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A Level Chemistry > Chapter 20 - Acids, bases and pH > Flashcards

Chapter 20 - Acids, bases and pH Flashcards

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1
Q

What does the Arrhenius model suggest about acids?

A

They dissociate and release H+ ions when dissolved in water

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2
Q

What does the Arrhenius model suggest about alkalis?

A

They dissociate and release OH- ions when dissolved in water

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3
Q

What is an alkali?

A

A soluble base

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4
Q

What is a Brønsted-Lowry acid?

A

A proton donor

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5
Q

What is a Brønsted-Lowry base?

A

A proton acceptor

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6
Q

What is a conjugate acid-base pair?

A

Two species that can be interconverted by the transfer of a proton

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7
Q

Formula for the hydronium ion

A

H3O+

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8
Q

What does H+ really represent in an equation?

A

The hydronium ion

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9
Q

What type of scale is pH?

A

Logarithmic

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10
Q

What does a low value of H+ indicate?

A

A high pH

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11
Q

What does a high value of H+ indicate?

A

A low pH

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12
Q

How to work out pH?

A

pH = -log[H+]

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13
Q

How to work out [H+]?

A

10^-pH

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14
Q

What is important to remember about calculating the pH of strong acids?

A

They completely dissociate:

[H+(aq)] = [HA(aq)]

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15
Q

What happens to weak acids when dissolved in solution?

A

They partially dissociate

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16
Q

What is Ka?

A

The acid dissociation constant

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17
Q

What does pH measure?

A

Hydrogen ion concentration

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18
Q

What is the equation of Ka for a weak acid before assumptions?

A

[H+(aq)] x [A-(aq)]

[HA(aq)]

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19
Q

How to find pKa?

A

pKa = -log(Ka)

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20
Q

How to find Ka from pKa?

A

10^-pKa

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21
Q

What characteristics of pKa and Ka will a strong acid have?

A

Large Ka value, small pKa

22
Q

What characteristics of pKa and Ka will a weak acid have?

A

Small Ka value, large pKA

23
Q

What are the units for Ka?

A

mol dm^-3

24
Q

What is produced when a weak acid dissociates?

A

An equilibrium

25
Q

What is the first approximation we use when calculating pH for a weak acid?

A

You ignore the H+ ions produced from the dissociation of water because the dissociation from the acid is greater
You assume all H+ ions come from the acid, so [H+(aq)] = [A-(aq)]

26
Q

What is the second approximation we use when calculating pH for a weak acid?

A

Because the dissociation is so small, you assume that only a tiny amount of H+ is produced
[HA(aq)] eqm = [HA(aq)] start

27
Q

What is the simplified version of Ka we get?

A

Ka = [H+(aq)]^2

[HA(aq)] start

28
Q

How to find [H+] using the simplified Ka expression?

A

[H+] = √(Ka x [HA(aq)]

29
Q

What experiment would you conduct to measure Ka?

A

Prepare a standard solution of weak acid of unknown concentration
Measure the pH using a pH probe

30
Q

When will approximation 1 break down?

A

If the pH of the acid is more than 6, [H+] from the dissociation of water is 10^-7, which is significant compared to the [H+] from the acid of 10^-6
It breaks down for very weak acids

31
Q

When will approximation 2 break down?

A

When [H+] becomes significant and there is a large difference between [HA] eqm and [HA] start - [H+]
It breaks down for stronger weak acids with a Ka value of > 10^-2

32
Q

What is Kw?

A

The ionic product of water

33
Q

Equation for Kw

A

Kw = [H+][OH-]

34
Q

What is the value of Kw at RTP?

A

1 x 10^-14

35
Q

Units for Kw

A

mol^2 dm^-6

36
Q

When will a solution be acidic?

A

When [H+] > [OH-]

37
Q

When will a solution be neutral?

A

When [H+] = [OH-]

38
Q

When will a solution be alkaline?

A

When [OH-] > [H+]

39
Q

For a strong base, how do you calculate pH?

A

Use [base] as [OH-]

40
Q

How do you calculate the pH of weak bases?

A

Don’t need to know

41
Q

For a dibasic base, how do you calculate [OH-]?

A

2 x [dibasic base]

42
Q

What is a di/tribasic acid?

A

Releases 2/3 protons

43
Q

Acid + carbonate

A

Salt + water + carbon dioxide

44
Q

The ionic equation for acid + carbonate

A

2H+ + CO3 2- -> H2O + CO2

45
Q

Acid + base

A

Salt + water

46
Q

The ionic equation for acid + base

A

2H+ + MgO -> Mg 2+ + H2O

47
Q

Acid + alkali

A

Salt + water

48
Q

The ionic equation for acid + alkali

A

H+ + OH- -> H2O

49
Q

Acid + metal

A

Salt + hydrogen

50
Q

The ionic equation for acid + metal

A

2H+ + Zn -> Zn 2+ + H2

51
Q

What is important to remember about ionic equations?

A

An acid will always be represented by H+

52
Q

What is a mono/di/tribasic acid?

A

1/2/3 protons can be replaced in a reaction

A Level Chemistry (29 decks)

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