Dyeing And Bleaching Paper 2 May/June 2015

Question 6

  1. (a)        State three methods of bleaching.
    (b)        List six bleaching agents.
    (c)        Mention three precautionary measures to be taken when bleaching.


Most candidates were unable to exhibit a thorough knowledge of bleaching agents involved in bleaching process, instead they were mentioning the trade names of the finished products like Jik, Hypo which are not acceptable. What is requested of them are: sodium hydrosulphite; caustic soda; chlorine; hydrogen peroxide etc. Candidates misinterpreted the question by highlighting the precautionary measures after bleaching such as washing hands with detergent and not the measures to be taken during the bleaching processes. For instance, wearing apron/overall to avoid stains; wearing of rubber gloves etc. The candidates’ are yet to understand the content of this topic.  They were expected to respond to the question in the following manner:


(i)       Hypochloride bleaching;
(ii)       Oxidation bleaching;
(iii)       Hydrogen peroxide bleaching;
(iv)       Sodium chlorite bleaching;
(v)       Fluorescent whitening bleaching;
(vi)       Hydrosulphite bleaching;
(vii)      Chlorine bleaching.


(i)      Chlorine;
(ii)      Caustic soda/Sodium hydroxide;
(iii)      Sodium hydrosulphite;
(iv)      Thinner;
(v)      Hydrogen peroxide;
(vi)      Sodium hypochlorite;
(vii)      Sodium Chlorite;
(viii)     Turpentine;
(ix)     Calcium hypochloride;
(x)      Fluorescent whitening.


(i)       Wear safety/rain/industrial boots.
(ii)      Wear nose and mouth masks.
(iii)      Wear rubber gloves.
(iv)      Use apron/overall.
(v)       Wear safety glasses/sun shade.