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Chemistry Unit 4 > Acids and Bases > Flashcards

Acids and Bases Flashcards

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1
Q

Define a Bronsted-Lowry acid.

A

A proton donor.

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2
Q

Define a Bronsted-Lowry acid.

A

A proton donor.

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3
Q

Define a Bronsted-Lowry base.

A

A proton acceptor.

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4
Q

When acids and bases react, what happens to the protons?

A

They are transferred from the acid to the base.

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5
Q

Is water an acid or a base?

A

It can act as both.

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6
Q

Give an example of a strong acid and explain why it is classified as such.

A

HCl, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.

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7
Q

Give an example of a strong base and explain why it is classified as such.

A

NaOH, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.

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8
Q

Give an example of a weak acid and explain why it is classified as such.

A

CH3COOH, because it only dissociates slightly in water. Only small numbers of H+ ions are formed. It forms an equilibrium that lies well over to the left.

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9
Q

Give an example of a weak base and explain why it is classified as such.

A

NH3, because it only dissociates slightly in water. Only small numbers of OH- ions are formed. It forms an equilibrium that lies well over to the left.

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10
Q

What happens when a strong or weak acid is added to water?

A

Water acts as a base and accepts the proton, forming H3O+ ions. This is an equilibrium.

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11
Q

What equilibrium exists in water?

A

2H2O –> H3O+ + OH- or
H2O –> H+ + OH-
These are equilibriums that lie well over to the left.

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12
Q

What is Kw?

A

The ionic product of water.

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13
Q

Why does Kw exist?

A

Because water only dissociates very slightly, we take the concentration of water to be constant. If we use the equation for Kc, and multiply it by [H2O], this gives us another constant.

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14
Q

What is the equation for Kw?

A

Kw = [H+][OH-] or, in pure water, Kw = [H+]^2

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15
Q

What are the units of Kw?

A

mol^2 dm^-6

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16
Q

What is the value of Kw at 298K?

A

1.00x10^-14

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17
Q

What condition affects Kw?

A

Temperature.

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18
Q

How can we calculate the pH of a strong base from it’s concentration?

A

There is one mole of OH- ions for every one mole of the base, assuming it dissociates completely in water. So, [OH-] = [B]. We can then use the equation for Kw to calculate [H], and use this to calculate the pH.

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19
Q

Give the equation for pH.

A

pH = -log10[H+]

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20
Q

What do square brackets represent?

A

Concentration in mol dm^-3

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21
Q

Define a monoprotic acid.

A

Each molecule of acid will release one proton when it dissociates.

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22
Q

Define a diprotic acid.

A

Each molecule of acid will release two protons when it dissociates.

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23
Q

How can we calculate the pH of a strong monoprotic acid from it’s concentration?

A

Assuming the acid completely dissociates in water, the H+ concentration is the same as the acid concentration. We then use this to calculate pH.

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24
Q

How can we calculate the pH of a strong diprotic acid from it’s concentration?

A

Assuming the acid completely dissociates in water, the H+ concentration is double the acid concentration. We then use this to calculate pH.

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25
Q

What is Ka?

A

The acid dissociation constant.

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26
Q

What are the units of Ka?

A

mol dm-3

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27
Q

Give an expression for Ka.

A 
Ka = [H+][A-] all over [HA] or,
Ka = [H]^2 over [HA] (assuming all the H+ ions come from the acid, [H+] = [A-])
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28
Q

Give the equation for pKa.

A

pKa = -log10(Ka)

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29
Q

What indicator would you use for a strong acid-strong base titration?

A

Methyl orange or phenolphthalein.

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30
Q

What indicator would you use for a strong acid-weak base titration?

A

Methyl orange

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31
Q

What indicator would you use for a weak acid-strong base titrarion?

A

Phenolphthalein

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32
Q

What indicator would you use for a weak acid-weak base titration?

A

No indicator will work, because there’s no sharp pH change.

33
Q

Define a Bronsted-Lowry base.

A

A proton acceptor.

34
Q

When acids and bases react, what happens to the protons?

A

They are transferred from the acid to the base.

35
Q

Is water an acid or a base?

A

It can act as both.

36
Q

Give an example of a strong acid and explain why it is classified as such.

A

HCl, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.

37
Q

Give an example of a strong base and explain why it is classified as such.

A

NaOH, because it almost completely dissociates in water. For the sake of calculation, we assume it dissociates completely.

38
Q

Give an example of a weak acid and explain why it is classified as such.

A

CH3COOH, because it only dissociates slightly in water. Only small numbers of H+ ions are formed. It forms an equilibrium that lies well over to the left.

39
Q

Give an example of a weak base and explain why it is classified as such.

A

NH3, because it only dissociates slightly in water. Only small numbers of OH- ions are formed. It forms an equilibrium that lies well over to the left.

40
Q

What happens when a strong or weak acid is added to water?

A

Water acts as a base and accepts the proton, forming H3O+ ions. This is an equilibrium.

41
Q

What equilibrium exists in water?

