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.

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

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

3.3 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  

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

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

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 35^oC    (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 

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) 

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
(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 

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 / C_a x V_a=n_a /c = m
                              V        M    C_b x V_b   n_b       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
(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

•  
• 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

(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

• 
• 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

  (5)

[12]
TOTAL: 150