Exam Questions I've Gotten Wrong

Question 1

Chlorine gas can be added to cold, dilute alkaline solution to form bleach. Write the equation for this reaction.

Answer 1

Cl2 + 2NaOH –> NaClO + NaCl + H2O

Question 2

A student bubbles chlorine gas through aqueous potassium iodide. A reaction takes place. State what the student would observe.

Answer 2

yellow/orange/brown

Question 3

CaCO3 –> reaction 2 –> CaO. What type of reaction is reaction 2?

Answer 3

thermal decomposition

Question 4

What is meant by the term base?

Answer 4

Accepts H+ ions

Question 5

(d) A student prepares a solution of calcium nitrate from calcium carbonate.
What reagent would the student need to use?
Write the equation for the reaction

Answer 5

HNO3

CaCO3 + 2HNO3 –> Ca(NO3) + H2O + O2

Question 6

Avogadro’s constant

Answer 6

6.02x10^23

Question 7

Draw a diagram showing hydrogen bonding with two H2O molecules

Answer 7

Two H2O molecules with delta + at H and delta - at O, and two lone pairs on each O, hydrogen bond from a H to a lone pair on the O of another molecule

Question 8

State and explain two anomalous properties of ice

Answer 8

Lower density than water as molecules held apart by hydrogen bonds
Relatively high melting point as hydrogen bonds strong

Question 9

What intermolecular force is present in PH3?

Answer 9

Permanent dipole dipole interaction

Question 10

BF3 bond angle?

Answer 10

120’

Question 11

8. Diphenylethanedione is a pale yellow colour, which disappears when it is reduced.
   The colour results from the arrangement of the delocalised π-bond electrons.
   Explain what is meant by the term delocalised π-bond electrons. (2)

Answer 11

delocalised electrons
electrons are spread over more than two atoms AW (1)
π-bond
formed by overlap of p-orbitals/ diagram to show (1)

Question 12

4-Methylphenylamine can be manufactured from benzene in three stages
Describe how benzene could be converted by these three stages into 4-methylphenylamine.
Include the structures of the intermediate compounds A and B. State the reagents and conditions. Give a balanced equation for each stage.
(12)

Answer 12

methylation stage (can come anywhere)
CH3Cl / CH3Br (1)
AlCl3
 / FeBr3
 etc. (1)
equation – e.g. C6H6
 \+ CH3Cl → C6H5CH3
 \+ HCl (1)
intermediate name or unambiguous structure (1)
4 marks
intermediates and equations will vary if methylation is done
after nitration or reduction
 nitration stage
(conc) H2SO4
(1)
(conc) HNO3
(1)
equation – e.g.: C6H5CH3
 \+ HNO3
 → C6H4
(CH3
)NO2
 \+ H2O (1)
intermediate – name or unambiguous structure (1)
4 marks 
Plymstock School 9
 reduction stage
tin/iron (1)
HCl (1)
equation – e.g.: C6H4
(CH3
)NO2
 \+ 6[H] → C6H4
(CH3
)NH2
 \+ 2H2O
 or with H+
 also on left to give C6H4
(CH3
)NH3
\+
(1)
3 marks
allow other suitable reducing agents:
Quality of Written Communication mark for a well organised
answer with the three stages clearly distinguished and sequenced (1)
1 mark

Question 13

1. Hydroxyethanal, HOCH2CHO, is sometimes referred to as the ‘first sugar’ as it is the simplest possible molecule that contains both an aldehyde group and an alcohol group.
   (ii) Outline the mechanism for this reduction.
   Use curly arrows and show any relevant dipoles.

(4)

Answer 13

curly arrow from H–
to Cδ+
dipoles and curly arrow from C=O bond to O
ALLOW curly arrow to C even if dipole missing or incorrect
intermediate
curly arrow from intermediate to H δ+ in H2O/ H+
and if H2O
is used it must show the curly arrow from the O–H bond to the O
lone pairs are not essential

Question 14

4. Chloral hydrate is broken down in the body after several hours. One reaction is oxidation to trichloroethanoic acid.
   Complete the equation for this reaction below.
   (1)

Answer 14

CCl3CH(OH)2

+ [O] → CCl3COOH + H2O (1)

Question 15

10. In this question, one mark is available for spelling, punctuation and grammar.
    Tollens’ reagent can be used to identify the aldehyde group in cinnamaldehyde.
    • Describe how you would make Tollens’ reagent and carry out this test in the laboratory.
    • Explain what happens to both the Tollens’ reagent and the cinnamaldehyde in this reaction. Identify the organic product.
    (8)

Answer 15

method
silver nitrate (1)
ammonia / ammoniacal (1)
warm / heat (1)
silver (mirror) / brown ppt forms (1)
explanation
silver ions reduced / Ag+
 \+ e–
 → Ag (1)
aldehyde oxidised to a carboxylic acid (1)
correct structure – eg C6H5CHCHCOO–
/COOH (1)
quality of written communication
mark for correct spelling, punctuation and grammar in at least two sentences (1)

Question 16

5. Suggest two reasons why standard enthalpy changes of combustion determined experimentally are less exothermic than the calculated theoretical values. (2)

Answer 16

Any two from the following:
 Heat released to the surroundings
ALLOW heat loss
 Incomplete combustion OR incomplete reaction
OR not everything burns
IGNORE reference to evaporation
 Non-standard conditions

Question 17

6. In the vapour state, hydrogen and iodine undergo the following reaction.
   H2(g) + I2(g) 2HI(g) reaction 2.1
   Write an equation, including state symbols, for the bond enthalpy of I − I.

