Question

Which of the following solutions can act as a buffer?
A. 0.1 molar aq.NaCl
B. 0.1 molar aq.$C{H}_{3}COOH$ + 0.1 molar aq.NaOH
C. 0.1 molar aq. Ammonium acetate
D. 0.1 molar $H_{3}P{O}_4$

Answer 1

Hint: We can change the pH of a solution in many ways such as adding an acid, base or water. Therefore buffer solutions are the solutions which resist the change in pH due to addition of an acid or a base. This does not mean that pH does not change it simply means it would be less than expected.

Complete Step by step answer: There are three kinds of buffer solutions which are given by:
Acid buffer, basic buffer and salt buffer. Out of all the buffer solutions given the above formed solution from the option is a salt buffer, 0.1 molar of aq.ammonium acetate is a solution of salt which itself can act as a buffer. Such a salt is the salt of a weak acid and weak base. In this case the salt is a mixture of acetic acid-a weak acid and ammonium acetate -a weak base.
$C{H}_{3}COON{H}_4\rightleftharpoons C{H}_{3}CO{O}^{-}+N{H}_4^{+}$
When an acid is added it reacts with $C{H}_{3}CO{O}^{-}$ to produce acetic acid and when a base is added it reacts with ammonium ion to produce $N{H}_{4}OH$.

Therefore we can conclude that the correct option is C.

Note: A buffer capacity or buffer is maximum when the concentration of a weak acid and its salt or weak base and its salt are equal.One can calculate buffer capacity as well by the number of moles of an acid or base required to be added to one litre of the buffer solution so as to change its pH by one unit.