Acids, Bases & Salts (WJEC GCSE Chemistry)

Exam Questions

3 hours26 questions

Easy

Medium

Hard

4 marks

Selwyn carried out an experiment to prepare copper(II) chloride crystals.

The diagrams show the stages of the experiment he carried out.

Choose apparatus from the box to label the diagrams.

evaporating basin conical flask filter funnel electronic balance
filter paper beaker test tube

q1a-wjec-gcse-chemistry-june-2022-2f

How did you do?

1 mark

In Stage 1 Selwyn added copper(II) carbonate until all the dilute hydrochloric acid was used up.

Tick (✓) the box next to the statement which best describes what Selwyn would see when all the acid had been used up.

bubbling increases $□$

bubbling stops $□$

bubbling decreases $□$

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1 mark

The gas formed in Stage 1 turns limewater milky. Underline the name of this gas.

oxygen hydrogen carbon dioxide nitrogen

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2 marks

Choose words from the box to complete the following sentences.

evaporation filtration distillation neutralisation

The process used to remove the unreacted copper(II) carbonate in Stage 2 is called ...................................

The process used to remove water in Stage 3 is called .........................................

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1 mark

The container holding the crystals has a mass of 29.8 g. Using the information given in Stage 4, calculate the mass of the crystals formed.

Mass of crystals formed = ............................... g

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3 marks

The chemicals and apparatus needed to prepare crystals of copper(II) sulfate are shown below.

q1a1-wjec-gcse-chemistry-june-2016-1f

There are three stages to the preparation of copper(II) sulfate crystals.

Using the chemicals and apparatus shown on the opposite page, draw diagrams to show how each stage would be carried out.

q1a2-wjec-gcse-chemistry-june-2016-1f

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1 mark

Name the process described in Stage 2.

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1 mark

Choose substances from the box to complete the word equation for the reaction taking place.

carbon dioxide hydrogen copper(II) sulfate

water copper(II) chloride

copper(II) carbonate + sulfuric acid → .............................. + .............................. + ..............................

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4 marks

The following pie chart shows the main uses of sulfuric acid in a developing country.

q3a-wjec-gcse-chemistry-june-2016-3f

Calculate the percentage of sulfuric acid used to make detergents.

[2]

Percentage = ................................... %

ii)

In this country, 200 000 tonnes of sulfuric acid are used each year. Calculate the mass of sulfuric acid used each year to make fertilisers.

[2]

Mass of sulfuric acid = ................................... tonnes

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3 marks

State what is observed when magnesium reacts with sulfuric acid.

[1]

ii)

Explain how magnesium could be used to distinguish between sulfuric acid and ethanoic acid.

[2]

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1 mark

Magnesium sulfate can be made by adding excess magnesium oxide to sulfuric acid. Magnesium oxide is insoluble in water.

State why excess magnesium oxide is added.

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2 marks

The following apparatus could be used to remove the excess magnesium oxide from the solution. Complete the labelling of the diagram.

q4a-wjec-gcse-chemistry-june-2015-1f

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1 mark

State how you can obtain crystals from the solution.

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1 mark

Complete the word equation for the reaction.

magnesium oxide + sulfuric acid → .............................. + ..............................

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1 mark

If the reaction was carried out with hydrochloric acid, instead of sulfuric acid, magnesium chloride would be formed.

Write the chemical formula for magnesium chloride.

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1 mark

Copper(II) sulfate was made by reacting copper(II) carbonate with an acid.

Give the name of the acid used.

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2 marks

The first stage of the preparation is the addition of excess copper(II) carbonate to the acid. Give two observations that show a reaction is taking place.

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2 marks

Describe how you would prepare copper(II) sulfate crystals from the mixture in part (b).

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1 mark

A different salt can be made by reacting copper(II) oxide with dilute hydrochloric acid.

Complete the word equation for the reaction that takes place.

copper(II) oxide + hydrochloric acid → .............................. + ..............................

