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Chemistry > Chapter 12 > Flashcards

Chapter 12 Flashcards

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1
Q

What does an acid release?

A

Protons

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2
Q

What does a base accept?

A

Protons

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3
Q

What are Bronsted-Lowry acids?

A

Proton donors

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4
Q

What do Bronsted-Lowry acids release when they are mixed with water?

A

They release hydrogen ions

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5
Q

What are Bronsted-Lowry bases?

A

Proton acceptors

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6
Q

When Bronsted-Lowry bases are in solution, what do they grab?

A

Hydrogen ions from water molecules

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7
Q

What do strong acids do?

A

They dissociate almost completely in water-nearly all the H+ ions will be released

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8
Q

Give an example of a strong acid:

A

Hydrochloric acid

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9
Q

What is the equation for the dissociation of hydrochloric acid?

A

HCl –> H+ + Cl-

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10
Q

Give an example of a strong base:

A

Sodium hydroxide

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11
Q

What do strong bases do?

A

They dissociate almost completely in water

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12
Q

What is the equation for the dissociation of sodium hydroxide?

A

NaOH –> Na+ + OH-

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13
Q

What do weak acid do?

A

They only partially dissociate -dissociate very slightly in water, so only small numbers of H+ ions form

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14
Q

What is the main difference for the dissociations of strong acids and weak acids equations?

A

For weak acids an equilibrium forms which lies well over to the left, representing the partial dissociation

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15
Q

What do weak bases do in water?

A

They only slightly protonate in water, and the equilibrium lies well over to the left

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16
Q

How do acids get rid of a proton?

A

They can only get rid of a proton if there’s a base to accept them

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17
Q

What does HA + B react to form?

A

BH+ +A-

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18
Q

What are conjugate pairs?

A

They are species that are linked to the transfer of a proton

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19
Q

What is the species that has lost a proton?

A

The conjugate base

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20
Q

What is the species that has gained a proton?

A

The conjugate acid

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21
Q

In the reaction HCl+H2O –> H30+ + Cl-, what is the conjugate base of HCl?

A

Cl-

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22
Q

When acids and bases react, what is formed?

A

A salt and water

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23
Q

If the concentration of H+ ions produced is equal to the concentration of OH- ions produced, what type of solution has been produced?

A

A neutral solution

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24
Q

What is a neutral solution?

A

One where (H+) = (OH-)

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25
Q

What is the standard enthalpy change of neutralisation?

A

The enthalpy change when standard solutions of an acid and a base react together, under standard conditions, to produce 1 mole of water

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26
Q

What is a salt?

A

A compound consisting of an ionic assembly of anions and cations

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27
Q

What is the standard enthalpy change of neutralisation for weak acids and weak bases to do with?

A

The reaction between H+ and OH- ions, and the enthalpy to do with dissociation

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28
Q

What happens when strong acids and strong bases react togehter in neutralisation reaction?

A

As both the strong acids and bases fully dissociate in solution, there is no dissociation enthalpy for the acid or base, just enthalpy for the reaction of the H+ and OH- ions

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29
Q

Why is the standard enthalpy of neutralisation of neutralisation very similar for all the reactions of strong acids and strong bases?

A

When they react together in neutralisation reactions, it is just the enthalpy for the reaction of H+ and OH- ions, which is very similar for all the reactions of strong acids and strong bases H+ + OH- –> H20

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30
Q

Why does the standard enthalpy change of neutralisation for reactions involving weak acids or bases vary?

A

The enthalpy of dissociation varies, depending on the acid or base used, as the standard enthalpy change of neutralisation includes enthalpy to do with the reaction between H+ and OH- ions, and the enthalpy change to do with dissocotiation

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31
Q

What is the pH a measure of?

A

The hydrogen ion concentration of the solution

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32
Q

What is the equation to work out the value of pH?

A

pH = -log(H+)

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33
Q

What is a monoprotic acid?

A

Where each mole of acid produces one mole of hydrogen ions

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34
Q

For strong, monoprotic acids, what does the concentration of H+ ions equal?

A

The acid concentration, as they dissociate fully

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35
Q

What cab polyprotic acids do?

