Question

Buffer capacity is maximum when the ratio of [salt]:[acid] is
A. 1:2
B. 1:10
C. 10:1
D. 1:1

Answer 1

The buffer capacity of a buffer solution is a measurement of its magnitude of its resistance to change in pH on addition of an acid or a base, buffer capacity depends on the ratio of salt and acid, if a buffer solution has higher concentration its buffer capacity will be greater.

Complete solution:
A buffer solution is the solution which maintains its pH significantly constant even upon the addition of a small amount of acid or base.
There are two types of buffer solution :
1. Basic buffer solution
2. Acidic buffer solution
The amount of hydrogen or hydroxide ions that a buffer can absorb without a significant change in pH is known as buffer capacity of the buffer solution
$Buffer{\text{ }}capacity{\text{ }} = \dfrac{{number{\text{ }}of{\text{ }}moles{\text{ }}of{\text{ }}{H^ + }{\text{ }}ions{\text{ }}or{\text{ }}O{H^ - }{\text{ }}ions{\text{ }}added{\text{ }}in{\text{ }}solution}}{{PH{\text{ change}} \times V{\text{volume of solution (L)}}}}$
Large buffering capacity means it contains a large amount of buffering components and it can absorb a lot of ${H^ + }$ or $O{H^ - }$ ions and show negligible PH change.
$Buffer{\text{ }}capacity{\text{ }} = \dfrac{{number{\text{ }}of{\text{ }}moles{\text{ }}of{\text{ }}{H^ + }{\text{ }}ions{\text{ }}or{\text{ }}O{H^ - }{\text{ }}ions{\text{ }}added{\text{ }}in{\text{ }}solution}}{{PH{\text{ change}} \times V{\text{volume of solution (L)}}}}$
We also know that
$\Delta PH = \log \left[ {\dfrac{{salt}}{{acid}}} \right]$
Buffer capacity will be maximum when $\Delta PH$ is minimum.
Therefore, $\log \left[ {\dfrac{{salt}}{{acid}}} \right]$ should be minimum which is equal to zero.
We also know that
$\log \left[ 1 \right] = 0$
Therefore,
$\dfrac{{\left[ {salt} \right]}}{{\left[ {acid} \right]}} = 1$

Hence the correct option is D.

Note: Buffer solution always opposes the change of its PH value buffer solution is widely used in daily life and industrial area, buffer solution is used in biological system, it is used in agricultural area, it is used in preservation of food even buffer solution found in blood which help to maintain its PH.