Acid-Base Equilibrium

What are the three classifications of acids and bases?

1. Bronsted-Lowry

2. Arrhenius

3. Lewis

What are conjugate acid-base pairs?

Substances that differ only in the presence or absence of a proton

What determines the strength of an acid?

It willingness to donate protons

What is an amphiprotic substance?

A substance that can act as both a base and an acid, like water, for example.

What is acid-base equilibria?

It is where the forward and reverse rate of proton transfer is equal. 

What is the acid-dissociation constant (Ka)?

It is used to measure the relative strength of acids i.e. heir ease to donate a proton).

What does a large Ka value mean and what does a small Ka value mean?

A large Ka value means that equilibrium lays more to the RIGHT (I.e. the forward reaction is favoured) and a smaller Ka value means equilibrium lies more to the left. (I.e. The reverse reaction is favoured)

What is auto-ionization of, for example, water?

It is when a substance, in this case water, can undergo proton transfer with itself.

What is the Kc/Ion product of water?

Kw = [H30+][-OH], and the value is 1.0×10^-14

What is the Kc value of a neutral substance?

This is where [H+]=[-OH] and the kc value is 1×10^-7

How do I work out pH?

pH = -log[H+]

How do I get the pOH?

pOH = -log[-OH]

How do I get Kw?

Kw = [-OH][H+]

What is the relationship between Kw and the OH and H+ concentrations?

-logKw = -Log[H+] + -Log[-OH]

What useful relationship is there between pOH and pH?

pOH + pH = 14.00

How do I work out Ka value?

Ka = [H+][A-]/[HA]

what is pKa and how do I work it out?

pKa is a measure of the strength of an acid, the larger it is, the stronger the acid. pKa = -log[Ka]

How do I work out percentage ionization?

% = [H+]/[HA] x 100&

Whats the relationship between Ka and Kb?

Ka x Kb = Kw

What is a buffer?

It can best be described as a excess of weak and a limiting strong, resulting in weak and a salt.

Why do we avoid strong acid-base pairs for buffers?

Because they neutralise each other

What is buffer capacity?

It is the extent to which a buffer can resist changes in pH, it depends on the [HA] and [A-]

What is buffer range?

It is the pH range where the buffer is most effective, it is found by taking the pKa of the weak acid and +- 1.

What is the H-H equation and what do we use it for?

pH = pKa + Log [Base]/[acid]. It is only used for buffers

How do we use Ka to calculate pH?

If you have the Ka and the initial concentration of the weak acid, you can readily calculate the equilibrium [H+] and use that to find the pH