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6 marks

The picture below shows the universal indicator pH colour chart and the position of some substances on the pH scale.

q6-wjec-gcse-chemistry-june-2022-2f

Describe what is meant by the pH scale and what it tells us about the substances shown in the picture.

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5 marks

Higher Tier Only

Some household cleaners are a concentrated solution of ammonia.

To determine the concentration of an ammonia solution, 10.0 cm³of a household cleaner was titrated with dilute sulfuric acid of concentration 1.5 mol/dm^3.

The end-point was determined by using the indicator methyl orange.

The procedure was repeated three times and the mean volume of dilute sulfuric acid needed to neutralise 10.0 cm³ of the ammonia solution was found to be 12.0 cm³

q10a-wjec-gcse-chemistry-june-2022-2h

Use the equation below to calculate the number of moles of sulfuric acid in 12.0 cm³of the 1.5 mol / dm³solution.

[2]

$concentration = \frac{number of moles}{volume}$

Number of moles of sulfuric acid = .............................. mol

ii)

Ammonia solution reacts with sulfuric acid according to the equation below.

2NH₃ (aq) + H₂SO₄ (aq) $\overset{}{\to}$ (NH₄)₂SO₄ (aq)

Use the equation for the reaction to find the number of moles of ammonia in 10.0 cm³ of the household cleaner.

[1]

Number of moles of ammonia = ........................... mol

iii)

Calculate the concentration of ammonia in mol/dm³.

[2]

Concentration of ammonia = ............................. mol / dm³

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4 marks

The diagram shows two reactions of dilute hydrochloric acid.

q10b-wjec-gcse-chemistry-june-2022-2h

Predict the temperature change if dilute ethanoic acid, CH₃COOH, is added to sodium hydroxide instead of dilute hydrochloric acid. Give the reason for your answer.

[2]

ii)

A salt is formed when ethanoic acid is added to copper(II) carbonate.

I. Give the name of the salt.

[1]

II. The negative ion present in the salt is CH₃COO^–.

Underline the correct formula of the salt.

[1]

Cu(CH₃COO)₂ CuCH₃COO Cu₂CH₃COO Cu₂(CH₃COO)₂

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3 marks

The diagram shows three reactions which are used to prepare soluble salts.

q9a-wjec-gcse-chemistry-june-2019-2f

Name compound A.

[1]

ii)

Give the names of blue solution B and gas C formed in reaction 3.

[2]

blue solution B ....................................................................................................

gas C ....................................................................................................

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2 marks

Write the balanced symbol equation for reaction 1.

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2 marks

Reaction 1 was repeated using magnesium instead of zinc. Explain the difference, if any, that you would expect to see.

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3 marks

A student carries out a series of chemical tests on solutions of three unknown compounds, A, B and C. Her results are recorded in the table.

	A	B	C
Add dilute HCl	no reaction	fizzes	no reaction
Add BaCl₂(aq)	white precipitate forms	no reaction	no reaction
Add NaOH (aq)	green precipitate forms	pungent smelling gas given off, turns damp red litmus paper blue	no reaction
Add AgNO₃(aq)	no reaction	no reaction	cream precipitate forms
Flame test	no colour	no colour	apple-green flame

Use the information provided to give the chemical name for each of the compounds.

Compound A ...................................................................................................

Compound B ...................................................................................................

Compound C ...................................................................................................

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5 marks

Higher Tier Only

A technician wants to prepare 250 cm³ of a 0.25 mol/dm³ solution of lead nitrate, Pb(NO₃)₂.

Calculate the number of moles of lead nitrate required to make the solution.

[2]

Number of moles = ..................................................... mol

ii)

Calculate the mass of solid lead nitrate that should be dissolved to make the solution.

[2]

A_r(Pb) = 207 A_r(O) = 16 A_r(N) = 14

Mass = ..................................................... g

iii)

The only electronic balance available to the technician has a precision of ±0.01 g.

