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A Level Chemistry > Module 5: Chapter 20 - Acids, Bases, and pH > Flashcards

Module 5: Chapter 20 - Acids, Bases, and pH Flashcards

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1
Q

What is the solubility of group 1 salts?

A

They are all soluble

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2
Q

What is the solubility of nitrates (NO₃⁻)?

A

They are all soluble

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3
Q

What is the solubility of Halides?

A

All soluble except silver halides

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4
Q

What is the solubility of group 2 sulfates?

A

Solubility decreases down the group

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5
Q

What is the solubility of group 2 hydroxides?

A

Solubility increases down the group

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6
Q

What is a Brønsted-Lowry acid?

A

A proton donor

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7
Q

What is a Brønsted-Lowry base?

A

A proton acceptor

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8
Q

What is a monobasic acid?

A

An acid containing 1 hydrogen ion that can be replaced per molecule, i.e hydrochloric acid

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9
Q

What is a dibasic acid?

A

An acid containing 2 hydrogen ions that can be replaced per molecule, i.e sulfuric acid

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10
Q

What is a tribasic acid?

A

An acid containing 3 hydrogen ions that can be replaced per molecule, i.e phosphoric acid

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11
Q

Which metals will react with hydrochloric acid in a redox reaction?

A

Any metals more reactive than hydrogen (i.e not platinum gold silver or copper)

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12
Q

What is a cojugate acid-base pair?

A

A set of 2 species that transform into each other by the gain or loss of a proton

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13
Q

Which species will have more basic properties, the conjugate base of a strong acid or the conjugate base of a weak acid?

A

As a strong acid completely dissociates, the reaction is not reversible so the conjugate base does not have any basic properties. However, a weak acid only partially dissociates so the reaction can be reversed and the conjugate base does have basic properties. Therefore, the conjugate base of a weak acid has stronger basic properties

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14
Q

Identify the conjugate pairs

A
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15
Q

Identify the conjugate pairs

A
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16
Q

Identify the conjugate pairs

A
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17
Q

What is the definition of pH?

A

pH = -log₁₀[H⁺]

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18
Q

What is the equation for pH?

A

pH = -log₁₀[H⁺]

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19
Q

How many decimal places do you give pH to?

A

Always to 2dp

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20
Q

What is the equation for the concentration of hydrogen ion?

A

[H⁺] = 10⁻ᵖᴴ

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21
Q

What is the concentration of H₂SO₄ with a pH of 1.30?

A

0.0251 mol dm⁻³

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22
Q

What is the pH of the solution formed when 250cm³ of 0.300 mol dm⁻³ H₂SO₄ is made up to 2000cm³ with water?

A

1.12

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23
Q

What is the concentration of water?

A

55.6 mol dm⁻³

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24
Q

What is the ionic product of water, Kw?

A

The product of the ions formed in the partial dissociation of water, given by Kw = [H⁺(aq)] [OH⁻(aq)]

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25
Q

What is the ionic product of water at 298K?

A

Kw = 10⁻¹⁴ mol² dm⁻⁶

Look at the units!

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26
Q

What is the Kc equation for the partial dissociation of water?

A

Kc = [H⁺][OH⁻] / [H₂O][H₂O]

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26
Q

What is the equation for the partial dissociation of water?

A

H₂O + H₂O ⇌ H₃O⁺ + OH⁻

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27
Q

What is the equation for Kw?

A
  • Kw = [H⁺][OH⁻]
  • Kw = Kc [H₂O]²
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28
Q

When a solution is neutral what can be said about [H⁺] and [OH⁻]?

A

When neutral:
[H⁺] = [OH⁻]

29
Q

Work out the pH of water at 298K

A
30
Q

In the equation “H₂O ⇌ H⁺ + OH⁻”, what happens to Kw, pH and neutrality as temperature increases?

A

As temperature increases:
* Equilibrium moves in the endothermic direction (forward direction) oppose the increase in temperature
* Therefore Kw increases
* [H⁺] increases so pH decreases
* However it is still neutral as [OH⁻] also increases and [H⁺] = [OH⁻]

31
Q

Calculate the pH of pure water at 40 degrees celcius when Kw = 2.09 x 10⁻¹⁴ mol² dm⁻⁶

A

6.84

32
Q

What is the equation for [H⁺] in terms of Kw?

A

[H⁺] = √Kw

33
Q

Calculate the pH of 0.200 mol dm⁻³ NaOH(aq) at 298K

A

13.30

34
Q

Calculate the pH of 0.0500 mol dm⁻³ Ba(OH)₂(aq) at 298K

A

13.00

35
Q

Calculate the pH of the solution formed when 50cm³ of 0.250 mol dm⁻³ KOH is made up to 250cm³ of solution with water at 298K

A

12.70

36
Q

What is an example of a weak base?

