Question

Which of the following is used as an acid base indicator?
A) Potato
B) Tomato
C) Turmeric
D) Dry litmus

Answer 1

Hint:An indicator of acid and bases are the ones which show visible changes when exposed to acid or bases and both the changes are different from each other.
An indicator of acid and bases should not be acidic or basic in nature, as it could interfere with the actual results.


Complete Answer:
In order to answer this question, we will need to know what acid and bases are. There are a number of ways in which we can define the acid and bases.
According to Lewis acid definition, any species which is capable of accepting electrons, is termed as a Lewis acid, and any species which are capable of donating electrons in order to become more electrically stable species, are called Lewis bases.
In terms of Bronsted-Lowry definition of acid and bases, any species which is capable of liberating protons, which has the chemical symbol \[{{H}^{+}}\], in a solution, are acids. And any species which are capable of accepting protons, are called bases.
Lastly, the Arrhenius definition of acid and bases is based on the liberation of protons and hydroxide ions. The species which liberated protons in a solution are acids, and the ones which donate hydroxide ions are bases.
Now we will consider each of the options one by one, which are being provided to us in the question, and see which one is most appropriate.
The first option is potato, we all know that potato is made up of starch which can indicate the presence of iodine, at best, but not acid or base. So, the first option is incorrect.
For the second option, the tomato is acidic in nature as it contains ascorbic acid which is a weak acid. So, it cannot indicate the presence of acid or base as this would interfere with the actual results.
Turmeric turns yellow when exposed to acid and neutral solutions, and it turns bright red when exposed to basic solutions. So, clearly it can be used as an indicator. So, it is the correct option.
As per the last option, dry litmus cannot act as an indicator, because in dry litmus the protons of the acid would not dissociate and so it wouldn’t show the appropriate result. So, this option is also incorrect.

Hence, the correct option would be option C, which is turmeric.


Note:Potato is composed of starch which cannot indicate the acid base content in a solution. Tomato contains ascorbic acid so it will interfere with the actual results.
Turmeric bright red in base and yellow in acid and neutral solutions. Dry litmus cannot act as an indicator as the protons would not get the medium to dissociate.