buffers and neutralisations

Question 1

what is a buffer solution?

Answer 1

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

Question 2

what does a buffer solution contain?

Answer 2

a weak acid and its conjugate base

Question 3

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

Answer 3

mixing a solution of ethanoic acid with a solution of one its salt such as sodium ethanoate

Question 4

how do you prepare a weak acid buffer by partial neutralisation of the weak acid?

Answer 4

by adding an aqueous solution of an alkali to an excess of a weak acid

Question 5

what happens to equilibrium position when acid is added?

Answer 5

concentration of H+ ions increases which react with conjugate base therefore equilibrium position shifts to the left removing most of H+ ions

Question 6

what happens to equilibrium position when alkali is added?

Answer 6

Concentration of OH- increases therefore the small concentration of H+ reacts with conjugate base. HA dissociates shifting equilibrium position to the right to restore H+ ions

Question 7

when is the pH of a buffer solution the same as pKa value of HA

Answer 7

when [HA] = [A-]

Question 8

what is formula for Ka

Answer 8

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

Question 9

what happens when pH of blood falls below 7.35

Answer 9

causes acidosis, which causes fatigue, shortness of breath, shock or death

Question 10

what happens when pH of blood rises above 7.45

Answer 10

causes alkalosis, which causes muscle spasms, light-headedness, nausea

Question 11

what is equation for carbonic acid-hydrogencarbonate buffer system?

Answer 11

H2CO3 —- H+ + HCO3-

Question 12

what is the equivalence point?

Answer 12

equivalence point of a titration is the volume of one solution that exactly reacts with the volume of the other solution

Question 13

what is an acid-base indicator

Answer 13

acid-base indicator is a weak acid,HA, that has a different colour from its conjugate base, A-.

Question 14

what is the colour of the acid and base in the indicator, methyl orange

Answer 14

the weak acid is red
the conjugate base is yellow

Question 15

what is the end point of a titration

Answer 15

indicator contains equal concentration of HA and A- so colour will be in between the 2 colours

Question 16

what happens to equilibrium position when a basic solution is added to indicator?

Answer 16

OH- reacts with H+ in the indicator therefore HA dissociates and equilibrium shifts to the right . Colour changes to orange at end point then to yellow

Question 17

what happens when methyl orange is added to a basic solution and acid is added

Answer 17

H+ reacts with conjugate base shifting equilibrium to left. Colour changes to orange at end point then to red

Question 18

what is the Ka value at end point?

Answer 18

[HA] = [A-] therefore Ka = [H+]
pKa = pH