Question

Could a buffered solution be made by mixing aqueous solutions of \(\mathrm{HCl}\) and \(\mathrm{NaOH}\) ? Explain. Why isn't a mixture of a strong acid and its conjugate base considered a buffered solution?

Short answer

A buffered solution cannot be made by mixing aqueous solutions of \(\mathrm{HCl}\) and \(\mathrm{NaOH}\), as they are both strong acid and base, respectively. Their neutralization reaction produces water and \(\mathrm{NaCl}\), a salt that does not significantly contribute to the pH of the solution. Since there is no weak acid or weak base present, the solution does not have the ability to resist changes in pH upon the addition of small amounts of an acid or base. A mixture of a strong acid and its conjugate base, or a strong base and its conjugate acid, does not exhibit buffering behavior because it lacks the ability to maintain a constant pH when a small amount of acid or base is added.

Step-by-step solution

Investigate Properties of HCl and NaOH

Firstly, let's look at the properties of \(\mathrm{HCl}\) and \(\mathrm{NaOH}\). Hydrochloric acid (\(\mathrm{HCl}\)) is a strong acid and sodium hydroxide (\(\mathrm{NaOH}\)) is a strong base. When a strong acid is mixed with a strong base, they undergo a neutralization reaction and produce water and a salt. The general reaction of a strong acid and a strong base is: \( \) \[ \mathrm{HA} + \mathrm{BOH} \rightarrow \mathrm{H_2O} + \mathrm{AB} \] In this case, the neutralization reaction between \(\mathrm{HCl}\) and \(\mathrm{NaOH}\) is: \[ \mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{H_2O} + \mathrm{NaCl} \]

Determine the Resulting Solution

We need to determine if the resulting solution can resist changes in pH upon the addition of small amounts of an acid or base. The resulting solution of the reaction between \(\mathrm{HCl}\) and \(\mathrm{NaOH}\) consists of water and \(\mathrm{NaCl}\). Sodium chloride (\(\mathrm{NaCl}\)) is a salt and does not significantly contribute to the pH of the solution.

Decide if it is a Buffered Solution

Since there is no weak acid or weak base present in the resulting solution and a salt that does not influence the pH, this solution does not have the ability to resist changes in pH upon the addition of small amounts of an acid or base. Therefore, the mixture of \(\mathrm{HCl}\) and \(\mathrm{NaOH}\) does not create a buffered solution.

Discuss Strong Acid and Conjugate Base

A strong acid, like \(\mathrm{HCl}\), donates protons (H+) easily and completely ionizes in water. A strong acid's conjugate base has a negligible ability to accept protons. Similarly, a strong base, like \(\mathrm{NaOH}\), donates hydroxide ions (OH-) easily and completely ionizes in water, and its conjugate acid has a negligible ability to donate protons. Therefore, a mixture of a strong acid and its conjugate base or a strong base and its conjugate acid does not exhibit buffering behavior because it lacks the ability to maintain a constant pH when a small amount of acid or base is added.