Exactly how much lead nitrate should the technician weigh out to ensure that the concentration of the solution is as close as possible to 0.25 mol/dm³?

[1]

Mass ..................................................... g

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5a2 marks

Hydrochloric acid, HCl, reacts with sodium hydroxide solution to form sodium chloride and water only.

Write a balanced symbol equation for this reaction.

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6 marks

A group of students was asked to find the volume of hydrochloric acid solution needed to neutralise 25.0 cm³ of sodium hydroxide solution. They decided to titrate sodium hydroxide with hydrochloric acid.

q7b-paper-2f-june-2018-wjec-gcse-chemistry

Results

Titre	1	2	3
Volume of hydrochloric acid needed (cm³)	18.2	17.8	18.0

Name the piece of apparatus X.

[1]

ii)

Explain the purpose of the indicator.

[1]

ii)

Calculate the mean volume of hydrochloric acid needed to neutralise 25.0 cm³of the sodium hydroxide solution.

[1]

Mean volume = ............................ cm³

iv)

The change in temperature during the reaction can be monitored using a temperature sensor.
Sketch a graph on the axes below to show how the temperature changes as more and more acid up to a total of 30 cm³ is added.

[2]

q7iv-paper-2f-june-2018-wjec-gcse-chemistry

The experiment was repeated using hydrochloric acid of half the original concentration.
State the volume of hydrochloric acid that would be needed to change the indicator colour.

[1]

Volume = .................... cm³

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7 marks

Gwyn carried out an experiment to find the solubility of potassium nitrate at room temperature, 25 °C. The method he used is shown in stages 1-3.

Stage 1
He added solid potassium nitrate to 50 cm³ of water
until a saturated solution was formed.

Stage 2
He pipetted 25 cm³ of the saturated solution into a
pre-weighed evaporating basin. He put the basin and
the solution into a warm oven.

Stage 3
He removed the basin from the oven and allowed it to
cool. He weighed the basin and crystals after 2 hours.

His results are shown below.

Mass of evaporating basin	= 42.6 g
Mass of evaporating basin and potassium nitrate crystals	= 54.2 g

State what is meant by a saturated solution.

[1]

ii)

Use Gwyn’s results to calculate the solubility of potassium nitrate in g / 100g of water.

[2]
solubility = .......................................... g / 100 g of water

iii)

Gwyn’s experimental value for the solubility of potassium nitrate is much bigger than expected. Suggest how Gwyn should adapt stage 3 of his method in order to get a more accurate value. Explain your reasoning.

[3]

iv)

Gwyn was asked to find out if sodium chloride is more soluble in water than potassium nitrate. State which variable Gwyn must keep the same in his experiment in order for him to be able to compare the two solubilities.

[1]

.................................................................................

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4 marks

The solubility of potassium bromide at 20 °C is 64 g/100 g of water. Calculate the mass of solid that forms when a solution containing 43.9 g of potassium bromide in 50 g of water is cooled to 20 °C.

[2]

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

ii)

Calculate the number of moles of potassium bromide, KBr, in 64 g. Give your answer to two significant figures.

[2]

number of moles = ................................................................ mol

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5 marks

The diagram below shows some reactions of dilute sulfuric acid.

q5a-wjec-gcse-chemistry-june-2016-1h

Give the names of each of the substances A to E.

A ..................................................................................................

B ..................................................................................................

C ..................................................................................................

D ..................................................................................................

E ..................................................................................................

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1 mark

Give the chemical formula of ammonium sulfate.

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1 mark

The diagram shows the apparatus that was used to find the volume of hydrochloric acid needed to neutralise 25.0 cm³ of sodium hydroxide solution.

The balanced equation for the reaction between sodium hydroxide and hydrochloric acid is as follows.

NaOH + HCl $\overset{}{\to}$ NaCl + H₂O

q8a-wjec-gcse-chemistry-june-2016-3f

The acid was added slowly from the burette. The volume of acid needed to change the indicator colour was recorded.

