Question

Write reasons for the following:
(i) The dark zone of the flame has no oxygen.
(ii) Biogas is a better fuel than wood

Answer 1

Hint:The given statements are empirical and true thus, the reasoning for them are based on the general knowledge of us. We need a basic idea of flames and fuels concept.

Complete step-by-step answer:Let us given the valid reasons for the given statements one by one;
1. The dark zone of the flame has no oxygen-
-The flame in the candle is a result of the vaporisation of products produced by the chemical reaction taking place known as combustion in which wax reacts with oxygen in air to produce carbon dioxide.
-Flame is the area of combustion of a combustible substance. So, the substances which do not vaporise during the combustion, do not produce flame.
-The candle flame is categorised by the different colours shown to recognise the zone of burning. The flame colour depends upon the nature of substance undergoing combustion, amount of oxygen supplied and temperature.
-The candle flame has different zones as mentioned below;
a. Outermost zone-
A non-luminous zone which is blue in colour and is barely visible. Here, complete combustion of the substance takes place as plenty of air is present surrounding itself. It is the first zone and thus, hottest in temperature as compared to other zones.
b. Central or middle zone-
A luminous zone which is yellow in colour and is the major part of the flame. The wax vapours undergo incomplete combustion here as supply with air is not fulfilled here. This region is bright but is moderately hot. The incomplete combustion results in the formation of carbon particles which glow in this region making it brighter.
c. Inner zone-
It is the darkest zone mostly black in colour surrounding the wick of the candle. In this region very less or no combustion takes place as it has no supply of oxygen and thus is the least hot zone of the flame.
This zone is directly above the wick of the candle and the wax getting vaporized in this region does not get proper exposure to oxygen. Due to lack of oxygen supply, the wax here does not undergo burning.
2. Biogas is a better fuel than wood-
Basically, biogas is better than wood as for the fuel from wood, we need to cut trees resulting in deforestation and harm to nature. Whereas, biogas can be produced from organic waste matter which is the key to dispose of the waste in an effective manner. Other advantages of biogas are as discussed below;
a. It is eco-friendly as it does not leave any ash after burning and has higher calorific value.
b. Biogas production will reduce the soil and water pollution which are the major point of concern nowadays.
c. The generation of biogas produces organic fertiliser.
d. It is simpler and low-cost technology which can be utilised on a small scale too.

Note:We must have the better understanding about flames and combustion to define the black zone of combustion.
Also, compared to wood, biogas is the basic alternative for domestic cooking too.