Question three (third mandatory experiment)
Benzoic acid is much less soluble (insoluble) in
cold water so it comes (crystallises) out of
solution (2 × 3)
(e) DRYING; dry in warm oven (3)
Experiment
Flame tests (Li, Na, K, Ba,
Sr, Cu)
Recrystallisation of benzoic
acid
Tests for anions
Determination of relative
molecular mass of a volatile
liquid
Redox reactions of Group 7
elements
Hydrogen peroxide
decomposition
Study of effects of temp
and concentration on rate
Simple experiments on
equilibrium
Determination of total
suspended solids
Estimation of free chlorine
in water
Heat of neutralisation
Years
Year
2009
2011
2004
2009
2003
(f) DESCRIBE:
 Sample in melting point tube
 Mp tube strapped to thermometer
 Thermometer in melting block
 Heat block
 Note temperature range over which (or
temp at which) it melts (4 × 3)
DIFFER:
Impure lower m.p. and a wider melting point
range (2 × 3)
2008
2005
(g) USE: food preservative / disinfectant (6)
2010,
2002
2010
(a) IDENTIFY: Sulfur / S (5)
2006
2007
QUESTION 3
2011
(a) STAGE 1: crystals in minimum of hot water
(solvent) (5)
(b)
(i) charcoal (3)
(ii) pure (purified, recrystallized) benzoic acid
(3)
(c) STAGE 3: further cooling (place flask in
ice-water) / evaporate some more water (6)
(d) COMPARE:
Both substances soluble in hot water
(b)
DESCRIBE:
 Measure (take) 30 cm3 of the 0.20 M
thiosulfate solution

Dilute (make up) to 50 cm3
 Using deionised water (3 × 3)
(c) WHY: So that only one variable is changed
(6)
(d)
PLOT:
Correctly labelled (3)
Scaled axes (3)
All points plotted (3)
Straight line drawn (3)
CONCLUSION: Rate proportional to
concentration (6)
(3) BALANCING (3)
WHAT:
ppt dissolved => Na2SO3.
ppt undissolved => Na2SO4
(f)
SUGGEST:
add dilute acid (3)
carbon dioxide evolved (3)
(e) USE: 2.30 ± 0.05 (6)
2008
(f) WOULD: Decrease (3)
JUSTIFY: Reaction rate increases with
temperature because there are more collisions
reaching activation energy and the collisions
are more effective. (3)
(a) DRAW:
2009
(a)
DESCRIBE:
 Introduce salt into the flame of a
bunsen burner (2)
 Using soaked (dipped) splint (3)
 Sodium (Na) gives orange (yellow) flame
(3)
 Potassium (K) gives lilac flame (3)
Circle (ball, sphere, ring) with flames rising (5)
(b)
WHICH: KCl (potassium chloride) (3)
WHAT: white precipitate soluble in ammonia
solution (3)
(b)
WRITE:
2H2O2 → 2H2O + O2
FORMULAS: (3) BALANCING: (3)
(c) DRAW:
Apparatus with hydrogen peroxide and catalyst
separate (3)
Arrangement for mixing at a precise time (6)
(c)
OTHER:
Iron(II) sulfate solution (3)
WHICH: KNO3 / potassium nitrate (3)
(d) DESCRIBE:
To salt solution add ammonium molybdate
solution (3)
and a few drops of concentrated nitric acid
and warm gently (3)
yellow precipitate (ppt) formed (3)
(e) WRITE:
Na2SO3+ BaCl2 → BaSO3 + 2NaCl
Na2SO4+ BaCl2 →BaSO4 + 2NaCl
Suitable method of monitoring rate shown on
diagram {graduated cylinder over water} (3)
(d)
PLOT: see sample graph overleaf
 Axes accurately labelled with numbers
 Axes with correctly labelled units
 Eight points accurately plotted
 Curve accurately drawn from origin
(4 x 3)
2007
EXPLAIN:
Greatest rate because of the highest
concentration of H2O2 molecules and most
collisions (3)
(e)
(i) See graph below
4.0 – 6.0 cm3 min–1 (from correctly drawn
tangent) (6)
(a)WHAT: corrosive (4)
STATE: protective clothing (gloves, lab. coat)
(4)
(b) WHICH: burette (3)
(c) EXPLAIN: get average (mean) temperatures
of the two solutions or wait until both solutions
at same (room) temperature (6)
(d) LIST:
 Thermometer to 0.2o C or better
 Replace cover quickly (immediately)
 Stir constantly
 Prevent heat loss ANY THREE: (3 × 3)
(ii) 78 ÷ 1000 ÷ 24 = 0.00325 mol (3)
× 32 = 0.104 (3)
(e) WHAT: polystyrene a good insulator (3)
(f) CALCULATE:
50/1000 x 1 = 0.05 (6)
TAKING: 2814 J / 2.814 kJ (6)
420 x 6.7 (3) = 2814 (3)
HENCE:
2.814/0.05 = – 56.28 kJmol-1 (6)
(g) NAME: bomb calorimeter (3)
2006
(a) WHAT: intensity of colour ( absorbance) is
directly proportional to concentration (2 × 4)
(b) IDENTIFY: acidified potassium iodide or
DPD1 tablet. (3)
COLOUR: For iodide: brown/red
For DPD: red/pink (3)
Comparator method




