# What is double titration?

I an currently studying acid-base titrations. There is a concept of double titration. Can someone provide me an idea on what actually it is? Also what resources can I refer to?

• Did you search Google & Youtube? There are so many videos which explain it on the board. – M. Farooq Apr 26 at 14:51

Double titration is a method of determining the amount of substance present in the form of a solution along with another solution. It can be used in the case of a mixture of bases involving $$\ce{NaOH}$$, $$\ce{Na2CO3}$$ or $$\ce{NaHCO3}$$, $$\ce{Na2CO3}$$. These bases are titrated against strong acids with proper indicators. Generally a single indicator is not sufficient so two indicators are used.

Procedure:

Firstly Indicator 1 (generally phenolphthalein) is added to the solution and the solution is titrated against a strong acid of known normality which on complete neutralization gives endpoint 1. Then Indicator 2 (generally Methyl Orange) is added to the remaining solution and is titrated against a strong acid which gives endpoint 2.

For example: In case of titration of $$\ce{NaOH}$$, $$\ce{Na2CO3}$$ at the first endpoint only half of $$\ce{Na2CO3}$$ will be converted to $$\ce{NaHCO3}$$ At the second endpoint remaining half gram equivalent of $$\ce{Na2CO3}$$ and $$\ce{NaHCO3}$$ is neutralized. Thus by equating the gram equivalents acid 1 with half equivalent of $$\ce{Na2CO3}$$ and half equivalent of $$\ce{Na2CO3}$$ plus equivalent of $$\ce{NaHCO3}$$ to equivalent of acid 2 we can get the amount of $$\ce{NaHCO3}$$ and $$\ce{Na2CO3}$$ in the solution.

• Another option is titration with the pH meter. – Poutnik Apr 26 at 15:24