Five solutions were prepared at 25 °C, each by combining equal volumes of two 0.10 M reagents as listed below.
(i) CH₃COOH(aq) and CH₃COONa(aq)
(ii) HCl(aq) and NaCl(aq)
(iii) NH₃(aq) and NH₄Cl(aq)
(iv) NaOH(aq) and NaCl(aq)
(v) H₂CO₃(aq) and NaHCO₃(aq)
Assume solution volumes are additive and temperature-dependent changes in equilibrium constants are negligible.
(a) Identify every mixture that constitutes a buffer solution. For each buffer you select, clearly state the conjugate acid–base pair present and justify why both species remain in appreciable concentration after mixing.
(b) Choose one buffer from part (a). Describe qualitatively how the addition of a small amount of concentrated HCl(aq) would affect its pH compared with the effect on an equal volume of distilled water. Explain your reasoning in terms of the species present before and after the addition.