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Chemistry > Acids and bases > Flashcards

Acids and bases Flashcards

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1
Q

acidic ion

A

H+

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2
Q

alkaline ion

A

OH-

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3
Q

acid definition

A

proton donor

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4
Q

base definition

A

proton acceptor

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5
Q

weak acid definition

A

partially dissociates

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6
Q

strong acid definition

A

dissociates fully

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7
Q

pH definition

A

pH= - log [H+]

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8
Q

acid dissociation equation for ethanoic acid

A

Ka= [CH3COO-][H+]
[CH3COOH]

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9
Q

[H+] from pH

A

[H+] = 10-pH

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10
Q

dissociation of water equation

A

H2O ⇌ H+ + OH-

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11
Q

Kw of pure water

A

1 x10-14 mol2dm-6 (at 298K)

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12
Q

when is Kw used

A

to find [H+] from [OH-]

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13
Q

why does Kw increase with temp.

A

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

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14
Q

neutrality of water

A

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

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15
Q

buffer solution definition

A

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

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16
Q

pKa

A

-log(Ka)

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17
Q

strong acid pH ~

A

1

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18
Q

weak acid pH ~

A

4-5

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19
Q

strong base pH ~

A

13

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20
Q

weak base pH ~

A

9-10

21
Q

methyl orange
colour change acid > alkali

A

red > yellow

22
Q

methyl orange
end point

A

3.0 - 4.5

23
Q

phenolphthalein
​colour change acid > alkali

A

colourless > pink

24
Q

phenolphthalein
end point

A

8.3 - 10.0

25
Q

lower Ka value

A

less dissociation
weaker acid

26
Q

why is pKa calculated

A

to more easily see the strength of acids

27
Q

higher pKa value

A

weaker acid

28
Q

choosing an indicator

A

end point within ± 1 pH of equivalence point

29
Q

equation linking weak acid conc. and Ka

A

Ka = [H+]2
[HA]

30
Q

why is chloroethanoic acid stronger than ethanoic acid

A

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

31
Q

why is propanoic acid weaker than ethanoic acid

A

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

32
Q

conjugate pair

A

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

33
Q

amphoteric

A

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

34
Q

diprotic acids

A

donate 2 protons

35
Q

indicators

A

a weak acid whose conjugate pair is a different colour

36
Q

equivalence point in an acid base titration

A

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

37
Q

acidic buffer

A

solution of a weak acid and a salt of that acid

38
Q

acidic buffer example

A

propanoic acid + sodium propanoate

39
Q

basic buffer

A

mixture of a weak base and a salt of that base

40
Q

basic buffer example

A

ammonia + ammonia chloride

41
Q

how do acidic buffers work when acid is added

A

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

42
Q

how do acidic buffers work when alkali is added

A

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

43
Q

strong acid + strong base pH calculation

A

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

44
Q

weak acid + strong base pH calculation

A

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

45
Q

weak acid + salt pH calculation

A

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

46
Q

Kw equation

A

Kw = [H+] [OH-]

47
Q

addition of acid to acidic buffer calculation

A

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

48
Q

2 tests to distinguish between strong and weak acids

A

pH paper
Na2CO3 (disappearing cross)

Chemistry (15 decks)

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