ELECTRONIC STRUCTURE & IONIZATION ENERGY

SECTION A
ELECTRONIC STRUCTURE & IONIZATION ENERGY
1. (i) Zinc metal reacts with a solution of iron(III) sulfate to give a solution of zinc sulfate and solid
iron metal. Write the full electronic configuration in spd notation of the zinc ion in zinc sulfate.
(ii) Manganese(IV) oxide reacts with an aqueous solution of hydrochloric acid to produce
manganese(II) chloride, water and chlorine gas. Write the full electronic configuration in spd
notation of the manganese(II) ion and the chloride ion.
(Total 3 Marks)
2. Write in the abbreviated form of the electronic configuration, in box notation of chromium and
copper. Describe the reason(s) for the apparently anomalous arrangement of electrons in their
atoms.
(Total 4 Marks)
3. The following table shows the first three ionization energies (in kJ mol-1
) of elements in the
SAME group of the Periodic Table.
Element ?Hi1 ?Hi2 ?Hi3
A 383 437 3376
B 409 667 4881
C 425 765 5438
D 502 868 9929
E 527 914 13820
(a) In which group of the Periodic Table should the above elements be placed?
Explain your answer in terms of the first three ionization energies. (2 Marks)
(b) Which of the above elements has the smallest atomic number? Give reasons
for your choice.
(3 Marks)
(Total 5 Marks)
Turn to Page 3 for SECTION A – Question 4.
3
4. The following table shows the first four ionization energies of the elements A to E in kJ mol-1
.
Element ?Hi1 ?Hi2 ?Hi3 ?Hi4
A 800 2400 3700 25000
B 740 1500 7700 10500
C 900 1757 14850 21000
D 418 3069 4439 5876
E 577 1816 2745 11575
(a) In which group of the Periodic Table should each element be placed? (5 Marks)
(b) Calculate the energy needed to convert one mole of gaseous atoms of element
B into 1 mole of dipositive ions? Show your working. (2 Marks)
(Total 7 Marks)
MOLARITY CALCULATIONS
5. 5.00 g of lawn sand (a mixture of sand and ammonium sulfate) was weighed into a conical
flask and 25 cm3
of 2.0 mol dm-3 sodium hydroxide solution was pipetted into the same
flask. The conical flask was boiled for 20 minutes which ensured that all the ammonia had
been driven off, because:
(NH4)2SO4(s) + 2NaOH(aq) 2NH3(g) + Na2SO4(aq) + 2H2O(1)
The residue in the flask was cooled and filtered to remove the sand. The filtrate containing
unreacted NaOH was made up to 250 cm3
in a volumetric flask. 25 cm3
samples of this
solution were titrated against 0.1 mol dm-3 hydrochloric acid using bromothymol blue as an
indicator.
HCl(aq) + NaOH(aq) ? NaCl(aq) + H2O(l)
The mean titre was 15.65 cm
3
.
Calculate the percentage of ammonium sulfate by mass in the lawn sand. Show and
explain your working.
(Total 8 Marks)
BONDING & ENERGY
6. (a) Lithium amide is mainly used as a strong base in organic chemistry, often in
liquid ammonia solution. Draw a dot & cross diagram to show the bonding in
the amide ion. State and explain the shape of amide using the VSEPR theory.
Estimate the H-N-H bond angle. (5 Marks)
4
Question 6 continued.
(b) (i) Draw a dot & cross diagram to show the bonding in methanal, HCHO.
State and explain the shape of HCHO using the VSEPR theory. Estimate
the H-C-H bond angle. (4 Marks)
(ii) Methanal (HCHO) is a gas at room temperature whereas methanol
(CH3OH) is a liquid. Suggest an explanation for this. (3 Marks)
(Total 12 Marks)
7. A coffee-cup calorimeter contains 65.0 cm3
of a dilute solution of copper(II) sulfate
at a temperature of 22.8 °C. A small amount of magnesium powder also at 22.8 °C
is added to the solution. Copper metal is formed, and the temperature of the solution
rises to 35.3 °C. The copper is collected, dried and weighted, when it is found to
have a mass of 0.424 g.
(i) Calculate the total amount of energy released in this reaction, ignoring the
heat capacity of the magnesium and the calorimeter. Take the specific heat
capacity of the solution as 4.18 J g-1 K
-1
. Show and explain your working.
(ii) Calculate the enthalpy change for this reaction per mole of the copper
formed. Show and explain your working.
(Total 4 Marks)
8. Use the values for average bond enthalpies (E) from the table below to calculate the enthalpy
changes in each of the reactions (a) and (b)
Bond C-C C=C C-H C=O C-Cl H-Cl O-H O=O
E/kJ mol-1 346 611 412 743 339 431 463 497
(a) CH4 (g) + 2O2(g) ? CO2(g) + 2H2O(g) (3 Marks)
(b) CH3CH=CHCH3(g) + HCl(g) ? CH3CH2CH(Cl)CH3(l)
(3 Marks)
(c) Research and record the data book value for the standard enthalpy of
combustion of methane. How would your answer to (a) compare to the data
book value for the standard enthalpy of combustion of methane? Give a
reason or explain.
(2 Marks)
(Total 8 Marks)
9. (a) Draw a diagram of the energy distribution of gas particles in a system, at
temperature, T1. On the same diagram, show the shape the distribution at a
higher temperature T2. Note: temperature T
2
is higher than temperature T
1
. (3 Marks)
(b) Relate the two curves in (a) to the change in the rate of a gas phase reaction
with increased temperature. (2 Marks)
5
Question 9 continued.
(c) Draw a labelled energy profile showing the energy changes during an
exothermic reaction. Use this and the diagram drawn in (a) to explain how
catalysts increase the rate of reactions. (4 Marks)
(Total 9 Marks)
10. (a) Given the following data, construct a Hess’s Law cycle and calculate the
standard enthalpy of formation of ethane, ?H
?
f [C2H6
].
2C(s) + 3H2(g) ? C2H6 (g)
?H
?
c carbon = -394 kJ mol-1
?H
?
c hydrogen = -286 kJ mol-1
?H
?
c ethane = -1560 kJ mol-1
(4 Marks)
(b) Use the values for average bond enthalpies (E) from the table below along
with the standard enthalpy of atomisation of carbon to calculate the standard
enthalpy of formation of ethane, ?H
?
f [C2H6
] using the equation given in (a).
Displayed formula of ethane:

