Reactions of Acids (AQA GCSE Chemistry: Combined Science)

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.

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.

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.

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.

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.

Ca (s)  +  H₂SO₄ (aq)   →   CaSO₄ (aq)  +  H₂ (g)

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

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.

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.

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.

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.

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.