chemistry stpm term 2

1. PRA2 6AS/ 962 Paper 2 2015
1
Section A [15 marks]
Answer all questions in this section.
1 The radiusand charge of six cationsand anionsare shownbelow.
Ion P+
Q2+
R2+
X-
Y2-
Z2-
Radius/pm 238 152 140 180 145 200
If the ionicsolids PA ,QE and RI are of the same lattice type, whatisthe same lattice type,whatis
the correct orderof theirlattice energies,placingthe one withthe highestnumerical value first?
A RZ, QY, PX
B RZ, PX,QY
C QY, RZ,PX
D PX,QY, RZ
2 Dinitrogentetraoxide,N2O4 isformedwhennitrogendioxidedimerises,asshowninthe following
equation.
2NO2(g) →N2O4 ∆ H = -58.20 kJ mol-1
If the standardenthalpyof formationof NO2 is 33.94 kJmol-1
,calculate the amountof energy
absorbedwhen10.0 g of dinitrogentetraoxideisformed?
A 885 J
B 1052 J
C 1264 J
D 2477 J
3 The diagram belowshowsthe energylevel diagramforsodiumfluoride,NaF.
What isthe lattice formationenergyof sodiumfluorideinkJmol-1
?
A -62 B -594 C -928 D -1024

2. PRA2 6AS/ 962 Paper 2 2015
2
4 The standard reductionelectrode potentialforseveral half-reactionsat298 K are shownbelow:
Half-cell reactions E° (V)
O2 + 2H+
+ 2e → H2O2 +0.68
H2O2 + 2H+
+ 2e → 2H2O +1.77
H2SO4 + 2H+
+ 2e → H2SO3 + H2O +0.17
HNO3 + 3H+
+ 3e → NO + 2H2O +0.96
Basedon the above data,whichof the followingstatementsiscorrect?
A HNO3 isthe strongestoxidizingagent.
B SulphuricacidoxidisesH2O2 tooxygengas
C H2O2 spontaneouslydecomposestooxygengas.
D Nitricoxide isformedwhenH2SO4 isaddedtonitricacid.
Section B
[15 marks]

3. PRA2 6AS/ 962 Paper 2 2015
3
Section C
[30 marks]
Answerany two questionsin this section.
18 (a) By usingrelevantstandardelectrode potentials,determinewhetheran aqueoussolutionof
hydrogenperoxide canreactwithacidifiedpotassiummanganate(VII) solution.
[4 marks]
(b) The standard electrode potential, E°,of Fe3+
(aq)/Fe2+
(aq) half-cellisdeterminedbyusingan
electrochemical cell.The E°value of Fe3+
(aq)/Fe2+
(aq) is+0.77 V.
(i ) Draw a labeleddiagramof the set-upof the apparatuswhichisusedtodetermine the
standardelectrode potential, E°, of the Fe3+
(aq)/Fe2+
(aq) half-cell andindicate onthe
diagramthe directionof flow of electrons.
[4 marks]
(ii ) Write the overall equationforthe reactionandthe cell notationforthe electrochemical
cell in(b)(i).
[3 marks]
(iii)Ifthe cell e.m.f.obtainedinanexperimentis0.95 V, calculate the concentrationof
hydrogenionspresentinthe electrolyteata temperature of 25°C,giventhat the Nernst
equationfora cell at 25 °C is
E = E° - 0.0592 log Q
n
where Q is the reaction quotient
[4 marks]

4. PRA2 6AS/ 962 Paper 2 2015
4
19 The standard enthalpyof hydrationof copper(ll) sulphatereferstothe followingprocess:
CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s)
However,thisenthalpychange cannotbe measureddirectly.
When4.0 g of anhydrouscopper(ll) sulphate isaddedto50.0 g of water,the temperature changes
from27.0 °C to 35.0 °C.
When4.0 g of the hydratedsolidisaddedto50.0 g of water,the temperature changesfrom27.0 °C
to 25.7 °C.
a. Calculate the heatchange when4.0 g of anhydrouscopper(ll) sulphate dissolvesin50.0 g of
water. [2 marks]
b. Calculate the enthalpyof solution,inkJmol-1
,of anhydrouscopper(ll) sulphate. [3 marks]
c. Calculate the heatchange when4.0 g of hydratedcopper(ll) sulphate dissolvesin50.0g of
water. [2 marks]
d. Calculate the enthalpychange of solution,inkJmol-1
,of hydratedcopper(ll) sulphate.
[4 marks]
e. Calculate the enthalpyof hydrationof anhydrouscopper(ll)sulphate. [4 marks]
20 The firstionisationenergiesof the Period3elementsfromsodiumtoargonare givenbelow.
Element Na Mg Al Si P S Cl Ar
Firstionisationenergy(kJmol-1
) 494 736 577 786 1060 1000 1206 1520
a. Define the firstionisationenergyof anelementandwrite anequationusingmagnesiumas
an example. [2 marks]
b. Sketcha graph of firstionisationenergyof the Period3elementsandexplainyourgraph.
[6 marks]
c. State the acid-base nature of the oxidesof sodium, aluminiumandsilicon,anddescribe
theirreactionswithanaqueoussolutionof sodiumhydroxide andhydrochloricacid.Write
the equationsforall the reactionsinvolved.
[7 marks]

5. PRA2 6AS/ 962 Paper 2 2015
5
END OF QUESTION PAPER