Download IGCSE Revision Question Booklet Mark Scheme

Barnard Castle School
Chemistry Department
iGCSE Chemistry
Revision
Questions
MARK SCHEME
1.
(a)
He
(b)
carbon / silicon / germanium /
tin / lead
accept correctly written symbols
C / Si / Ge / Sn / Pb
(c)
1
copper
1
1
accept Cu
(d)
iodine
1
accept I or I2
[4]
2.
(a)
(b)
(i)
argon and potassium or
tellurium and iodine or
cobalt and nickel
accept correct symbols
allow argon and calcium
1
(ii)
it would place them in incorrect groups (owtte)
idea of not being placed with elements which have
similar properties or converse argument
accept would not have same number of electrons in
outer shell
allow it would put them in wrong period if linked to
argon and potassium / calcium
do not accept reasons based just on protons
do not accept metals and non-metals mixed up
1
any two from:
2
 each successive atom has one more electron
 atoms in the same group have the same number of electrons
in their outer shells / energy levels
number of electrons in outer shell = group number
 across a period an energy level / shell is being filled
 in the next period the next energy level / shell is being filled
accept period number = shell number
[4]
3.
(a)
2
Calcium
chloride
Lithium
sulphate
Potassium
carbonate
Sodium
nitrate
Add barium chloride
solution and dilute
hydrochloric acid.
A white precipitate
formed.
Do the flame test.
Yellow flame
produced.
Add silver nitrate
solution and dilute
nitric acid.
A white precipitate
formed.
Add hydrochloric
acid.
Carbon dioxide gas
given off.
all three correct = 2
one or two correct = 1
(b)
blue
1
precipitate
1
solid
(c)
(i)
any one from:
1
• mass spectrometry / spectroscopy
• atomic (absorption) spectrometry
• flame photometry
• infra-red spectroscopy
• ultra violet spectroscopy
• chromatography
(any valid method)
(ii)
any one from:
1
• rapid
• sensitive
• accurate
• small amounts
• easily automated
• easily computerised
(any valid)
[6]
4.
(a)
pipette / burette
1
(b)
named indicator
eg methyl orange / phenolphthalein
not universal
accept litmus but not litmus paper
1
(c)
25  0.4
1000
1
2 for correct answer
= 0.011
(d)
1KOH  1 HCl
1
 0.01 moles HCl in 35 cm3