C C
H
H H H
H H
Bond C-C C-H H-H ?H
?
at [C] = 717 kJ mol-1
E/kJ mol-1 346 412 436 (3 Marks)
(c) Comment on the discrepancy between the two calculated values for the
standard enthalpy of formation of ethane in (a) and (b). Stating with a reason,
which of the two values is likely to be more accurate.
(3 Marks)
(Total 10 Marks)
END OF SECTION A
TOTAL FOR SECTION A

70 MARKS
Turn to Page 6 for SECTION B
6
SECTION B
RATES OF REACTION
1. 1-bromobutane was hydrolysed by aqueous sodium hydroxide solution.
C4H9Br + NaOH ? C4H9OH + NaBr
1-bromobutane butan-1-ol
During the reaction the sodium hydroxide is used up. Samples of the reaction mixture
were drawn off at regular time intervals and analysed by titration with standard
hydrochloric acid to find out the concentration of sodium hydroxide.
The results are given in the table below:
Time / secs Concentration of hydroxide ion / mol dm-3
0 0.500
100 0.350
200 0.250
300 0.180
400 0.125
500 0.090
600 0.063
700 0.040
800 0.030
(a) From the above information, identify the independent variable and dependent variable.
Plot a suitable graph. The graph MUST be a hand drawn, plotted on graph paper.
Note: NO marks are awarded for identifying the independent and dependent variable.
(3 Marks)
(b) Select 4 suitable points along your graph [see part (a)] and draw tangents to find the
rates. Construct a table of “Rate” against “Concentration”. Note: The rates need to be
calculated and the calculations shown.
(4 Marks)
(c) Plot a graph of Rate against Concentration. (3 Marks)

