Question

Consider these acids $$ \begin{array}{ccccc} \hline \text { Acid } & \text { A } & \text { B } & \text { C } & \text { D } \\\ K_{\text {a }} & 1.6 \times 10^{-3} & 9 \times 10^{-4} & 2 \times 10^{-6} & 3 \times 10^{-4} \\ \hline \end{array} $$ (a) Arrange the acids in order of increasing acid strength from weakest to strongest. (b) Which acid has the smallest \(\mathrm{p} \mathrm{K}_{\mathrm{a}}\) value?

Short answer

Question: Arrange the given acids in order of increasing acid strength from weakest to strongest and identify the acid with the smallest pKa value. The Ka values for the acids are: - Acid A: 1.6 x 10^(-3) - Acid B: 9 x 10^(-4) - Acid C: 2 x 10^(-6) - Acid D: 3 x 10^(-4) Answer: The order of acids from weakest to strongest is: Acid C, Acid D, Acid B, and Acid A. Acid A has the smallest pKa value of ≈ 2.8.

Step-by-step solution

Examine Ka values

Compare the given Ka values of the acids. Remember that a higher Ka value corresponds to a stronger acid: $$ \begin{array}{cccc} \text { Acid } & \text { A } & \text { B } & \text { C } & \text { D } \\ K_{a} & 1.6 \times 10^{-3} & 9 \times 10^{-4} & 2 \times 10^{-6} & 3 \times 10^{-4} \\ \end{array} $$

Arrange the Acids

Now that we've examined the Ka values, we can arrange the acids from weakest to strongest based on their Ka values: - Weakest: Acid C (2 x 10^(-6)) - Acid D (3 x 10^(-4)) - Acid B (9 x 10^(-4)) - Strongest: Acid A (1.6 x 10^(-3)) So, the order of acids from weakest to strongest is: C, D, B, and A. (b) Identifying the Acid with the Smallest pKa Value

Calculate pKa Values

To find the pKa values, use the formula pKa = -log(Ka) for each of the given acids: - Acid A: pKa = -log(1.6 × 10^(-3)) - Acid B: pKa = -log(9 × 10^(-4)) - Acid C: pKa = -log(2 × 10^(-6)) - Acid D: pKa = -log(3 × 10^(-4))

Determine the Smallest pKa Value

Now, let's compare the calculated pKa values and identify which acid has the smallest pKa value: - Acid A: pKa ≈ 2.8 - Acid B: pKa ≈ 3.0 - Acid C: pKa ≈ 5.7 - Acid D: pKa ≈ 3.5 Acid A has the smallest pKa value of ≈ 2.8.