A

Ammonia solution

37
Q

What is Ka?

A

Acid dissociation constant, it is simply Kc applied to the dissociation of an acid (multiplied by the concentration of water)

38
Q

What is the formula for Ka?

A
  • Ka = [H⁺][A⁻]/[HA]
  • Ka = Kc x [H₂O]
  • Ka = [H⁺]²/[HA] (in aqueous solutions ONLY)
39
Q

What are pKa values?

A

Values used to compare acid strength

40
Q

What is the equation for pKa?

A

pKa = - log₁₀(Ka)

41
Q

What is the equation for Ka in terms of pKa?

A

Ka = 10⁻ᵖᴷᵃ

42
Q

What is the Ka value of a stronger acid?

A

higher

43
Q

What is the pKa value of a stronger acid?

A

lower

44
Q

What is the Ka value of a weaker acid?

A

Lower

45
Q

What is the pKa value of a weaker acid?

A

Higher

46
Q

What can be said in an aqueous solution of a weak acid?

A

[H⁺]eqm = [A⁻]eqm

and therefore, Ka = [H⁺]²/[HA]

47
Q

What are the assumptions in the formula “Ka = [H⁺]²/[HA]”

A
  1. The [H⁺] from dissociation of water is insignificant
  2. The amount of dissociation is so small that we can ssume that the initial concentration of the undissociated acid has remained constant
48
Q

When can “Kw = [H⁺][OH⁻]” be used?

A

In all aqueous solutions

49
Q

When can “Kw = [H⁺][H⁺]” be used?

A

For Pure water ONLY

50
Q

When can “Ka = [H⁺][A⁻]/[HA]” be used?

A

All solutions containing a weak acid

51
Q

When can “Ka = [H⁺]²/[HA]” be used?

A

For weak acids in water ONLY

52
Q

What is the only factor which can affect Kw and Ka?

A

Temperature

53
Q

Calculate the pH of 0.1 mol dm⁻³ propanoic acid (pKa = 4.87)

A

2.94

54
Q

Calculate the concentration of a solution of methanoic acid with pH of 4.02 (Ka = 1.35 x 10⁻⁵ mol dm⁻³)

A

6.76x10⁻⁴ mol dm⁻³

55
Q

What is an alkali?

A

A base that dissolves in water, forming OH⁻(aq)

56
Q

if “HA + (aq) -> H₃O⁺(aq) + A⁻(aq)”, why is the hydronium ion treated as H⁺(aq)?

A

A free hydrogen ion does not exist in solution, it forms a hydronium ion with water. In an aqueous solution (such as an acid) we can use hydronium ion and hydrogen ion interchangeably

57
Q

What is H₃O⁺?

A

The hydronium ion

58
Q

What is the dot and cross diagram for the hydronium ion?

A
59
Q

What are 2 examples of weak acids?

A
  • Carboxylic acids
  • Citric acid
60
Q

How does an acid form its conjugate base?

A

By releasing a proton

61
Q

How does a base form its conjugate acid?

A

By gaining a proton

62
Q

What does H⁺(aq) actually represent?

A

H₃O⁺(aq)

63
Q

Whats the equation for [H⁺(aq)] of a weak acid?

A

[H⁺(aq)] = √Ka[HA(aq)]

64
Q

When does the assumption that the dissociation of water is negligible in the equation for Ka break down?

A

If the pH > 6, then the [H⁺(aq)] from the dissociation of water will be significant compared to the dissociation of the weak acid. Therefore, this assumption breaks down for very weak acids or very dilute solutions

65
Q

When does the assumption that the concentration of an acid is much greater than the H⁺ concentration at equilibrium (and therefore [HA]start = [HA]end) break down?

A

This approximation only holds true for weak acids with a small Ka value, it breaks down when [H⁺(aq)] becomes significant and therefore there is a large difference between [HA]start and [HA]end. Therefore it is not justified for stronger weak acids with Ka > 10⁻² mol dm⁻³ and for very dilute solutions

66
Q

When is a solution acidic?

A

When [H⁺] > [OH⁻]

67
Q

When is a solution neutral?

A

When [H⁺] = [OH⁻]

68
Q

When is a soluton alkaline?

A

When [H⁺] < [OH⁻]

69
Q

What is pOH?

A

A similar scale to pH, but rather than considering the concentrations of hydrogen, it uses the concentrations of hydroxide

70
Q

What is the relationship between pH and pOH?

A

pH + pOH = 14
at 298K

71
Q
A

A Level Chemistry (31 decks)

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