ACID

Question 1

you don’t get H+ ions alone in water, but as…

Answer 1

hydroxonium ions H3O+

Question 2

what is a monobasic acid ?

Answer 2

releases one proton in solution

Question 3

what is another name for monobasic acid ?

Answer 3

monoprotic acid

Question 4

what is the conjugate base ?

Answer 4

species that has lost a proton

Question 5

what is the conjugate acid ?

Answer 5

species that has gained a proton

Question 6

how is water a special case for conjugate pairs ?

Answer 6

• reacts with acid to form conjugate acid

- reacts with base to form conjugate base

Question 7

what is the pH scale a measure of ?

Answer 7

[H+]

Question 8

pH =

Answer 8

-log10 [H+]

Question 9

Kw =

Answer 9

[H+] [OH-]

Question 10

what are always the units for Kw ?

Answer 10

mol2 dm-6

Question 11

why is temp the only variable that will change Kw ?

Answer 11

dissociation of water is endothermic, so warming will shift equil. to right, increasing Kw

Question 12

for strong monobasic acids, [Acid] =

Answer 12

[H+]

Question 13

Ka =

weak acids

Answer 13

[H+]^2 / [HA]

Question 14

pKa =

Answer 14

-log10 Ka

Question 15

the smaller the value of pKa ..

Answer 15

the stronger the acid

Question 16

give the definition for buffer

Answer 16

a solution that minimises changes in pH when small amounts of acid or base are added

Question 17

why can buffers only resist small amount of acid/base ?

Answer 17

the weak acid / conjugate base gets used up

Question 18

how are acidic buffers made ? (summary)

Answer 18

setting up equilibrium with weak acid and conjugate base

Question 19

describe first way to make acidic buffer

Answer 19

• mix weak acid w/ the salt of its conjugate base
• salt fully dissociates into ions
• weak acid partially dissociates

Question 20

describe second way of making acidic buffer

Answer 20

• mix excess of weak acid and strong alkali
• all base reacts w/ acid
• left over weak acid partially dissociates

Question 21

what does an acidic buffer contain ?

Answer 21

• lots of undissociated acid
• lots of the acid’s conjugate base
• enough H+ ions to make solution acidic

Question 22

before using a pH probe, what must you do ?

Answer 22

calibrate by placing in distilled water and setting to 7, then to standard solutions of pH 4 and pH 10

Question 23

what are the axis in pH curves ?

Answer 23

x - vol of alkali added

y - pH

Question 24

what is the vertical part of a pH curve ?

Answer 24

equivalence point

[H+] = [OH-]

Question 25

methyl orange from low to high pH

Answer 25

red to yellow

Question 26

phenolphthalein from low to high pH

Answer 26

colourless to pink

Question 27

what is Kw at RTP ?

Answer 27

1 x 10^ -14

Question 28

what assumptions are made for strong acid calc ?

Answer 28

• water dissociation is negligible

- acid fully dissociated [HA] = [H+]

Question 29

what assumptions made for strong alkali calc ?

Answer 29

• water dissociation is negligible

- alkali fully dissociated

Question 30

how can aqueous solution of acid contain hydroxide ions ?

Answer 30

water dissociates

Question 31

what to remember w/ triprotic calculations

Answer 31

multiply [H+] by 3

Question 32

outline process of making diluted solution for titration

Answer 32

1. measure w/ 10cm3 volumetric pipette
2. add to 100cm3 volumetric flask
3. make up to mark w/ deionised water
4. mix well