Which pairs of substances will form a buffer when mixed in equal concentrations?
A)NaOH and HCl
B)NH3 and NH4+
C)H2O and NH3
D)KCl and NaCl
E)HF and F-
To determine which pairs of substances will form a buffer when mixed in equal concentrations, we need to understand what a buffer is and how it is formed.
A buffer is a solution that helps maintain a relatively constant pH when small amounts of acid or base are added to it. Buffers are generally composed of a weak acid and its conjugate base, or a weak base and its conjugate acid.
To form a buffer, we need a weak acid and its conjugate base, or a weak base and its conjugate acid, in equal concentrations. Let's analyze each option:
A) NaOH and HCl: NaOH is a strong base and HCl is a strong acid, so this pair will not form a buffer.
B) NH3 and NH4+: NH3 is a weak base, and NH4+ is the conjugate acid formed by the addition of a proton to NH3. Since we have a weak base and its conjugate acid, this pair will form a buffer.
C) H2O and NH3: H2O is not a weak acid or a weak base, so this pair will not form a buffer.
D) KCl and NaCl: KCl and NaCl are both salts, and salts do not act as weak acids or weak bases, so this pair will not form a buffer.
E) HF and F-: HF is a weak acid, and F- is the conjugate base formed when HF loses a proton. Since we have a weak acid and its conjugate base, this pair will form a buffer.
Therefore, the pairs that will form a buffer when mixed in equal concentrations are B) NH3 and NH4+ and E) HF and F-.