Acids (Edexcel GCSE Chemistry)

Ammonium phosphate and ammonium sulfate are made from ammonia.

These compounds can be used as fertilisers.

Ammonia solution is alkaline.

Which of the following could be used to show that ammonia solution is alkaline?

Ammonium phosphate and ammonium sulfate are made from ammonia.

These compounds can be used as fertilisers.

Give one advantage of using fertilisers made from ammonia rather than using manure.

The fertiliser ammonium phosphate was made by reacting ammonia solution with dilute phosphoric acid.

i) In the first step, 25 cm³ of dilute phosphoric acid was placed in a beaker.

Give the name of a piece of apparatus that could be used to measure out the 25 cm³ dilute phosphoric acid.

(1)

ii) Complete the word equation for this reaction.

   ammonia + ................................... → .....................................

(1)

iii) Some ammonium phosphate solution was made.

Describe how pure, dry crystals of ammonium phosphate are obtained from the ammonium phosphate solution.

(2)

The formula of ammonium sulfate is (NH₄)₂SO₄ What is the empirical formula of ammonium sulfate?

A student added some sulfuric acid gradually to a solution of ammonia until it was in excess.

What happens to the pH during this reaction?

What is the ionic equation for neutralisation?

The method used to prepare a salt depends on its solubility in water.

Complete Figure 19 by placing one tick in each row to show whether the salt is soluble or insoluble.

Figure 19

Lead nitrate solution mixed with sodium sulfate solution forms lead sulfate as a precipitate.

Pb(NO₃)₂+ Na₂SO₄ → PbSO₄ + 2NaNO₃

In an experiment, the theoretical yield of lead sulfate for this reaction was 2.85 g.
In the experiment only 2.53 g of lead sulfate is obtained.

Calculate the percentage yield of lead sulfate in this experiment.

Give your answer to two significant figures.

The method used to make the lead sulfate is:

• pour 100 cm³ lead nitrate solution into a beaker

• add drops of sodium sulfate solution until a precipitate is seen

• allow the precipitate to settle to the bottom of the beaker

• pour off the liquid

• use a spatula to transfer the solid lead sulfate onto a filter paper.

Explain two ways of improving this experimental method in order to increase the amount and quality of lead sulfate that could be obtained from 100 cm³ of lead nitrate solution.

Ammonium nitrate is produced from ammonia and nitric acid on a large scale in industry.

Ammonium nitrate can also be made in the laboratory by titrating ammonia solution with dilute nitric acid.

NH₃ + HNO₃ → NH₄NO₃

Ammonium nitrate crystals can then be obtained by evaporating off some of the water from the solution.

Give two reasons why this laboratory method is not suitable for use on a large scale in industry.

Calcium reacts with hydrochloric acid to form the salt, calcium chloride and another product. 

calcium  +   hydrochloric acid            →         calcium chloride  + ___________

What is the unknown product?

Which statement correctly describes a strong acid? 

Higher Only

Some acids such as hydrochloric acid are described as strong acids.

Some acids such as ethanoic acid are described as weak acids.

 i) Explain the difference between a strong acid and a weak acid.

(2)

ii) Give a reason why adding hydroxide ions to an acid solution leads to an increase in pH.

(1)

The salt zinc nitrate can be made by reacting zinc oxide, ZnO, with dilute nitric acid, HNO₃.

Write the balanced equation for this reaction.

50 cm³ of potassium hydroxide solution of concentration 40g dm^–3 is needed for an experiment.

Calculate the mass of potassium hydroxide that must be dissolved in water to make 50 cm³ of solution of this concentration.

mass of potassium hydroxide = ..................................................................... g

Salts of metals can be made by reacting one of the metal’s compounds with the appropriate acid.

Plan an experiment to prepare pure, dry crystals of magnesium sulfate, MgSO₄ , by reacting a suitable magnesium compound with a suitable acid.

You may use equations if you wish.

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?

State two characteristic properties of metals.

property 1 ....................................................................

property 2 ....................................................................

Acids are used to make salts.

Give the name of the acid used to make chlorides.

Salts of metals can be prepared by reacting the metal with an acid to produce the salt and hydrogen.

i) Describe the test to show that the gas is hydrogen.

(2)

ii) Nickel is a metal. Explain how the structure of a nickel atom, Ni, changes when it forms a nickel ion, Ni²⁺.

(2)

A nickel sulfate solution is made by dissolving 23.5 g of nickel sulfate to make 250 cm³ of solution.

concentration = ...................................................... g dm^-3

Excess solid nickel carbonate is added to dilute sulfuric acid in a beaker.

nickel carbonate + sulfuric acid → nickel sulfate + carbon dioxide + water

Nickel sulfate is formed in solution.

Describe how a sample of pure, dry nickel sulfate crystals can be obtained from the mixture of nickel sulfate solution and excess solid nickel carbonate in the beaker.

