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Indicator colour question.

I have come across this question asking what colour change occurs at the end point of the titration of sodium carbonate with hydrochloric acid if a methyl orange indicator is used.

The data sheet shows methyl orange as appearing red in acidic solutions and yellow in alkaline solutions and having a pH range of 3.2- 4.4.

The correct answer is given as C.

I would assume that as it is a strong acid- strong base reaction, the equivalence point would be at pH=7 and am unsure why this indicator is used, as the titration pH should not enter its range.

Any help would be appreciated.
(edited 1 year ago)
Original post by Tagsmags
I have come across this question asking what colour change occurs at the end point of the titration of sodium carbonate with hydrochloric acid if a methyl orange indicator is used.

The data sheet shows methyl orange as appearing red in acidic solutions and yellow in alkaline solutions and having a pH range of 3.2- 4.4.

The correct answer is given as C.

I would assume that as it is a strong acid- strong base reaction, the equivalence point would be at pH=7 and am unsure why this indicator is used, as the titration pH should not enter its range.

Any help would be appreciated.


It’s a strong acid-weak base titration, as Na2CO3 is a weak base. As such, the equivalence point will be below 7, so methyl orange may be a suitable indicator.

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