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VITEEE 2009 Paper

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Question : 60 of 120

Marks: +1, -0

pH of a buffer solution decreases by 0.02 units when 0.12 g of acetic acid is added to 250 ml of a buffer solution of acetic acid and potassium acetate at 27°C . The buffer capacity of the solution is

0.1
10
1
0.4

Solution:

Buffer capacity,

\beta=\frac{dC_{HA}}{d_{pH}}

,

where,

dC_{HA}

= no. of moles of acid added per litre

d_{pH}

= change in pH

dC_{HA}=\frac{\text{moles of acetic acid}}{\text{volume}}=\frac{\frac{0.12}{60}}{\frac{250}{1000}}=\frac{1}{125}

∴

\beta=\frac{\frac{1}{125}}{0.02}=\frac{1}{2.5}=0.4

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