Question

A weak acid type indicator was found to be 60% dissociated at pH = 9. What will be the percent dissociation at pH = 8

Answer 1

Answer:

80%

Explanation:

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Answer 2

The percentage of dissociation is 80%.

Given:

A weak acid type indicator was found to be 60% dissociated at pH = 9.

To find:

Its percentage of dissociation at pH 8.

Solution:

The dissociation with pH follows the below relationship-

$pH=pKa+log(A^-/HA)$.

Now $(A^-/HA)=6$

Thus we can write-

$pH=pKa+log(A^-/HA)\\9=pKa+log6\\pKa=8.22$.

Thus, the value of pKa is 8.22 and pH is 8.

$pH=pKa+log(A^-/HA)\\ 8=8.22+log(A^-/HA)\\log(A^-/HA)=-0.22\\(A^-/HA)=10^{(-0.22)}\\(A^-/HA)=0.80\\(A^-/HA)=0.80×100\\(A^-/HA)=80\%$

The percentage of dissociation is 80%.

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