A

They can lose more than one proton

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36
Q

What does each molecule of a strong diprotic acid release?

A

Two protons when it dissociates

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37
Q

What is Ka?

A

The dissocotiation constant

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38
Q

For a weak aqueous acid, what equilibrium do you get?

A

HA with H+ and A-

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39
Q

For weak acids, is the concentration of H+ ions equal to the acid concentration?

A

No

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40
Q

For a weak acid, as only a tiny amount of HA disocotiates, what can we assume?

A

(HA)&raquo_space; (H+) so (HA) at start = (HA) at end

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41
Q

For the dissocotiation of the weak acid HA, what is the equation of Ka?

A

Ka = (H+)^2 / (HA)

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42
Q

For weak acids, why do we assume (H+) = (A-)?

A

We assume that the dissocotiation of the acid is much greater than the dissocotiation of water, so we can assume all the H+ ions came from the acid, so (H+) = (A-)

43
Q

What does the ionic product of water depend on?

A

The concentration of H+ and OH- ions

44
Q

What is Kw?

A

The ionic product of water

45
Q

What is the equation for Kw?

A

Kw = (H+)(OH-)

46
Q

For pure water, what is the ratio of H+ ions to OH- ions?

A

1:1 ratio

47
Q

At 298K, what is the value of Kw always?

A

10^-14

48
Q

What is pKw?

A

-logKw

49
Q

What is pKa?

A

-logKa

50
Q

How do you get the value of Ka from pKa?

A

Ka = 10^-pKa

51
Q

What is the value of pKw at 298K?

A

14

52
Q

What is a pH meter?

A

A device which tells you the pH of a solution

53
Q

How do you make sure a pH meter is calibrated correctly?

A

You place it in deionised water, and adjust the reading so that it is 7.00
Do the same with a standard solution of pH 4 and pH10

54
Q

What is the pH of 1 moldm^-3 HCl?

A

0.00

55
Q

What is the pH of 1 moldm^-3 C2H5COOH?

A

2.44

56
Q

What is the pH of 1 moldm-3 NaCl?

A

7.00

57
Q

What is the pH of 1 moldm-3 NaOH?

A

14

58
Q

What does 10^-pH equal?

A

(H+)

59
Q

When a strong acid is diluted by a factor of 10, what happens to the pH?

A

It increases by 1

60
Q

When a weak acid is diluted by a factor of 10, what happens to its pH?

A

The pH increases by 0.5

61
Q

What do titrations of acids and bases allow you to find?

A

The exact amount of base required to neutralise and acid

62
Q

For a titration curve which plots pH against volume of base/acid added, what does the initial pH depend on?

A

The strength of the acid. A strong acid will have a lower starting pH

63
Q

What does the titration curve of a strong acid against a strong base look like?

A

Starts at a low pH, ends at a high pH. Large change in pH at equivalence

64
Q

What does the titration curve of a strong acid against a weak base look like?

A

Starts at a low pH, ends at a fairly neutral pH (7-9). Large change in pH at equivalence point, not as large as strong acid against strong base curve.

65
Q

What does the titration curve of a weak acid against a strong base look like?

A

Starts at a fairly neutral pH (5-7) ends at a high pH. Large change in pH but not as large as strong acid against strong base curve

66
Q

What does the titration curve of a weak acid against a weak base look like?

A

Starts at fairly neutral pH (5-7) and ends at fairly neutral pH (7-9). Change in pH at equivalence point is not very large

67
Q

What is the point at the centre of the equivalence line for a titration of acid aganist base line?

A

The equivalence point

68
Q

What is the equivalence point?

A

Where the concentration of H+ ions = the concentration of OH- ions. The point where the acid has been neutralised

69
Q

What does the final pH of a titration curve of acid against base depend on?

A

The strength of the base

70
Q

When carrying out a titration, how do you know when your sample has been neutralised?

A

You use an indicator which changes colour to show when your sample has been neutralised

71
Q

At which point in your titration do you need the indicator to change colour?

A

At the end point of your titration, therefore you need to pick an indicator that changes colour over a narrow pH range

72
Q

What are the two main indicators that are used for acid-base titrations?

