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Question 1

buffer solution

Answer 1

system that minimises pH changes when small amounts of an acid or a base are added

Question 2

what are the 2 components in buffer solutions

Answer 2

• a weak acid

- conjugate base

Question 3

what do weak acids, HA remove?

Answer 3

added alkali

Question 4

what do conjugate bases, A- remove?

Answer 4

added acid

Question 5

what happens to the pH as the buffer works?

Answer 5

pH changes but only by a small amount

Question 6

on addition of an acid, H+(aq)

Answer 6

• [H+(aq)] increases
• H+(aq) ions react with the conjugate base, A-(aq)
• equilibrium position shifts to the left, removing most of the H+(aq)

Question 7

on addition of an alkali, OH-(aq)

Answer 7

• [OH-(aq)] increases
• small concentration of H+(aq) ions react with OH-(aq) ions: H+(aq) + OH-(aq) → H₂O(l)
• HA dissociate, shifting the equilibrium position to the right to restore most of H+(aq) ions

Question 8

[H+(aq)] and [A-(aq)] for weak acids and buffers

Answer 8

for weak acids: [H+(aq)]= [A-(aq)]

for buffers: [H+(aq)]≠ [A-(aq)]

Question 9

calculate the pH when the buffer solution contains 0.100 moldm⁻³ CH₃COOH and 0.3 moldm⁻³ CH₃OONa.
Ka (CH₃COOH)= 1.74X10⁻⁵ moldm⁻³

Answer 9

calculate [H+(aq)] from Ka, [HA(aq)], and [A-(aq)]
[H+(aq)] = Ka X [CH₃COOH(aq)]/ [CH₃COO-(aq)]
= 1.74X10⁻⁵ X0.1/0.3
= 5.80X10⁻⁶ moldm⁻³
find pH
pH= -log[H+(aq)]=-log(5.80X10⁻⁶)= 5.24

Question 10

what is the end point of a titration

Answer 10

• indicator contains equal concentrations of HA and A-

- colour will be in between the 2 extreme colours

Question 11

what is an indicator?

Answer 11

weak acid

Question 12

what is the vertical section of a pH curve

Answer 12

pH increases on addition of a very small volume of base

- acid and base concentration similar

Question 13

equivalence point of the titration

Answer 13

volume of one solution that exactly reacts with the volume of the other solution