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OCR A 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)

20
Q

How to find Ka from pKa?

A

10^-pKa

21
Q

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

A

Large Ka value, small pKa

22
Q

What are spectator ions?

A

Ions that do not change during reaction

23
Q

General equation for neutralisation of acids with carbonates

A

Acid + carbonate —> salt + water + carbon dioxide

24
Q

General equation for neutralisation of acid’s with metal oxides

A

Acid + base —> salt + water

25
Q

General equation for neutralisation of acid’s with alkalis

A

Acid + alkali —> salt + water

26
Q

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

A

Smaller ka value, lager pka value

27
Q

What are the units for Ka?

A

Mol dm^-3

28
Q

What is produced when a weak acid dissociates?

A

HA ->

29
Q

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

A

Monobasic so [H+]=[A-]
On the side there is a very small concentration of H plus ions from the dissociation of water however it is extremely small and will be neglected

30
Q

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

A

[HA]eqm=[HA]start-[H+]eqm
Weak dissociation so [H+] small and neglected so…
[HA]eqm=[HA]start

31
Q

What is the simplified version of Ka we get?

A

Ka = [H+]^2/[HA]

32
Q

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

A

[H+] = (square root) ka X [HA]

33
Q

What experiment would you conduct to measure Ka?

A
  • preparing a standard solution of a weak acid of known concentration
  • measuring the pH of the standard solution using a pH meter
34
Q

When will approximation 1 break down?

A

Very weak acids or very dilute solutions

35
Q

When will approximation 2 break down?

A

Not justified for stronger weak acids with Ka > 10^-2 moldm^-3 and very dilute solutions

36
Q

What is Kw?

A

The ionic product of water

37
Q

Equation for Kw

A

Kw = [H+][OH-]

38
Q

What is the value of Kw at RTP?

A

1X10^-14 mol^2dm^-6

39
Q

Units for Kw

A

mol^2dm^-6

40
Q

When will a solution be acidic?

A

[H+]>[OH-]

41
Q

When will a solution be neutral?

A

[H+]=[OH-]

42
Q

When will a solution be alkaline?

A

[H+]

43
Q

For a strong base, how do you calculate pH?

A

[H+] = kw(1X10^-14)/[OH-]

then -log(H+)

44
Q

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

A

Each mole of dibasic base releases 2 moles of OH-ions

45
Q

What is monobasic, dibasic, and tribasic acid?

A

The total number of hydrogen ions in the acid that can be replaced per molecule in an acid-base reaction

OCR A A-Level Chemistry (28 decks)

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