0.01  1000
= 0.29
35
2 for correct answer
0.3 = (1)
(with correct working = (2))
1
[6]
5.
(a)
25 (cm3)
1
(b)
strong alkali
1
(c)
burette
1
plus any sensible reason:
1
eg
●
more accurate
●
smaller divisions
●
tap allows better control
etc
[4]
6.
(a)
 water
(allow acid*)
3
 (metal) hydroxide (solution)/alkali
(allow metal salt / compound)
 hydrogen
(allow hydrogen)
for 1 mark each
(*if named acid then matching salt)
or
but
(b)
 oxygen / chlorine / halogen
 for 1 mark
 oxide / chloride / halide
gains 1 mark
 named oxide(s)
gains 2 marks
(accept fully correct formulae throughout)
idea that
 hydrogen and iodine would only react if heated to > 200°C / a
high temperature (ignore reference to light / dark)
 reactivity decreases down the Group / iodine is lower in the Group
than
bromine / iodine is the lowest in the Group
2
(or converse N.B. credit this idea here even if given in (d))
for 1 mark each
½H2 + ½ Cl2  HCl
(c)
H2 + Cl2  2HCl or
for 1 mark
(d)
idea that (or converse)
 in atoms lower down the Group the electrons in the outer shell /
highest energy level (of electrons) are further from the nucleus
or
shielded by more (inner) shells / electrons
[but not simply “more electrons”]
or
1
2
are less strongly attracted to the nucleus
 so an electron is less easily gained
for 1 mark each
[8]
7.
add aluminium/Devarda’s alloy
1
gas turns litmus blue
1
ammonia evolved
1
(b)
any valid method for compounds
-infra-red spectroscopy
-ultra violet spectroscopy
-mass spectroscopy
-gas liquid chromatography
-high pressure liquid chromatography
-any other valid method
do not accept abbreviations
1
(c)
any valid answer
-electronics
-computers
-fibre optics
-magnetometry
linked to some idea how it has helped
ie, smaller, greater sensitivity, ease of operation/automation, greater
versatility.
1 mark for technology, 1 mark for its effect.
2
(a)
[6]
( 1
)
2
D
3
B
( 4
5
8.
(a)
)
A
( 6
7
)
4
C
or outside boxes or in line in order
1 mark for each of 4 correct
(b)
the substance has disappeared/no bits/no lumps
(the liquid) is clear
(the liquid) is the same all the way through
any 2 for 1 mark each
2
[6]
9.
(a)
(i)
not fully ionised / dissociated or partially ionised
accept weak acids produce fewer H+ if equal
concentration or equal amounts of acid specified
do not accept just weakly ionised
1
(ii)
Test: Universal Indicator / pH indicator/ full range indicator
do not accept other indicators
1
Result: e.g. stronger is a darker red or
weaker is orange, yellow, paler red etc.
or correct pH numbers < 7
accept redder
accept pink for paler red
do not accept green
1
or
pH meter (1)
result linked
correct pH values (1)
or
Test: Mg / Zn / Fe / Sn or a carbonate/
hydrogencarbonate (1)
Any suitable test but not titration
Result: e.g. stronger is quicker / faster rate /
more bubbles / more gas / more correctly named gas (1)
(b)
Quality of Written Communication
The answer to this question requires ideas in good English in a sensible order
with correct use of scientific terms. Quality of written communication should
be considered in crediting points in the mark scheme.
maximum 2 marks if ideas not well expressed
acids produce hydrogen ions
1
acids are proton donors
1
Link: hydrogen ions (Arrhenius) and protons (Bronsted-Lowry)
1
[6]
10.
(a)
yellow / yellow orange orange
1
(b)
(i)
zinc carbonate
1
(ii)
copper bromide
1
(iii)
magnesium sulphate
1
(c)
(white) precipitate / solid
do not accept cloudy or milky
do not accept residue
green precipitate = 0
1
[5]
11.
lower water heating costs
1
reduce soap used / no scum
not no blocked showers
1
less maintenance / use of plumber / don’t need to buy new heater or shower /
no descaling needed (pipes or showers) / no cleaning of blocked pipes
1
[3]
12.
(a)
light or caloric or beat
(b)
(i)
any one from
1
max 1
lime
magnesia
barytes
argilla
silex
accept chemical names or correct formula
(ii)
(c)
no methods available at that time to
split the compounds into elements
accept unable to split up (the substance)
any two from
1
max 2
(Mendeleev’s table.)
contains only elements
divides metals and non-metals
contains far more elements which were discovered later
groups elements according to properties
puts elements in order of atomic number
or atomic mass or table includes these numbers
can use it to work out or is linked to electronic structures
left gaps for missing elements which had not been discovered
[5]
13.
(a)
(b)
(i)
calcium
1
(ii)
oxygen
1
(iii)
nitrate
1
Quality of written communication
for correct linking of ideas
1
answers based on evaporation
e.g. sun evaporates water
1
answers based on condensation to form water or rain
e.g. clouds rise and cool
starting point of description does not have to start
with evaporation
1
(c)
(i)
nitrate at 34 mg/l on bar chart
1
(ii)
(dissolve) carbon dioxide / CO2
1
pressure
1
[9]
14.(a) ideas that
 hydrogen is in a group / is with the halogens
