Sure, let's analyze the scenario step-by-step to understand how the solution will change when water is added to it.
1. Initial pH and Concentration of H⁺:
Initially, the ethanoic acid solution has a pH of 3.
The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration [tex]\([H⁺]\)[/tex].
So, for a pH of 3:
[tex]\[
\text{initial } [H⁺] = 10^{-3} = 0.001 \text{ M}
\][/tex]
2. Effect of Adding Water:
When 20 ml of water is added, the solution becomes more dilute. The concentration of hydrogen ions [tex]\([H⁺]\)[/tex] will decrease because the total volume of the solution increases while the total amount of hydrogen ions remains the same initially.
3. New Concentration of H⁺:
Assuming a dilution factor of 10 (which indicates the final volume becomes ten times the original volume), the new concentration of hydrogen ions [tex]\([H⁺]\)[/tex] will be:
[tex]\[
\text{new } [H⁺] = \frac{\text{initial } [H⁺]}{\text{dilution factor}} = \frac{0.001 \text{ M}}{10} = 0.0001 \text{ M}
\][/tex]
4. Calculating New pH:
To find the new pH after dilution, we use the new concentration of hydrogen ions:
[tex]\[
\text{new pH} = -\log_{10}(\text{new } [H⁺]) = -\log_{10}(0.0001) = 4
\][/tex]
Now let's interpret the changes in the solution:
- The initial concentration of H⁺ ions was 0.001 M and now it's 0.0001 M.
- The pH has increased from 3 to 4, indicating that the solution has become less acidic after dilution.
Given these points, let's analyze each of the options:
A. The concentration of H⁺ will increase.
- Incorrect. The concentration of H⁺ actually decreases due to dilution.
B. The amount of H⁺ will increase.
- Incorrect. The amount of H⁺ ions stays the same; only the concentration changes.
C. The amount of H⁺ will decrease.
- Incorrect. The amount remains the same but the concentration decreases.
D. The concentration of H⁺ will decrease.
- Correct. Adding water dilutes the solution, thereby decreasing the concentration of H⁺.
Thus, the correct answer is:
D. The concentration of H+ will decrease.
