12.1.2 - Hydrogen ion concentration and the pH scale

Question 1

What is the equation you would use if you wanted to find pH from the concentration of H+ ions?

Answer 1

pH = -log(H+)

Question 2

How do we calculate H+ concentration from pH?

Answer 2

10^-pH

Question 3

When we get the concentration of H+ from pH of a diprotic acid, what must we do?

Answer 3

Half the answer.

Question 4

How would you calculate the pH of a solution with an acid and water?

Answer 4

1) Work out hydrogen ion concentration by multiplying the concentration of acid by the proportion of acid over total volume.
2) -log(H+)

Question 5

How do you calculate the pH of a solution where both an acid and alkali have been added?

Answer 5

1) Work out the moles of H+ and OH- ions.
2) Mol of H+ - mol of OH-
3) Turn the mol of H+ into concentration by using volume.
4) -log(H+)

Question 6

Why do we use Ka?

Answer 6

To calculate the pH of weak acids

Question 7

What are two assumptions that we make when working out the pH of a weak acid?

Answer 7

1) When a weak acid dissociates, we can assume the concentrations of H+ ions and the other product are the same as they are in a 1-1 ratio.
2) If Ka is small we can assume the concentration of the negative product is the same as the initial concentration of the acid.

Question 8

How do you convert between PKa and Ka?

Answer 8

PKa = -log(Ka)
Ka = 10^-PKa

Question 9

What does a larger Ka value mean in relation to the strength of an acid?

Answer 9

Stronger acid as a greater concentration of H+

Question 10

What does a smaller KPa value mean in terms of the strength of an acid?

Answer 10

Stronger acid