5.1.3 Acids, Bases and Buffers

Question 1

what is an acid

Answer 1

proton donors

Question 2

what is a base

Answer 2

proton acceptors

Question 3

what is a conjugate base

Answer 3

the base formed after the acid loses its proton

Question 4

what is a conjugate acid

Answer 4

the acid formed after a proton is gained

Question 5

what is a strong acid

Answer 5

when the H+ ions completely dissociate

Question 6

what is a weak acid

Answer 6

when the H+ ions slightly dissociate

Question 7

what is amphoteric

Answer 7

when a substance can act as both an acid and a base

Question 8

why is water an ampholyte

Answer 8

it can accept or donate a proton

Question 9

give examples of a strong acid

Answer 9

HCl, H2SO4, HNO3

Question 10

give examples of a weak acid

Answer 10

CH3COOH, H2CO3

Question 11

give examples of a strong base

Answer 11

NaOH, KOH

Question 12

give examples of a weak base

Answer 12

NH3

Question 13

describe equilibrium in strong acids and bases

Answer 13

equilibrium lies to the right as most of the acid molecules have dissociated the solution is a strong electrical conductor

Question 14

describe equilibrium in weak acids and bases

Answer 14

equilibrium lies to the left hand side as most of the acid molecules do not dissociate and the solution is a weak electrical conductor

Question 15

pH=

Answer 15

-log[H+]

Question 16

[H+]=

Answer 16

10^-pH

Question 17

what is a strong monobasic acid

Answer 17

only one proton is donated per acid molecule e.g HCl

Question 18

what is a strong dibasic acid

Answer 18

two protons are donated per acid molecule e.g H2SO4

Question 19

what equation is associated with neutral

Answer 19

[H+]=[OH-]

Question 20

what equation is used with water and what is the Kw constant

Answer 20

Kw=[H+][OH-] so Kw=[H+]^2 because [H+]=[OH-] Kw=1x10^-14 at 298k and 1atm

Question 21

give the calculation for weak acid

Answer 21

[H+]=square root of Kax[HA]
ka=H+^2/HA
H+=A-

Question 22

give the calculation for bases

Answer 22

[H+]=Kw/[OH-]

Question 23

give the calculation for water

Answer 23

Kw=[H+]^2

Question 24

give the calculation for buffers with a salt

Answer 24

[H+]=Ka x (HA/A-)

Question 25

give the calculation for buffers with a strong base

Answer 25

nHA new = nHA initial - nOH- | [H+]=Ka x (HA/A-)

Question 26

describe the dissociation of water

Answer 26

-endothermic so increasing temperature shifts equilibrium to the right increasing H+ so pH decreases

Question 27

give the basic reaction for a weak acid

Answer 27

HA H+ + A-

Question 28

give the basic reaction for ionic product of water

Answer 28

H2O H+ + OH-

Question 29

give the calculation of working out pH of a diluted

Answer 29

[H+]=old volume/new volume x old [H+] | pH=-log[H+]

Question 30

how do you construct a pH curve

Answer 30

- measure initial pH of the acid - add alkali in small amounts - record pH - when approaching end point add smaller amount

Question 31

describe equilibrium in indicators and give the equation

Answer 31

- HA H+ + A- - in acid there is a lot of H+ so equilibrium favours the left hand side - in alkali the H+ is used up so equilibrium shifts to the right

Question 32

what is the endpoint in indicators

Answer 32

when there are equal amounts of both colours HA=A-

Question 33

what is the equivalence point in indicators

Answer 33

- when the number of moles of acid exactly match the number of moles of alkali - [H+]=[OH-]

Question 34

what is a buffer

Answer 34

solutions that resist changes in pH upon addition of small amounts of acid or alkali

Question 35

what does a buffer contain

Answer 35

- a solution of a weak acid and high concentration of its conjugate base and excess HA - HA=A- + H+

Question 36

describe what happens to equilibrium when a acid is added to a buffer

Answer 36

- acid provides more H+ that react with A- | - equilibrium shifts to the left hand side and pH is raised and restored

Question 37

describe what happens to equilibrium when an alkali is added to a buffer

Answer 37

- provides OH- that react with H+ tp form water | - equilibrium shifts to the right hand side and pH is lowered and restored

Question 38

give the equation for the buffer system in the blood and explain it

Answer 38

- H2CO3 H+ + HCO3- - this carbonic acid-hydrogen carbonate equilibrium acts as a buffer to control the pH of the blood - present in blood plasma to maintain a pH of 7.35-7.45