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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?

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

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    $\begingroup$ Another option is titration with the pH meter. $\endgroup$ – Poutnik Apr 26 at 15:24

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