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AQA Physical Chemistry > Acids and Bases > Flashcards

Acids and Bases Flashcards

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1
Q

Define an acid

A

A proton (H+) donor

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2
Q

What is a monobasic acid?

A

For every 1 mole of acid, 1 mole of H+ is produced

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3
Q

What is a dibasic acid?

A

For every 1 mole of acid, 2 moles of H+ are produced

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4
Q

What is a tribasic acid?

A

For every 1 mole of acid, 3 moles of H+ are produced

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5
Q

Define a base

A

A proton (H+) acceptor

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6
Q

What is a monobasic base?

A

For every 1 mole of base, 1 mole of OH- is produced

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7
Q

What is a dibasic base?

A

For every 1 mole of base, 2 moles of OH- are produced

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8
Q

What is a tribasic base?

A

For every 1 mole of base, 3 moles of OH- are produced

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9
Q

What are 3 examples of a strong acid?

A
  • HCl- HNO3- H2SO4
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10
Q

What does a strong acid do?

A

Fully dissociates in solution to produce H+ (aq)

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11
Q

What are 3 examples of a strong base?

A
  • NaOH- KOH- Ca(OH)2
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12
Q

What does a strong base do?

A

Fully dissociates in solution to produce OH- (aq)

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13
Q

What are 3 examples of a weak acid?

A
  • H3PO4- HF- CH3COOH
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14
Q

What do weak acids do?

A
  • They do not fully dissociate in solution to produce H+- They exist in equilibrium
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15
Q

What do weak bases do?

A
  • They do not fully dissociate in solution to produce OH_- They partially react with H2O to form OH- (aq)
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16
Q

What are 2 examples of a weak base?

A
  • NH3- CH3NH2
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17
Q

How do you find pH?

A

-log10[H+]

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18
Q

How do you find [H+]?

A

10^-pH

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19
Q

How do you calculate the pH of a strong acid?

A
  • Because they fully dissociate there will be a ratio between [acid] and [H+] based on wether they are mono/di/tri basic- For a dibasic strong acid, if one mole of acid reacts then 2 moles of H+ will be produced
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20
Q

How do you calculate the pH of a weak acid?

A
  • Ka is used- [H+] = (sqr root of) Ka x [HX]
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21
Q

How do you calculate the pH of a strong base?

A
  • Kw is used- [H+] = kw/[OH-]
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22
Q

What are the 3 steps to calculating the pH of a strong acid?

A

1 - Find the acid concentration2 - Use stoichiometry and knowledge of mono/di/tribasic acids to find concentration of hydrogen ions3 - Use -log (base 10) [H+]

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23
Q

What are the 3 steps to finding the concentration of a strong acid?

A

1 - Find the pH2 - Calculate [H+] using 10^-pH3 - Use stoichiometry to find [acid]

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24
Q

What is Ka?

A

The equilibrium constant of the dissociation of a weak acid, it is a quantitative measurement of the strength of a weak acid

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25
Q

What is the difference between a large value of Ka and a small value of Ka?

A

The larger the value of Ka, the stronger the acid

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26
Q

Why is Ka used for weak acids?

A

Weak acids do not fully dissociate in solution (they exist in equilibrium)

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27
Q

What is the equation for the Ka of HX <=> H+ + X- ?

A

Ka = [H+][X-] / [HX]

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28
Q

What do you need to know to be able to calculate the pH of a weak acid?

A

1 - Ka value2 - Acid concentration

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29
Q

What do you need to know to be able to calculate the concentration of a weak acid?

A
  • Ka value- pH
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30
Q

What is a base?

A

A proton acceptor

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31
Q

What is an alkali?

A

A type of soluble base that releases OH- ions in solution

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32
Q

What are the 4 types of base?

A
  • Metal hydroxides- Ammonia- Metal oxides- Metal carbonates
33
Q

Which bases are alkalis?

A
  • Metal hydroxides- Ammonia
34
Q

What are examples of metal hydroxides?

A
  • NaOH- KOH- Ca(OH)2
35
Q

What are examples of metal oxides?

A
  • Na2O- K2O- MgO- CuO
36
Q

What are examples of metal carbonates?

A
  • Na2CO3- K2CO3- MgCO3- CaCO3
37
Q

What do strong alkalis do?

A

Fully dissociate in solution

38
Q

What do weak alkalis do?

A

Partially dissociate in solution

39
Q

What is water?

A

Amphoteric (can act as an acid and as a base)

40
Q

What is Kw?

A

The dissociation constant for the dissociation of water

41
Q

What is Kw used for?

