Consider a solution prepared by mixing a weak acid HA, HCl, and NaA. Which of the following statements best describes what happens? a. The \(\mathrm{H}^{+}\) from the \(\mathrm{HCl}\) reacts completely with the \(\mathrm{A}^{-}\) from the NaA. Then the HA dissociates somewhat. b. The \(\mathrm{H}^{+}\) from the \(\mathrm{HCl}\) reacts somewhat with the \(\mathrm{A}^{-}\) from the NaA to make HA, while the HA is dissociating. Eventually you have equal amounts of everything. c. The \(\mathrm{H}^{+}\) from the \(\mathrm{HCl}\) reacts somewhat with the \(\mathrm{A}^{-}\) from the NaA to make HA while the HA is dissociating. Eventually all the reactions have equal rates. d. The \(\mathrm{H}^{+}\) from the \(\mathrm{HCl}\) reacts completely with the \(\mathrm{A}^{-}\) from the NaA. Then the HA dissociates somewhat until "too much" \(\mathrm{H}^{+}\) and \(\mathrm{A}^{-}\) are formed, so the \(\mathrm{H}^{+}\) and \(\mathrm{A}^{-}\) react to form HA, and so on. Eventually equilibrium is reached. Justify your choice, and for choices you did not pick, explain what is wrong with them.

Step by step solution

01

Understand the exercise

Here, we have three components in the mixture: a weak acid HA, a strong acid HCl, and a salt NaA. We need to determine how the ions interact with each other to find the correct description of what happens when these solutions are mixed.

02

Reaction details

The reaction between HCl and NaA looks like: \[ \mathrm{NaA} + \mathrm{HCl} \rightleftharpoons \mathrm{HA} + \mathrm{NaCl} \] The reaction between HA and NaA looks like: \[ \mathrm{HA} \rightleftharpoons \mathrm{H}^{+} + \mathrm{A}^{-} \] Now let's analyze the given options to determine which description best represents what happens.

03

Option a

In option a, the H+ from HCl reacts completely with A- from NaA, and then HA dissociates somewhat. This implies that the strong acid reaction goes to completion before the weak acid dissociation starts. Because strong acids are completely ionized in water, the scenario in option a may happen, but it is not an accurate description of the entire process.

04

Option b

Option b says that the H+ from HCl reacts somewhat with A- from NaA to make HA, while the HA is dissociating, eventually reaching a balanced state with equal amounts of everything. This option doesn't reflect how the ions interact with each other, as there's no reason for eventual equal amounts of all compounds.

05

Option c

Option c says that the H+ from HCl reacts somewhat with A- from NaA to make HA while the HA is dissociating. Eventually, all the reactions have equal rates. This answer is plausible; since the system will tend towards equilibrium, the rates of the forward and backward reactions will eventually become equal.

06

Option d

In option d, the H+ from HCl reacts completely with A- from NaA, then the HA dissociates somewhat until "too much" H+ and A- are formed. Because of the excess ions, H+ and A- react to form HA again, and so on, eventually reaching equilibrium. Like option a, this scenario implies that the strong acid reaction goes to completion before the weak acid dissociation starts. Although the system will eventually move towards equilibrium, the process is not entirely accurate.

07

Final choice and explanation

Based on the analysis above, the best description of what happens when these solutions are mixed is found in option c. The H+ from HCl reacts somewhat with A- from NaA, while HA is dissociating. All reactions have an equilibrium state, and eventually, the rates of the forward and backward reactions will equalize. Option a and d are wrong because they assume the strong acid reaction (involving HCl) has to complete before the weak acid dissociation starts. Option b is wrong because there is no explanation for reaching a state with equal amounts of everything.

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