A mixture of oxygen and ethyne is burnt for welding

2 H C ≡ C H + S O 2 → 4 C O 2 + 2 H 2 O+ Heat When ethayne is burnt in air,it gives a sooty flame .This is due to incomplete combusition caused by limited supply of air.However if ethyne is burnt with oxygen,it gives a clean flame with temprature 3000 ∘ c because of complete combusition.This acetylene flame is used for welding.It is not possible to attain such a high temprature without mixing oxygen.This is the reason why a mixture of ethyne and air is not used. (a) An organic compound X of molecular formula C 2 H 4 O 2 gives brisk effervescence with sodium hydrogencartbonate. Give the name and formula of X. (b) A mixture of ethyne (acetylene) and oxygen is burnt for welding . Can you tell why a mixtrue of ethyne and air is not used (c ) Name a chemical rection which is characteristic of unsatureated hydrocarbons (like alkneses and alkynes).

i. Ethyne is an unsaturated hydrocarbon. On combustion in air, it produces a yellow flame with lots of black smoke. ii. Due to this incomplete combustion, heat produced is low and temperature obtained is also low. iii. For welding purposes, high temperature is required. iv. When a mixture of acetylene and oxygen is used, complete combustion is achieved and very high temperature required for welding is obtained. Hence, a mixture if acetylene and oxygen is used for welding instead of a mixture of acetylene and air.

SOLUTION When ethyne is burnt in air, it gives a sooty flame. This is due to incomplete combustion caused by limited supply of air. However, if ethyne is burnt with oxygen, it gives a clean flame with temperature 3000 o C because of complete combustion. This oxy-acetylene flame is used for welding. It is not possible to attain such a high temperature without mixing oxygen. This is the reason why a mixture of ethyne and air is not used.

When ethyne is burnt with air, it gives a yellow sooty flame which has much lower temperatures. This is because ethyne is not burnt completely. So, statement 1 is correct. When pure oxygen is used, the flame is cleaner, the combustion of ethyne is complete, and much higher temperatures can be used with lesser quantities of ethyne. So, statement 2 is correct. Moreover, air contains many gases other than oxygen which may be undesirable in the process of welding. This is why oxygen is used instead of air.

The required is: 2 C H = C H + 5 O 2 ​ → 4 C O + 2 H 2 ​ O + heat Now, We can easily explain that when ethyne is brunt in air, it gives a sooty flame. This is due to incomplete combustion caused by limited supply of air. Similar, When ethyne is burnt with oxygen, it gives a clean flame due to complete combustion. This oxy-acetylene flame is used for welding. So, It is not possible to attain such a high temperature without mixing of oxygen. This is the required reason. Reason Combustion of ethane in air produces a yellow flame with black smoke due to the presence of unburnt carbon in it. Due to this incomplete combustion heat produced is also low and a high temperature usually needed for welding cannot be attained. A mixture of oxygen and ethane can not be burnt for welding.

Ethyne burns in air with a sooty flame because of incomplete combustion caused by the limited supply of air. However, ethyne burns in oxygen with a clean flame with a temperature of 3000°C because of complete combustion. This oxy-acetylene flame is used for welding. Such a high temperature cannot be achieved without mixing oxygen. Therefore, a mixture of ethyne and air is not used for welding.