Which one of the following mixtures is suitable for making buffers?
1 H3PO4 and NaH2PO4
2 Na2CO3 and NaHCO3
3 NH4Cl and NH3
a. 1 only
b. 2 only
c. 3 only
d. 1 and 2 only
e. 1, 2, and 3
Buffers are a weak acid and one of its salts or a weak base and one of its salts.
To determine which one of the following mixtures is suitable for making buffers, we need to understand what a buffer is and the components required to create it.
A buffer is a solution that helps maintain a stable pH level by resisting changes in acidity or alkalinity when small amounts of acid or base are added. Buffers can be made by combining a weak acid with its conjugate base or a weak base with its conjugate acid.
Now let's analyze each of the given mixtures to see if they contain appropriate components for making buffers:
1. H3PO4 and NaH2PO4:
- H3PO4 is a weak acid (phosphoric acid).
- NaH2PO4 is the conjugate base of H3PO4 (sodium dihydrogen phosphate).
This mixture contains both a weak acid and its conjugate base, which are suitable for making a buffer.
2. Na2CO3 and NaHCO3:
- Na2CO3 is a strong base (sodium carbonate).
- NaHCO3 is a weak acid (sodium bicarbonate).
This mixture contains a strong base and a weak acid, which are not ideal for making a buffer. It lacks the conjugate base for the weak acid component.
3. NH4Cl and NH3:
- NH4Cl is a salt formed from a strong acid (hydrochloric acid) and a weak base (ammonium chloride).
- NH3 is a weak base (ammonia).
This mixture contains a weak base and its conjugate acid, which are suitable for making a buffer.
Based on this analysis, the suitable mixtures for making buffers are:
a. 1 only (H3PO4 and NaH2PO4)
c. 3 only (NH4Cl and NH3)
Therefore, the correct answer is d. 1 and 3 only.