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OCS AS LEVEL CHEMISTRY A 2023 VERSION 2 DEPTH IN CHEMISTRY GRADED A+ GUARANTEED PAS

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1 This question is about the properties and reactions of the Group 2 element strontium. (a) The relative atomic mass of strontium can be determined using a mass spectrometer. (i) Explain what is meant by the term relative atomic mass of an element. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] (ii) A sample of strontium has a relative atomic mass of 87.73. The sample consists of: • 82.9% Sr-88 • 6.9% Sr-87 • one other isotope. Determine the other isotope of strontium in the sample. isotope of strontium = .......................................................... [2] 3 © OCR 2023 Turn over (b) The table below shows two physical properties of the element strontium. Melting point high Electrical conductivity very good Explain these physical properties of strontium, in terms of bonding and structure. Include a labelled diagram in your answer. Diagram Explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5] (c) A student adds a small amount of strontium to water. When the reaction has finished, the student measures the pH of the final solution. (i) Write the equation for the reaction of strontium with water. ...................................................................................................................................... [1] (ii) Describe two observations which would be different if the student had used calcium in place of strontium. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] 4 © OCR 2023 (d) When hydrated strontium chloride is heated, the water of crystallisation is removed, leaving a residue of anhydrous strontium chloride. A student carries out an experiment to find the value of x in the formula of hydrated strontium chloride, SrCl 2 •xH2O. The student‟s method is outlined below. Step 1 Weigh an empty crucible. Add SrCl 2 •xH2O to the crucible and reweigh. Step 2 Heat the crucible and contents for 10 minutes. Allow to cool and reweigh. Step 3 Heat the crucible and residue for another 5 minutes. Allow to cool and weigh the crucible and residue. Repeat step 3 a further two times. The student‟s results are shown below: Mass of empty crucible/g 15.96 Mass of crucible + SrCl 2 •xH2O/g 18.65 First mass of crucible + residue/g 17.66 Second mass of crucible + residue/g 17.61 Third mass of crucible + residue/g 17.58 Fourth mass of crucible + residue/g 17.58 (i) Calculate the value of x in SrCl 2 •xH2O. Give your answer to 2 significant figures.

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Oxford Cambridge and RSA




OCS AS LEVEL
CHEMISTRY A 2023
VERSION 2 DEPTH IN
CHEMISTRY GRADED A+
GUARANTEED PASS
ANSWERS AT THE LAST PAGE



AS Level Chemistry A
H032/02 Depth in chemistry
Time allowed: 1 hour 30 minutes

You must have:
* 7 6 4 9 0 9 1 6 8 4 *




• the Data Sheet for Chemistry A
(sent with general stationery)
You may use:
• a scientific or graphical calculator

* H 0 3 2 0 2 *

, First name(s)

Last name


INSTRUCTIONS
• Use black ink. You may use an HB pencil for graphs and diagrams.
• Answer all the questions.
• Where appropriate, your answers should be supported with working. Marks may be
given for a correct method even if the answer is incorrect.
• Write your answer to each question in the space provided. If additional space is
required, you should use the lined page(s) at the end of this booklet. The question
number(s) must be clearly shown.

INFORMATION
• The total mark for this paper is 70.
• The marks for each question are shown in brackets [ ].
• Quality of extended responses will be assessed in questions marked with an
asterisk (*).
• This document consists of 20 pages.

,
, 2

Answer all the questions.

1 This question is about the properties and reactions of the Group 2 element strontium.

(a) The relative atomic mass of strontium can be determined using a mass spectrometer.

(i) Explain what is meant by the term relative atomic mass of an element.

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

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

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

...................................................................................................................................... [2]

(ii) A sample of strontium has a relative atomic mass of 87.73.

The sample consists of:
• 82.9% Sr-88
• 6.9% Sr-87
• one other isotope.

Determine the other isotope of strontium in the sample.




isotope of strontium = .......................................................... [2]




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