Buffers and neutralisers chp 21

Question 1

what is a buffer solution

Answer 1

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

Question 2

what are the components of a buffer solution

Answer 2

• the weak acid, HA, removes added alkali
• the conjugate base, A-, removes added acid

Question 3

what happens to the buffer solution as soon as one of its components has been used up

Answer 3

it will lose its buffering ability

Question 4

how do you prepare weak buffer solutions from a weak acid and its salt

Answer 4

• mix an acid and its salt, e.g CH3COOH and CH3COONa in water
• when acid added to water it dissociates to form H+ ions and conjugate base but some will remain as its undissociated form
• salts of weak acids are ionic compounds, when added to water it dissociates into ions to form more of the acids conjugate base

Question 5

how do you prepare a buffer solution from the partial neutralisation of a weak acid

Answer 5

• add an alkali to an excess of weak acid
• weak acid is partially neutralised forming conjugate base
• some of weak acid is left unreacted
• resulting solution contains mixture of salt of the weak acid and unreacted weak acid

Question 6

How do the components of the buffer solution act independently to remove added acid or alkali

Answer 6

achieved by shifting buffers equilibrium system either right or left

Question 7

how do conjugate bases remove added acid in buffer solutions

Answer 7

• [H+] increases
• H+ ions react with conjugate bases, A-
• Equilibrium position shifts to the left removing most of the H+ ions

Question 8

how do weak acids remove added alkali in buffer solutions

Answer 8

• [OH-] increases
• small concentration of H+ ions react with OH- ions to form water
• HA dissociates, shifting equilibrium position to the right to restore most of the H+ ions

Question 9

what is the pH of buffer solution equal to

Answer 9

• equal to pKa value of HA

Question 10

over how wide a range should a buffer solution be used

Answer 10

over 2 pH units

Question 11

what can you change to give different buffer solutions

Answer 11

• you can change weak acid used to give buffer solutions that can be used over different pH ranges

Question 12

formula for the pH of a buffer solution

Answer 12

Question 13

what is an example of a buffer solution found in the body

Answer 13

• carbonic acid-hydrogencarbonate buffer system maintains blood pH

Question 14

what is it called when blood pH increases and decrease outside of optimum levels

Answer 14

• when blood pH drops below 7.35 is it called acidosis
• when blood pH raises above 7.45 is it called alkalosis

Question 15

what do they different parts of the pH titration curve for addition of a base to an acid mean

Answer 15

Question 16

what is the equivalence point of a pH titration curve

Answer 16

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

Question 17

what is an acid-based indicator

Answer 17

• a weak acid
• that has a distinctively different colour from its conjugate base
• HA is one colour
• A- is another colour

Question 18

what occurs to the indicator at the end point of a titration

Answer 18

• the indicator contains equal concentrations of HA and A-
• the colour will be in-between the colours of HA and A-

Question 19

What is the pH value of the end point of a titration equivalent to

Answer 19

it is the same as the pKa value of HA

Question 20

what is pKa

Answer 20

measure of the acidity of a substance.

Question 21

what does the pH titration graph for an base being added to an acid look like

Answer 21

Question 22

what does the pH titration graph for a acid being added for a base look like

Answer 22