Which is the correct method for testing for hydrogen gas?

Which is not true about the test for carbon dioxide gas?

The word equation for the reaction between copper carbonate and dilute sulfuric acid is

i) Complete the balanced equation for this reaction.

CuCO₃ + ............................... → ............................... + CO₂ + H₂O

(2)

ii) Calculate the relative formula mass of copper carbonate, CuCO₃. (relative atomic masses: C = 12.0, O = 16.0, Cu = 63.5) (2) relative formula mass of CuCO₃ = ...........................

iii) What is the chemical test to show that a gas is carbon dioxide?

(1)

Figure 12 shows a conical flask containing dilute sulfuric acid.

Copper carbonate is added to the acid in the flask. The copper carbonate is added one spatula measure at a time until the reaction has finished.

Figure 12

i) State two observations that would show the reaction has finished.

(2)

ii) Describe how you would obtain a solution of copper sulfate from the mixture and how you would obtain pure, dry copper sulfate crystals from this solution.

Your description should include the apparatus you would use. You may wish to use diagrams in your answer.

(6)

The electronic configuration of carbon is 2.4 The electronic configuration of oxygen is 2.6

Draw a dot and cross diagram for a molecule of carbon dioxide.

Show outer electrons only.

Indicators are used during a titration to observe the end point. 

Different indicators turn different colours in acids and alkalis.

Which indicator displays the correct colour in each solution?

Hydrochloric acid reacts with solid B.

Solid B is an alkali.

A student carries out an experiment to see how the pH changes when different masses of solid B are added to dilute hydrochloric acid.

The student uses the following method.

step 1 use a measuring cylinder to measure out 100 cm³ of dilute hydrochloric acid

step 2 pour the acid into a beaker

step 3 measure the pH with a pH probe

step 4 add half a spatula of solid B and stir

step 5 repeat steps 3 and 4 until the pH stops changing.

i) Give a safety precaution that should be taken during the experiment.

(1)

ii) Give an improvement to step 4 that would produce more accurate results.

(1)

iii) What is the most likely change in pH during the experiment?

(1)

iv) If some methyl orange indicator is added to the acid in step 2, the mixture changes colour during the experiment.

State the colour change.

(2)

   colour at start in acid ....................................

   colour at end ..........................

Concentrated hydrochloric acid can be broken down using electricity. The apparatus that can be used is shown in Figure 6.

Figure 6

i) Give the name of the piece of apparatus labelled X.

(1)

ii) The rod labelled Y in Figure 6 is made of graphite. What is the name of this piece of apparatus?

(1)

iii) Give one reason why graphite is a suitable material to make Y.

(1)

iv) Complete the balanced equation for the reaction that occurs.

(1)

..........HCl → H₂+ Cl₂

Below are five steps in the preparation of a soluble salt. The sentences are not in the correct order.

1. Heat to evaporate most of the water

2. Add solid copper(II) oxide until no more dissolves

3. Measure out 25 cm³ of dilute sulfuric acid

4. Leave in a warm place to cool and crystallise

5. Filter to remove the excess solid

What is the correct order of the sentences?

Silver nitrate solution and dilute hydrochloric acid react to product silver chloride solution and nitric acid.

What is the state symbol for the silver chloride produced?

The scientist John Dalton lived over 200 years ago.

John Dalton suggested an early model of atoms. When Dalton first described atoms he said that

• all elements are made of atoms

• atoms are not formed of any smaller particles

• all atoms of the same element are identical.

Give two differences between Dalton’s model of atoms and today’s model of atoms.

Dalton also investigated different gases.

One of the gases that Dalton investigated was ethene.

The structure of one molecule of ethene is shown in Figure 8.

Figure 8

Give the molecular formula and the empirical formula of ethene.

molecular formula ............................................................................................

empirical formula ............................................................................................

Another gas that Dalton investigated was chlorine. Chlorine gas reacts with water. The two products are a solution of hydrogen chloride and the substance HClO.

i) Complete the balanced equation for this reaction, including the three missing state symbols.

(3)

 ........... (..........) + ........... (..........) ........... (..........) + HClO (aq)

ii) Hydrogen chloride solution is acidic. The formulae of four ions are shown in Figure 9.

Figure 9

Give the formula of the ion in Figure 9 that causes the hydrogen chloride solution to be acidic.

(1) formula .............................................................................................

iii) An acid reacts with an alkali.

Give the name of this type of reaction.

(1)

iv) Describe what you would see when some copper carbonate powder is added to a beaker of dilute sulfuric acid.

(2)

Higher Only

A solution of sulfuric acid with a pH of 4 has a hydrogen ion concentration of 1 x 10^-4 mol/dm³.

Another acid has a hydrogen ion concentration of 1 x 10^-6 mol/dm³.

What is the pH of this acid?

