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

Chapter 20 - Acids, Bases and pH Flashcards

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1
Q

What is a Bronsted-Lowry acid?

A

A proton donor

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2
Q

What is a Bronsted-Lowry base?

A

A proton acceptor

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3
Q

What is a conjugate acid-base pair?

A

A pair containing 2 species that can be interconverted by the transfer of a proton

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4
Q

What is the formula for a hydronium ion?

A

H3O +

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5
Q

What is a monobasic acid?

A

An acid that releases one proton (H+) per acid molecule

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6
Q

What is a dibasic acid?

A

An acid that releases 2 protons (H+) per acid molecule

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7
Q

What is a tribasic acid?

A

An acid that releases 3 protons (H+) per acid molecule

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8
Q

What is the ionic equation for neutralisation?

A

H+ (aq) + OH- (aq) → H2O (l)

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9
Q

What happens when an acid reacts with a metal (what type of reaction is this)?

A

Acid + metal → salt + hydrogen
Redox reaction

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10
Q

What happens when an acid reacts with a carbonate (what type of reaction is this)?

A

Acid + carbonate → salt + water + carbon dioxide
Neutralisation reaction

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11
Q

What happens when an acid reacts with an alkali/base/metal oxide (what type of reaction is this)?

A

Acid + base/metal oxide/alkali → salt + water
Neutralisation reaction

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12
Q

Who was the founder of pH?

A

Soren Sorenson

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13
Q

What is the mathematical relationship between pH and [H+ (aq)], what is the reverse of this?

A

pH = -log[H+ (aq)]

[H+ (aq)] = 10^-pH

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14
Q

Why is pH more convenient measurement for acid concentrations than [H+]?

A

pH makes numbers manageable as [H+] deals with negative indices over a very wide range

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15
Q

Why is the pH scale a logarithmic scale?

A

A change of one pH number is equal to a 10 times difference in [H+ (aq)]

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16
Q

How can you calculate the concentration of H+ ions in strong mono, di and tribasic acids?

A

Mono: [H+] = [HA]
Di: 2[H+] = [HA]
Tri: 3[H+] = [HA]

17
Q

What is a strong acid?

A

An acid that completely dissociates in aqueous solution

18
Q

What is a weak acid?

A

An acid that only partially dissociates in aqueous solution

19
Q

How can you show the partial dissociation of a weak acid?

A

HA (aq) ⇌ H+ (aq) + A- (aq)

20
Q

What is the acid dissociation constant, Ka?

A

Ka = [H+][A-] / [HA]

Units are always mol dm-3

21
Q

What information is provided by Ka values?

A

Strength of acid/extent of dissociation

22
Q

What does the value of Ka suggest?

A

The larger the numerical value of Ka, the further the equilibrium is to the right. Therefore, the larger the Ka value, the greater the dissociation and the greater the acid strength

23
Q

What is the mathematical relationship between Ka and pKa?

A

pKa = -logKa

Ka = 10^-pKa

24
Q

What is the relationship between weak acid strength, Ka and pKa?

A

The stronger the acid, the larger the Ka value and the smaller the pKa value.
The weaker the acid, the smaller the Ka value and the larger the pKa value

25
Q

How can you simplify the Ka expression?

A

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

[H+] at equilibrium, [HA] at start

26
Q

What two assumptions must be made to simplify the Ka expression?

A
  1. HA dissociates to produce equilibrium concentrations of H+ and A- that are equal
    [H+] ≈ [A-]
  2. Only a small proportion of HA dissociates, so we can assume that [HA]&raquo_space; [H+] therefore [HA] start ≈ [HA] end
27
Q

How can Ka for a weak acid be determined experimentally?

A

Prepare a standard solution of the weak acid of known concentration, and then measure the pH of the standard solution using a pH meter

28
Q

What is the expression for Kw?

A

Kw = [H+][OH-]

29
Q

What is Kw?

A

The ionic product of water

30
Q

What is the importance of Kw?

A

It sets up a neutral point in the pH scale, it changes with temperature but controls the concentration of H+ and OH- in aq solutions

31
Q

How can we show a solution being acidic, alkaline and neutral through Kw?

A

Acidic: [H+] > [OH-]
Alkaline: [H+] < [OH-]
Neutral: [H+] = [OH-]

32
Q

How can you calculate the pH of a strong base?

A
  • the concentration of the base
  • the ionic product of water, Kw
33
Q

What is a monobasic base?

A

Where 1 mol of the base releases 1 mol of OH- ions

34
Q

How do you calculate the pH of weak bases?

A

Do not need to do at A level - only partially ionise

OCR A Level Chemistry (29 decks)

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