TRANS-MARA WEST ASSESSMENT TEST
233/2
CHEMISTRY
PAPER 2
JULY/AUGUST 2014
MARKING SCHEME
1.
2.
(a)
(i)
hydrogen/H2
(ii)
(iii)
Calcium hydroxide formed in partially soluble in water
Testing for carbon (IV) oxide gas
Step 2 – carbon (iv) oxide
Step 4 – hydrogen acid
(ii)
Ca (H CO3)2(aq)
CaCO3(s) + H2O (l) + CO2 (g)
(iii)
- Add a soluble sulphate (Na2SO4 or K2SO4) or dil. H2SO4 to aq. CaCl2
- filter the mixture to obtain CaSO4 as residue
- dry the solid between filter papers or tissue paper
(iv) Used as plaster of Paris in hospital to set fractured bones
(b)
(i)
(a)
(i)
W and Z
Belong to the same chemical family.
(ii) X2O7
(iii) X
Its ionic radius is larger than its atomic radius or has 1 electron in the outermost energy
that can easily be lost.
(iv) Atomic radius of Z is smaller than that of Y because Z has a greater nuclear charge
(more protons) that tends to pull its outer electrons more strongly inwardly reducing the
size of the atom.
(b)
(i)
2NaOH(aq) + H2SO4(aq)
(ii) (I)
(II)
Na2SO4(aq) + H2O(l)
No. of moles of acid used = 40 x 0.5
mole =0.02 (½mk)
100
Mole ratio
Base: Acid = 2:1
No. of moles of base reacted = 2 x 0.02
= 0.04 mole. (½mk)
1
3
0.04mol in 100cm
=
1000 x 0.04 = 0.4mol.
3
?--------------1000cm
100
(III)
Mass of NaOH in 1 litre of solution =
(0.4x40)
=
1.6g (½mk)
Mass of unreacted substance =
(17.6-1.6)g (½mk) = 16g (½mk)
3.
(a)
i)
calcium carbide (CaC2)
1
(ii) Conc. Sulphuric (IV) acid/conc. H2SO4
(iii) - C ≡ C (iv) Step 3 = polymerization
Step 5 = hydration
Step 6 = hydrogenation
(v) Preparation of margarine (hardening of oil into fats)
(vi) Step 2 = C2H2 (g) +HCl(g)
C2H3Cl(g) (ignore state symbols, accept structural
formulae)
(b)
4
C2H2 (g) + H2 (g)
C2H4 (g) (Condition as in step 2apply)
(i) (I)
K1 and K3
(II)
K2 and K5
(ii) K4
(iii) 2CH3 CH2 CH2 C – OH +2k
2CH3 CH2 CH2 COOK + H2
(a)
this is the energy change that occurs when a substance is formed from its substituent
elements.
(b)
(i)
- enthalpy of combustion of hydrogen gas
(1mk)
- enthalpy of formation of water.
(1mk)
(ii)
2CO2 (g) +3H2O (l)
H=+ 1560Kj/mol
Energy
C2H(aq)7/2O2(g)
Reaction progress
2C
+ 3H2 (g)
C2H6(g)
(iii)
Hf
7
+4O2
3O2
H2
H3
2CO2 (g) + 3H2O (l)
2
/2O2
H1
Hf +
H1 =
H2 +
H3
Hf
=H2 +
H3 -
H1
Hf = (-394) + 2 (-286) – (-1560) kJ
Hf = (-788 -572) kJ-((-1360 +1560kJ)
+200kJ
(c)
(i)
H=MC
=
500 kg x 4.2Kj x 21.5K
1000 Kg
=
(0.5 x 4.2 x 21.5Kj) =
(ii)
6.
(a)
i)
ii)
(b)
i)
ii) (a)
(c)
i)
(a)
ii)
(b)
45.15Kj
30g ethane evolves 1560Kj
?g ------------------ 45.15kJ
= 45.15k x 30
1560
5.
T
45.15kJ x 30g
1560kJ
= 0.868g
A and C
Ba2+(aq) + SO2-4(aq)
BaSO4(s)
Pb2+(aq) + SO2-4(aq)
PbSO4
Magnesium stearate /scum/magnesium octadecanate
volume of soap solution required to form lather is the lowest before and after
boiling.
(b)
C-volume of soap solution required to form lather reduced after boiling.
Addition of Na2CO3
Distillation
Use of ion exchange resins
Addition of Ca (OH)2
Bauxite
Iron
Silicon
i)
3
ii)
I)
- High temperature is expensive to attain and maintain
OR
-
Al2O3 is a very poor conductor of electricity at very high
temperature.
(II)
Adding cryolite (impurity) to molten aluminium oxide
- Denser than the electrolyte
- Insoluble in the electrolyte
iii)
Al3+(aq) + 3e
Al(aq)
Q=It
Q= (40,000 X 60 X 60) C=144000000C
(c)
3F -----------------------27g Al
(3 x 96500) c ---------- 27g Al.
144000000c?
=
7
144000000 x 27
3x96500
g
=
144000000 x 27
289500
≈ 13.43kgAl
=
13430g
(a)
-
Ammoniacal brine/ammoniate brine
Sodium hydrogen carbonate/NaHCO3
Ammonium chloride/NH4Cl
Calcium chloride/CaCl2
(b)
2NH4Cl (aq) + Ca (OH) 2(aq)
NaHCO3(s)
(c)
(d)
(e)
-
heat
CaCl2 (aq) +2H2O (l) + 2NH3 (g)
Na2CO3(s) + H2O(l) + CO2(g)
Filtration
Decomposition
Limestone/Calcium carbonate
-
Pump sea water to shallow basins/bonds
Evaporation of water takes place
Sodium chloride crystallizes out.
4