The dissociation constant of weak acid is 1\times10 ^{-4}. In order to prepare a buffer solution with pH=5 [Salt]/[Acid] ratio should be

  • Option 1)

    1:10

  • Option 2)

    4:5

  • Option 3)

    10:1

  • Option 4)

    5:4

 

Answers (1)

 

Value of Ka -

K_{a}=\frac{[H^{+}]\:[\bar{X}]}{[HX]}


P(K_{a})=-log(K_{a})

- wherein

At a given temperature T,  Ka is a measure of the strength of the acid  HX. Ka  is dimensionless quantity.

 

 p(H)= p(K_a)+ \log \frac{[salt]}{[acid]}

5= - \log (K_a)+ \log \frac{[salt]}{[acid]}

= - \log (1*10^{-4})+ \log \frac{[salt]}{[acid]}

5= 4+ \log \frac{[salt]}{[acid]}

\log \frac{[salt]}{[acid]}= 1

\frac{[salt]}{[acid]}= 10:1

 


Option 1)

1:10

Incorrect

Option 2)

4:5

Incorrect

Option 3)

10:1

Correct

Option 4)

5:4

Incorrect

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