solution end fraction end style× 100

The ABV values of four different brands of gin are shown.

Brand of gin ABV (%)
A 40
B 42
C 44
D 46

A sample of one of these gins was found to contain an ethanol concentration of 7.50 mol dm–3.

By calculating the percentage of ethanol by volume (ABV) of this sample, deduce the brand of this gin.

[Assume the density of ethanol, C2H5OH = 0.79 g cm–3]

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