A

Methyl orange and phenophalein

73
Q

What colour is methyl orange at a low pH?

A

Red

74
Q

What colour is phenolphthalein at a low pH?

A

Colourless

75
Q

What colour is methyl orange at a high pH?

A

Yellow

76
Q

What colour is phenolphthalein at a high pH?

A

Pink

77
Q

What is the approximate pH colour change for methyl orange?

A

3.1 to 4.4

78
Q

What is the approximate pH colour change for phenolphthalein?

A

8.3 to 10

79
Q

For a strong acid-strong base titration, what indicator would you use?

A

Either methyl orange or phenolphthalein, as there’s a rapid pH change for both indicators

80
Q

For a strong acid-weak base titration, what indicator would you use?

A

Only methyl orange as as the pH changes rapidly for the methyl orange pH range

81
Q

For a weak acid-strong base titration, what indicator would you use?

A

Phenolphthalein

82
Q

For a weak acid-weak base titration, what indicator would you use?

A

Neither, so a pH meter should be used

83
Q

How can you work out the pKa of a weak acid?

A

You can use the titration curve for a weak acid/strong base titration. At the half-equivalnce point the pH = pKa

84
Q

What is the half-equivalence point?

A

The stage of the titration where half of the acid has been neutralised

85
Q

For a weak acid that dissociates HA to A- and H+, what does the concentration of HA equal at the half-equivalence point?

A

Concentration of HA= concentration of A-

86
Q

At the half equivaence point, what does Ka equal?

A

The concentration of hydrogen ions, so pKa = pH

87
Q

What does a pH chart allow you to do in a titration?

A

It allows you to follow pH changes

88
Q

What is a buffer?

A

A solution that minimises changes in pH when a small amount of an acid or base are added

89
Q

Do buffer solutions only work for small amounts or large amounts of acid and base solutions?

A

They only work for slight changes

90
Q

What do acidic buffers contain?

A

A weak acid and its conjugate base

91
Q

When creating a buffer solution, what can you mix an excess of a weak acid with?

A

A strong base

92
Q

Give an example of a weak acid and strong base you can mix together to form a buffer solution?

A

Ethanoic acid and sodium hydroxide

93
Q

Give an example of an equilibrium formed in a buffer solution?

A

CH3COOH in equilibium with CH3COO- + H+

94
Q

In a buffer solution, what happens when a small amount of an acid is added to the equilibrium?

A

The concentration of H+ ions increases. Most of the extra H+ ions combine with the CH3COO- ions to form CH3COOH. This shifts the equilibrium to the left, reducing the H+ ions concentration, lowering it close to its original value so the pH doesn’t change by much

95
Q

In a buffer solution, what happens when you add a small amount of a base to the equilibrium?

A

The OH- ion concentration increases. Most of the extra OH- ions react with H+ ions to form water, removing H+ ions from the solution. This causes more CH3COOH to dissociate to form H+ ions, shifting the equilibrium to the right, causing the H+ ion concentration to increase to its original value, so the pH doesn’t change by much

96
Q

How are alkaline buffers made?

A

From a weak base and one of its salts

97
Q

Give an example of 2 compounds that can be used to form an alkaline buffer:

A

Ammonia solution (base) and ammonium chloride (a salt of ammonia)

98
Q

When reacting ethanoic acid(weak acid) with sodium hydroxide(strong base) why does the pH change quickly to start?

A

The base is strong and contains with a lot of H+ ions

99
Q

When reacting ethanoic acid(weak acid) with sodium hydroxide(strong base) why does the pH change slow down after the start?

A

A buffer solution of sodium ethanoate in ethanoic acid which resists further dramatic pH change

100
Q

Why does the pH change drastically at the equivalence point?

A

All the ethanoic acid is used up and the equivalence point is reached

101
Q

How is the pH in blood controlled?

A

Using a carbonic acid-hydrogencarbonate buffer system

102
Q

How are the levels of H2CO3 controlled?

A

By respiration

103
Q

How are the levels of HCO3- controlled?

A

By the kidneys

104
Q

What is the equation required to calculate the pH of a buffer solution?

A

pH = pKa + log (A-/HA)

Chemistry (25 decks)

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