A-level Chemistry aqa paper 1 practice

This question is about a titration.
1.
A student dissolves an unknown mass of sodium hydroxide in water to make 200 cm3 of an
aqueous solution.

A 25.0 cm3 sample of this sodium hydroxide solution is placed in a conical flask and is titrated
with 0.150 mol dm–3 sulfuric acid.

The equation for this reaction is shown.


2 NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2 H2O(l)

The table shows the results of the titrations.


Titration Rough 1 2 3

Final reading / cm3 20.75 40.35 21.05 40.60

Initial reading / cm3 0.00 20.75 1.20 21.05

Titre / cm3 20.75 19.60 19.85 19.55


(a) Calculate the mass of sodium hydroxide used to make the original solution.




Mass of sodium hydroxide _______________ g
(5)




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, (b) The student uses a funnel to fill the burette with sulfuric acid before starting the titration.
After filling, the student forgets to remove the funnel from the top of the burette.

Suggest why this might affect the titre volume recorded.

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(1)

(c) State one advantage of using a conical flask rather than a beaker for the titration.

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(Total 7 marks)

This question is about time of flight (TOF) mass spectrometry.
2.
(a) Define the term relative atomic mass.

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(2)




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,(b) A sample of krypton is ionised using electron impact.

The mass spectrum of this sample of krypton has four peaks.

The table shows data from this spectrum.


m/z 82 83 84 86

Relative intensity 6 1 28 8


Calculate the relative atomic mass (Ar) of this sample of krypton.

Give your answer to 1 decimal place.




Ar _______________
(2)

(c) In a TOF mass spectrometer, ions are accelerated to the same kinetic energy (KE).

The kinetic energy of an ion is given by the equation

Where:
KE = kinetic energy / J
m = mass / kg
v = speed / m s–1

In a TOF mass spectrometer, each 84Kr+ ion is accelerated to a kinetic energy of
4.83 × 10−16 J and the time of flight is 1.72 × 10−5 s




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, Calculate the length, in metres, of the TOF flight tube.

The Avogadro constant, L = 6.022 × 1023 mol−1




Length of flight tube _______________ m
(4)
(Total 8 marks)

This question is about Group 7 elements and their compounds.
3.
(a) Chlorine is used to treat water even though it is toxic to humans.

Give one reason why water is treated with chlorine.

Explain why chlorine is added to water even though it is toxic.

Give an equation for the reaction of chlorine with cold water.

Reason ____________________________________________________________

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Explanation _________________________________________________________

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Equation

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(3)




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