Reactions of Acids (AQA GCSE Chemistry)

Figure 1 shows a bottle of vinegar which is used to flavour food. 

Vinegar is an aqueous solution of ethanoic acid, CH₃COOH.

Figure 1 

Ethanoic acid is described as a weak acid.

What is the ion present in aqueous solutions of all acids?

Discuss the difference in pH between a weak acid and a strong acid of the same concentration.

Figure 2 shows the apparatus used to find the concentration of ethanoic acid in vinegar.

Figure 2 

27.00 cm³ of a 1.0 mol dm^-3 solution of NaOH was required to neutralise 25.00 cm³ of vinegar.

Calculate the concentration of ethanoic acid in the vinegar.

The balanced chemical equation between iron and hydrochloric acid is:

Fe (s) + 2 HCl (aq) → FeCl₂ (aq) + _____ (g)

What is the name and symbol of the missing product?

What class of compound is the other product in the reaction?

Describe a suitable method for separating the FeCl₂.

State what type of reaction this is and explain, using appropriate half equations the species being oxidised and those being reduced.

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

calcium  +   hydrochloric acid            →         calcium chloride  + ___________

What is the unknown product?

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?

Sodium hydroxide neutralises sulfuric acid in the following reaction:

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

Sulfuric acid is a strong acid.

Explain what the term “strong acid” means, discussing how the strength of an acid is linked to its pH value.

Write down the ionic equation for this neutralisation reaction and include the state symbols.

A chemist used a volumetric pipette to add 25.0 cm³ of a solution of sodium hydroxide of unknown concentration to a conical flask.

The chemist then carried out a titration to find out the volume of 0.150 mol/dm³ sulfuric acid needed to neutralise the sodium hydroxide.

Describe how the chemist would complete the titration.

You should state a suitable indicator and give the colour change that would be observed.

Soluble salts can be formed by reacting metals with acids.

Give two other types of substances that can react with an acid to form a soluble salt.

Magnesium chloride is a soluble salt.

Give the formula of magnesium chloride.

Calcium sulfate is another soluble salt that can be formed by the reaction between calcium and dilute sulfuric acid.

State two observations that could be made during this reaction.

A student wanted to investigate the volume of hydrogen produced when different masses of calcium were reacted with dilute sulfuric acid.

They use the equipment shown in Figure 1

The student made an error when setting up the apparatus.

State what the error is and describe what would happen if the student used the equipment.

What is the ionic equation for neutralisation?

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?

This question is about alkalis and bases.

Give the name and formula of the ion present in aqueous solutions of all alkalis.

Explain the difference between the terms base, alkali and alkaline solution.

Metals, metal hydroxides and metal oxides can neutralise acids. 

Name one other type of compound that can neutralise an acid.

Write the simplest ionic equation which represents a neutralisation reaction.

This question is about acids and alkalis.

A dilute solution of hydrochloric acid is considered a strong acid.

Justify how an acid can be described as both strong and dilute.

A 1.0 × 10⁻⁴ mol/dm³ solution of HCl has a pH of 4.0

What is the pH of a 1.0 × 10⁻⁶ mol/dm³ solution of the same acid? 

Explain your answer.

This question is about the reactivity of metals.

One method that can be used to determine the order of reactivity of metals is to add the metals to cold water and to dilute hydrochloric acid.

The observations made when strips of four metals are added separately to cold water and to dilute hydrochloric acid are shown in Table 1.

Table 1

One reason for not completing the reaction of platinum with dilute hydrochloric acid is the high cost of platinum (roughly £25 per gram). 

Suggest how the reaction of platinum with dilute hydrochloric acid could be completed without increasing the cost of the experiment.

Explain why the experiment with potassium and dilute hydrochloric was not completed.

Explain why it is not possible to produce a reactivity series using just the observations with cold water.

Magnesium reacts slowly with cold water but quickly with dilute hydrochloric acid. 

Explain two reasons why the reaction with cold water is slower than the reaction with hydrochloric acid.

This question is about chemical analysis.

Two students have solid powders of three metal compounds, X, Y and Z.

• Compound X is a black powder.
• Compound Y is a grey powder.
• Compound Z is a white powder.

The students both use the same method for their first experiment.

1. Measure 1.0 g of each powder into a separate test tube
2. Add 5.0 cm³ of dilute sulfuric acid into each test tube
3. Record any observations

The observation of both students are shown in Table 1.

Table 1

Both student's observations for compound X are correct, however student 1 did not leave the reaction to stand for enough time to see the blue solution.

Suggest the identity of compound X. Justify your answer, including a balanced equation. 

Student 1 concludes that compounds Y and Z are metal carbonates because they fizz lots.

Evaluate student 1's conclusion.

The students burn a small amount of compounds Y and Z in a blue Bunsen flame. 

The students forget to record the results but they know one compound gives a white flame and the other gives a yellow flame. 

Student 1 suggests that compound Y is magnesium and student 2 suggests that compound Z is magnesium oxide. 

Which student is correct? Explain your reasoning using the observations from both experiments.

Both students agree that compound Z contains sodium. 

Student 1 thinks that it is sodium carbonate while student 2 thinks it is sodium hydrogen carbonate.

Sodium carbonate and sodium hydrogen carbonate are both basic.

Explain how the students could use universal indicator solution to determine the identity of compound Z.

Sodium hydroxide is a strong alkali.

Explain what is meant by a strong alkali.

Sodium hydroxide can be neutralised with citric acid. 

Write the word equation for this reaction.

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.

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

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. 

This question is about hydrochloric acid.

Hydrochloric acid has some domestic uses such as cleaning tiles and rust.

It is recommended that dilute hydrochloric acid is used in these situations.

What is the difference between the pH of dilute hydrochloric acid compared to the pH of concentrated hydrochloric acid? 

Give a reason for your answer.    

A solution of hydrochloric acid, with a concentration of 1.5 g / dm³, has a pH value of 1.45. 

Predict the pH value when it is diluted to make a solution with a concentration of 0.015 g / dm³. Explain your reasoning.

The reaction of hydrochloric acid with sodium carbonate solution is an example of a neutralisation reaction. 

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

A student plans to complete a titration experiment using hydrochloric acid and sodium hydroxide. 

They have a choice of three possible indicators:

• Methyl orange
• Phenolphthalein
• Universal indicator 

Evaluate the suitability of each indicator for this titration.

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?

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.

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. 

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. 

A student carrying out a titration finds that a 25.0 cm³ solution of 0.500 mol/dm³ hydrochloric acid neutralises 35.0 cm³ of sodium hydroxide. 

The balanced symbol equation for the reaction is:

NaOH + HCl  →    NaCl  + H₂O

What is the concentration of the sodium hydroxide?

This question is about the preparation of magnesium sulfate.

A group of students are asked to prepare a sample of magnesium sulfate.

The students suggest four possible ways to do this:

1. Magnesium + sulfuric acid
2. Magnesium carbonate + sulfuric acid
3. Magnesium hydroxide + sulfuric acid
4. Magnesium oxide + sulfuric acid

Which of the student's suggestions can be classed as a redox reaction? Justify your choice including relevant equations.

Explain which reaction produces the most hazardous products.

Describe how to prepare a sample of magnesium sulfate using suggestion 2.