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Practical Skills (OCR GCSE Combined Science A (Gateway): Chemistry): Exam Questions

Exam code: J250

37 mins15 questions

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Practical Skills

1a2 marks

The Haber process is used to make ammonia, NH3.

N2 + 3H2 ⇌ 2NH3

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]

How did you do?

1b4 marks

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]

How did you do?

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

Comment on how correct both predictions are [4]

How did you do?

2b6 marks

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]

How did you do?

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

What is the mobile phase in this experiment?

How did you do?

3b1 mark

Explain how paper chromatography separates the colours in ink.

How did you do?

3c
Sme Calculator4 marks

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]

How did you do?

44 marks

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]

How did you do?