Question

Which acid is used in the rubber industry as a coagulating agent?
A.Methanoic acid
B.Ethanoic acid
C.Propanoic acid
D.Butanoic acid

Answer 1

Hint: Rubber is extracted from the coagulation of latex.Latex, in its natural form, is a suspension of tiny rubber particles in an aqueous medium. These particles show the property of scattering of light, which makes the latex solution appear white and homogenous just like milk.

Complete step by step answer:
Formic is the acid used as a coagulating agent for coagulating latex and getting a high – quality natural rubber product.
Formic acid satisfies all the requirements for a good coagulating agent.
The particles have a uniform charge distribution on their surface. This charge creates a repulsive force between the individual particles. When there is repulsion between particles, they can not coagulate because during coagulation, particles are supposed to come close to each other and the repulsive force between like charges does not let that happen. Thus, there is a need for removal or neutralization of this force. The neutralization should be done with such a substance which is neither too weak nor too strong. This is because a weak acid would be used in more quantity and would be less efficient. Similarly, a strong acid would cause a sudden drop in pH, leading to non homogenous or irregular coagulation of the latex particles. This would affect the mechanical properties of rubber.
Thus, formic acid is used as a coagulant. It neutralizes the charges on latex particles, thus eliminating the forces of repulsion between the particles. This leads to efficient coagulation of latex to form rubber products.

Hence option A is correct.

Note:
Acetic acid is a weak acid and it can not be used because it is consumed in larger volumes and the product is not of as good a quality as that obtained by formic acid.
Strong acids would cause formation of irregular layers, hence, the mechanical strength of the product is compromised. Therefore, strong acids are not used.