Higher Only

X and Y are solutions of two different acids.

The concentration of acid in each solution, in mol dm⁻³, is the same.

Solution X has a pH of 3.40 and solution Y has a pH of 4.40.

i) State what could be used to measure these pH values of 3.40 and 4.40.

(1)

ii) What is the concentration of hydrogen ions in solution X compared with that in solution Y?

(1)

Higher Only

An experiment is planned to record the change in pH as a powdered base is added to 50 cm³ dilute hydrochloric acid.

 The method suggested is

i) State how you could change the method so that the amounts of dilute hydrochloric acid and of the base can be measured more accurately.

(2)

dilute hydrochloric acid .............................................................................................

base ...................................................................................................

ii) During the experiment the pH changes from 2 to 10.

If phenolphthalein indicator is added at the beginning of the experiment, a colour change occurs as the base is added.

 State the colour change that occurs.

(1)

 colour at start .............................................................................................

 colour at end .............................................................................................

iii) Explain, in terms of the particles present, why the pH increases during the experiment. 

(2)

Some properties of four solids, A, B, C and D, are shown in Figure 6.

The solids, in no particular order, are copper carbonate, copper oxide, magnesium metal and sodium hydroxide.

Figure 6

Identify the solids A, B, C and D, explaining how the information in Figure 6 supports the identification of each solid.

Higher Tier Only 

Dilute hydrochloric acid is a strong acid.

i) Explain why dilute hydrochloric acid is described as a strong acid.

(2)

ii) 1 cm³ of hydrochloric acid of pH 2 is made up to a volume of 10 cm³ with distilled water. State the pH of the new solution.

(1)

pH = ..........................................................

Higher Tier Only 

Magnesium oxide reacts with dilute hydrochloric acid to produce magnesium chloride solution and water.

MgO (s) + 2HCl (aq) → MgCl₂ (aq) + H₂O (l)

Write the ionic equation for this reaction.

Higher Only

In an experiment magnesium hydroxide powder is added in 0.1 g portions to 25 cm³ of dilute hydrochloric acid until the magnesium hydroxide is just in excess.

Universal indicator paper can be used to test the pH of the solution after each addition of magnesium hydroxide.

i) Give the name of an alternative piece of equipment that can be used to measure pH.

(1)

ii) State and explain how the pH changes as the magnesium hydroxide is added to the dilute hydrochloric acid.

(4)

Higher Only

Copper carbonate reacts with dilute nitric acid.

i) During the reaction the copper carbonate powder completely disappears. State what can be deduced about the amount of acid used.

(1)

ii) During the reaction, the pH of the mixture changed from 2 to 6. By what factor has the concentration of the hydrogen ions in the mixture changed?

(1)

Using different reactants, a solution of copper sulfate was prepared.

Describe what should be done to obtain copper sulfate crystals from this copper sulfate solution.

Higher Only

When chloride ions are added to a pale blue solution containing copper ions, the mixture turns yellow.

This is a reversible reaction.

pale blue solution + chloride ions  yellow solution + water

What effect does the removal of chloride ions have on the colour of the yellow mixture?   

Higher Only

Hydrated copper sulfate has the formula CuSO_4.5H₂O. The formula tells us that each mole of copper sulfate contains 5 moles of water.

A sample of CuSO₄.5H₂O was heated gently until all the water was removed to form anhydrous copper sulfate, CuSO₄.

CuSO₄.5H₂O → CuSO₄ + 5H₂O

The mass of water formed was 4.5 g.

Calculate the mass of hydrated copper sulfate that was heated.

(relative atomic masses: H = 1.0, O = 16.0; relative formula mass: CuSO₄.5H₂O = 249.5)

mass of CuSO₄.5H₂O = ............................................................... g

Copper(II) chloride is soluble in water.

Calculate the mass of copper(II) chloride that needs to be dissolved in 100 cm³ of water to make a solution with concentration 50 g dm^-3.

Higher Only

Give one change to the method in part a) that would result in a more concentrated solution.

Copper(II) chloride solution reacts with sodium hydroxide solution. Sodium hydroxide is an alkali.

Define alkali.

Complete the symbol equation for the reaction by adding the state symbols.

CuCl₂ (...) + 2NaOH (.....) → Cu(OH)₂ (.....) + 2NaCl (.....)

A student wanted to find the volume of dilute sulfuric acid that would react with 25.0 cm³ of potassium hydroxide solution.

They used the equipment in Figure 1.

Figure 1

Write the balanced symbol equation for the reaction.

Explain why universal indicator would not be a suitable indicator to be used in this titration.

The student carried out 4 titrations.

Figure 2 shows their results.

Figure 2

Calculate the mean volume of acid.

The student uses this mean volume of acid to produce a salt solution in the conical flask.

Devise a plan to produce a sample of dry salt from this solution.