12.12 - Hydrogen Ion Concentration and the pH Scale

Question 1

What do strong acids do in solution?

Answer 1

Fully dissociate

Question 2

What does this mean for the concentration of hydrogen ions after a strong acid has dissociated?

Answer 2

It is equal to the initial concentration of the acid

Question 3

What equation links the pH of an aqueous solution and its hydrogen ion concentration?

Answer 3

pH = -log[H+]

Question 4

What is [H+] measured in?

Answer 4

mol dm-3

Question 5

When rearranged for [H+], what does the equation state?

Answer 5

[H+] = 10^(-pH)

Question 6

Why is calculating [H+] more difficult for weak acids?

Answer 6

They don’t fully dissociate

Question 7

What new value helps to calculate [H+] for a weak acid?

Answer 7

Ka, the acid dissociation constant

Question 8

For a weak acid with chemical formula HA, what is the expression for Ka?

Answer 8

([H+][A-])/[HA]

Question 9

What is the chemical equation for the dissociation of HA in aqueous solution?

Answer 9

HA H+ + A-

Question 10

What does this equation tell you about [H+] and [A-}?

Answer 10

They are equal

Question 11

Why?

Answer 11

Because they have a 1:1 ratio in the reaction

Question 12

What does this simplify the Ka expression to?

Answer 12

Ka = [H+]^2/[HA]

Question 13

If Ka is a small number, what is a reasonable assumption to make?

Answer 13

The concentration of HA at equilibrium is the same as the initial concentration of HA

Question 14

What equation links pKa and Ka?

Answer 14

pKa = -logKa