A

2H2O –> H3O+ + OH- or
H2O –> H+ + OH-
These are equilibriums that lie well over to the left.

42
Q

What is Kw?

A

The ionic product of water.

43
Q

Why does Kw exist?

A

Because water only dissociates very slightly, we take the concentration of water to be constant. If we use the equation for Kc, and multiply it by [H2O], this gives us another constant.

44
Q

What is the equation for Kw?

A

Kw = [H+][OH-] or, in pure water, Kw = [H+]^2

45
Q

What are the units of Kw?

A

mol^2 dm^-6

46
Q

What is the value of Kw at 298K?

A

1.00x10^-14

47
Q

What condition affects Kw?

A

Temperature.

48
Q

How can we calculate the pH of a strong base from it’s concentration?

A

There is one mole of OH- ions for every one mole of the base, assuming it dissociates completely in water. So, [OH-] = [B]. We can then use the equation for Kw to calculate [H], and use this to calculate the pH.

49
Q

Give the equation for pH.

A

pH = -log10[H+]

50
Q

What do square brackets represent?

A

Concentration in mol dm^-3

51
Q

Define a monoprotic acid.

A

Each molecule of acid will release one proton when it dissociates.

52
Q

Define a diprotic acid.

A

Each molecule of acid will release two protons when it dissociates.

53
Q

How can we calculate the pH of a strong monoprotic acid from it’s concentration?

A

Assuming the acid completely dissociates in water, the H+ concentration is the same as the acid concentration. We then use this to calculate pH.

54
Q

How can we calculate the pH of a strong diprotic acid from it’s concentration?

A

Assuming the acid completely dissociates in water, the H+ concentration is double the acid concentration. We then use this to calculate pH.

55
Q

What is Ka?

A

The acid dissociation constant.

56
Q

What are the units of Ka?

A

mol dm-3

57
Q

Give an expression for Ka.

A 
Ka = [H+][A-] all over [HA] or,
Ka = [H]^2 over [HA] (assuming all the H+ ions come from the acid, [H+] = [A-])
58
Q

Give the equation for pKa.

A

pKa = -log10(Ka)

59
Q

What indicator would you use for a strong acid-strong base titration?

A

Methyl orange or phenolphthalein.

60
Q

What indicator would you use for a strong acid-weak base titration?

A

Methyl orange

61
Q

What indicator would you use for a weak acid-strong base titrarion?

A

Phenolphthalein

62
Q

What indicator would you use for a weak acid-weak base titration?

A

No indicator will work, because there’s no sharp pH change.

63
Q

What is the point at which you have enough acid/alkali for neutralisation called?

A

Equivalence point.

64
Q

How do diprotic acids nuetralise?

A

In two stages.

65
Q

What does a titration curve with a diprotic acid look like?

A

It has two equivalence points.

66
Q

Define a buffer.

A

A solution that resists changes in pH when small amounts of acid or alkali are added.

67
Q

How do you make an acidic buffer?

A

Mix a weak acid with a salt of the acid (usually sodium).

68
Q

Give the equation for an acidic buffer.

A

Weak acid –> H+ + acid ion (from the salt). This is an equilibrium.

69
Q

What happens when you add small amounts of acid to an acidic buffer?

A

The H+ concentration will increase. Most of the extra H+ ions react with the acid ion to form the acid, shifting the equilibrium to the left and therefore restoring the H+ concentration to near it’s original value, so the pH doesn’t change.

70
Q

What provides the large number of acid ions in an acidic buffer?

A

The salt of the acid completely dissociating.

71
Q

What happens if a small amount of base is added to an acidic buffer?

A

The OH- concentration increases. Most of these ions react with the H+ ions to form water - removing H+ ion. This causes the equilibrium to shift to the right to produce more H+ ions, restoring the solution to near it’s original pH.

72
Q

What provides the large number of acid molecules in an acidic buffer?

A

The weak acid barely dissociating.

73
Q

How do you make a basic buffer?

A

Mix a weak base with the salt of that base (usually chlorine).

74
Q

Give the equation for a basic buffer.

A

base + water –> +ve base ions + OH-

This is an equilibrium.

75
Q

What provides the large amounts of +ve base ions in a basic buffer?

A

The basic salt completely dissociating

76
Q

What provides the large amounts of base molecules in a basic buffer?

A

The weak base barely dissociating.

77
Q

What happens to a basic buffer if small amounts of a base are added?

A

The OH- concentration increases. Most of these will react with the +ve base ions to form the base and water. The equilibrium will shift to the left, removing extra OH- ions from the solution, restoring the solution to near it’s original pH.

78
Q

What happens to a basic buffer if small amounts of acid are added?

A

The H+ concentration will increase. Most of these will react with the OH- ions to from water. The equilibrium will then shift to the right to replace these OH- ions, restoring the solution to near it’s original pH.

79
Q

Give an application of buffers.

A

Blood, shampoo, biological washing powders.

Chemistry Unit 4 (11 decks)

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