8 Which of the following aqueous mixtures will result in a b

8. Which of the following aqueous mixtures will result in a buffer? (1) 0.1 L of 1.0 M HCI added to 0.2 L of 1.0 M NaOH (2) 0.2 L of 1.0 M HCI added to 0.1 L of 1.0 M NaF (3) 0.3 L of 1.0 M NaCl added to 0.2 L of 1.0 M HCI (4) 0.2 L of 1.0 M NaOH added to 0.1 L of 1.0 M NaF (5) 0.1 L of 1.0 M NaOH added to 0.2 L of 1.0 M HF

Solution

A buffer can be formed from any of the following combinations:

a) Weak acid when mixed with the salt of its conjugate base

b) Weak base when mixed with the salt of its conjugate acid

c) Strong Acid neutralized with weak base

d) Strong Base neutralized with weak acid

For the above given options:

1) It is a mixture of HCL (Strong acid) and NaOH (Strong base), which results in formation of salt (NaCl) and some excess unreacted base (NaOH). So this would not result in a buffer.

2) It is a mixture of Strong acid (HCl) and salt NaF, which would produce a weak acid HF. But since all the NaF is used in producing HF, there is no F^- which would act as a conjugate base. So this would not result in a buffer.

3) It is a mixture of a Strong Acid (HCl) and a salt (Nacl), reaction of which would not result in a buffer.

4) it is a mixture of a Strong Base (NaOH) and a salt (NaF), the reaction of which would not result in a bufffer.

5) It is a mixture of 0.1 moles of strong base (NaOH) and a 0.2 moles of weak acid (HF), reaction of which will produce F^-(NaF). Since there is excess of HF, combination of HF and F^- produced from the reaction, ( a weak acid and its conjugate base), will result in a buffer.