MAY 2010
SEC Chemistry Paper 2B
Marking Scheme
1.
(a)
(b)
(c)
non-metal
Group 4
1
1
no
losing or gaining four electrons (energetically) unfavourable
if answer is ‘cannot be ionised’ award ½
1
1
yes
4 covalent bonds
1
1
Total: 6 marks
2.
Diamond
High
sublimination
temperature
Conducts
electricity
3.
Graphite
Dry Ice
X
X
X
Total: 6
marks
When iron metal reacts with hydrochloric acid, hydrogen
1x7
gas and iron(II) chloride are produced. This is a redox
reaction. Iron is oxidized as it has lost electrons. With
hydrochloric acid, the oxidation number of the chlorine atom
is unchanged as it is a spectator ion.
Total: 7 marks
4.
(a)
-
(b)
-
1
yellow
1
increase in water and thus shift LHS (accept backwards
reaction)
1
orange
1
sulfuric acid provides H+
1
increase in H+ hence shift to RHS (accept forward
reaction)
Total: 5 marks
Page 1 of 6
5.
(a)
(b) (i)
(ii)
1 mole occupies 22.4 dm3
? mole occupy 4 dm3.
=4/22.4 = 0.179 moles
1
1:1
Therefore 0.179 moles
½
½
1 mole NH4NO2 weighs (14x2) + (1x4) + (16x2)=64g
1
1
1
0.179 mole weighs ?
= 11.456g
Total: 6 marks
6.
7.
8.
(a) 1 mole C5H8O12N4 = (12x5) + (1x5) + (16x12) + (14x4) = 316
(b) (i) 1 mole weighs 316g
? moles weigh 100g
= 0.316mole
(ii) 1 mole PET gives 1 mole PETN (may not be given but shown in
working)
½
0.316 mol PET gives 0.316 mol PETN
½
(iii) 1 mol PET weighs (12x5) + (1x12) + (16 x4) = 136g
0.316 mol PET weighs?
= 43.0g
(a)
1
1
1
1
1
1
(b)
A methanol
B ethanol
alcohols
1
1
1
(c)
structure
1
(d)
Add sodium or PCl5 to a sample in a dry beaker
1
Hydrogen/Hydrogen chloride evolved
1
(accept also esterification provided that they mention carboxylic
acid as the other reactant, c. sulphuric acid and ester smell as
observation)
Total: 6 marks
(a)
Water containing dissolved minerals passes through rocks and
as it trickles down, water evaporates.
1
(b)
Rough sketch of stalactite and stalagmites showing their
position relative to each other.
Label of stalactite
Label of stalagmite
1
1
1
(c)
-
the slightly acidic water dissolves some of the limestone,
carrying it downward
When the water evaporates, the limestone appears to
Page 2 of 6
1
-
have flowed downward
Some of the water does not evaporate until it has fallen
through the air, and landed on the floor, the remaining
limestone building the stalagmite.
(award ½ for referring to dripping water)
½
½
Total: 6 marks
9.
(a) (i)
Water
1
(ii)
(iii)
(b) (i)
(ii)
From the sugar (accept thermal decomposition of sugar)
Carbon
Blue to white
Water of crystallization lost
OR
Becomes anhydrous which is white
1
1
(c)
1
1
From white to yellow (½) on heating and back to white (½) on
cooling
1
Total: 6 marks
10. (a)
Cu(s) + 2 H2SO4(aq) → CuSO4(aq) + SO2(g) + 2 H2O(l)
1 mark for substances
1 mark for balancing
(b)
(c)
2
½ mark each for:
Flask
Stopper
Tubing
Gas syringe
-
2
No
sulfur dioxide is soluble in water
1
1
Total: 6 marks
Page 3 of 6
Section B
11. (a)
(b)
(c)
(d)
iron (III) oxide
1
A, B and C = limestone, coke and iron ore
D = hot air
E = molten iron
F = slag
Fe2O3 + 3CO → 2Fe + 3CO2
3
1
1
1
2
Calcium carbonate
CaCO3(s) → CaO(s) + CO2(g)
CaO(s) + SiO2 → CaSiO3(s)
1
2
2
(e)
-
not pure
4% C and other impurities
Brittle
½
½
1
(f)
-
Any one of: cutlery, fork, knife, spoon, sink, fridge etc
Iron rusts so is unsuitable for the use
1
1
(g)
-
Car B (Valletta Sea-front)
Sea breeze contains NaCl which accelerates rusting
1
1
Total: 20 marks
12. (a)
(b)
any material that is burned or altered to obtain energy and to
heat or to move objects
energy released to burn one mole of substance
completely in air
1
1
1
(c)
(i) 2H2 + O2 → 2H2O
(ii) 2CH3OH + 3O2 → 2CO2 + 4H20
(iii) 2C8H18 +25O2→16CO2+ 18H20
(d)
Graphite
(e)
Octane
Most exothermic reaction
(f)
hydrogen – easy to ignite, but must be stored in tanks
carbon – easy to store, must be ground to be ignited easily
(g)
Hydrogen – forms water
octane – 1 mole octane produces 8 moles of carbon dioxide
greenhouse effect
2
2
2
(1 mark)
Page 4 of 6
1
1
1+1
1+1
½+½
½+½
1
Total: 20 marks
13. (a) (i)
Diagram
Sharing by overlap of circles
Sharing 3 electrons
Remaining 2 electrons
(ii) In order to react must break bond
Bond is strong triple bond
(b) (i) NH3
(ii) N2(g) + 3H2(g) Ù 2NH3(g)
Substances
Balancing
States
(iii) Fertilizers, nitric acid or any other correct answer.
(award ½ for ‘nitrates for plants’)
(iv) NH4Cl + NaOH → NaCl + H2O + NH3
Substances
Balancing
States
Do not accept aqueous reactants.
(v) Very soluble,
would form a solution
(vi) Turns moist red litmus blue OR
Fumes when in contact with conc HCl
(c) (i)
Nitrogen monoxide
(ii)
NO
NO2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
Total 20 marks
14. (a) (i)
(ii)
(iii)
(iv)
(b) (i)
(ii)
(iii)
(iv)
(c) (i)
Halogens
If answer is ‘group 7’ award only ½ .
Br2 or I2 is less reactive. If Br or I is given award ½
Add chlorine to a solution of bromide ions.
Reddish-brown bromine is displaced
1
1
1
1
1
1
Bleach,
antiseptic or
any other correct use
NaCl
Hydrogen (accept also formula)
Chlorine (accept also formula)
NaOH is the by-product
NaOH gives an alkaline solution
Thistle funnel or dropping funnel with conc HCl
1
Heat source
1
Manganese dioxide in flask
1
Page 5 of 6
1
1
1
1
1
Method of collecting chlorine is appropriate (accept also gas
syringe)
1
Apparatus set-up
1
Washing and drying not specified in question. Do not
penalise if they do not dry it.
(ii)
(iii)
No
Poisonous must be prepared in fume cupboard
4 HCl + MnO2 → MnCl2 + Cl2 + 2H2O
Substances
balancing
Page 6 of 6
1
1
1
1