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GCSEChemistryOCRChemistry A (Gateway)Exam Questions7. Practical SkillsPractical Skills

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

Exam code: J248

57 mins24 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]

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1b2 marks

Ammonia is used to make fertilisers.

Fertilisers usually contain nitrogen.

Name the two other elements that fertilisers usually contain. ........................................ and ..........................................

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1c2 marks

Ammonium sulfate is a salt used as a fertiliser.

Ammonium sulfate can be made in a laboratory in a batch process.

Ammonia solution is titrated with dilute sulfuric acid to make a solution of ammonium sulfate, as shown in the diagram.

q19c-paper-2-june-2019-ocr-gcse-chem

Describe how you would make dry crystals of ammonium sulfate from ammonium sulfate solution.

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1d4 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 ........................................................

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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

Comment on how correct both predictions are

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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]

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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

What is the mobile phase in this experiment?

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3b1 mark

Explain how paper chromatography separates the colours in ink.

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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]

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4a4 marks

The Group 7 elements are known as the halogens.

The halogens have similar chemical properties.

Their physical properties vary with increasing atomic number.

Look at the table of information about the halogens.

Halogen

Symbol

Atomic number

Molecular formula

Atomic radius (pm)

Reaction of halogen with sodium iodide solution

fluorine

F

9

F2

64

Makes iodine and sodium fluoride

chlorine

Cl

17

Cl2

99

Makes iodine and sodium chloride

bromine

Br

35

Br2

114

.................................. ..................................

iodine

I

53

I2

133

No reaction

astatine

At

85

.................

.................

No reaction

i) Predict the molecular formula and atomic radius of astatine. Put your answers in the table.

[2]

 ii) Predict the reaction of bromine with sodium iodide solution. Put your answer in the table.

[1]

 iii) Explain your answer to (ii) in terms of the reactivity of the halogens.

[1]

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4b4 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]

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54 marks

Chemical tests are used to identify gases, anions and cations.

  • A student has an unknown solution.

  • She thinks that the solution contains copper(II) ions and bromide ions.

Describe the chemical tests she does to confirm the presence of these two ions in the solution.

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