20.4 The pH of weak acids

Question 1

what does [H⁺] depend upon?

Answer 1

concentration of acid
acid dissociation constant

because there is an equilibrium

Question 2

what is assumption 1 for the pH of weak acids?

Answer 2

[H⁺] = [A⁻]

Question 3

what is assumption 2 for the pH of weak acids?

Answer 3

[HA]ₛₜₐᵣₜ = [HA]ₑₙₔ

you assume that a weak acid’s dissociation is too small to change the concentration

so the [HA] at the start is almost equal to [HA] at the end
so they can be made equal

Question 4

how can Kₐ be determined experimentally?

Answer 4

preparing a standard solution of the weak acid
measuring pH using a pH meter

Question 5

from what value for Ka is a weak acid strong?

Answer 5

when Ka is greater than 10^-2

Question 6

what happens if the Ka is greater than 10^-2?

Answer 6

you can no longer assume that [HA] at the start is equal to [HA] at the end