To determine which of the given solutions is a good buffer, we need to understand what constitutes a buffer solution. A buffer solution typically includes:
1. A weak acid and its conjugate base, or a weak base and its conjugate acid.
2. The concentrations of the weak acid and its conjugate base, or vice versa, should be roughly equal and significant enough to maintain buffer capacity.
Let's analyze each option:
1. 0.15 M HCl and 0.15 M Cl⁻:
- HCl is a strong acid, not a weak acid. A buffer solution requires a weak acid and its conjugate base or a weak base and its conjugate acid.
- Since HCl is a strong acid, it completely dissociates in water, which is not suitable for a buffer solution.
- Therefore, this is not a buffer solution.
2. 0.001 M HCN and 0.15 M CN⁻:
- HCN (hydrocyanic acid) is a weak acid, and CN⁻ (cyanide) is its conjugate base.
- However, the concentration of HCN (0.001 M) is much lower than that of CN⁻ (0.15 M), which means they are not in approximately equal concentrations.
- For effective buffering, the concentrations should be roughly equal. Hence, this is not the most appropriate buffer solution.
3. 0.0001 M CH3COOH and 0.0001 M CH3COO⁻:
- CH3COOH (acetic acid) is a weak acid, and CH3COO⁻ (acetate) is its conjugate base.
- The concentrations are equal, which is a good sign. However, both concentrations are very low (0.0001 M), which may not provide adequate buffering capacity.
- Buffering capacity is typically better with higher concentrations of the buffering agents. Therefore, while it could act as a buffer, it is not the best option due to low concentration.
4. 0.2 M HF and 0.2 M F⁻:
- HF (hydrofluoric acid) is a weak acid, and F⁻ (fluoride) is its conjugate base.
- The concentrations of HF and F⁻ are equal (0.2 M), which is favorable for a buffer solution.
- Additionally, the concentrations are relatively high, which ensures a good buffering capacity.
- Therefore, this is the most appropriate choice for a buffer solution.
Considering the analysis above, the best option for a good buffer solution is:
0.2 M HF and 0.2 M F⁻.
So, the correct answer is:
4. 0.2 M HF and 0.2 M F⁻
