3.1.12 acids and bases

Question 1

bl acid

Answer 1

proton donor

Question 2

bl base

Answer 2

proton acceptor

Question 3

lewis acid

Answer 3

electron pair acceptor

Question 4

lewis base

Answer 4

electron pair donor

Question 5

conjugate base

Answer 5

acid that has donated its proton

so is now an honorary base kinda cause it has space to accept a proton

Question 6

conjugate acid

Answer 6

base thats accepted a proton

honorary acid because can donate that proton

Question 7

strong acid

Answer 7

completely dissociates when in solution

Question 8

weak acid

Answer 8

partially ionises in solution

Question 9

monoprotic acid

Answer 9

release 1 H+ per molecule

Question 10

monobasic base

Answer 10

release 1 OH- per molecule

Question 11

pH is defined as

Answer 11

the conc H+ ions present in a solution on a logarithmic scale

pH = -log[H+]

Question 12

for every uncrease of 1pH the [H+] decreases by factor

Answer 12

10

so at pH 1, [H+] is 0.1

and at 2 it is 0.01

etc

Question 13

when finding the pH of a strong acid

Answer 13

find [H+]
make sure to chekc acid is mono di tri

Question 14

to find [H+] from pH

Answer 14

[H+] = 10^-pH

Question 15

working out pH of diluted acid

Answer 15

moles are same

so find new [H+] by doing moles divided by new volume (c1v1=c2v2)

and find pH

Question 16

pH always given in

Answer 16

2dp

Question 17

Kw is

Answer 17

the ionic product of water

water partially ionises because it can act as a bl acid or base

H2O <–> H+ + OH-

the Kw is gotten from getting the Kc expression for this reversible reaction

Kc = [H+][OH-] / [H2O]
Kc x [H2O] = [H+][OH-]

constant x constant = constant. [H2O] is basc constant because barely any ionise

Question 18

Kw at 25 c or 298k

Answer 18

1 x 10^-14

Question 19

why does Kw change with temperature

Answer 19

Kc changes with temperature

and the f reaction is endothermic so more dissociation

so if Kc is changed and the []s are changed then Kw will change

this is why as temps rise water gets more acidic but it is still neutral because [H+]=[OH-]

Question 20

finding pH of strong acid and strong base mixed together

Answer 20

moles of H+ and OH-

who is limiting? subtract their moles from the moles of excess to get moles remaining of whoever was in excess

finding [] of whoevers remaining by doing remaining moles / total volume

if OH- excess then use ioninc product of water

if H+ in excess use pH eq directly

Question 21

if they say pH change

Answer 21

find initial pH

ending pH so the changes in moles after whatevers been added

THE DIFFERENCE between them

Question 22

pH of a weak acid

Answer 22

weak acid dissociation constant, Ka

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

and because its alone and ONLY BECAUSE ITS ALONE

the weak acid approximation

Ka = [H+]^2 / [HA]

Question 23

why must use ka for weak acids

Answer 23

they dissociate reversibly and partially

therefore reversible reaction of

HA <=> H+ + A-

Question 24

a large Ka means

Answer 24

eqm lies more to the left

bigger numerator and smaller denominator therefore more dissociation so its a stronger acid

Question 25

small Ka

Answer 25

eqm lies more to right less dissociation, weak acid is moreso in protonated form so weaker acid

Question 26

pKa

Answer 26

log of Ka pKa = -log(Ka) and you can get Ka from pKa value because Ka = 1o^-pKa

Question 27

what does it mean if **pKA** is large

Answer 27

WEAKER ACID because a large Ka gives a small pKa, just like a large [H+] gives a small pH value

Question 28

units of Ka!!!!

Answer 28

like Kc or Kp cancel out units of eq make sure check if want units

Question 29

when HA is reacted with strong base

Answer 29

HA + OH- --> A- (+H2O) for every 1 mole of OH-, 1 mole of HA is reacted and 1 mole of A- is formed **if OH- in excess** use Kw **if HA in excess** use weak acid DISSOCIATION constant

Question 30

titration

Question 31

neutralisation

Question 32

equivalence point

Answer 32

moles H+ = moles OH- you should be able to tell when this is by colour change of an indicator therefore indicator must be sharp colour change at certain pH

Question 33

whats usually an indicator and why

Answer 33

weak acid because their partial ionisation means there is protonated and deprotonated forms in solution and colour change when one becomes other so used in titration bc when acid added for ex eqm shifts to decrease H+ by shifting to protonated form, HA. when HA > A-, colour change and if titrating in OH-, shifts to oppose change by more H+ to react with the OH- so more deprotonated. when A- > HA, colour change the titration basc forces the eqm to one side so get a colour change

Question 34

endpoint

Answer 34

when colour change ideally equivalence and endpoint should be same. this is why depending on what titrating, choice of indicator changes

Question 35

characteristics of good indicator

Answer 35

colour change is sharp and distinct no ambiguity on when changes endpoint = equiv point

Question 36

SA SB

Answer 36

equiv point ~~ 7 sharp increase in pH (if flask is acid) as get closer to endpoint large vertical section on pH curve signifies equiv point

Question 37

WA SB the start of it half neutralisation

Answer 37

equiv point above 7 buffer region resists changes to pH when small amounts of acid or alkali are added at equiv point, this is neutralisation. thevolume of base added here, half it. the pH at half neutralisation is the pKa so you can find Ka from pKa then identify WA from that because each WA have own Ka

Question 38

SA WB

Answer 38

equiv below 7

Question 39

WA WB

Answer 39

gradual increase in pH so no sharp change in pH so cant titrate with indicator because there will be no sharp colour change

Question 40

when sketching pH curves

Answer 40

- whos in flask therefore where gonna start up or down - calculate initial pH with given info - calculate end pH - see if WA SB or whats the combination - have equiv point above at or below 7 based on the combination

Question 41

a buffer is

Answer 41

a solution that resists large changes in pH when small amounts of acid or alkali are added to it or when it is diluted

Question 42

how to make a buffer

Answer 42

WEAK ACID AND ITS SALT - so add them together just like that - or add limited amount of strong base which will be used up and form salt WEAK BASE AND ITS SALT - so add them together just like that - or add limited amount of strong acid which will be used up and form salt

Question 43

how do acidic buffers work

Answer 43

[HA] and [A-] are much much higher than [H+] so when

Question 44

finding the pH of a buffer

Answer 44

[H+] = [HA] / [A-] this is the dissociatio constant rearranged for H+ and Ka removed because its a constant the pH of the buffer depends on the ratio of [HA]:[A-] A- is from salt

Question 45

when OH is added to acidic buffers

Answer 45

HA <=> H+ + A- reacts with H+ therefore H+ decreases so shifts to replace lost H+ so more dissociation so [ha] decreases slightly and [a-] increases slightly so ratio remains fairly constant

Question 46

when H+ is added to acidic buffers

Answer 46

shifts to decrease H+ so in direction of b reaction so more protonation of A- [ha] increases slightly [a-] decreases slightly so ratio remains fairly constant

Question 47

when h2o added to either buffer (dilution)

Answer 47

HA and A- diluted by same amount so ratio remains the same

Question 48

for basic buffers see notes

Answer 48

see notes