 only seven groups / no group O / no noble gases / fewer elements
 halogens are in the first group / Group 1
 other elements are in one group higher (or example)
 modern table only has two elements in the top row / period
 modern table not in order of atomic weight/mass
 metals and non-metals not at opposite ends
3
(NB allow converse answers throughout)
any three for 1 mark each
(b)
ideas that
 all rows / periods are the same length / have seven elements
 all elements had to be in one of the groups
 he didn’t know about the noble gases / not all the elements had been
discovered
 he didn’t know about atomic/proton number/electron structure
 he arranged elements in order of atomic weight/mass
any one for 1 mark
1
(c)
(i)
ideas that
tellurium and iodine are in reverse order
for 1 mark
1
(ii)
elements are arranged in order of proton (atomic) number
or based on electron structure/outer shell electrons
(so tellurium is correctly placed before iodine)
[tellurium = ‘dead mark’]
each for 1 mark
2
[7]
15.
(a)
(i) liquid
1
allow l
(ii) solid
1
allow s
allow responses written in table
(b)
fluorine
1
accept F, reject fluoride
(c)
hydrogen bromide
reject hydrogen bromine
accept HBr/BrH
1
allow responses written in table
[4]
16.
(i)
Bonds broken
4 × (C - H)
2 × (O = O)
each for 1 mark
4
Bonds formed
2 × (C = O)
4 × (O - H)
each for 1 mark
(ii)
Total energy change in breaking bonds
(4 × 413) + (2 × 498)
each gains 1 mark
4
Total energy change in forming bonds
(2 × 805) + (4 × 464)
but
to break bonds = 2648
to form bonds = 3466
each gains 2 marks
(iii)
nett energy transfer = 818 (kj)
this energy is released in the reaction/is an exothermic reaction
(credit answers consistent with (ii) or derived
from the initial information)
each for 1 mark
2
[10]
17.
(a)
(b)
acidic
1
reacts
1
hard
1
tastes
1
(i)
scum / no lather / precipitate
1
(ii)
rain water is soft / pure / nothing dissolved
/ no limestone
not distilled
1
(iii)
lake water is hard / not soft / contains calcium compounds /
dissolved limestone
not impurities
1
(iv)
softened by boiling / loses hardness
1
temporary hardness removed /
decomposition of calcium salts
1
[9]
18.
(a)
2.8.2. magnesium or 2.8.8.2. calcium
inner shell (2)
outer shell (2)
intermediate shell/s correct
element named to match structure
each for 1 mark
(Structure correct for element name but not in group
2,award 2 marks)
4
(b)
Similar
hydrogen and/or an alkali/hydroxide produced
for 1 mark
5
Reasons:
chemical reaction involves loss of an electron
Na + Li have the same number of electrons in the outer shell
(do not allow same group of p.table)
each for 1 mark
Different
rate of reaction faster for sodium*
for 1 mark
Reason:
outer electron more easily lost from the sodium atom
[* allow sodium hydroxide produced]
for 1 mark
[9]
19.
any series of chemical tests that
work should be given credit
identifying all four substances
unambiguously with no errors gains
6 marks
eg
flame test: yellow / orange means
sodium ions so sodium sulfate
ignore incorrect flame test colours for other
compounds
1
add NaOH to remaining three samples
1
no (white) ppt / ammonia means
ammonium ion so ammonium sulfate
(damp red) litmus* goes blue means ammonium
sulfate
* or UI / pH indicator goes blue / purple
1
1
(white) ppt means magnesium ions
/ magnesium ions
1
add excess NaOH to the two
samples which gave a (white) ppt:
1
ppt dissolves then aluminium sulfate
ppt insoluble means magnesium sulfate
or
add NaOH:
no ppt: ammonia produced means
ammonium sulfate
the other one with no ppt is sodium sulfate
add excess NaOH to the two
samples which gave the white ppt
ppt dissolves then aluminium sulfate
ppt insoluble then magnesium sulfate
[6]
20.
(a)
sodium carbonate / sodium
hydrogencarbonate / sodium
bicarbonate
Na2CO3 / NaHCO3
ie
sodium / sodium ions (1 mark)
carbonate / carbonate ions
(1 mark)
incorrect formula including Na and
CO3 = 1 mark
2
(b)
calcium chloride
CaCl2
2
ie
calcium / calcium ions (1 mark)
chloride / chloride ions (1 mark)
incorrect formula including Ca and Cl = 1 mark
(c)
iron or iron(II) ions
Fe2+
ferrous ions
ignore anions
ignore nickel / chromium
do not accept iron(III) or ferric ions5
1
[5]
21.
(a)
(i)
to remove solids
1
(ii)
to kill germs / bacteria / microbes etc
1
(i)
any two from:
2
(ii)
●
check for dissolved minerals
●
check for microbes
●
which could be harmful to health
any two sensible answers such as:
●
monitor continuously
●
record results
●
immediate graphical display
●
take samples automatically
2
etc
(c)
cost of fuel / heat etc
1
(d)
(i)
calcium / magnesium
accept symbols
1
(ii)
produces scale (owtte)
1
reduces efficiency / blocks pipes etc
1
(iii)
any sensible reason eg good for health
1
[11]
22.
ideas that
 x = the energy required / taken in / used* to break the bonds of
water / reactant [*not used up / formed]
gains 1 mark

