3 Crude oil is a mixture of hydrocarbons and provides many useful chemicals when processed - CIE - A-Level Chemistry - Question 3 - 2016 - Paper 1

From fraction A to fraction F, there is an increasing molecular size, which corresponds to a higher number of carbon atoms per molecule, leading to longer carbon chains.

1. Viscosity: It increases with higher fractions, as larger molecules are more viscous.
2. Flammability: It decreases from fractions A to F, with lighter fractions being more flammable due to simpler structures.

The equation for the cracking process can be represented as:
$C_nH_{2n} \rightarrow C_2H_4 + C_{(n-2)}H_{(2(n-1))}$

1. Use of ethene: Ethene is widely used in the production of plastics such as polyethylene. Its unsaturated nature allows it to undergo polymerization easily.
   Explanation: The double bond in ethene is reactive and facilitates the formation of long polymer chains.

2. Use of the other hydrocarbon: Depending on the specific hydrocarbon, it could be used as a fuel or a solvent.
   Explanation: Many hydrocarbons from cracking are effective fuels due to their combustion properties.

Oxides of nitrogen are produced in internal combustion engines due to the high temperature and pressure conditions. Under these conditions, nitrogen and oxygen react to form nitrogen oxides (NO and NO2). This reaction is facilitated by the heat generated during combustion.

The reaction can be represented as:
$2NO + 2CO \rightarrow 2N_2 + 2CO_2$

1. $2NO + O_2 \rightarrow 2NO_2$
2. $SO_2 + NO_2 + H_2O \rightarrow H_2SO_4$

1. Harm to aquatic life: Acid rain can lower the pH of water bodies, adversely affecting fish and other aquatic organisms.
2. Damage to vegetation: It can lead to the leaching of nutrients from soil and damage leaves, rendering plants weaker and less productive.