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Chemistry > Physical Chemistry > Flashcards

Physical Chemistry Flashcards

1
Q

What causes the equilibrium constant K to change ?

A

Temperature

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2
Q

In the reaction between N2O4 - 2NO2 what happens when the temp increases and when the temp decreases ?

A

Increases - it turns browner like NO2

Decreases - it turns yellower like N2O4

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3
Q

What happens to K during exothermic reactions ?

A

Increase in temp = K decreases
Decrease in temp = K increases

K increases when the forward reaction is favoured

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4
Q

What happens to K in endothermic reactions?

A

Increase in temp = K increases
Decrease in temp = K decreases

K increases when the forward reaction is favoured

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5
Q

Does the presence of a catalyst affect K ?

A

No

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6
Q

What substances are ignored in calculations to obtain the equilibrium constant ?

A

Pure solids and liquids (except if they are products)

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7
Q

Where does the equilibrium position lie of K } 1 ?

A

It lies to the right (products)

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8
Q

Where is the position of equilibrium when K {1 ?

A

To the left - the reactants

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9
Q

What value of K means that the equilibrium position is central ?

A

When K=1

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10
Q

What is the value of Kw the ionic product of water ?

A

10^-14 at 25C

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11
Q

Is the reaction H2O - [H^+] + [O-] endothermic or exothermic ?

A

Endothermic

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12
Q

What is the definition of an acid ?

A

Any substance capable of donation a proton

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13
Q

What is the definition of an alkali ?

A

Any substance capable of accepting a proton

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14
Q

What substance is left behind when an acid donates a proton ?

A

Conjugate base

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15
Q

What substance if left behind when a base accepts a proton ?

A

A conjugate acid

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16
Q

Does water donate or accept protons ?

A

Both - this gives it an amphoteric nature

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17
Q

What are examples of strong acids ?

A

HCl; H2SO4; HNO3

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18
Q

Where does the equilibrium lie in strong acids ?

A

To the right so Ka is meaningless

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19
Q

What is Ka ?

A

The equilibrium constant of an acid. It indicates the strength of an acid

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20
Q

Which chemicals dissociate fully ?

A

All strong acids and bases

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21
Q

What is the percentage of disassociation in weak acids ?

A

Less than 10%

22
Q

Where does the equilibrium lie in weak acids ?

A

To the left

23
Q

What are the qualities of a strong acid ?

A

Low pH
Fast reaction with a metal
High conductivity

24
Q

What are the qualities of a weak acid ?

A

Higher pH
Slower reaction with a metal
Lower conductivity

25
Q

What is the difference in the volume of base required to titrate strong and weak acids.

A

None (if they’re both monoprotic) as the strong acid fully dissociates and the weak acid is in equilibrium.

26
Q

What is needed to make a neutral salt?

A

A strong acid and a strong base

27
Q

What is needed to make an acidic salt ?

A

A strong acid and a weak base.

28
Q

What is needed to make a basic salt ?

A

A strong base and a weak acid

29
Q

What is an example of an insoluble salt ?

A

Barium carbonate

30
Q

What is a buffer solution ?

A

A solution that maintains its pH when small amounts of acid or alkali are added

31
Q

What is an acidic buffer made from ?

A

A solution of weak acid + the salt of that weak acid + a strong base

32
Q

What is a basic buffer made from ?

A

A weak base + the salt of that weak base + a strong acid

33
Q

What is in plenty reserve in a buffer reaction ?

A

The weak acid or weak base plus the conjugate acid or conjugate base made from the salt

34
Q

What are examples for f strong bases ?

A

Group 1+2 metal hydroxides

35
Q

What are examples of weak bases ?

A

NH4OH; amines

36
Q

What will happen in a reaction between a weak base and a weak acid ?

A

This reaction is not impossible as complete disassociation will not occur

37
Q

What equation allows you to obtain the acid : salt ration in a buffer ?

A

pH=pKa-log(10)acid/salt

38
Q

What equation allows you to obtain the salt : acid ratio ?

A

pH=pKa+log(10)salt/acid

39
Q

What is the pKa value?

A

The inverse log of Ka (the acid disassociation constant) which determines the strength of the acid. Lower pKa indicates a stronger acid

40
Q

What happens to a buffer solution if water is added ?

A

The pH still remains constant as equal amounts of H+ and OH- were added

41
Q

What are indicators ?

A

Weak acids

42
Q

What is KIn ?

A

The acid indicator dissociation constant ?

43
Q

How does an indicator work ?

A

The undissociated form HIn has a distinctly different colour from the conjugate base In- (in a good indicator). The concentrations of the 2 colour forms depend on the H+ concentration of the solution i.e. the pH.

44
Q

When does the colour change happen in indicators ?

A

HIn= In- therefore KIn = H+ or H3O+

45
Q

What is the equation for calculating the acid indicator dissociation constant ?

A

KIn = [H3O+][In-] / [HIn]

Or [KIn] / [H3O+] = [In-] / [HIn]

46
Q

When does colour change in indicators happen (in theory) ?

A

When HIn. = In- so Kin = H+ and pKin = pH

47
Q

When does the colour change occur in indicators in reality ?

A

The colour change can not be seen until [In-] and [HIn] differ by a factor of ten therefore when pH = pKin +/- 1

48
Q

What is the requirement of an indicator used in a titration ?

A

It must change colour when the pH of the solution is changing very rapidly

49
Q

How are titration curves drawn?

A

Using data collected by measuring the pH continuously (with a pH meter) as alkali is added to an acid.

50
Q

Which indicators can be used on strong acid strong alkali solutions ?

A

All indicators

51
Q

What indicators can be used on weak acid strong alkali mixtures ?

A

Acidic indicators

52
Q

Which indicators can be used on strong acid weak alkali solutions ?

A

Alkali indicators

Chemistry (7 decks)

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