Question

Which of the following mixtures will be a buffer when dissolved in a liter of water?

A. 0.2 mol HBr and 0.1 mol NaOH
B. 0.1 mol Ca(OH)₂ and 0.3 mol HI
C. 0.3 mol NaCl and 0.3 mol HCl
D. 0.2 mol HF and 0.1 mol NaOH

Answer 1

Option D: 0.2 mol HF and 0.1 mol NaOH

The mixture that forms a buffer when dissolved in water is 0.2 mol HF and 0.1 mol NaOH, which is option D. This is because HF is a weak acid and NaOH is a strong base, and together they form the weak acid's conjugate base, providing buffering capacity.

Step-by-step explanation:

To identify which mixture will form a buffer when dissolved in water, we need to look for a combination of a weak acid and its conjugate base or a weak base and its conjugate acid. When analyzing the options given:

• 
  
• Option A: 0.2 mol HBr and 0.1 mol NaOH. HBr is a strong acid and therefore will not create a buffer with its salt.
• 
  
• Option B: 0.1 mol Ca(OH)2 and 0.3 mol HI. Both of these are strong bases and acids, respectively, so they will not form a buffer.
• 
  
• Option C: 0.3 mol NaCl and 0.3 mol HCl. HCl is a strong acid and NaCl is a salt that does not have any buffering capacity.
• 
  
• Option D: 0.2 mol HF and 0.1 mol NaOH. HF is a weak acid and when combined with NaOH, it forms NaF which is the sodium salt of the conjugate base F-. This mixture can act as a buffer.

Therefore, the correct answer is Option D: 0.2 mol HF and 0.1 mol NaOH.