Question

1) An aqueous solution contains 0.34 M nitrous acid.

One Liter of this solution could be converted into a buffer by the addition of:

(Assume that the volume remains constant as each substance is added.)

0.17 mol HCl

0.35 mol HCl

0.35 mol KNO₂

0.086 mol Ca(OH)₂

0.34 mol KCl

2)  

An aqueous solution contains 0.26 M ammonium chloride.

One liter of this solution could be converted into a buffer by the addition of:

(Assume that the volume remains constant as each substance is added.)

0.25 mol NH₃

0.06 mol Ba(OH)₂

0.25 mol KCl

0.26 mol HI

0.12 mol HI

Answer 1

Buffer solution is a solution which resists the change in pH.

Buffers are of two types.

1. Acidic buffer

2.Basic buffer

Acidic buffer solution is a mixture of weak acid and salt formed by this weak acid with a strong base.

Similarly basic buffer is a mixture of weak base and salt formed by this weak base with a strong acid.

Number of moles of nitrous acid in 1 L of 0.34 M nitrous acid:

Number of moles of nitrous acid= (0.34 moles/L)*1L = 0.34 moles

Nitrous acid (HNO_{​​​​2}​​​ ) is a weak acid. In order to make buffer with nitrous acid, salt of nitrous acid with a strong base is required.

HCl is a strong acid. Hence it cannot form buffer with nitrous acid.

KCl is a salt formed by strong base (KOH) and strong acid (HCl). Hence it cannot form buffer.

Calcium hydroxide is a strong base and when 0.086 moles of calcium hydroxide is added to 0.34 moles of nitrous acid,

0.172 moles Ca(NO_{​​​​​2})₂ is formed. Hence solution it forms a buffer.

0.35 moles of Potassium Nitrite (salt of strong base (KOH) and weak acid (nitrous acid) is added to 0.34 moles of nitrous acid forms a buffer.

2)

Ammonium chloride is a salt of weak base ( ammonia) and strong acid (HCl).

Number of moles of ammonium chloride in 1 L of 0.26 M solution is 0.26 moles

0.25 moles of aqueous ammonia or ammonium hydroxide with 0.26 moles of ammonium chloride forms basic buffer.

0.26 moles of KCl is a salt of strong base with a strong acid. It cannot form buffer.

HI is a strong acid and it cannot form a buffer.

0.06 moles of Ba(OH)₂ also cannot form buffer.