but
= the energy required taken in / used to break the bonds in
water or activation energy
gains 2 marks
 y = the energy released given out when bonds form
gains 1 mark
 but
= the energy released / given out when hydrogen / oxygen form
gains 2 marks

 z = 1856 - 1370 or (+)486 kJ
for 1 mark
or difference between x and y
or net energy transferred
 overall, energy is taken in / absorbed in the reaction
or
the reaction is endothermic
or
energy required to break existing bonds is > energy released when new
bonds form
for 1 mark
[6]
23.
(a)
any four from
max 4
sulphuric acid measured by pipette
accept diagram
potassium hydroxide in burette
accept diagram
if solutions reversed award 1 mark
note initial reading
use of indicator
note final reading or amount used
(b)
34 2
1000
= 0.068
2
award full marks for correct
answer with no working
(c)
1
0.5 moles H2SO4 reacts with 1 mole
KOH
1
moles H2SO4 in 25.0 cm3
= 0.068 × 0.5
1
moles H2SO4 in 1 dm3

0.068  0.5  1000
25
1
= 1.36 mol dm–3
[9]
24.
(a)
calcium
1
allow formulae
carbonate
(b)
(i)
1
soap
1
allow 2 marks for
“contains CaSO4 / Ca(HCO3)2 / Ca2+ / Mg2+”
(ii)
(c)
forms scum / no bubbles / no lather
allow 1 mark for “contains Ca / Mg”
do not allow “contains CaCO3”
1
taste / strengthen bones, teeth etc /
health reason e.g. less heart disease /
makes better beer
1
(shake with) soap; makes scum / no lather
1
boil (a fresh sample)
1
retest with soap
1
result/comparison
1
alternative answers:
boil (not to dryness)
cloudiness in water/some deposit formed
if a comparison is made with a sample of a soft
water, a further 2 marks would be possible
(d)
ion-exchange
1
[10]
25.
(a)
(i)
e.g. moles NaOH = moles of acid
or formula:
0.2 ×
45
= 0.009
1000
15M1 = 0.2 × 45
1
rounding to 0.01 loses mark
1000
= 0.6(M)
15
M1 = 0.6(M)
= 0.009 ×
1
ecf for arithmetical error
correct answer 2 marks
(ii)
36
2
ecf – (a)(i) × 60
correct answer 2 marks
0.6 × 60 gets 1 mark
relative formula mass of ethanoic acid
= 60 for 1 mark
0.6 × incorrect molar mass gains second mark only
(b)
(i)
(iii)
(iv)
A = hydrogen / H2
1
B = sodium hydroxide / NaOH or
sodium oxide / Na2O
1
C = ethyl ethanoate (acetate) /
CH3COOC2H5 / CH3CO2C2H5
1
D = (concentrated) sulphuric acid /
H2SO4
do not accept dilute sulphuric acid
E = sodium ethanoate (acetate) /
CH3COONa / CH3CO2Na
1
1
[9]
26.
(a)
breaking of C-H bonds
breaking of O-O bonds
making of C-O bonds
for 1 mark each
4
making of H-O bonds
(b)
X
energy needed to break bonds
has to be supplied/activation energy
Y
energy released when bonds form
Z
= Y-X
overall, energy is released/reaction is exothermic
each for 1 mark
5
[9]
27.
(a)
Mendeleev arranged known elements in order of mass or properties
reject explanation in terms of electrons
and / or atomic number
1
gaps in Periodic Table / group 1
1
(b)
does not last long enough to experiment / very little of it
allow it has a short half-life
1
(c)
(i)
(much) more violent
accept more reactive
1
(ii)
since outer electron / or shell further from nucleus
do not credit lower down group
larger / more shells neutral
1
therefore more easily lost
accept screening by inner electrons
1
[6]
28.
(a)
Group 2 / Alkaline Earth Metals
for 1 mark
1
(b)
(i)
MgCl2/Mg2+ (Cl–)2
(or equation with correct answer)
for 1 mark
1
(ii)
ionic / electrovalent
1
for 1 mark
[3]
29.
(a)
evidence of Fe = 56, O = 16
gains 1 mark
3
but
(56 × 2) + (16 × 3)
gains 2 marks
but
160
gains 3 marks
(b)
evidence of 112*/160
gains 1 mark
2
but
70*
gains 2 marks
* (credit answers consistent with part (a))
[5]
30.
(a)
positive
1
for 1 mark
(b)
any reference to loss of electrons
for 1 mark
2
reference to charge being +2 (in (a))
or to loss of 2 electrons (in (b))
for 1 mark
[3]
31.
(a)
Idea that
5
the electrons do not belong to specific atoms/delocalised electrons
[credit if done on appropriate diagram]
metal atoms form positive ions
the attraction which exists between particles with opposite charges, holds the metal
together
no specific bonds exist between adjacent atoms/ions
atoms/ions can slide over each other so allowing metals to bend
each for 1 mark
(b)
some electrons in the structure are delocalised/free to move
for 1 mark
4
these free electrons carry the electric current
for 1 mark
from left to right across the period, atoms of elements have
more free electrons
gains 1 mark
but
from left to right across the period, atoms of elements have more free
electrons because they have more electrons in the outer shells
gains 2 marks
[9]
32.
(a)
(i)
are identical / the same
or have the same number of protons /
the same proton number / electrons
not similar
1
(ii)
any two of
2
low melting point
low boiling point
brittle (solid)
do not credit just solid
poor conductor of heat
or heat insulator
poor conductor of electricity
or electrical insulator
accept just poor / low conductor or
just insulator once only
dull surface
or not shiny
cannot be hammered / bent (into shape)
or not malleable
cannot be stretched (into shape)
or not ductile
does not make a clanging
sound (when struck)
or not sonorous
acidic oxides
low density
(b)
copper
1
iron
1
correct symbols
(c)
zinc
1
can be bent (easily)
or malleable
or can be joined easily
do not credit just can be joined
2
not reactive
or does not corrode
or does not react (with hot water)
accept does not rust
(d)
(i)
chlorine
do not credit chloride
1
(ii)
one / 1
same number / amount
1
[10]
33.
(i)
electrons
1
for 1 mark
(ii)
covalent
1
for 1 mark
(iii)
made of small molecules:
usually gas or liquid
) dependent on
have low melting points ) having first
have low boiling points ) point above
forces between molecules are weak
any 1 for 1 mark
3
[5]
34.
(a)
Quality of written communication: All scientific words used correctly
(covalent, bonds, atoms)
1
any two from
2

