Which of these pairs of substances in aqueous solution would constitute a buffer?
a. HCl + KCl
b. KHPO4 + K2HPO4
c. KOH + KCl
d. HCl + KOH
A buffer consists of
a. a weak acid and a salt of the weak acid.
b. a weak base and a salt of the weak base.
To determine which pairs of substances in aqueous solution would constitute a buffer, you need to check if they consist of a weak acid and its conjugate base or a weak base and its conjugate acid. This is because a buffer solution is made up of a weak acid-base pair that can resist large changes in pH.
Let's evaluate each pair of substances to see if they meet the requirements:
a. HCl + KCl:
HCl is a strong acid, not a weak acid, so it does not qualify as a component of a buffer. KCl is a neutral salt and does not contribute to the acid-base equilibrium. Therefore, this pair does not constitute a buffer.
b. KHPO4 + K2HPO4:
KHPO4 is a weak acid, and K2HPO4 is its conjugate base. As a result, this pair consists of a weak acid-base pair and would constitute a buffer.
c. KOH + KCl:
KOH is a strong base, not a weak base, so it does not qualify as a component of a buffer. KCl is a neutral salt and does not contribute to the acid-base equilibrium. Therefore, this pair does not constitute a buffer.
d. HCl + KOH:
Both HCl and KOH are strong acids and bases, respectively. As a result, this pair does not consist of a weak acid-base pair and would not constitute a buffer.
In conclusion, the correct pair of substances that would constitute a buffer is b. KHPO4 + K2HPO4.