F.6/Chemistry 2/Mock Exam Marking/15-16/ P.1 of 4

F.6/Chemistry 2/Mock Exam Marking/15-16/ P.1 of 4

S.K.H. LAM KAU MOW SECONDARY SCHOOL

Form 6 Chemistry Paper 2

Mock Examination Marking (2015-2016)

1.(a)(i)(1)Method 1

burning potassium in chlorine, as KCl is the only product / all reacting atoms used / all products are useful / only method 1 gives 100% atom economy / only one product / no co- product / no other products / no by-products / no atoms lost / no waste / addition reaction. 1

(2)A lot of energy / high temperature is required OR reaction produces a low yield of KCl / reagents of method 1 are expensive / reagents are dangerous and safety precautions / reaction conditions are expensive 1

(ii)acetic acid / dimethyl ether / ethene, propene / formaldehyde / hydrogen1

(ref. Book 6 P.120 Fig. 47.32 )

(iii)Proper drawing on the shape of an energy profile of an endothermic reaction

AND Proper label on y-axis 1

(b)(i)(1) number of molecules1

(2)the number of particles with (energy greater than) the activation energy1

(ii)(1)peak moves to the RHS and is lower1

(2)higher reaction rate as more particles have (energy greater than) the activation energy 1

(iii)a catalyst increases reaction rate as the activation energy is less 1

the number of particles with the required activation energy is greater1

(c)(i) Proper method of measuring pH e.g. use of pH meter1

(ii)first order with respect to CH3CH2Br 1

firstorder with respect to NaOH1

(Deduction bywritten explanation or calculation needed.)

(iii)(1)rate = k[CH3CH2Br] [NaOH]1

(2)Second 1

(3)6 x 10-21

(d)(i)N2 + 3H2 2NH31

(ii)iron1

(iii)more molecules on the left hand side and equilibrium moves to the right1

reaction is exothermic and hence low temperature to move equilibrium to right1

2.(a)(i)1 – 100 nm (units required)1

(ii)Vulcanization† / vulcanisation† 1

(iii)(1)Coordination number is defined as the number of atoms (or ions) immediately surrounding an atom (or ion) in a crystal lattice. 1

(2)81

†Correct spelling

(b)(i) HOCH2CH2OH, 1,1

(ii)1

(iii)PET is biodegradable / degraded by acid / alkali while PS is not.1

Explain the difference PET and PS in terms of type of bond / structure1

As PET is a polyester with the ester groups, it can be hydrolysed easily by the bacterial action or by treating with acid or alkali to form a shorter fragments for degradation.

Hydrocarbon-based polymer such as PS polystyrene, which have stronger carbon-carbon single bonds that cannot be broken by acid, alkali or the bacterial action.

(iv)1

(v)In a pure metal, all the atoms are of the same size. The layers of atoms can slide past one another easily when a force is applied. 1

In an alloy, atoms of a different size are added. This distorts the regular structure of the pure metal. 1

The alloy is harder as layers of atoms in the alloy are difficult to slide past one another when a force is applied. 1

(c)(i), β-glucose1,1

(ii)In the structure –OH groups are used to form intrachain / interchain / intersheet hydrogen bond 1

fewer –OH groups can interact with water molecules in the environment1

(iii)Shells of lobsters and crabs / the external skeletons of insects / spiders1

Accepts other sources e.g. the exoskeletons of arthropods such as crustaceans (e.g. shrimps) and insects and the beaks and internal shells of cephalopods, including squid and octopuses.

(iv)As the presence of hydroxyl groups and the amide groups, the chains of chitin pack side by side and are held together 1

by forming the strong extensive hydrogen bonds between the polymeric chains.1

3.(a)(i)Lilac / pale purple / violet1

(ii)(1) Yellow / orange / orange-red precipitate1

ALLOW yellow / orange / red solid (reject brown)

(2)Silver (mirror OR precipitate OR solid) OR black precipitate/solid1

(iii)Prepare a series of standard solutions of permanganate ions. (Using light of the selected colour, ) record the absorbance of each solution. 1

Plot the absorbance against the concentration of permanganate ions. Using absorbance of the sample, find the concentration from the calibration curve. 1

(b)(i)Aqueous layer.

The heptanoic acid reacts with sodium hydroxide to give sodium heptanoate which is solublein the aqueous layer. 1

(ii)regenerate the heptanoic acid1

(iii)Remove final traces of water using a (solid) drying agent (or proper e.g. of drying agent), and filter off the drying agent. 1

(c)(i) To stop the dyes from {dissolving / running / going / mixing} into water 1

Ignore refs to correct statements eg "to allow water to rise up paper".

Accept reverse argument based on what happens if water level is above dyes.

(ii)(1)C and D1

(2)insoluble in water1

Reject ref to not enough dye

(iii)1*

(or by measurement:

distance moved by food dye from base line 44-46 (mm)

distance moved by solvent from base line 57-58mm))

Rf = 0.772 - 0.8071

*step mark

(d)(i)To prevent ions from colliding with and deflected by air molecules. 1

(ii)(1)molecular ion is 58 OR m/z is 58 1

ALLOW peak on the right is 58 OR parent ion is 58

The Mr OR molecular mass is 58 with no evidence is not sufficient

(58 – (36 + 6) = 16) so x = 11

ALLOW x = 1

ALLOW Z is C3H6O

(2)CH3CH2CHOOR CH3COCH31

ALLOW other correct structures, eg enols, ethers and cyclic structures

eg CH2=CHCH2OH OR CH2=CHOCH3 OR structure of cyclopropanol

(3)C2H5+1

ALLOW CH3CH2+ OR COH+ OR HCO+

The positive sign must be included

(iii)C=O because of absorption between 1640 and 1750 cm–1

AND

O–H (broad) absorption between 2500 to 3300 cm–11

ALLOW any values within the wavenumber range

IGNORE C–O

Carboxyl group OR carboxylic acid 1

IGNORE alcohol, ester, aldehyde, ketone or amide