OCR Gateway GCSE Chemistry

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GCSEChemistryOCR GatewayTopic Questions3. Chemical Reactions3.3 Types of Chemical Reactions

3.3 Types of Chemical Reactions

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1a6 marks

A farmer wants to test the pH of soil samples. He researches information about different pH test kits.

q19-paper-3-nov-2020-ocr-gcse-chem

Look at the information he finds.

    pH of soil sample
pH test kit Price pH2 pH4 pH7 pH9 pH14
A £4.95 Red Yellow Green Blue Purple
B £10.99 Yellow Yellow Pink Pink Pink
C £11.50 Pink Orange Yellow Blue Blue
D £2.99 Colourless Colourless Colourless Pink Pink
E £12.75 Red Orange Yellow Yellow Yellow

Evaluate the advantages and disadvantages of the pH test kits and suggest which pH test kit the farmer should use.

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1b
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After testing the soil samples, the farmer finds that the soil in one of his fields is acidic.

Acidic soil can be neutralised by spreading magnesium carbonate, MgCO3, onto the soil.

The farmer uses 25.0 kg of magnesium carbonate.

Calculate the number of moles of magnesium carbonate the farmer uses.
(Ar: C = 12.0; Mg = 24.3; O = 16.0)

Give your answer to 3 significant figures.

Number of moles of magnesium carbonate = .......................................................... 

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2a6 marks

A teacher investigates neutralisation. She uses hydrochloric acid, HCl, and sodium hydroxide, NaOH.

HCl + NaOH → NaCl + H2O

She slowly adds 1.0 cm3 portions of the hydrochloric acid to 20.0 cm3 of 1.0 mol/dm3 sodium hydroxide.

She records the pH until she has added an excess of acid.

Look at her results.

Volume of hydrochloric acid
added (cm3)		 pH
0 12.0
1 11.8
2 11.6
3 11.4
4 11.2
5 7.0
6 3.0
7 2.8
8 2.5
9 2.3
10 2.3

i)
Plot a graph of the pH value against the amount of hydrochloric acid added and draw a line of best fit.

q20ai-paper-3-june-2019-ocr-gcse-chem[3]
ii)
Use your graph to estimate the volume of hydrochloric acid when the pH is 10.

Volume of hydrochloric acid = ................................................... cm3 [1]

iii)
What happens to the concentration of hydroxide ions, OH-, as the hydrochloric acid is added to the sodium hydroxide?

[1]

iv)
Acidic solutions contain hydrogen ions, H+. Alkaline solutions contain hydroxide ions, OH-.

Write the balanced ionic equation for neutralisation.

[1]

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2b2 marks

Higher Only

Hydrochloric acid, HCl (aq), is a strong acid. Ethanoic acid, CH3COOH (aq), is a weak acid.

Explain the difference between a strong and a weak acid.

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2c
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i)
Nitric acid, HNO3, is another strong acid.

Nitric acid has a pH of 2.

The teacher adds enough water to reduce the concentration of the nitric acid by a factor of 100.

Calculate the new pH of the nitric acid.

pH = .......................................................... [2]

ii)
Nitric acid, HNO3, can also neutralise sodium hydroxide, NaOH.

Sodium nitrate, NaNO3, and water are made.

Write a balanced symbol equation for this reaction.

[1]

iii)
Describe how dry sodium nitrate crystals can be made using this reaction.

[2]

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3a2 marks

Sodium oxide, Na2O, is a white solid.

Draw a dot and cross diagram to show the ions in sodium oxide.

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3b
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i)
Sodium oxide reacts with water.

An aqueous solution of sodium hydroxide is made.

Write the balanced symbol equation for this reaction, including state symbols.
[3]
ii)
Sodium hydroxide neutralises acids. It is an alkali.

Which ion do solutions of alkalis contain?
[1]
iii)
A salt is made when sodium hydroxide neutralises sulfuric acid.

Name this salt.
[1]
iv)
A sample of hydrochloric acid has a pH of 1.04.

A student adds water to the hydrochloric acid until the pH is 3.04.

The concentration of hydrogen ions decreases.

Calculate the factor by which the hydrogen ion concentration has decreased.

Decrease in hydrogen ion concentration = .......................................................... [2]

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1a2 marks

Magnesium burns in oxygen to make magnesium oxide.

The reaction involves both oxidation and reduction.

Complete the equation by adding the state symbols for magnesium and oxygen at room temperature.

2Mg (….) + O2 (….) ➞ 2MgO (s)

magnesium + oxygen ➞ magnesium oxide

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1b1 mark

Which element is oxidised and which element is reduced?

oxidised: ……………………………….
reduced: ……………………………….

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1c3 marks

Magnesium oxide reacts with water to make an alkaline solution.

Describe how you would measure the pH of the magnesium hydroxide solution.

A pH meter is not available.

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2a3 marks

Acids are substances that turn universal indicator paper red.

i)
What makes a substance acidic?

[1]

ii)
Sodium hydroxide, NaOH, is an alkali.

Sodium hydroxide neutralises sulfuric acid, H2SO4. The reaction makes a salt called sodium sulfate, Na2SO4. Water is also made.

Complete the balanced symbol equation for this reaction.

........ NaOH + H2SO4 → Na2SO4 + ........ H2O

[2]

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2b3 marks

A student investigates the reaction of an aqueous solution of sodium hydroxide and sulfuric acid. During the experiment, the student tests the pH of the solution with universal indicator.

i)
Suggest a piece of equipment that the student could use instead of universal indicator paper to test the pH of the solution.
[1]
ii)
Describe how to use the equipment suggested in (b)(i)

[2]

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2c6 marks

Potassium chloride is a mineral found in many foods.

A student wants to make a salt called potassium chloride, KCl , by neutralisation of an acid by an alkali.

Describe how to make a pure, dry sample of potassium chloride in a laboratory by neutralisation.

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3a4 marks

A student has a solution of hydrochloric acid, HCl, and a solution of sodium hydroxide, NaOH.

He wants to make a pure, dry sample of sodium chloride.

Describe how he can do this.

Include the apparatus he should use and his method.

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3b1 mark

Write a balanced symbol equation for the reaction.

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3c3 marks

The student also investigates other reactions.

The table shows the salts he can make from different starting materials.

Complete the table.

Acid used Other starting material Salt made
Sulfuric acid Copper oxide ................................
................................ Zinc carbonate Zinc nitrate
Hydrochloric acid ................................ Magnesium chloride

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3d1 mark

What type of reaction happens when sulfuric acid reacts with copper oxide?

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4a2 marks

Zinc nitrate can be made by reacting zinc oxide with nitric acid, HNO3.

Write a balanced symbol equation for this reaction.

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4b4 marks

A student suggests this method for preparing zinc nitrate.

1. Measure 50 cm3 of dilute nitric acid into a beaker.
2. Add one spatula measure of zinc oxide.
3. Heat the mixture until crystals of zinc nitrate are made.

Her method will not make a pure dry sample of zinc nitrate.

What improvements should she make to the method to make sure that:

  • the reaction is complete
  • the zinc nitrate can be separated from the nitric acid and the zinc oxide?

Explain your answer.

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4c2 marks

Describe why this reaction is a neutralisation reaction.

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52 marks

A student adds calcium to dilute hydrochloric acid. The mixture begins to fizz.

Write a balanced symbol equation for this reaction.

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