large numbers of covalent bonds
allow giant lattice / structure

between atoms
do not accept between molecules

(covalent) bonds strong
accept need much energy to break
(b)
W
X
C
Y
(c)
Z
each carbon has 4 electrons
one shared pair
four shared pairs
1
1
1
Cu2+ + 2e–  Cu
this answer only
1
[7]
35.
(a)
(b)
(i)
40 + 12 + 48
1
= 100
1
(ii)
carbon dioxide
must be name
1
(i)
suitable line - narrow neat single
curve not dot to dot
points all correct 2 marks
one point incorrect 1 mark
two points incorrect 0 marks
(ii)
reaction with X forms less gas
must include X or Y
do not penalise for H2 / O2 if (a)(ii) already
penalised
do not accept is finished in less time or slower/faster
reaction or lower on graph
(iii)
concentration (of acid)
decreases or less reacting
particles or molecules
not strength of acid decreases
not acid/CaCO3 runs out/is used up
2
1
1
max 2
surface area of calcium carbonate decreases
less collisions between reacting particles
not smaller (amount of) CaCO3
[9]
36.
(a)
Mg + 2H+  Mg2+ + H2
* reactants correct in every detail
* products correct in every detail
if the spectator ions are sown then (1) mark should
be credited but only if they are shown correctly on
both sides
e.g.
Mg + 2H+ + 2CI-  Mg2+ + 2CI- + H2
2
(b)
24 (parts) of magnesium  2 (parts)
of hydrogen or equally clear working
(so) 6 grams/g (are needed)
unit required
1
1
(c)
(i)
1
two (and no more) atoms shown to be
sharing their single electrons
examples
do not credit if anything which contradicts the
impression that these are hydrogen atoms
H
H
H H
H H
H H
H H
Electron
e
e
Proton
(ii)
(d)
Electron
e
e
Nucleus
(single) covalent (bond)
2
(×100)
34
1
1
=6
(just 6 is worth (1) mark)
2
× 100 = 6 or similar is (0)
32
do not credit 5.8823529 and the like
1
[8]
37.
(a)
Zn + 2HC 1  ZnC12 + H2
1
(b)
(i)
12.5
1
(ii)
steeper curve
same volume of gas evolved
do not credit two intersects of straight lines
accept a sharp bend
2
(iii)
any two from:
2
stir it
accept mix it better
heat it
accept warm it
use a more finely divided catalyst
accept use a better catalyst or more finely divided
zinc
do not credit use acid of a higher
(c)
(i)
any one from
1
zinc is more reactive than copper
accept zinc is above copper in the reactivity series
zinc displaces copper
accept it is higher than copper in the reactivity
series
(ii)
zinc + copper sulphate  copper + zinc sulphate
ignore the presence of acid or water
accept a balanced equation
1
[8]
37.
(i)
two
1
or 2
(ii)
magnesium and
chloride
either order
not positive / negative
do not credit’chlorine’
1
accept Mg++ and Cl
do not credit just Mg and Cl–
accept cation(s) and anion(s)
(iii)
2
(iv)
electrons
1
1
accept charges
(v)
any three from

