Ordinary level 2026 North West mock Engineering science 2 guide

MARKING GUIDE FOR REGIONAL MOCK: ENGINEERING SCIENCE 2026

1a.

(i) $C_2H_2$ (acetylene or Ethyne)
(ii) $CaC_2 + 2H_2O \longrightarrow Ca(OH)_2 + C_2H_2$
(iii) Using the equation above:
- $64\text{g of } CaC_2 = 74\text{g of } Ca(OH)_2$
- $2.5\text{g of } CaC_2 = \frac{74 \times 2.5}{64} = 2.89\text{g of } Ca(OH)_2$

1b.

(i) Quantity of electricity used $Q = I \times t$
- $Q = 2\text{A} \times 15 \times 60 = 1800\text{C}$
- $96000\text{C} \longrightarrow 1\text{F}$
- $1800\text{C} \longrightarrow \frac{1800\text{C} \times 1\text{F}}{96000\text{C}} = 0.0188\text{F}$
(ii) $Li^+ + e^- \longrightarrow Li$
- $1\text{F} \longrightarrow 1\text{mole}$
- $0.0188\text{F} \longrightarrow \frac{0.0188\text{F} \times 1\text{mole}}{1\text{F}} = 0.0188\text{F}$
(iii) $2H^+(aq) + 2e^- \longrightarrow H_2(g)$
- $2 \times 96000\text{C} \longrightarrow 24000\text{cm}^3$
- $1800\text{C} \longrightarrow \frac{1800 \times 24000}{2 \times 96000} = 225\text{cm}^3$

1c.

(i) Catalytic cracking breaks long-chain hydrocarbons into shorter, more useful ones using a catalyst. This process produces more branched, cyclic, and aromatic hydrocarbons, which have higher octane numbers. The petrol made from catalytic cracking is high-octane, meaning it burns smooth in engines and resists knocking.
(ii) Air pollution, global warming.

1d.

(i) A strong acid is one that completely ionises in water. Examples: Hydrochloric acid ( $HCl$ ), Sulphuric acid ( $H_2SO_4$ ).
- A weak acid is one which ionises partially in water. Examples: Ethanoic acid ( $CH_3COOH$ ), Carbonic acid ( $H_2CO_3$ ).
(ii) $CaCO_{3(s)} + 2HCl_{(aq)} \longrightarrow CaCl_{2(aq)} + H_2O_{(l)} + 2CO_2$
- Carbon dioxide is given off.

1e.

(i) The atomic number is 56, and it represents the number of protons present in the nucleus of Barium.
(ii) Number of neutrons $= 137 - 56 = 81$
(iii) Number of electrons $= 56$
(iv) Barium forms $Ba^{2+}$ instead of $Ba^+$ because losing two electrons gives it the stable noble-gas configuration of Xenon, while losing only one electron leaves it in a less stable state. Therefore, $Ba^{2+}$ is much more energetically favourable.

1f.

(i) Mass of Magnesium $= 15\text{g}$
- Molar mass of $Mg = 24\text{g/mol}$
- Moles of $Mg = \frac{15}{24} = 0.625\text{mol}$
(ii) $2Mg + O_2 \longrightarrow 2MgO$
- $Mg:MgO = 1:1$
- So, moles of $MgO$ formed = moles of $Mg$ used
- Moles of $MgO = 0.625\text{mol}$