PHYSICAL SCIENCES
PAPER 2
GRADE 12 
NSC EXAMS
PAST PAPERS AND MEMOS NOVEMBER 2018

MEMORANDUM 

QUESTION 1
1.1 C ✔✔ (2)
1.2 C ✔✔ (2)
1.3 C ✔✔ (2)
1.4 A ✔✔ (2)
1.5 D ✔✔ (2)
1.6 B ✔✔ (2)
1.7 B ✔✔ (2)
1.8 D ✔✔ (2)
1.9 D ✔✔ (2)
1.10 B ✔✔ (2) [20]

QUESTION 2
2.1 ANY ONE

  • (Alcohol/ethanol) is flammable/catches fire easily.
  • To heat it evenly.
  • Water bath is used for low heat/low temperature.
  • Alcohol/ethanol will evaporate too quickly.
    Accept/
    (Alcohol/ethanol) is volatile.  (1)

2.2
2.2.1  Esterification/condensation  (1)
2.2.2  H2SO4  (1)
2.2.3  Esters   (1)
2.3

  • M(ester)       = 144   =  2
    M(C4H8O)        72
    ∴  2 x C4H8O = C8H16O2 

Marking guidelines:

  • If only answer given, award 2 marks on final
  • If 72 g·mol-1 calculated without substituting, no   mark   is   awarded (2)

2.4  Ethyl hexanoate   (2)
Note

  • Accept any other ethyl ESTER from QUESTION 2.3.

2.5 POSITIVE MARKING FROM QUESTION 2.4.
1 kgujygayud
Marking criteria

  •  Whole structure correct 2/2
  • Only functional group correct : Max: 1/2
  • Accept  -OH as condensed  (2)[10]

QUESTION 3
3.1 Marking guidelines/

  • If any one of the underlined key phrases in the correct context is omitted, deduct 1 mark
  • The temperature at which the vapour pressure of a substance equals atmospheric/external pressure.  (2)

3.2
3.2.1Carboxyl (group)
Accept

  • Carboxylic  (1)

3.2.2 Propanoic acid/propanoësuur  (1)
3.2.3
2 khuiahdik
Marking criteria

  • Whole structure correct: 2/2
  • Only functional group correct: 1/2

IF

  • More than one functional group/wrong functional group 0/2
  • If condensed structural formulae used: Max: 1/2

3 khaghkudghuia
3.3 A  -  Lowest boiling point./Shortest chain length. 
3.4
3.4.1 The same molecular mass/molecular size. 
3.4.2 Primary

  • OH group is bonded to a C atom bonded to one other C atom. 
    OR
  • OH group is bonded to a C atom that has two H atoms.

3.4.3 Marking guidelines

  • BOTH have hydrogen bonding.
  • Compare number of sites for hydrogen bonding.
  • Compare strength of IMFs.
  • Compare energy required.
  • Both compounds/X and B have (in addition to London forces and dipole-dipole forces) hydrogen bonding.
  • Compound X/CH3CH2CH2OH/propan-1-ol/alcohol has one site for hydrogen bonding and compound B/ethanoic acid/carboxylic acid has two/more sites for hydrogen bonding OR B/ethanoic acid/carboxylic acid has two/more sites for hydrogen bonding. 
  • Intermolecular forces in compound B/ethanoic acid/carboxylic acid are stronger than intermolecular forces in compound X/CH3CH2CH2OH/ propan-1-ol/alcohol.
    OR
    Intermolecular forces in compound X/CH3CH2CH2OH/ propan-1-ol/alcohol are weaker than intermolecular forces in compound B/ethanoic acid/carboxylic acid.
  • More energy is needed to overcome/break intermolecular forces in compound B/ethanoic acid/carboxylic acid than in compound X/CH3CH2CH2OH/ propan-1-ol/alcohol.
    OR
    Less energy is needed to overcome/break intermolecular forces in compound X/CH3CH2CH2OH/propan-1-ol/alcohol than in compound B/ethanoic acid/carboxylic acid.   (4)  [15]

QUESTION 4
4.1
4.1.