Add reagent to sample (3)
Colour develops (3)
Compare with chart ( (3)
Best match gives concentration (3)
(d) SPECIES: chlorine (Cl2) (6)
(f) WHAT: rise less steep (3)
GIVE: need for greater conc. of chlorine in
swimming pool water to kill pathogens (harmful
bacteria, harmful micro-organisms) added by
swimmers (3)
Half the final volume (3)
(e)
(i)
2004
Note: changes may be shown on the candidate’s
graph paper or through a suitable sketch.
(a)
(i) so that crystals will form on cooling,
to maximise yield (5)
(ii) insoluble: filtration of hot solution (3)
remained on filter paper (in funnel) / not able
to pass through (3)
soluble: filtration of recrystallised benzoic
acid (cold filtration) (3)
passed through filter paper (funnel) (3)
(ii)
2005
(a) EQUATION:
2H2O2 → O2 + 2H2O
(b) DRAW:
 Reaction vessel with hydrogen peroxide
and catalyst (3)
 Catalyst in neck of horizontal flask.
 Bring flask to vertical and start clock
(3)


Delivery tube connected to gas
collection system (3)
Clear method of measuring (e.g.
inverted graduated cylinder) (3)
(c) WHICH: finely (3)
REASON: greater surface area available (3)
(d) GRAPH:
Labelled and scaled axes (3)
Points plotted correctly (6)
Curve drawn [has to be drawn to (0, 0)] (3)
Note: the (6) for points plotted correctly not
given if graph paper not used.
(e) USE:
3
(i): 26.5 – 28.5 cm (3)
3
(ii): 6.0 – 8.0 cm min
–1
(6)
(iii)Let solution cool fully (efficiently) / cool in
ice-water (crushed ice) (3)
(iv)Leave in oven at 100 oC (3)
(v)
(b)
(i)
Correct diagram with instrument for
measuring temperature including one
valid label (6)
 Detail of setting up
 Sample in melting point tube for melting
point apparatus [Stated or labelled in
diagram]
 method of heating *
 Bunsen (hotplate) for aluminium block
[Can be got if shown on diagram – even
if unlabelled]
 Heat slowly (gently)*
 Observe the substance as it is heated*
 Note temperature (range) at which it
melts
DIAGRAM (6) + 3X3
* Accept only two from these three points

(ii)
Lower (3)
Melting over wider range of temperatures (3)
(iii) Preservative / disinfectant (antiseptic,
biocide, fungicide) (3)
2003
(a) Easily vaporised (5)
(b)
Method
Diagram:
 Flask, sealed (covered) with foil with
small hole (pinhole)* , immersed so that
at least half is under water. (* Label
required: any one correct label). (3)
Mass:
 Get mass of flask and foil (3) [add
liquid and arrange as in diagram]
 Heat until flask appears empty (3)
 Cool (dry) and reweigh (3)
 Get mass of sample by subtraction (3)
Volume:
 Fill flask and empty into graduated
(measuring) cylinder (3)
Temperature:
 Use thermometer to read temperature
of water. (3)
(c) Barometer (6)
(d)
(e)
2002
(a) IDENTIFY: sulfur (5)
(b) PREPARING:
Use burette (3)
To measure 80 cm3 of 0.1 M soln (3)
Make up with deionised (distilled) water* (3) to
100** cm3 (3)
(c)
PLOT:
 Axes correct and correctly labelled (3,
3)
 Points correctly plotted (3) [not given if
graph paper not used]
 Correct straight line shown passing
through origin (3)
CONCLUSION:
Rate directly proportional to the concentration
(6)
[Accept increased conc gives increased rate
for 3 marks]
(d)
HOW LONG:
Rate from graph = 0.4 (3)
1/t = 0.4 (3)
t = 2.5 (3)]
(e)
EXPLAIN: rate and time inversely related (6)