A solution has a pH of 10.3. When a solid is dissolved in the solution, the pH changes to 9.6. What can be inferred from this observation?

A. The solid is basic.

B. The solid contains hydroxide ions.

C. The solid is acidic.

D. The solid contains hydrogen ions.

Answer: option C. the solid is acidic.

Explanation:

You can reasoning that since the initial solution has a pH of 10.3 it is basic, and since the pH decreases to 9.6, it became less basic, which necessarily means that the solid is acidic.

Neverthelless, I will give you a step by step rigurous proof:

1) The initial solution has a pH = 10.3, that means that the solution is basic.

The [OH⁻] concentration may be calculated in this way:

2) pH + pOH = 14

⇒ pOH = 14 - 10.3 = 3.7

pOH = - log [OH⁻] = 3.7 ⇒

[OH⁻] = 1.995 * 10⁻⁴ M

3) Since, the pH decreased to 9.6 means that concentration of [OH⁻] decreased.

You can calculate how much it decreases:

pOH = 14 - 9.6 = 4.4

- log [OH⁻] = 4.4

[OH⁻] = 3.98 * 10 ⁻⁵ M

4) Then, some [OH⁻] was neutralized by the solid, which means that the solid content either [H+] or an electron acceptor meaning that it is acidic.

A, 7 or high pH is A Basic