  • (A series of organic) compounds that can be described by the same general formula/functional group.   (2 or 0)
    OR
    (A series of organic) compounds in which one member differs from the next by a CH2  group   (2)

4.1.2 Substitution/halogenation/bromination  (1)
4.1.3  HBr  (1)
4.1.4  
4 jhgujygauygd
Marking criteria

  • Br on first C atom: Max: 1/2
  • Whole structure correct   2/2

IF

  • Br2 but rest of structure correct  (2)

4.1.5 C5H12  +  8O2 → 5CO2  +  6H2O     Bal 
Marking guidelines

  • Reactants             Products               Balancing
  • Ignore double arrows and phases.
  • Marking rule 6.3.10/Nasienreël 6.3.10.
  • If condensed structural formulae used : Max: 2/3   (3)

4.1.6 Marking guidelines/Nasienriglyne

  • If any one of the underlined key phrases in the correct context is omitted, deduct 1 mark

The (chemical) process in which longer chain hydrocarbons/longer chain alkanes are broken down to shorter/more useful hydrocarbons/molecules/ chains/alkanes and alkenes.  (2)
4.1.7
5 jhgvyagyud
Marking guidelines

  • One or more H atoms omitted : Max: 1/2
  • Condensed or semi-structural formula:Max: 1/2  (2)

4.2
4.2.1 Butan-2-ol OR  2-butanol
IF:

  • Butanol  or butan-1-ol 1/2  (2)

4.2.2
6 jhgygauygd
Marking criteria

  • Only functional group correct: Max/Maks: 1/2
  • Whole structure correct: 1/2  (2)  [17]

QUESTION 5
5.1Temperature (1)
5. 2 NOTE
Give the mark for per unit time only if in context of reaction rate.
 ANY ONE

  • Change in concentration  of products/reactants per (unit) time. 
  • Change in amount/number of moles/volume/mass of products or reactants  per (unit) time.
  • Amount/number of moles/volume/mass of products formed/reactants used per (unit) time.
  • Rate of change in concentration/amount/number of moles/volume/mass. (2 or/of 0)   (2)

5.3 14 (min)  (2)
5.4
5.4.1 Graph  B 

  •  (Experiment 3) has the highest (acid) concentration/more particles/higher number of moles.   (2)

5.4.2 (Graph/grafiek) C 

Related Items

  • (Experiment 5) is at highest temperature/more particles with sufficient kinetic energy/HCℓ is at 35oC    (2)

5.5
5.5.1 Speeds  up  the  reaction./Increases  the  reaction  rate./Provides  alternate pathway./Lowers the (net) activation energy. (1)
5.5.2 Equal to  (1)
5.6 
7 jhkuahukda
Marking guidelines

  • Substitute 65 g∙mol-1 in n = m
                                                M
  • Substitute change in mol to calculate  rate.
  • Substitute change in time to calculate  rate.
  • Final answer:
         1,65 x 10-3 mol∙min-1 
    Range/Gebied:
    1,43 x 10-3 to/tot 1,65 x 10-3 (mol∙min-1)

Notes

  • Ignore if zeros omitted in calculation of reaction rate.
  • Accept negative answer i.e. -1,65 x 10-3 mol·min-1  (4)  [15]

QUESTION 6
6.1

  • When the equilibrium in a closed system is disturbed, the system will re- instate a (new) equilibrium  by favouring the reaction that will cancel/oppose the disturbance.     (2)

6.2 Endothermic

  • Decrease in temperature favours the exothermic reaction.
  • The   reverse   reaction   is   favoured.
    OR
    Number of moles/amount/concentration of N2O4/colourless gas increases.
    OR
    Number of moles/amount of NO2/brown gas decreases. (3)

6.3
6.3.1 Increases (1)
6.3.2 Remains the same (1)
6.3.3 Increases  (1)
6.4  CALCULATIONS USING NUMBER OF MOLES
Marking guidelines/Nasienriglyne

  •  ∆n(N2O4) = 20% of x/0,2x. 
  • USE ratio: N2O4 : NO2 : = 1 : 2. 
  • n(N2O4)eq/ewe = n(N2O4)initial/begin - ∆n(N2O4).
  • n(NO2)eq/ewe = n(NO2)initial/begin + ∆n(NO2).
  • Divide equilibrium moles by 2 dm3
  • Correct Kc expression (formulae in square brackets).
  • Substitution of Kc value
  • Substitution of concentrations into correct Kc expression. 
  • Final answer/Finale antwoord: 1,6 (mol) 

