BASIC CONCEPTS HW MS 1. 2. (ii) C13H28[1]

(i)

120130 (1)

1

boiling point increases with increase in Mr/molecular formula/number of carbon atoms/chain length (1) more intermolecular forces/electrons/surface area/ surface interactions/van der Waal forces (1)

2[3]

3.

C9H20 C7H16 + C2H4 (1)[1]

4.

Recognises that either a catalyst or high temperature (heat is not sufficient) is required cracking suitable balanced equation 1 reforming equation or statement indicating formation of a ring/cyclic compound suitable balanced equation with H2 1 (balanced equation showing formation of a ring scores both marks) isomerisation suitable balanced equation The processed products are: used in fuels/used in petrol better /more efficient fuels/increase octane number/rating alkenes (from cracking) produce polymers/alcohols H2 used for Haber process/fuels/hydrogenation of oils QWC SPAG look for two complete sentence that present a coherent argument

1

1 1

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5.

(a) octane, hexadecane. if C penalise once. (b) fractional distillation (c) (i)

400 +/- 5 545 +/- 5 1

1

1

2 (ii) (iii) (iv) 2-methylpentane C, B and A 1 1

the more branching/the shorter the chain the lower the boiling point/ less energy needed to separate the molecules long chain have greater surface area/surface interactions/more VdW forces or converse argument about short/branched chains.

1 1

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(d)

(i)H C H2 2

H C C2H 2H

H C C C C C H

H H H H

H

C C C H2

H

n

o

t C j 6 Hu

1

s2 t

o

rH2

o

r

H C H

H

1 (ii) (iii) C6H14 C=H12 + H2 better fuels/more volatile/lower boiling point/reduces knocking/ increases octane rating/used as (petrol) additives (e) (i) Mr of (CH3)3COH = 74 1 1 1 1

% oxygen = (16/74) 100 = 21.6 % (ii) (CH3)3COH + 6O2 4CO2 + 5H2O 1 mark for CO2 and H2O only

2[16]

6.

(i)

Any branched isomer of heptane with correct name, e.g. 2-methylhexane (1) 2

+

H

(ii)2

2[4]

7.

CH3CH(OH)CH3 + 4O2 3CO2 + 4H2O /C3H8O (1 mark if correct formula for all four chemicals and 1 mark for correct balancing)[2]

8.

Variation in boiling points. As chain length increases, boiling point increases

(max = 4 marks) 1 1 1 1

due to increased number of electrons/ surface area/ more van der Waals forces / intermolecular forces/ more surface interactions As branching increases, boiling point decreases straight chains can pack closer together/ straight chains have greater surface area/ more van der Waals forces /more intermolecular forces/ more surface interactions Isomerisation (max = 4 marks) (produces) branched chain alkanes

1

equation to illustrate any isomerisation (of octane) 1i n t o a n y o n e o o f r o a n r y o t h e r b o r r a n c h e d i s o m e r o f

Branched chains are better/more efficient fuels/used as additives because they are more volatile/easier to ignite/burn more easily/higher octane number(rating)/lower boiling points/reduces knocking (pinking) QWC mark use of suitable chemical terms such as van der Waals, intermolecular forces/ intermolecular bonds/volatile/ knocking/ pinking/pre-ignition reasonable spelling, punctuation and grammar throughout 1

1

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9.

Structural/chain/positional isomers have the same molecular formula, different structure but-1-ene/ but-2-ene/ methylpropene (any three or two with correct structures and names) 4 marks for structural isomerism Cis-trans /geometric isomerism cis & trans but-2-ene clearly identified C=C prevents rotation each C in the C=C double bond must be bonded to two different atoms or groups 4 marks for cis-trans isomerism QWC: Well organised answer making use of correct terminology to include any three from: structural, geometric, cis-trans, molecular formula, restricted, rotation, stereoisomerism, stereoisomers, chain isomerism, positional isomerism, if all isomers are correctly named / cyclobutane/ methylcyclopropane

1 3 1 1 1 1

1[9]

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10.

(a) separation by (differences in) boiling point (b) C7H16 C4H10 + C3H6 (c) (i) Any ofH H H H H 3C C C H C H C C H H H H

1 1

1H H H H H H H H 3C H H H H H C3H

C

(ii)

C7H16 C7H14 + H2 (d) (i) 2,2-dimethylpentane

(or by structural formula)

1 1

(ii) (iii) (iv)

3-methylhexane, 3,3 dimethylpentane or (3)-ethylpentane in any unambiguous form. 2 2,2,3-trimethylbutane if branched, difficult to pack/less surface interaction/less points of contact less van der Waals forces/ less intermolecular bonds/less energy needed to boil 1 1 1[10]

11.

Bonding:

-bond formed by overlap of (adjacent) p-orbitals/-bond labelled on diagram 1 diagram to show formation of the -bondH C H3

1m a l l o w e d C r a m m a r kC

H C H C

m i n i m u f o r d i a g o r

C

C

C

C

Shape/bond angles: tetrahedral around the CH3 1 1 1

bond angle = 10928/ (109-110) trigonal planar around each C in the C=C bond angle = 120 (118-122) Cis-trans cis & trans correctly labelled eg but-2-ene require a double bond because it restricts rotation each C in the C=C double bond must be bonded to two different atoms or groups 1 QWC Allow mark for well constructed answer and use of three terms like: orbital, tetrahedral, trigonal, planar, rotation, spatial, stereoisomers, geometric 1 1

1 1

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