Question

When $\,5\,$ drops azolitmin $\, + 0.5\% \,$aqueous solution of bleach is mixed the change in colour appear is:
A.Red
B.Blue
C.Lilac
D.Black

Answer 1

This reaction is a type of acid-base indicator reaction. We have to first analyse the reaction between azolitmin and aqueous solution of bleach in order to find out the colour change. Here, azolitmin is the indicator which is actually a fraction of litmus and bleach is mainly basic. We have to analyse the colour change happening when azolitmin reacts with a base.

Complete answer:
Let us first understand an acid-base indicator reaction;
-A weak acid or a weak base is an acid-base indicator. A colour other than the ionic form of the indicator is the undissociated form of the indicator. At a single hydrogen ion concentration, an indicator does not change colour from pure acid to pure alkaline, but instead changes colour over a spectrum of hydrogen ion concentrations. This period is considered an interval of colour transition. It is expressed in the spectrum of $\,pH\,$.
-Weak acids are titrated under mildly alkaline conditions in the presence of indicators that alter. It is important to titrate weak bases in the presence of indicators that shift under slightly acidic conditions.
-Now, coming to the question;
Azolitmin is in the $\,pH\,$range of $\,5.0 - 8.0\,$. It changes to red colour when treated with acid and changes to blue colour when reacted with a base . From this it is clear that option B is the correct answer for this question as bleach is basic in nature.
So, the correct answer is “Option B”.

Note:
Azolitmin is a purple-red colouring substance derived from natural litmus or synthesised in the presence of ammonia, lime, and potash by oxidising orcinol. In various types of lichens, litmus can be found.