An acid-base indicator has $K_{a} = 3.0 \times 10^{- 5}$ . The acid form ofthe indicator is red and the basic form is blue. Then pH is ___________ when indicator is 75% blue.

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Solution

The correct option is D 5
As we know,

$p H = p K I n + l o g [I n] / [H I n]$

so when the indicator is 75% red.

$p H = p K I n + l o g [I n] / [H I n] = 5 - l o g 3 + l o g 0.25 / 0.75 = 4.04$

and when the indicator is 75% blue.

$p H = p K I n + l o g [I n] / [H I n] = 5 - l o g 3 + l o g 0.75 / 0.25 = 5$

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Similar questions

K_{a} = 3.0 \times 10^{- 5}

K_{a} = 3.0 \times 10^{- 5}

K_{H I n} = 3.0 \times 10^{- 5}

[H^{+}]

75 %

75 %

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