A solution of sodium hydroxide has a concentration of (2.1 x 10^-1)mol/L. What colour does the solution turn when a few drops of indigo carmine are added?

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Answer 1 · 2017-07-02T22:27:36

The solution will be will be yellow.

What is the pH?

#["OH"^"-"] = 2.1 × 10^"-1"color(white)(l) "mol/L"#

#"pOH" = -log(2.1 × 10^"-1") = 0.68#

#"pH = 14.00 - pOH = 14.00 - 0.68 = 13.34"#

What colour is the indicator?

Indigo carmine is blue at pH 11.4 and yellow at pH 13.0.

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Since pH > 13.0, the indicator will be #color(orange)("yellow")#.