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

Chapter 20 - Acids, bases and pH Flashcards

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?

24
Q

What is produced when a weak acid dissociates?

A

An equilibrium

25
What is the first approximation we use when calculating pH for a weak acid?
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
What is the second approximation we use when calculating pH for a weak acid?
Because the dissociation is so small, you assume that only a tiny amount of H+ is produced [HA(aq)] eqm = [HA(aq)] start
27
What is the simplified version of Ka we get?
Ka = [H+(aq)]^2 | [HA(aq)] start
28
How to find [H+] using the simplified Ka expression?
[H+] = √(Ka x [HA(aq)]
29
What experiment would you conduct to measure Ka?
Prepare a standard solution of weak acid of unknown concentration Measure the pH using a pH probe
30
When will approximation 1 break down?
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
When will approximation 2 break down?
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
What is Kw?
The ionic product of water
33
Equation for Kw
Kw = [H+][OH-]
34
What is the value of Kw at RTP?
1 x 10^-14
35
Units for Kw
mol^2 dm^-6
36
When will a solution be acidic?
When [H+] > [OH-]
37
When will a solution be neutral?
When [H+] = [OH-]
38
When will a solution be alkaline?
When [OH-] > [H+]
39
For a strong base, how do you calculate pH?
Use [base] as [OH-]
40
How do you calculate the pH of weak bases?
Don't need to know
41
For a dibasic base, how do you calculate [OH-]?
2 x [dibasic base]
42
What is a di/tribasic acid?
Releases 2/3 protons
43
Acid + carbonate
Salt + water + carbon dioxide
44
The ionic equation for acid + carbonate
2H+ + CO3 2- -> H2O + CO2
45
Acid + base
Salt + water
46
The ionic equation for acid + base
2H+ + MgO -> Mg 2+ + H2O
47
Acid + alkali
Salt + water
48
The ionic equation for acid + alkali
H+ + OH- -> H2O
49
Acid + metal
Salt + hydrogen
50
The ionic equation for acid + metal
2H+ + Zn -> Zn 2+ + H2
51
What is important to remember about ionic equations?
An acid will always be represented by H+
52
What is a mono/di/tribasic acid?
1/2/3 protons can be replaced in a reaction

A Level Chemistry (29 decks)

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