8 khgyjuagdua
CALCULATIONS USING CONCENTRATION
Marking guidelines

  • Initial n(N2O4)/x divide by 2 dm3.
  • ∆c(N2O4) = 20% of initial concentration/0,1x.
  • USE ratio/GEBRUIK verhouding: c(N2O4) : c(NO2)  = 1 : 2.
  • c(N2O4)eq/ewe = c(N2O4)initial/begin - ∆c(N2O4).
  • c(NO2)eq/ewe = c(NO2)initial/begin + ∆c(NO2).
  • Correct Kc expression (formulae in square brackets).
  • Substitution of Kc value/Vervanging van Kc-waarde.
  • Substitution of concentrations into Kc expression.
  • Final answer/Finale antwoord: 1,6 (mol) 

OPTION 3
9 jkhgjyagyudh(8) [16]

QUESTION 7
7.1
7.1.1 An acid is a proton donor. (2)
7.1.2 H2O  (1)
7.1.3 HSO-4    (2)
7.2
7.2.1 Reaction of a salt with water/H2O. 
Accept

  • Reaction of cations or anions with water  (2)

7.2.2 
ans kjgkygad
Marking guidelines

  • Reactants    Products
  • The formation of OH  (aq) neutralises the excess acid.
  • Ignore single arrows and phases
  • Marking rule 6.3.10
  • Ignore balancing.

7.3
7.3.1

  • pH = -log[H3O+]
    5  = -log[H3O+]
    [H3O+] = 1 x 10-5 mol·dm-3 (3)

7.3.2 POSITIVE MARKING FROM QUESTION 7.3.1.
Marking guidelines

  • Any formula : c = n / n = m / Ca x Va=na /c = m
                                V        M    Cb x Vb   nb       MV
  • Substitute V = 4 x 109 dm3 
  • Calculate na(reacted) = na(initial) - na(final) 
  • Use  n(CaO) : n(H3O+) = 1:2
  • Substitution of 56 g∙mol-1 
  • Final answer : m = 1,08 x 106 g to/tot 1,09 x 106 g  

IF final answer is negative: Max: 6/7
10 ighaiygduyag(7) [20]

QUESTION 8
8.1
8.1.1 Loss of electrons./Verlies aan elektrone.  (2 or/of 0)            (2)
8.1.2 Fe → Fe3+ + 3e
Marking guidelines

  •  ans kljhkuhad
  • Ignore if charge omitted on electron.
  • If charge (+) omitted on Fe3+: Example:  Fe → Fe3 + 3e- 
    Max1/2  (2)

8.1.3 Reducing agent   (1)
8.1.4

  • Fe is a stronger reducing agent  than Cu  and (Fe) will be oxidised  (to Fe3+).
    OR
  • Cu is a weaker reducing agent  than Fe and (Cu) will not be oxidised  (to Cu2+). (3)

8.1.5 Zinc/Zn 

  • Stronger reducing agent (than Fe).
    OR
  • Zn will undergo oxidation (before Fe).
    OR
  • Cu is a weaker reducing agent (than Fe). (2)

8.2
8.2.1 3Cu2+ + 2Fe  → 3Cu + 2Fe3+                Bal.
Marking guidelines/Nasienriglyne

  • Reactants              Products               Balancing 
  • Ignore double arrows.
  • Marking rule 6.3.10   (3)

8.2.2
jgjagdug
(4) [17]

QUESTION 9
9.1

  • A cell in which electrical energy is converted to chemical energy.  (2 or 0)
    OR
  • A cell in which electrical energy/electricity is used to obtain a chemical change/reaction. (2 or 0) (2)

9.2 Any soluble copper(II) salt e.g

  • CuSO4/Cu(NO3)2/CuCℓ2  (1)

9.3  Marking guidelines

  • alisjiouad
  • Ignore if charge on electron is omitted.
  • If a charge of an ion is omitted e.g. Cu2 + 2e- → Cu  Max.:  1/2 (3)

9.4 Platinum/Pt  AND  silver/Ag/  (2) [8]

QUESTION 10
10.1
10.1.1 Haber (process)
10.1.2 Ostwald (process)
10.2
10.2.1Ammonium nitrate/Ammoniumnitraat/NH4NO3 
10.2.2  Iron/iron oxide/Fe/FeO 
10.3       

  • 2NH3    +  H2SO4   →  (NH4)2SO4     Bal 

Marking guidelines

  • Reactants              Products             Balancing
  • Ignore double arrows.
  • Marking rule 6.3.10

10.4 khuygaud
10.4 b kbkahbda  (5)

[12]
TOTAL: 150 

Last modified on Wednesday, 22 September 2021 08:49