GCSEChemistry: Combined ScienceOCR GatewayTopic Questions7. Practical Skills7.1 Practical Skills

Practical Skills (OCR Gateway GCSE Chemistry: Combined Science)

Topic Questions

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1a2 marks

The Haber process is used to make ammonia, NH3.

N2 + 3H2 ⇌ 2NH3

a)
The reaction reaches a dynamic equilibrium.

i)
What happens to the rate of the forward and backward reactions at dynamic equilibrium?
[1]
ii)
What happens to the concentrations of the reacting substances at equilibrium?
[1]

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1b4 marks
b)
Calcium sulfate is another salt.

A student made some calcium sulfate.

Look at the method he used:

  • pour 100 cm3 of calcium nitrate solution into a beaker
  • add drops of sodium sulfate solution until a precipitate appears
  • allow the precipitate to settle to the bottom of the beaker
  • pour off the liquid
  • use a spatula to transfer the solid calcium sulfate onto a piece of filter paper.
Describe and explain two ways that the student could improve his method to increase the amount of pure, dry calcium sulfate made.

1 ........................................................

2 ........................................................

[4]

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2a4 marks

Two students, A and B, want to make some solid zinc sulfate.

They make some predictions.

q20-paper-1-specimen-2016-ocr-gcse-chemistry

a)

Comment on how correct both predictions are

[4]

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2b6 marks

b)

i) 
Zinc oxide, ZnO, is reacted with nitric acid, HNO3.

The reaction makes zinc nitrate, Zn(NO3)2, and water, H2O.

Write a balanced symbol equation for this reaction..

[2]

ii)
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.
[4]

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3a1 mark

A forensic scientist is investigating the ink that has been used to forge the signature on a cheque.

She separates the colours in some inks using paper chromatography.

Look at the diagram of her apparatus.

q23-paper-1-june-2018-ocr-gcse-chem

a)
What is the mobile phase in this experiment?

[1]

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3b1 mark
b)
Explain how paper chromatography separates the colours in ink.

[1]

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3c
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c)
Look at the results of the scientist’s experiment.

q23c-paper-1-june-2018-ocr-gcse-chem

i)
Look at the green spot for ink A.

Calculate the Rf value for the green spot.

Answer = ...................................... [2]

ii)
Which ink was used to forge the signature on the cheque?

Explain how you can tell.

[2]

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44 marks
a)
All halogens react with alkali metals to make a salt.

i)
All halogens have similar chemical reactions.

Explain why in terms of electronic structure.

[1]

ii)

Sodium reacts with bromine to make sodium bromide, NaBr.

Construct the balanced symbol equation for this reaction.

[2]

iii)
What is the formula of the product of the reaction between astatine and potassium?

[1]

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