1 (a) (i) Electrostatic attraction between positive and negative ions
1 ALLOW oppositely charged ions
ALLOW cations and anions
ALLOW ‘+’ for
... [Show More] positive and ‘-‘ for negative
IGNORE references to metal and non-metal
IGNORE references to transfer of electrons
(ii)
Ba showed with either 0 or 8 electrons
AND
O is shown with 8 electrons with 6 dots and 2 crosses (or
vice versa)
Correct charges on both ions
2
For the first mark,
if eight electrons are shown around Ba, the ‘extra’
electrons around O must match the symbol chosen
for the electrons for Ba.
IGNORE inner shells
Circles not required
Brackets not required
(iii) FIRST CHECK THE ANSWER ON THE ANSWER LINE
IF answer = 5.89 1021 award 2 marks for calculation
Moles of barium oxide
n(BaO) =1.50/153.3 OR 9.78 10–3
Number of barium ions
(9.78 10–3
6.02 x 1023) = 5.89 1021
3 SF AND standard form required
2
ALLOW 0.00978 up to calculator value
0.009784735
ALLOW ECF from incorrect moles of BaO
Common incorrect answers are shown below
IF 137.3 is used for the molar mass ALLOW 1 mark
total for 6.58 x 1021 (0.010924981 mol) OR 6.56 x
1021 (0.0109 mol)
IF 153 is used for the molar mass ALLOW 1 mark
total for 5.90 1021
(b) (i) Barium chloride does not conduct electricity when solid
AND
2 IGNORE use of ‘free’ instead of ‘mobile’
ALLOW ions are not free to move
H032/02 Mark Scheme June 2017
7
Question Answer Marks Guidance
because it has ions which are fixed (in position/in lattice)
Barium chloride conducts when in aqueous solution
AND
because it has mobile ions
ALLOW ions are held (in position/in lattice)
ALLOW ions are not mobile
IGNORE charge carriers
DO NOT ALLOW electrons moving
ALLOW one mark for comparison that does not
identify (s) and (aq).
(ii) Test for sulfate/SO4
2–
White precipitate forms (when barium chloride solution is
mixed with a solution containing sulfate ions)
2 IGNORE hydrochloric acid
ALLOW white solid
IGNORE cloudily
DO NOT ALLOW test results linked to incorrect
anion
(iii) FIRST CHECK THE ANSWER ON THE ANSWER LINE
IF answer = 2 awards 2 marks
M(BaCl2) = ((137.3 + (35.5 2)) = 208.3 (g mol–1
)
244.3 – 208.3 = 36
AND
36/18 = 2
2
ALLOW 208 (g mol–1
)
ALLOW ECF for incorrectly calculated molar mass
provided the final answer is rounded to the nearest
whole number
(c) (i) (1s2
) 2s2 2p6
1 IGNORE 1s2 seen twice
ALLOW upper case letters AND subscripts
(ii) Products of reaction
A = Barium hydroxide/Ba(OH)2
B = Ammonia/NH3
The formula for barium nitride
Ba3N2
Balanced equation AND state symbols
Ba3N2(s) + 6H2O(l) 3Ba(OH)2(aq) + 2NH3(g)
State symbols are required
4 ANNOTATE ANSWER WITH TICKS AND
CROSSES ETC
ALLOW one mark for correct products incorrectly
labeled
Formulae must be correct
No ECF from any incorrect formula
ALLOW multiples
Correct equation with state symbols scores 4 marks
Total 16
H032/02 Mark scheme June 2017
8
Question Answer Marks Guidance
2* Please refer to marking instructions on page 5 of mark
scheme for guidance on how to mark this question.
Level 3 (5–6 marks)
All three scientific points are covered in detail and
explained thoroughly.
The method is logically structured and clear calculations
are shown for an appropriate mass of metal and suitable
volume of acid. The drawing of a tangent and
determination of the gradient is communicated well.
Level 2 (3–4 marks)
Candidates cover all three scientific points but
explanations may be incomplete.
OR
Two of the scientific points are described thoroughly with
no omissions.
There is a line of reasoning presented with some
structure. The information presented is relevant and
supported by some evidence. e.g. there are clear
calculations to justify mass and acid volume supported by
some working and units; a simple description for
determining initial rate related to tangent but no detail of
how to measure gradient.
Level 1 (1–2 marks)
6 Indicative scientific points
1. Method
measure the mass of (excess) zinc
(using 2 decimal place balance)
measure volume of hydrochloric acid
(using measuring cylinder)
mix zinc and acid in a flask
measure gas volume at time intervals
2. Calculations
moles of hydrogen
72/24000 = 0.00300 mol
the minimum mass of zinc
0.003 65.4 = 0.20 g
moles of hydrochloric acid
Zn + 2HCl ZnCl2 + H2
0.00300 2 = 0.00600 mol
volume/concentration of acid
If [HCl(aq)] = 0.1 mol dm–3
appropriate
volume of acid = 0.006 1000/0.1 = 60 cm3
If [HCl(aq)] ≥ 0.3 mol dm–3
, too low (≤ 20 cm3
)
If [HCl(aq)] ≤ 0.03 mol dm–3
too high (≥ 200 cm3
)
3. Processing results
Plot a graph of volume against time
Draw a tangent at t = 0
The gradient of tangent = initial rate [Show Less]