The titration was carried out four times and the volume of acid added each time was recorded in the table below.

Run	1	2	3	4
Volume of hydrochloric acid (cm³)	33.5	29.5	29.6	29.4

State why an indicator was used in this experiment.

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1 mark

State whether the acid or the alkali is the more concentrated. Give a reason for your answer.

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5 marks

Calculate the mean volume of hydrochloric acid needed to neutralise 25.0 cm³ of the sodium hydroxide solution.

[1]

ii)

Using all the information provided and your mean volume, describe how a pure sample of sodium chloride crystals could be made.

[4]

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2 marks

Higher Tier Only

The concentration of sodium hydroxide solution can be determined by titration.

25.0 cm³ of 0.10 mol/dm³ sulfuric acid were placed in a conical flask and titrated with sodium hydroxide solution. It was found that 21.5 cm³ of sodium hydroxide were required to neutralise the acid.

The equation for the reaction between sodium hydroxide and sulfuric acid is as shown.

2NaOH + H₂SO₄ $\overset{}{\to}$ Na₂SO₄ + 2H₂O

Calculate the number of moles of sulfuric acid in 25.0 cm³ of 0.10 mol/dm³ solution.

Number of moles of sulfuric acid = ................................... mol

How did you do?

1 mark

Higher Tier Only

Calculate the number of moles of sodium hydroxide in 21.5 cm³ of solution.

Number of moles of sodium hydroxide = ................................... mol

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2 marks

Higher Tier Only

Calculate the concentration of the sodium hydroxide solution.

Concentration of sodium hydroxide = ................................... mol/dm³

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2 marks

Higher Tier Only

A reaction between the same solutions of sodium hydroxide and sulfuric acid can produce a different salt called sodium hydrogensulfate as shown in the following equation.

NaOH + H₂SO₄ $\overset{}{\to}$ NaHSO₄ + H₂O

State the volume of sodium hydroxide solution needed to react with 25.0 cm³ of 0.10 mol/dm³ sulfuric acid to give sodium hydrogensulfate. Give your reasoning.

Volume = ................................... cm³

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10a

3 marks

Grapes contain tartaric acid.

Place a tick (✓) in the box with the expected value for the pH of tartaric acid and explain your choice.

pH value
1	$□$
5	$□$
7	$□$
9	$□$
13	$□$

Explanation ...................................................

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10b

5 marks

Tim was asked to carry out an experiment to investigate the effect of food on the pH of saliva.

At the start of the experiment the pH of saliva in Tim’s mouth was 6.9. He ate an apple and the pH of his saliva was measured every 5 minutes for 45 minutes.

The results of the experiment are shown in the table below.

Time (minutes)	0	5	10	15	20	25	30	35	40	45
pH	6.9	5.7	5.0	4.5	4.5	5.0	5.7	6.1	6.4	6.6

Five points have already been plotted. Complete the graph.

[3]

q6b-wjec-gcse-chemistry-june-2015-1f

ii)

Use the graph to give the minimum pH value obtained during the experiment.

[1]

iii)

Use the graph to predict when the pH of Tim’s saliva will return to its original value.

[1]

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11a

1 mark

One method of preparing a salt is by reacting a base with a dilute acid. The information below shows the stages a pupil follows to make a salt.

q1a-wjec-gcse-chemistry-june-2014-1f

Use the information in the diagrams to answer the following questions.

State what the pupil can see when all the acid has been used up.

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11b

2 marks

Name the process used in stage 2.

[1]

ii)

Name the substance removed during stage 3.

[1]

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11c

2 marks

Give the name of the base used in this experiment.

[1]

ii)

Give the name of the salt formed in this experiment.

[1]

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12a

2 marks

The apparatus below can be used to measure the temperature as a neutralisation reaction takes place.

