Question

State whether each of the following would increase, decrease, or leave the initial pH unchanged and explain your reasoning: Using the same weak acid, but having a higher concentration. Decrease the initial pH because having a higher concentration of weak acid is the same as adding more H+ into a solution which means there is more acid being added into a solution and because of this it will decrease the pH of a solution. Using 80.00 mL of this weak acid instead of 40.00 mL. Will not change the initial pH because having a greater volume of weak acid will not affect the concentration of weak acid (H+ ions). Using a different weak acid that has a larger Ka value. Increase the initial pH because the larger the Ka value the more concentration to dissociate into H+.

Answer 1

Answer:

1. Decrease the pH

2. The pH remains unchanged

3. Decrease the pH

Explanation:

We can calculate the pH of a weak acid using the following expression:

$pH=-log [H^{+} ]=-log\sqrt{Ka \times Ca }$   [1]

where,

Ka is the acid dissociation constant

Ca is the initial concentration of the acid

State whether each of the following would increase, decrease, or leave the initial pH unchanged and explain your reasoning

1. Using the same weak acid, but having a higher concentration. According to eq. [1], a higher Ca leads to a higher [H⁺] and a lower pH.
2. Using 80.00 mL of this weak acid instead of 40.00 mL. pH refers to a concentration, which is an intensive property, so it does not change when we change the amount of matter.
3. Using a different weak acid that has a larger Ka value. According to eq. [1], a higher Ka leads to a higher [H⁺] and a lower pH.