A

Calculating the pH of a strong base

42
Q

What is the Kw equation?

A

Kw = [H+][OH-]

43
Q

What is the Kw value for pure water at 298k at a pH of 7?

A

1 x 10^-14 mol^2dm^-6

44
Q

What happens to Kw when you increase the temperature?

A
  • Endothermic reaction is favoured- Equilibrium shifts to the right- Kw increases
45
Q

What happens to Kw when you decrease the temperature?

A
  • Exothermic reaction is favoured- Equilibrium shifts to the left- Kw decreases
46
Q

What do you need to know to be able to calculate the pH of a strong base?

A

1 - Conc of a strong base2 - Kw = 1x10^-14 mol.dm^-3

47
Q

What steps to you need to follow to calculate the pH of a strong base?

A

1 - Find [OH-]2 - Use kw expression to find [H+]3 - Use -log[H+]

48
Q

What do you need to know in order to calculate the concentration of a strong base?

A
  • Kw value- pH
49
Q

How can you calculate pKa?

A

-logKa

50
Q

How can you calculate Ka from pKa?

A

Ka = 10^ -pKa

51
Q

What is the relative strength of an acid with a high pKa value?

A

Weaker acid

52
Q

What is the relative strength of an acid with a high Ka value?

A

Stronger acid

53
Q

What is the relative strength of an acid with a low pKa value?

A

Stronger acid

54
Q

What is the relative strength of an acid with a low Ka value?

A

Weaker acid

55
Q

How can you calculate pKw?

A

-logKw

56
Q

How can you calculate Kw from pKw?

A

10^-pKw

57
Q

What happens to pKw when Kw is increased?

A

pKw decreases

58
Q

What happens to pKw when Kw is decreased?

A

pKw increases

59
Q

What is a pH curve?

A

A titration using a pH probe to monitor changes in pH during the addition of a base (alkali) to an acid

60
Q

What is the equivalence point?

A

The point at which the graph is vertical and therefore the point at which neutralisation happens

61
Q

What can the equivalence point tell us?

A

The volume of base needed to neutralise acid

62
Q

When carrying out a titration, what should you do near the equivalence point?

A

Use smaller increments

63
Q

What three things can you read from any pH curve?

A
  • [H+]- [OH-]- A suitable indicator
64
Q

How can you calculate [H+] from a pH curve?

A

10^-pH

65
Q

How can you calculate [OH-] from a pH curve?

A

Calculate [H+] then divide Kw by [H+]

66
Q

How can you select an indicator for a pH curve?

A

Choosing an indicator with a pH range inside the equivalence region

67
Q

What can you calculate from a weak acid, strong base pH curve?

A

The Ka for the weak acid- Find vol.base needed for neutralisation- Half volume- Find pH at half volume- pH = pKa- Ka = 10^-pKa

68
Q

What is a buffer solution?

A

A buffer solution maintains an approximately constant pH despite the addition of water and small amounts of acid or base

69
Q

What does an acid buffer contain?

A

A weak acid and the salt of the weak acid

70
Q

How does an acid buffer oppose the change if the buffer is diluted?

A
  • Adding water will decrease [H+]- Equilibrium shifts to the right to oppose the change - More acid dissociates to increase the [H+] to what is was before
71
Q

How does an acid buffer oppose the change if alkali or base is added?

A
  • Decreases [H+] by neutralisation- Equilibrium shifts to the right to oppose the change- More acid dissociates to increase the [H+] to what it was before
72
Q

How does an acid buffer oppose the change if acid is added?

A
  • Increases [H+]- Equilibrium shifts to the left to oppose the change- [H+] is decreased to what is was before - Conjugate base associates with H+ to form acid
73
Q

What does a basic buffer contain?

A

A weak base and the salt of the weak base

74
Q

How does a basic buffer oppose the change if water is added?

A
  • Decrease [OH-] - Equilibrium shifts to the right to oppose the change- More base and water reacted together top form more OH- to maintain the pH
75
Q

How does a basic buffer oppose the change if acid is added?

A
  • [OH-] decreased because of neutralisation- Equilibrium shifts to the right to oppose the change and maintain [OH-]
76
Q

How does a basic buffer oppose the change if alkali is added?

A
  • Increase [OH-]- Equilibrium shifts to the left to oppose the change and maintain [OH-] conc- Conjugate acid reacts with more OH-
77
Q

What does an acid buffer contain?

A
  • Weak acid- Salt of the weak acid
78
Q

What do you need to know to be able to calculate the pH of an acid buffer?

A
  • [Acid]- [Salt]- Ka of the acid

AQA Physical Chemistry (12 decks)

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