(is a) giant structure/lattice structure

crystalline / hard
accept just 'crystals(s)’

high melting point / solid

high boiling point

conductor (of electricity)
when dissolved in water
or conductor (of electricity) when ions are free to
move

conductor (of electricity)
when molten

soluble in water
3
[7]
38.
(a)
(b)
proton
+ (1)
both required
neutron
1
both required
electron
 (1)
both required
2.8.3
3
1
accept words or diagram to this effect
(c)
(d)
(i)
24
1
(ii)
52
1
any one of
1
 gains one or more electrons
accept gains an electron
 becomes an anion
do not credit becomes an ion
 becomes a negative ion
(e)
sodium ions have a (single) positive
charge and chloride ions have a
1
(single) negative charge
do not credit ‘chlorine ions’ but
allow this error to be carried forward
ions with opposite charge are
attracted (to each other)
or the positive ions and the negative ions are
attracted (to each other)
or the sodium ions and the chloride ions are
attracted (to each other)
1
(positive and negative) ions are
arranged alternatively (in each
direction or dimension)
or ions with the same charge are repelled (by each
other) no mark for just ionic bonds
1
[10]
39.
(a)
Mg S O4
24 + 32 + 16 ( 4) or 64 / evidence of all Ar’s
gains 1 mark
2
but (Mr) = 120
gains 2 marks
(b)
evidence that
24(g) magnesium would produce 120(g) mapesiurn sulphate
gains 1 mark
2
or correct scaling by 1/6
but
20(g) magnesium sulphate
gains 2 marks
[credit error carried forward from (a) with full
marks in (b)]
[4]
40.
(a)
(i)
high temperature
accept temperature given if  400°C
ignore value if “high” stated, unless silly value
endothermic or reaction takes in energy
1
(ii)
or  H is +ve
independent marks
1
low pressure
or up to and including 10 atmospheres
1
(low pressure) favours a reaction in which
more molecules are formed
2 moles  4 moles
(2 molecules  4 molecules)
independent marks
(b)
1
(iii)
nickel and it is a transition / transitional
element / metal (owtte) or nickel and
variable oxidation state / number or it is
similar to other named transition elements
e.g. iron
1
(i)
(bonds broken =) 2005 (kJ)
1
(bonds formed =) 2046 (kJ)
1
energy change =
2005 – 2046 = (–)41
for correct subtraction ignore sign
1
(ii)
(exothermic)
if in part (b)(i) answer is not 41
answer is consequential on endothermic or
exothermic shown
accept correct reasoning for incorrect answer from
(b)(i)
energy given out forming new bonds
do not accept energy needed to form new bonds
1
greater than energy put in to break old bonds
accept exothermic and more energy given out than
taken in for 1 mark
accept negative value for energy change or energy
in products less than energy in reactants for 1 mark
1
[10]
41.
(a)
correct representation of 1 atom
of hydrogen e.g.
2
H
gains 1 mark
but
correct representation of 1 molecule
of hydrogen e.g. or H-H
H
H
gains 2 marks
(b)
idea that:
hydrogen/metals form positive ions/lose electrons
gains 1 mark
4
but
hydrogen and the metals form positive ions/lose electrons
gains 2 marks
hydrogen/non-metals form covalent bonds/share electrons
gains 1 mark
but
hydrogen and the non-metals form covalent bonds/share electrons
gains 2 marks
[6]
42.
(a)
electrons
neutrons
protons
3
for 1 mark each
(b)
mass number
no. of neutrons
14
8
for 1 mark each
2
[5]
43.
(a)
covalent bonds
for 1 mark
1
(b)
any reference to shared electrons
gains 1 mark
2
but
idea that bond is shared pair of electrons
gains 2 marks
[3]
44.
(a)
the concentration of the (nitric) acid is decreasing
