One day Amit went to a bicycle repair shop to get broken iron part of his younger brother's bicycle welded. This shop has a gas welding set. At that time the main welder Mr. Ahmad was not present in the shop. Mr. Ahmad's assistant Chhotu offered to do the welding of broken bicycle part. When Chhotu started doing welding, Amit observed that a yellow sooty flame was being produced by the welding torch. By using this flame, Chhotu was unable to weld the two pieces of broken iron part together. Being a science student of class X Amit could understand the mistake being made by Chhotu. He pointed the mistake to Chhotu. Chhotu then followed the instructions of Amit and succeeded in welding the broken Iron part. By that time Mr. Ahmad had also arrived. He thanked Amit for correcting the mistake of Chhotu. He also advised Chhotu to be careful in future.
(a) Which organic compound is used in gas welding?
(b) What was the reason for the yellow sooty flame being produced by the welding torch?
(c) Why the yellow sooty flame could not weld the broken iron pieces?
(d) What was the mistake being made by Chhotu which was corrected by Amit?
(e) What was the colour of the flame produced by welding torch now and why could it weld broken iron pieces together?
(f) What values are displayed by Amit in this episode?

Explanation

(a) The organic compound used in gas welding is acetylene (or ethyne). It is a gas.
(b) The reason for the production of yellow sooty flame by the welding torch was the incomplete combustion of acetylene in air. This is because air does not contain sufficient oxygen to bring about the complete compution of acetylene (which has high percentage of carbon in it).
(c) The temperature of yellow sooty flame obtained by burnig acetylene in air is not very high. This temperature of welding torch flame is insufficient to melt iron and weld the iron pieces together.
(d) Chhotu was using the combustion of acetylene in air welding. He should have used the combustion of acetylene in pure oxygen for welding. Acutally, Chhotu, forgot to open the knob of oxygen cylinder before welding to mix oxygen with acetylene before lighting the welding torch. Amit asked Chhotu to use oxygen-acetylene flame welding.
(e) The colour of oxygen-acetylene flame produced by burning a mixture of oxygen and acetelene in the welding torch was blue. The blue oxygen-acetylene flame is extremely hot and produces a very high temperature whihc is sufficient of melt iron and weld the two broken iron pieces together.
(f) The values displayed by Amit in this episode are (i) Awareness (or knwoledge) that in gas welding a mixture of acetylene and pure oxygen is burned in the welding torch so as to produce a very high temperature and (ii) Desire to help others.