Bronsted-Lowry + pH + Kw of water + weak acids and bases

Question 1

What is an acid and base?

Answer 1

Acid: proton donor
strong acid = fully dissociates in aqueous solutions, eg hydrochloric acid, sulfuric acid
weak acid = slight dissociates in aqueous solutions, eg ethanoic acid

Base: proton acceptor
eg KOH, Ba(OH)2, NaOH

Question 2

Give all the equations needed.

Answer 2

pH = –log10[H+]
[H+]=10^-pH
*remember to double it if the acid has 2 protons eg H2SO4

ionic water equation:
Kw = [H+][OH–] –> Kw = [H+]^2
at room temp, Kw = 1x10^-14 (remember this)

weak acids equations
Ka = [H+][A-]/[HA]
can be simplified to: Ka = [H+]^2 / [HA]
pKa = -log10 Ka

Question 3

How is Kw varied with temperature?

Answer 3

if temp increases:
equilibrium shifts to the endothermic side to oppose the temp increase
- kw increases
- [H+] increases so pH decreases

Question 4

definition of neutral?

Answer 4

[H+] = [OH-]

Question 5

How to know based on kPa/Ka if an acid is strong or weak?

Answer 5

small kPa = bigger Ka = stronger acid
bigger kPa = small Ka = weaker acid

Question 6

must be able to use Kw to find the pH of a strong base.

Answer 6

tips: finding pH of strong bases means that [H+] is not equal to [OH-]
must use:
[OH-] = Kw/[H+]

how to do:
old volume/new volume x conc of the strong base = [OH-]

[H+] = Kw / [OH-]

pH = -log [H+]

boom.

Question 7

how to do a mixture of strong acid + base calculations

Answer 7

1. find moles of [H+] and [OH-]
2. find XS and by how much
3. find new volume
4. find new conc. –> XS moles/new vol
5. if OH- in XS, do [H+] = Kw/[OH-]
6. once you have [H+], find pH

boom.