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The graphs below show how the temperature changes when acids A and B are added separately to 25 cm³ of sodium hydroxide solution.

q6a2-wjec-gcse-chemistry-june-2014-3f

Use the graphs opposite to find the

volume of acid required to neutralise the sodium hydroxide solution in both experiments,

[1]

ii)

maximum temperature rise for acid B.

[1]

How did you do?

12b1 mark

State which acid, A or B, is stronger and give a reason for your answer.

Stronger acid .....................................

Reason ...............................................................................

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12c3 marks

Describe how an indicator could be used to find the exact volume of acid needed for neutralisation.

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13a

2 marks

Higher Tier Only

A laboratory technician prepared a solution of sodium hydroxide, NaOH, in the following way.

He weighed out accurately 2.0 g of sodium hydroxide.
He dissolved the sodium hydroxide in 250 cm³ of water.

The relative formula mass (M_r) of sodium hydroxide is 40.

Use this information to calculate the concentration of this sodium hydroxide solution in mol/dm³.

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13b

4 marks

Higher Tier Only

A student was asked to carry out a titration to check the concentration of the sodium hydroxide solution. She carried out the titration using the apparatus shown below.

q7a-wjec-gcse-chemistry-june-2014-3h

The equation for the reaction taking place is as follows.

NaOH + HCI $\overset{}{\to}$ NaCl + H₂O

The titration was carried out three times and the results obtained are shown below.

	Titration
	1	2	3
Volume of hydrochloric acid added (cm³ )	22.2	22.7	22.6

Calculate the number of moles of hydrochloric acid that reacted and hence the concentration of the sodium hydroxide solution.

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14a5 marks

The diagram below shows some reactions of dilute hydrochloric acid.

wjec-gcse-jun14-1h-q5a

Give the names of each of the substances A to E.

A ..............................................................................................................

B ..............................................................................................................

C ..............................................................................................................

D ..............................................................................................................

E ..............................................................................................................

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14b

1 mark

Give the chemical formula of zinc chloride.

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2 marks

Higher Tier Only

Indigestion is caused by excess hydrochloric acid in the stomach. The calcium carbonate in an antacid tablet neutralises the excess acid.

Calcium carbonate reacts with hydrochloric acid according to the equation below.

CaCO₃ + 2HCl $\overset{}{\to}$ CaCl₂ + H₂O + CO₂

q9a-wjec-gcse-chemistry-june-2018-2h

To determine how much calcium carbonate is present, a crushed indigestion tablet was mixed with water and titrated with dilute hydrochloric acid of concentration 1.0 mol / dm³. The end-point was determined using the indicator phenolphthalein. The procedure was repeated three times and the mean volume of hydrochloric acid solution needed to neutralise one tablet was found to be 15.2 cm³.

Calculate the number of moles of hydrochloric acid in 15.2 cm³ of the 1.0 mol / dm³ solution.

Number of moles = .................................................... mol

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1 mark

Higher Tier Only

Calculate the number of moles of calcium carbonate in one tablet.

Number of moles = .................................................... mol

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3 marks

Higher Tier Only

Calculate the mass of calcium carbonate in one tablet. Give your answer in milligrams, mg.

A_r(Ca) = 40 A_r(C) = 12 A_r(O) = 16

Mass of calcium carbonate = .................................................... mg

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1 mark

The diagram shows the labelling on the packet of indigestion tablets.

Each tablet contains:

calcium carbonate
magnesium carbonate
sucrose and glucose
flavouring
talc
saccharin
sodium and magnesium stearate

680 mg
80 mg
250 mg

Suggest an explanation for the difference between your answer in part (c) and the information given on the packet.

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2 marks

Higher Tier Only

An analytical chemist was asked to check the amount of vitamin C in a tablet. Vitamin C tablets contain ascorbic acid, C₆H₈O₆, and a starch “filler” which holds them together.

