acid and bases (2)

Question 1

how to use ion product of water

Answer 1

shows relationship between [H3O+] or [OH-] in aq

know one conc of one species and use Kw to find other

Question 2

Kw equation - for water - ions

Answer 2

[H3O+][OH-]

= 1x10(-14)

Question 3

Kw equation - acid and bases

Answer 3

Kw = Ka x Kb = 1x10(-14)

Question 4

Kb

Answer 4

weak base

calculate Ka for its conjugate acid

Question 5

Ka

Answer 5

weak acid

calculate Kb for its conjugate base

Question 6

pH and conc of acid

Answer 6

[H+] varies in aq therefore difficult to compare

use pH=-log[H+]

Question 7

weak acid and [H+] - dissociate partially

e.g. ethanoic acid - 0.1M

Answer 7

1- make equation of acid with water
2- have initial conc of each molecule
3- have conc of molecules at equilibrium
4- Ka=[CH3COO-][H3O-] / [CH3COOH] = 1.8x10(-5)
5- solve x - assuming a is v. small - change in concentration [H+]
6- pH = -log[H+]

Question 8

Henderson-Hasselbalch equation

Answer 8

pH = pka + log([A-]/[HA])

Question 9

contribution of water

Answer 9

OH- and H3O+ ions - inversely proportional

Question 10

acidic - water

Answer 10

[H3O+] - relatively high

[OH-] - relatively low

Question 11

basic - water

Answer 11

[H3O+] - relatively low

[OH-] - relatively high

Question 12

general dissociation of acid equation

Answer 12

HA + H2O A- + H3O+

once dissociated uncharged HA -> charged A-

Question 13

stronger acid

Answer 13

ionised in aq solution therefore partition into aq phase

Question 14

weaken acid

Answer 14

not ionised therefore likely to partition into membrane

Question 15

effect of local environment - pH decrease

Answer 15

decrease in dissociation of weak acid - increase [H+]

therefore acid system HAA-+H+ respond increase [H+] and shifts left

Question 16

effect of local environment - pH increase

Answer 16

increase in dissociation of weak acid

Question 17

acid in pure water - a equilibrium

Answer 17

is set up = conjugated base etc

know amount of acid dissociated

Question 18

pKa corresponds to pH at 50% of acid dissociated

Answer 18

pHpKa - >50% dissociated

Question 19

[A-]

Answer 19

conjugated base

Question 20

[HA]

Answer 20

conc of acid

Question 21

equation at pure water

Answer 21

[H3O+] = [OH-]