accept the number of acid particles is
decreasing or there are fewer collisions
(the volume of carbon dioxide remains at 83 cm3)
when the concentration of the (nitric) acid is zero
accept no acid remains or all the acid
is used up or no acid particles
(b)
(c)
1
1
line starts at origin is steeper and
remains to the left of the original line
1
graph line levels off at 83 cm3 and
before 12 minutes
tolerance  square
1
change the temperature
accept increase or decrease the temperature
accept change (increase or decrease) the
concentration (of the nitric acid)
ignore amounts of reactants or changes in pressure
or stirring or use of catalyst
1
[5]
45.
(a)
sodium
1
(b)
neutralisation
1
(c)
increase/inc. number
1
(d)
H+
1
(e)
OH–
1
(f)
H+ + OH–  H2O
1
[6]
46.
(a)
2 Na + Cl2  2 NaCl allow 2 Na+ Cl–
for 1 mark
(allow Na + ½Cl2  Na Cl)
1
(b)
(i)
1
idea that
it has strong (attractive) forces/bonds between ions / charged
particles
for 1 mark
(not ‘..it has a rigid structure’- this defines a solid or ‘...particles
close together’ - they are in a liquid)
(ii)
ideas that
2
there is increased vibration of ions / particles on heating
ions have sufficient energy to overcome attractive forces / to
break out of the
rigid structure / to move about
(must be in terms of increased energy of particles lions)
each for 1 mark
(iii)
(c)
 ions can go to electrodes / ions are free to move
for 1 mark
[do not credit ‘ions carry charges’]
ideas that
 it has stronger attractive forces between atoms/particles (not ‘ions’)
 each carbon atom forms covalent bonds with neighbouring atoms
each for 1 mark
1
2
[7]
47.
(a)
Mr (SiO2) = 60
if Mr incorrect ecf for max 2
1
60 g SiO2  28 g Si
correct answer for 3 marks
1
2.14 g SiO2  1 g Si
allow 2, 2.1, 2.14 (or anything rounding to 2.14),
2.16 or 2.2
a unit is not required but an incorrect unit loses the
third mark
1
OR Mr (SiO2) = 60
moles if silicon needed =
(1)
1
= 0.0357
28
mass of SiO2 needed = 0.0357 × 60
(1)
= 2.14 g
(1)
allow 2, 2.1, 2.14 (or anything rounding to 2.14),
2.16 or 2.2
OR Mr (SiO2) = 60
(1)
 60 
mass SiO2 = 1 ×  
 28 
(1)
= 2.14 g
(1)
allow 2, 2.1, 2.4 (or anything rounding to 2.14), 2.16
or 2.2
(b)
(i)
MgO(s) + 2HCl(aq)  MgCl2(aq) + H2O(l)
penalise incorrect symbols correctly balanced
equation for 1 mark
state symbols for 1 mark
allow correct multiples / fractions
2
H
(ii)
H
Si
1
H
H
or
H
H
H
H
Si
H or H
H
Si
H
or
H
H
Si
H
H
ignore inner shell electrons of silicon
allow correct drawings without symbols
must clearly indicate four shared pairs of electrons
with one electron from each atom
(iii)
Si
H
1.4
0.15
28
1
= 0.05
= 0.15
1
3
for whole number ratio can be implied
Si H3
1
1
1
1
accept H3 Si or any correct formula with 1:3 ratio
if in step 1 they get either of ratios incorrect they
lose first 2 marks but can be ecf for 3rd and 4th
mark
evidence of mass / Ar
1 mark
proportions of each
whole number ratio
correct formula
1 mark
1 mark
1 mark
(iv)
C
1
accept c
(c)
any four from:
4
 giant structure / macromolecule / lattice / giant molecule
allow giant molecular / giant atomic structure
 each silicon atom joined to four other atoms
(or diagram)
 covalent bonds
 bonds are strong or large amount of energy needed to break bonds
accept hard to break bonds
 large number of bonds to be broken
mention of giant ionic structure or intermolecular
forces or intermolecular bonds max 1 mark
diamond or carbon discussion max 3 marks unless
clearly linked to silicon
[15]