(d) From your graph in part (c) deduce the Order of Reaction. (1 Mark)
(e) Write a rate equation with respect to the concentration of hydroxide ions. (2 Marks)
(f) Calculate the rate constant k from the gradient of the graph, drawn in part (c). Show your
working.
(2 Marks)
(Total 15 Marks)
7
ORGANIC CHEMISTRY
2. (a) Write the condensed formulae of the following compounds:
(i) 2,3-Dichlorohex-2-ene
(ii) 2-Methylbutane
(iii)
(iv)
Butan-1,3-diol
2,2-Dihydroxy-1-phenyl-pentan-3-one
(Total 4 Marks)
(b) Draw displayed formulae of two other isomers of compound (ii)
(Total 2 Marks)
(c) Which of the above compounds exhibits geometrical isomerism? Draw
skeletal formulae of the isomers. Name the isomers.
(Total 5 Marks)
(d) Which of the above compounds exhibits stereoisomerism? Draw the
displayed 3D (three dimensional) formulae the isomers. Suggest how these
isomers could be distinguished from one another.
(Total 5 Marks)
(Total 16 Marks)
3. A student was given the following instructions for the preparation and identification of a carbonyl
compound:
To 40 cm3
of water in a flask, carefully add 6 cm3
of concentrated sulfuric acid and set up the
apparatus as shown below.
Make up a solution of 28 g of sodium dichromate Na2Cr2O7 in 15 cm3
of water, add 20 cm3
of the
alcohol C3H8O and pour the solution into the dropping funnel.
Boil the acid in the flask and add the mixture containing the alcohol at such a rate that the
product is slowly collected in the receiver in the ice-water bath.
Na2Cr2O7
(aq) + C3H8O
water
condenser
ice/water mixture
H2SO4
(aq)
receiver
water
8
Question 3 continued.
3. Redistil the crude product and collect the fraction that boils between 48 and 50?C.
The equation for the reaction is:
3C3H8O + Na2Cr2O7 + 4H2SO4 ? 3C3H6O + Na2SO4 + Cr2(SO4)3 + 7H2O
(a) In the apparatus above, why is the water fed in at the lower end of the
condenser?
(1 Mark)
(b) Why is the receiver cooled in ice/water? (1 Mark)
(c) (i) Calculate how many moles of Na2Cr2O7 were used?
(1 Mark)
(ii) Use the density of the alcohol (0.79 g cm-3
) to calculate the mass
and hence the number of moles of alcohol used in the
preparation. Explain which reagent is in excess. (3 Marks)
(iii) The student obtained 7.2 g of the carbonyl compound. Calculate
the percentage yield obtained. (2 Marks)
(iv) Suggest why the percentage yield is well below 100%. (2 Marks)
(d) Identify the possible isomers of C3H8O. Note: Your answer/s MUST be
relevant to the reaction described in question 3.
What type of isomerism do the above isomers of C3H8O display? (3 Marks)
(e) The carbonyl compound gave a yellow precipitate on addition of 2,4-
dinitrophenylhydrazine but did not reduce ammoniacal silver nitrate or
Fehlings solution.
(i)
(ii)
Identify (Name) the carbonyl compound C3H6O.
Draw the displayed formula of the 2,4-dinitrophenylyhydrazine
product, the yellow precipitate.
(1 Mark)
(1 Mark)
(iii) Which isomer of C3H8O was used in the preparation? (1 Mark)
(f) The yellow precipitate formed on addition of 2,4-dinitrophenylhydrazine
is a derivative that can be used to identify the carbonyl compound
(i) Name the method that you would use to purify the derivative. (1 Mark)
(ii) Describe what must be done with the purified derivative to
characterise the carbonyl compound? (2 Marks)
Turn to Page 9 for SECTION B – Question 4.
(Total 19 Marks)
9
4. Alkenes react with hydrogen bromide at room temperature.
(a) Draw displayed formulae of the products formed in the reaction
between 2-methylpent-1-ene and hydrogen chloride at room
temperature. (2 Marks)
(b) Draw the reaction mechanism for the reaction in part (a) (above
reaction). Explain the mechanism. Mechanism must contain curly
arrows. (4 Marks)
(c) Explain in detail (with the aid of a diagram and referring to part
(b) above) why products are formed. (3 Marks)
(Total 9 Marks)
5. (a) 1-Chloro-3-ethylcyclopentane is heated under reflux with
aqueous sodium hydroxide. Draw the skeletal formula of the
organic product formed. (1 Mark)
(b) 2-Bromo-2-methylpentane is heated under reflux with ethanol
and concentrated sodium hydroxide. Draw the skeletal formulae
of the organic products formed. (2 Marks)
(c) Draw the reaction mechanism for the reaction in part (b) [5(b)]
/above reaction]. Explain the mechanism. Mechanism must
contain curly arrows.
(4 Marks)
(d) Compare and contrast the reaction mechanisms of part (a) and
part (b).
(4 Marks)
(Total 11 Marks)
END OF SECTION B
TOTAL FOR SECTION B 70 MARKS