Ascorbic acid reacts with sodium hydroxide solution according to the equation below:

C₆H₈O₆ + NaOH $\overset{}{\to}$ NaC₆H₇O₆ + H₂O

q8a-wjec-gcse-chemistry-june-2015-3h

To determine how much vitamin C is present, a tablet was dissolved in water and titrated with sodium hydroxide solution of concentration 0.10 mol/dm³. The endpoint was determined using the indicator phenolphthalein. The procedure was repeated three times and the mean value of sodium hydroxide solution needed to neutralise a vitamin C tablet was found to be 17.5 cm³.

Calculate the number of moles of sodium hydroxide in 17.5 cm³ of the 0.10 mol/dm³ solution.

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1 mark

Calculate the relative molecular mass, M_r, of ascorbic acid, C₆H₈O₆.

A_r(H) = 1 A_r(O) = 16 A_r(C) = 12

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2 marks

Higher Tier Only

The label on the bottle states that each tablet contains 300 mg (0.3 g) of vitamin C.

Using your answers to parts (a) and (b) show whether this statement is correct.

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6 marks

Sodium chloride is made when sodium hydroxide solution reacts with dilute hydrochloric acid.

NaOH + HCl → NaCl + H₂O

Describe a laboratory method for making crystals of pure sodium chloride from sodium hydroxide solution and dilute hydrochloric acid.

Diagrams may be used as part of your answer.

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6 marks

Describe the similarities in the reactions of ethanoic acid and sulfuric acid with metals, carbonates and bases. Describe and explain any differences observed. You should include relevant equations in your answer.

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5a1 mark

This question is about titrations.

Phenolphthalein is a common indicator for the titration of sodium hydroxide with hydrochloric acid because it is colourless in acidic and neutral conditions but pink / purple in basic conditions.

Suggest why an indicator is required for the titration of hydrochloric acid with sodium hydroxide.

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5b5 marks

Higher tier only

An experiment was completed titrating 25.0 cm³ of the hydrochloric with 0.100 mol / dm³ sodium hydroxide solution.

The titration results are shown in Table 1.

Table 1

	Rough	Run 1	Run 2	Run 3
Initial burette reading / cm³	0.00	0.00	23.30	0.05
Final burette reading / cm³	24.15	23.30	46.65	23.15

Calculate the concentration of the hydrochloric acid.

Use only the student’s concordant results.

Concordant results are those within 0.10 cm³ of each other.

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6a2 marks

Sodium hydroxide is a strong alkali.

Explain what is meant by a strong alkali.

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6b1 mark

Sodium hydroxide can be neutralised with citric acid.

Write the word equation for this reaction.

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6c4 marks

Higher tier only

A student neutralised a 0.125 mol / dm³ sodium hydroxide solution with citric acid.

3NaOH + C₆H₈O₇ → 3H₂O + Na₃C₆H₅O₇

This is the method used.

Pipette 25 cm³ of sodium hydroxide solution into a conical flask.
Add a few drops of universal indicator to the sodium hydroxide solution.
Using a measuring cylinder, add 20 cm³ of 0.050 mol / dm³ citric acid solution.

Explain why this method will not fully neutralise the sodium hydroxide solution.

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6d1 mark

Explain why litmus would not be a suitable indicator for this reaction.

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6e2 marks

The neutralisation of sodium hydroxide by citric acid can be completed by titration.

Explain why a pipette would be used to measure the sodium hydroxide solution but a burette would be used to measure the citric acid solution.

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7a3 marks

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

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

Give the word equation for this reaction.

[1]

ii)

State two observations that would be made during this reaction.

[2]

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7b7 marks

Barium sulfate is an insoluble compound.

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]

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7c5 marks

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)

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

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7d1 mark

Higher tier only

Magnesium hydroxide, Mg(OH)₂, is another compound formed from a Group 2 metal.

When it reacts with hydrochloric acid, magnesium chloride and water is formed. Write the simplest ionic equation, including state symbols, for this reaction.

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