WESTMINSTER SCHOOL
THE CHALLENGE 2013
CHEMISTRY
Thursday 2 May 2013
Time allowed: 30 minutes
Please write in black or blue ink.
Write your answers in the spaces provided.
For examiner use only
Total
Mark
Blank Page
C1
This question is about separating mixtures.
Use one of the five techniques below to state the quickest way of separating the
following mixtures (each listed technique may be used once, more than once or not at
all).
Filtration
Dissolving
Evaporation
Chromatography
Fractional
Distillation
(i)
sugar & water
………………………………………………. (1)
(ii)
ethanol & sand
………………………………………………. (1)
(iii)
ethanol & propanone
………………………………………………. (1)
(iv)
sand & sugar
………………………………………………. (1)
(v)
water & calcium carbonate
………………………………………………. (1)
[Total: 5]
Please turn over
C2
This question is about identifying unknown substances.
A Westminster student has forgotten to label five bottles which contain the following
clear and colourless aqueous solutions;

water,

bicarbonate of soda [sodium hydrogen carbonate],

vinegar [ethanoic acid],

caustic soda [sodium hydroxide],

hydrochloric acid.
The student labels each of the unknown solutions with a letter A – E and performs a
series of simple test-tube experiments where he systematically adds one solution to
another. The results of the investigation are below.
A
B
C
D
E
A
B
C
D
E
X
Temperature
increases.
Solution B
goes from pH
1 to pH 13
No observable
change.
Solution C
goes from pH
11 to pH 12
Effervescence.
Solution C
goes from pH
11 to pH 1
Temperature
increases.
Solution D
goes from pH
5 to pH 13
No observable
change.
Solution D
goes from pH
5 to pH 1
Effervescence.
Solution D
goes from pH
5 to pH 10
Temperature
increases.
Solution A
goes from pH
13 to pH 1
No observable
change.
Solution A
goes from pH
13 to pH 12
Temperature
increases.
Solution A
goes from pH
13 to pH 5
No observable
change.
Solution A
goes from pH
13 to pH 12
X
Effervescence.
Solution B
goes from pH
1 to pH 12
No observable
change.
Solution B
goes from pH
1 to pH 2
No observable
change.
Solution B
goes from pH
1 to pH 2
Effervescence.
Solution C
goes from pH
11 to pH 5
X
No observable
change.
Solution E
goes from pH
7 to pH 13
No observable
change.
Solution E
goes from pH
7 to pH 1
No observable
change.
Solution E
goes from pH
7 to pH 10
No observable
change.
Solution E
goes from pH
7 to pH 5
No observable
change.
Solution C
goes from pH
10 to pH 9
No observable
change.
Solution D
goes from pH
5 to pH 6
X
X
(a) Identify each of the five substances.
A ………………………………………………………………………………………………. (1)
B ………………………………………………………………………………………………. (1)
C ………………………………………………………………………………………………. (1)
D ………………………………………………………………………………………………. (1)
E ……………………………………………………………………………………………….. (1)
(b) Write a word equation for the reaction taking place between solution B and solution
C.
……………………………………………………………………………………………….… (3)
[Total: 8]
Please turn over
C3
This question is about monitoring the rate of a chemical reaction.
A student investigating the rate of the chemical reaction between magnesium and an
excess of hydrochloric acid obtains the following results:
Time
0 10 20 30 40 50 60 70 80 90
/s
Volume of gas collected
0 18 30 40 48 53 57 58 58 58
/ cm3
(a) Write a word equation for the reaction taking place.
……………………………………………………………………………………………….… (2)
(b) Circle the word that best describes the pH of the solution after the reaction has
finished.
Acidic
Neutral
Alkaline
(1)
(c) Draw a labelled diagram to illustrate how you would perform the experiment.
(3)
(d) Using graph paper below plot a graph of the experimental data. Draw an
appropriate line or curve of best fit.
(2)
(e) At what time did the reaction finish?
……………………………………………………………………………………………….… (1)
Please turn over
(f) At what time was half of the magnesium used up?
……………………………………………………………………………………………….… (1)
(g) When was the reaction fastest?
……………………………………………………………………………………………….… (1)
(h) The student decides to repeat the experiment, this time increasing the temperature of
the solution to T2. On your graph on the previous page sketch the curve you would
expect to see. Label this curve T2.
(2)
(i) On the axes below sketch a graph of how the rate of this reaction would change with
time.
(1)
(j) The student doubled the concentration of the acid. What volume of gas would he
now collect?
……………………………………………………………………………………………….… (1)
[Total: 15]
C4
This question is about extracting metals from their ores.
‘Chromium is manufactured by heating chromium oxide with aluminium. Potassium
cannot be manufactured by displacement reactions with other metals, instead electricity
must be used to separate the element from its ore. If manganese is heated with
aluminium oxide there is no reaction. Chromium is alloyed with iron to make stainless
steel. In stainless steel the chromium reacts preferentially with oxygen and water in the
atmosphere preventing rust formation. If manganese is heated with chromium oxide,
chromium is produced.’
List the five metals mentioned in the paragraph above in order of their reactivity.
…………………………………
Most reactive
…………………………………
…………………………………
…………………………………
…………………………………
Least reactive
[Total: 5]
[Total marks for this section: 33]