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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
What is the difference in the volume of base required to titrate strong and weak acids.
None (if they’re both monoprotic) as the strong acid fully dissociates and the weak acid is in equilibrium.
26
What is needed to make a neutral salt?
A strong acid and a strong base
27
What is needed to make an acidic salt ?
A strong acid and a weak base.
28
What is needed to make a basic salt ?
A strong base and a weak acid
29
What is an example of an insoluble salt ?
Barium carbonate
30
What is a buffer solution ?
A solution that maintains its pH when small amounts of acid or alkali are added
31
What is an acidic buffer made from ?
A solution of weak acid + the salt of that weak acid + a strong base
32
What is a basic buffer made from ?
A weak base + the salt of that weak base + a strong acid
33
What is in plenty reserve in a buffer reaction ?
The weak acid or weak base plus the conjugate acid or conjugate base made from the salt
34
What are examples for f strong bases ?
Group 1+2 metal hydroxides
35
What are examples of weak bases ?
NH4OH; amines
36
What will happen in a reaction between a weak base and a weak acid ?
This reaction is not impossible as complete disassociation will not occur
37
What equation allows you to obtain the acid : salt ration in a buffer ?
pH=pKa-log(10)acid/salt
38
What equation allows you to obtain the salt : acid ratio ?
pH=pKa+log(10)salt/acid
39
What is the pKa value?
The inverse log of Ka (the acid disassociation constant) which determines the strength of the acid. Lower pKa indicates a stronger acid
40
What happens to a buffer solution if water is added ?
The pH still remains constant as equal amounts of H+ and OH- were added
41
What are indicators ?
Weak acids
42
What is KIn ?
The acid indicator dissociation constant ?
43
How does an indicator work ?
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
When does the colour change happen in indicators ?
HIn= In- therefore KIn = H+ or H3O+
45
What is the equation for calculating the acid indicator dissociation constant ?
KIn = [H3O+][In-] / [HIn] Or [KIn] / [H3O+] = [In-] / [HIn]
46
When does colour change in indicators happen (in theory) ?
When HIn. = In- so Kin = H+ and pKin = pH
47
When does the colour change occur in indicators in reality ?
The colour change can not be seen until [In-] and [HIn] differ by a factor of ten therefore when pH = pKin +/- 1
48
What is the requirement of an indicator used in a titration ?
It must change colour when the pH of the solution is changing very rapidly
49
How are titration curves drawn?
Using data collected by measuring the pH continuously (with a pH meter) as alkali is added to an acid.
50
Which indicators can be used on strong acid strong alkali solutions ?
All indicators
51
What indicators can be used on weak acid strong alkali mixtures ?
Acidic indicators
52
Which indicators can be used on strong acid weak alkali solutions ?
Alkali indicators

Chemistry (7 decks)

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