Acids and bases

Question 1

acidic ion

Answer 1

H⁺

Question 2

alkaline ion

Answer 2

OH^-

Question 3

acid definition

Answer 3

proton donor

Question 4

base definition

Answer 4

proton acceptor

Question 5

weak acid definition

Answer 5

partially dissociates

Question 6

strong acid definition

Answer 6

dissociates fully

Question 7

pH definition

Answer 7

pH= - log [H⁺]

Question 8

acid dissociation equation for ethanoic acid

Answer 8

K_a= [CH₃COO^-][H⁺]
[CH₃COOH]

Question 9

[H⁺] from pH

Answer 9

[H⁺] = 10^-pH

Question 10

dissociation of water equation

Answer 10

H₂O ⇌ H⁺ + OH^-

Question 11

K_w of pure water

Answer 11

1 x10^-14 mol²dm^-6 (at 298K)

Question 12

when is K_w used

Answer 12

to find [H⁺] from [OH^-]

Question 13

why does K_w increase with temp.

Answer 13

the dissociation of water is endothermic so increasing temp. increases dissociation

Question 14

neutrality of water

Answer 14

pure water is neural at all temperatures by definition so pH scale shifts with temp.

Question 15

buffer solution definition

Answer 15

a mixture which resists change in pH when small amounts of acid or base are added

Question 16

pK_a

Answer 16

-log(K_a)

Question 17

strong acid pH ~

Answer 17

1

Question 18

weak acid pH ~

Answer 18

4-5

Question 19

strong base pH ~

Answer 19

13

Question 20

weak base pH ~

Answer 20

9-10

Question 21

methyl orange
colour change acid > alkali

Answer 21

red > yellow

Question 22

methyl orange
end point

Answer 22

3.0 - 4.5

Question 23

phenolphthalein
​colour change acid > alkali

Answer 23

colourless > pink

Question 24

phenolphthalein
end point

Answer 24

8.3 - 10.0

Question 25

lower K_a value

Answer 25

less dissociation weaker acid

Question 26

why is pK_a calculated

Answer 26

to more easily see the strength of acids

Question 27

higher pK_a value

Answer 27

weaker acid

Question 28

choosing an indicator

Answer 28

end point within ± 1 pH of equivalence point

Question 29

equation linking weak acid conc. and K_a

Answer 29

K_a = _[H_⁺]² [HA]

Question 30

why is chloroethanoic acid stronger than ethanoic acid

Answer 30

the electronegative Cl atom pulls electon density away in the anion increasing its stabilty so chloroethanoic acid dissociates more readily

Question 31

why is propanoic acid weaker than ethanoic acid

Answer 31

greater alkyl induction due to longer carbon chain pushes e^- density down the chain reducing stability of anion, therefore less dissociation

Question 32

conjugate pair

Answer 32

an acid-base pair that differs by one proton in their formulas

Question 33

amphoteric

Answer 33

a substance which can act as either an acid or a base

Question 34

diprotic acids

Answer 34

donate 2 protons

Question 35

indicators

Answer 35

a weak acid whose conjugate pair is a different colour

Question 36

equivalence point in an acid base titration

Answer 36

where an equal number of moles of H⁺ and OH^- have been mixed the reaction mixture is neutral

Question 37

acidic buffer

Answer 37

solution of a weak acid and a salt of that acid

Question 38

acidic buffer example

Answer 38

propanoic acid + sodium propanoate

Question 39

basic buffer

Answer 39

mixture of a weak base and a salt of that base

Question 40

basic buffer example

Answer 40

ammonia + ammonia chloride

Question 41

how do acidic buffers work when acid is added

Answer 41

extra H+ ions react with A- to form HA [H+] = Ka x [acid]/[salt] Ka is constant minimal change in [acid]/[salt] therefore minimal change in pH

Question 42

how do acidic buffers work when alkali is added

Answer 42

extra OH- ions react with HA to form A- and H2O [H+] = Ka x [acid]/[salt] Ka is constant minimal change in [acid]/[salt] therefore minimal change in pH

Question 43

strong acid + strong base pH calculation

Answer 43

moles of each excess formed conc. if OH^- in excess use K_w to find [H⁺] -log[H⁺]

Question 44

weak acid + strong base pH calculation

Answer 44

find moles of each find [acid] and [salt] formed using table use [H+] = Ka x [acid]/[salt]

Question 45

weak acid + salt pH calculation

Answer 45

use [H+] = Ka x [acid]/[salt]

Question 46

K_w equation

Answer 46

K_w = [H⁺] [OH^-]

Question 47

addition of acid to acidic buffer calculation

Answer 47

add acid moles to HA take away acid moles from A^- K_a = [H⁺] x ^[salt]/_[acid]

Question 48

2 tests to distinguish between strong and weak acids

Answer 48

pH paper Na₂CO₃ (disappearing cross)