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Salt of Strong Acid and Weak Base

In an acidic ...

Question

In an acidic indicator HIn has ionization constant is $10^{- 8}$ . The acid form of indicator is yellow and alkaline form is red. Which is correct statement?

Given: $l o g (2) = 0.3; l o g (3) = 0.48$

The pH range of indicator is 7 to 9.

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Change in pH is 0.96 when 75% yellow colour change to 75% red colour.

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This indicator is suitable for the titration of strong acid vs. strong base.

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pH of indicator is 8.3 when ratio of acid form to alkaline form is 2.

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Solution

The correct options are
A The pH range of indicator is 7 to 9.
B Change in pH is 0.96 when 75% yellow colour change to 75% red colour.
C This indicator is suitable for the titration of strong acid vs. strong base.
In most cases, the visible change takes place about 1 $p H$ unit either side of the $p K_{i n d}$ value.
Here, $p K_{i n d} = 8$
So, range of indicator is 7 to 9.

$p H_{1} = 8 l o g \frac{25}{75} = 8 + l o g \frac{1}{3}$

$p H_{2} = 8 l o g \frac{75}{25} = 8 + l o g 3$

Change in $p H = l o g 3 - l o g \frac{1}{3} = 2 l o g 3 = 0.96$

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Similar questions

H I n

10^{- 8}

l o g 2 = 0.3, l o g 3 = 0.48

H I n

9.0 \times 10^{- 9}

30

1

2

1

p H

H I n

K_{a} = 3 \times 10^{- 5}

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

[H^{+}]

75 %

75 %

1.0 \times 10^{- 6}

p H

80

80

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