Question

Incomplete combustion of petrol or diesel oil in automobile engines can be best detected by testing the fuel gases for the presence of _ _ _ _ _ _ _ _ _ _ _ _?
(A) Carbon monoxide and water vapour
(B) Carbon monoxide
(C) Nitrogen dioxide
(D) Sulphur dioxide

Answer 1

Hint: Incomplete combustion occurs when there is inadequate supply of oxygen or air. The gas released by this is highly toxic and reduces the ability of blood to transport oxygen by binding with haemoglobin to form carboxy-haemoglobin.

Complete step by step answer:
-We all know that different types of fuels are used to run automobiles. Basically a fuel is said to be a material which when reacted with other substances (like oxygen) releases energy in the form of heat or light. The heat engines have the ability to convert this heat energy released by the reaction of fuels into mechanical energy.
-When a fuel like petrol or diesel burns in air, it can receive oxygen in excess amount (since the air is 21% oxygen) and thus undergoes complete combustion. Complete combustion can occur only if plenty of oxygen is available and the elements present in fuel can fully react with it.
Fuels like petrol and diesel are usually made of hydrocarbons which are compounds of hydrogen and carbon. When they undergo complete combustion the carbon oxidised to form carbon dioxide and hydrogen oxidised to form water.
The reaction for complete combustion can be written as:
 ${C_x}{H_y}(g) + \left( {x + \dfrac{y}{4}} \right){O_2}(g) \to xC{O_2}(g) + \dfrac{y}{2}{H_2}O(l)$
For propane: ${C_3}{H_8} + 5{O_2} \to 3C{O_2} + 4{H_2}O$
-When petrol or diesel oil burns under conditions of inadequate supply of air or oxygen, the fuel does not burn completely and thus leads to incomplete combustion. During this the carbon oxidised to form carbon monoxide and hydrogen oxidised to form water. So, incomplete combustion produces carbon monoxide, carbon and water.
For example: propane undergoes incomplete combustion as:
$2{C_3}{H_8} + 7{O_2} \to 2C + 2CO + 2C{O_2} + 8{H_2}O$
The carbon released is in the form of soot and the carbon monoxide gas released is highly poisonous. When inhaled, carbon monoxide binds with the haemoglobin molecules to form carboxy-haemoglobin. This reduces the capacity of blood to transport oxygen.
So, incomplete combustion of petrol or diesel oil in automobile engines can be best detected by testing the fuel gases for the presence of carbon monoxide.

The correct option will be: (B) Carbon monoxide.

Note: Carbon monoxide is a colourless and odourless gas which reduces the binding sites for oxygen in blood, thus reducing the capacity to transport oxygen. It causes headache, dizziness, stomach ache, vomiting and nausea. Eventually it will lead to suffocation and death.