GCSE OCR 21st Century Science C7 Specimen Paper + Mark Scheme (Higher)

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Preview of GCSE OCR 21st Century Science C7 Specimen Paper + Mark Scheme (Higher)

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SPECIMEN H
GENERAL CERTIFICATE OF SECONDARY EDUCATION
TWENTY FIRST CENTURY SCIENCE A173/02
CHEMISTRY A
Unit A173: Module C7 (Higher Tier)
Candidates answer on the question paper
A calculator may be used for this paper
OCR Supplied Materials:
None Duration: 1 hour
Other Materials Required:
Pencil
Ruler (cm/mm)
Candidate Candidate
Forename Surname
Centre Number Candidate Number
INSTRUCTIONS TO CANDIDATES For Examiner's
Write your name clearly in capital letters, your Centre Number and Candidate Use
Number in the boxes above.
Max Mark
Use black ink. Pencil may be used for graphs and diagrams only.
Read each question carefully and make sure that you know what you have to 1 11
do before starting your answer. 2 5
Answer all the questions.
Write your answer to each question in the space provided, however additional 3 8
paper may be used if necessary. 4 8
INFORMATION FOR CANDIDATES 5 8
Your quality of written communication is assessed in questions marked with a 6 10
pencil (). 7 10
The Periodic Table is printed on the back page.
The number of marks for each question is given in brackets [ ] at the end of TOTAL 60
the question or part question.
The total number of marks for this paper is 60.
This document consists of 20 pages. Any blank pages are indicated.
© OCR 2011 [QN 600/1356/4] OCR is an exempt Charity Turn over

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Page 2

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Answer all the questions.
1 Methanoic acid, HCOOH, is a carboxylic acid that is present in bee stings.
(a) What is the formula of the functional group that is responsible for the characteristic
properties of carboxylic acids?
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(b) Methanoic acid is used to remove the limescale in kettles.
Limescale is made of calcium carbonate, which is insoluble in water.
Carboxylic acids react with carbonates in a similar way to other acids such as hydrochloric
acid.…read more

Page 3

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Methanoic acid is a weak acid and hydrochloric acid is a strong acid.
Describe a reaction, other than with carbonates, that shows that methanoic acid is an
acid.
Compare this with a similar reaction of hydrochloric acid to demonstrate why one is a
weak acid and the other a strong acid.
Include relevant balanced equations in your answer.
The quality of written communication will be assessed in your answer to this question.
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Page 4

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Sunflower oil is an example of a vegetable oil. The oil comes from the seeds of the sunflower
plant.
The chemicals in the oil are esters.
(a) When an ester is hydrolysed it forms an alcohol and a carboxylic acid.
This reaction is the reverse of the reaction that makes the ester.
Oils and fats are esters.
Write the name of the alcohol and the type of carboxylic acid to complete this word
equation for the hydrolysis of an oil.
oil + water ............................................…read more

Page 5

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An ester can be made by reacting an alcohol with a carboxylic acid. The technique used
involves four stages: reflux, distillation, purification and drying.
In the reflux stage, the alcohol and ester are heated with a little concentrated
sulfuric acid in a flask with a condenser attached in an upright position. Evaporated
liquid is allowed to run back into the flask.
In the distillation stage, the mixture is placed in a flask connected to a sloping
condenser and heated.…read more

Page 6

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A technician analyses a mixture of hydrocarbons using gas chromatography.
She first calibrates the equipment using standard hydrocarbons. The retention times of these
hydrocarbons are shown in the table.
hydrocarbon formula retention time
in minutes
methane CH 4 1.7
ethane C2H6 2.2
propane C3H8 3.5
butane C 4 H 10 4.0
pentane C 5 H 12 7.4
The technician then analyses the mixture of hydrocarbons. The recorder print out from this
analysis is shown below.
100
recorder
response
0
0 1.0 2.0 3.0 4.0 5.…read more

Page 7

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During gas chromatography, each component of a mixture is involved in a dynamic
equilibrium.
Explain how this separates the components in a mixture.
The quality of written communication will be assessed in your answer to this question.
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Page 8

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A company makes indigestion tablets that contain the active ingredient magnesium hydroxide.
This neutralises excess stomach acid to relieve the symptoms of acid indigestion. The tablets
also contain starch.
A chemist analyses samples from each batch of indigestion tablets that the company makes.
He uses quantitative analysis to find the mass of active ingredient in each tablet.
He tests 5 tablets from one batch.
He makes a suspension of each of the five tablets and titrates these with a solution containing
hydrochloric acid.…read more

Page 9

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Use the neutralisation equation below to work out the mass of magnesium hydroxide
that reacts with this mass of hydrochloric acid. This is the average mass of magnesium
hydroxide in each tablet.
The relative formula mass of hydrochloric acid, HCl, is 36.5.
Mg(OH) 2 + 2HCl MgCl 2 + 2H 2 O
average mass of magnesium hydroxide in each tablet = ............................................ g [2]
(iv) The company makes batches of 100 000 tablets.…read more

Page 10

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Use the table of titration results to assess the degree of uncertainty in your calculated value
of the mass of magnesium hydroxide in each tablet.
Explain your answer.
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