Question

In a paper mill bleaching powder is not added while preparing paper and the paper obtained was yellowish brown in colour what is the reason for this

Answer 1

The wood pulp used to make paper undergoes chemical pulping process in which the lignin is dissolved. After the chemical pulping process there are still some traces of lignin present in the wood pulp. This lignin gives the yellowish brown color to the paper and reduce the brightness of the paper. Hence to remove any color from the lignin bleaching is done to make the paper white.

Different elements used in bleaching are chlorine, oxygen and hydrogen peroxide.