Answer 17

I-I(g) → 2I(g)

Question 18

(ii) Magnesium reacts with dilute acids.
Describe what you would expect to see when magnesium ribbon is added to an excess of dilute hydrochloric acid.
(2)

Answer 18

Fizzes OR bubbles OR gas produced OR effervescing
DO NOT ALLOW ‘carbon dioxide gas produced’
DO NOT ALLOW ‘hydrogen produced’ without ‘gas’
Mg dissolves OR Mg disappears OR a solution is formed
ALLOW ‘it for Mg’
IGNORE Mg reacts
IGNORE temperature change
IGNORE steam produced

Question 19

3. An ore of strontium contains strontium carbonate, SrCO3.
   To obtain metallic strontium,
   • the SrCO3 is converted into strontium oxide, SrO;
   • SrO is then reduced to produce strontium.
   (i) Suggest how strontium carbonate is converted into strontium oxide.
   (1)

Answer 19

heat

Question 20

(i) State which two elements from the first twenty elements of the modern Periodic Table are not arranged in order of increasing atomic mass. (1)

Answer 20

K and Ar

Question 21

(ii) Explain why increasing the concentration of H2O2(aq) increases the rate of decomposition. (2)

Answer 21

More crowded particles
OR more particles per (unit) volume
ALLOW particles are closer together
DO NOT ALLOW ‘area’ instead of ‘volume’
IGNORE ‘more concentrated particles’
 more collisions per second
OR more frequent collisions
ALLOW collisions more often
OR increased rate of collision
OR collisions are more likely
OR there is a greater chance of collisions
‘More collisions’ is not sufficient

Question 22

(iv) Explain why the straight chain isomer of C10H22 (which is usually used as a jet fuel) is converted by the petroleum industry into its branched chain isomers. (1)

Answer 22

Branched chains have more efficient combustion

Question 23

Suggest a type of reactant that could be used to remove the HCl from the CH2CHCl monomer. (1)

Answer 23

alkali

Question 24

In the past, hydrogen peroxide was manufactured by reacting barium peroxide, BaO2, with ice-cold dilute sulfuric acid.
BaO2(s) + H2SO4(aq) → BaSO4(s) + H2O2(aq)
This method required the disposal of poisonous barium compounds.

Nowadays, hydrogen peroxide is manufactured using hydrogen gas, oxygen from the air and a substance called anthraquinone.
stage 1 H2 + anthraquinone → anthraquinol stage 2 O2 + anthraquinol → H2O2 + anthraquinone
Compare the manufacture of H2O2 from hydrogen and oxygen with the manufacture from barium peroxide described in (i).
Explain the advantages of the manufacture of H2O2 from hydrogen and oxygen.

(3)

Answer 24

Any three from the following:
 Oxygen comes from air
IGNORE hydrogen comes from the air
 No poisonous materials formed
OR no poisonous materials involved
IGNORE harmful
 No waste products formed OR atom economy is 100%
ALLOW higher atom economy
 Anthraquinone is regenerated OR recycled OR used again
OR Anthraquinone acts as a catalyst

Question 25

2. A student reacted 8.72 g of bromobutane with an excess of OH–. The student produced 4.28 g of butan-1-ol.
   In this reaction the hydroxide ion acts as a nucleophile.
   (i) What name is given to this type of reaction?
   (1)

Answer 25

Hydrolysis

Question 26

(ii) Suggest why the second electron affinity of oxygen is positive. (2)

Answer 26

“oxide” ion, O– and electron are both negative (1)

hence energy is required to overcome repulsion (1)

Question 27

(c) The lattice enthalpies of calcium oxide and magnesium oxide are different.
Comment on this difference.
In your answer you should make clear how the sizes of the lattice enthalpies are related to any supporting evidence.
(3)

Answer 27

differences in size of lattice enthalpies linked to ionic sizes/attraction
using more/less exothermic rather than bigger or smaller. (1)
Mg2+ is smaller/Mg2+ has greater charge density(1)
hence has stronger attraction for O2– (1)

Question 28

(b) Explain why the first ionisation energy of calcium is less positive than the second ionisation energy. (2)

Answer 28

Any two from
For second ionisation energy the electron lost is closer to the nucleus / AW (1);
For second ionisation energy the electron is lost from a particle that
is already positive (1);
For second ionisation energy there is one more proton than electron (1)
So outer electron more firmly attracted to the nucleus (1) 2
Allow ora

Question 29

(i) Suggest why oxygen free radicals, O, are often called diradicals. (1)

Answer 29

each atom has two unpaired electrons (1)