Question

determine whether or not each combination of substances can be used to create a buffer. 0.4 m koh, 0.2 m naoh choose... 0.1 m hcl, 0.1 m kcl choose... 1 m na2hpo4, 1 m nah2po4 choose... 0.05 m hno2, 0.05 m nano2 choose... 0.1 m hno2, 0.05 m naoh choose...

Explanation:

Step1: Recall buffer - forming criteria

A buffer is formed by a weak acid - conjugate base pair or a weak base - conjugate acid pair.

Step2: Analyze 0.4 M KOH, 0.2 M NaOH

KOH and NaOH are strong bases. A buffer cannot be formed from two strong bases. So the answer is no.

Step3: Analyze 0.1 M HCl, 0.1 M KCl

HCl is a strong acid and KCl is a salt. A buffer cannot be formed from a strong acid and its salt. So the answer is no.

Step4: Analyze 1 M Na₂HPO₄, 1 M NaH₂PO₄

Na₂HPO₄ and NaH₂PO₄ form a weak acid - conjugate base pair (H₂PO₄⁻ is the weak acid and HPO₄²⁻ is the conjugate base). So a buffer can be formed. The answer is yes.

Step5: Analyze 0.05 M HNO₂, 0.05 M NaNO₂

HNO₂ is a weak acid and NaNO₂ contains its conjugate base NO₂⁻. So a buffer can be formed. The answer is yes.

Step6: Analyze 0.1 M HNO₂, 0.05 M NaOH

The NaOH will react with HNO₂ to form NaNO₂. There will be a mixture of weak acid HNO₂ and its conjugate base NO₂⁻. So a buffer can be formed. The answer is yes.

Answer:

0.4 M KOH, 0.2 M NaOH: No
0.1 M HCl, 0.1 M KCl: No
1 M Na₂HPO₄, 1 M NaH₂PO₄: Yes
0.05 M HNO₂, 0.05 M NaNO₂: Yes
0.1 M HNO₂, 0.05 M NaOH: Yes