ACIDS BASES AND PH

Question 1

Definition of a Bronsted Lowry acid

Answer 1

acids are proton donors and they release H+ in water to form H3O+ ions

Question 2

Definition of a Bronsted Lowry base

Answer 2

a proton acceptor that forms OH- ions in water

Question 3

What is a conjugate acid and base

Answer 3

a conjugate acid is a species that gains a proton

a conjugate base is a species that has lost a proton

Question 4

Kw expression and units

Answer 4

Kw = [H+][OH-]

mol2dm-6

Question 5

Kw constant value and how can it be affected

Answer 5

1x10-14 mol2dm-6

unless the temperature changes

Question 6

Kw expression for pure water

Answer 6

Kw = [H+]2

Question 7

pH equation

Answer 7

-log[H+]

Question 8

How to use pH to figure out concentration of H+

Answer 8

10^-pH

Question 9

How does H+ concentration relate to acid concentration in monoprotic acids

Answer 9

H+ concentration = concentration of acid

Question 10

How does H+ concentration relate to acid concentration in diprotic acids

Answer 10

H+ concentration = 2 x acid concentration

Question 11

2 assumptions of dissociation of weak acids

Answer 11

1. the concentration of acid in equilibrium is roughly equal to the concentration of acid before dissociation
2. all H+ ions have come from the acid in solution, so [H+] = [A-]

Question 12

Ka expression for a weak acid

Answer 12

Ka = [H+]2 / [HA]

Question 13

What can we assume at the equivalence point on a titration curve

Answer 13

that [H+] = [OH-]

Question 14

Colour change point of methyl orange

Answer 14

pH 3 - 4.5

Question 15

Colour change point of phenolphthalein

Answer 15

pH 8.2 - 10

Question 16

What is a buffer

Answer 16

a chemical that resists a change in pH when small amounts of acid or base are added

Question 17

What is the role of acid buffers and how are they composed

Answer 17

resist pH change to keep the solution below pH7

they are made from a weak acid and ITS salt

Question 18

The two equations of an ethanoic acid buffer

Answer 18

CH3COOH <–> CH3COO- + H+
(weak acid dissociates weakly so equilibrium lies left)

CH3COO-Na+ <–> CH3COO- + Na+
(salt dissociates strongly so equilibrium lies to the right)

Question 19

What happens when acid is added to an acidic buffer

Answer 19

H+ ions will react with the negative ions in solution, there is a high concentration of these from the salt

more weak acid is produced so equilibrium shifts to the left

Question 20

What happens when a base is added to an acidic buffer

Answer 20

The OH- ions will react with the H+ ions from the dissociated weak acid

as this removes H+ ions from solution, more H+ ions will be dissociated from the weak acid to counteract the change in concentration

Question 21

What values are needed to calculate pH of a buffer

Answer 21

The Ka value
The concentration of the weak acid and its salt