Turn to Page 10 for SECTION C
10
SECTION C
In following equations, calculate the numbers of moles of substances denoted by letters a – d:
1. CO(g) + Cl2(g) COCl2(g)
At start 2 mole 4 moles 0 moles
At equilm 1.5 moles a b
(Total 1 Mark)
2. NH2COONH4(s) 2NH3(g) + CO2(g)
At start c 0 moles 0 moles
At equilm 3 moles 4 moles d
(Total 1 Mark)
3. An important reaction in the manufacture of sulfuric acid is:
2SO2 (g) + O2 (g) 2SO3 (g) ?H = -197 kJ mol-1
This reaction was intensively investigated by Bodenstein in 1905. In one of his experiments he
found that, at 1000K, equilibrium occurred when the partial pressures of the gasses in the mixture
were as follows:
P
SO2
= 0.557 atmospheres P
O2
= 0.170 atmospheres P
SO3
= 0.464 atmospheres
(a) Write an expression for the equilibrium constant, Kp, for this reaction in terms
of partial pressures (1 Mark)
(b) Use the partial pressures given above to calculate the value of Kp at 1000K,
including its units (3 Marks)
(c) What would be the effects on the value of Kp, if the following changes were
made to the system:
(i) the partial pressure of oxygen is increased by 0.500 atmosphere (1 Mark)
(ii) the temperature was lowered to 400K (1 Mark)
(Total 6 Marks)
4. Benzoic acid is a weak monobasic acid. Representing benzoic acid as HBen and its
conjugate base as Benexplain
how a solution containing benzoic acid and its
sodium salt can function as a buffer solution. Your answer MUST contain chemical
equations.
Turn to Page 11 for SECTION C – Question 5.
(Total 4 Marks)
11
5. Aspirin is a weak monobasic acid. The acid dissociation constant Ka for aspirin is
3.27 x 10-4 mol dm-3
at 25 °C. A chemist wishes to make a buffer solution with a pH
of 4.10 using aspirin and its sodium salt. The chemist starts with a solution
containing 0.04 mol dm-3
aspirin.
(a) Calculate the pH of the aspirin solution (2 Marks)
(b) Calculate [H3O
+
] for a solution with pH = 4.10 (1 Mark)
(c) Calculate the concentration of the sodium salt of aspirin required to produce a
solution with a pH of 4.10 (2 Marks)
(Total 5 Marks)
6. Balance the following redox equations, using the oxidation number method:
(a) SO3
2-
(g) + Ce4+
(aq) + H2O (l) ? SO4
2-
(aq) + Ce3+
(aq) + H+
(aq) (2 Marks)
(b) Cl2(aq) + OH(aq)
? Cl(aq)
+ ClO3

(aq) + H2O (l) (2 Marks)
(c) Explain what type of reaction is (b)? (1 Mark)
(Total 5 Marks)
7. Cresolphthalein is a common acid – base indicator which changes colour over with
the pH range 8.2 – 9.8.
Would cresolphthalein be a suitable indicator for the titration between 25.0 cm3
of
0.2 mol dm-3
hydrochloric acid and 0.2 mol dm-3
ammonia? Explain your answer.
What other method could be used to identify the end-point of the hydrochloric acid
and ammonia titration?
(Total 4 Marks)
Turn to Page 12 for SECTION C – Question 8.
12
Volume of 0.10 mol dm-3
potassium hydroxide added / cm3
Total volume of solution /
cm3
[H+
(aq)] / mol dm-3
or
[H3O
+
(aq)] / mol dm-3
pH
Initial volume of 0.10 mol dm-3
hydrochloric acid = 25.00 cm3
0 25.00
10.00
15.00
20.00
24.90
24.99
25.00
25.01
25.10
30.00
35.00
40.00
50.00
8. (a) Copy and complete the table below for the titration of 0.10 mol dm-3
potassium
hydroxide solution against a 0.10 mol dm-3
hydrochloric acid solution
(3 Marks)
(b) Plot a graph on graph paper. Clearly mark or indicate on the graph: the pH at
the start of the titration, pH at equivalence point, volume of potassium
hydroxide at equivalence point and pH when all of the potassium hydroxide
has been added.
(6 Marks)

 

Sample Solution

ACED ESSAYS