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A Level Chemistry > Acids and Bases > Flashcards

Acids and Bases Flashcards

1
Q

What is Bronsted Lowry acid?

A

A proton H+ donor.

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2
Q

What is Bronsted Lowry base?

A

A proton H+ acceptor.

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3
Q

What is amphoteric?

A

Any substance that can act as both an acid and a base.

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4
Q

What is produced when an acid and a metal react?

A

Salt and hydrogen.

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5
Q

What is produced when an acid and a carbonate react?

A

Salt, carbon dioxide and water.

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6
Q

What is produced when an acid and a hydrogen carbonate react?

A

Salt, carbon dioxide and water.

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7
Q

What is produced when an acid and a base react?

A

Salt and water.

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8
Q

What is produced when an acid and an alkali react?

A

Salt and water.

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9
Q

When is a salt formed?

A

When the acidic protons of an acid are replaced by mental ions or the ammonium ions.

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10
Q

What are metal oxides generally?

A

Bases except for a few exceptions that are amphoteric.

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11
Q

What are alkalis?

A

Bases that dissolve in water and the reaction between an acid and an alkali is the same as that between an acid and a base. Alkalis are solutions that contain hydroxide ions.

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12
Q

How is ammonia solution (an alkali) reacting with an acid written?

A

NH3 + HCl —–> NH4Cl (water is omitted)

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13
Q

What is a neutralisation reaction?

A

An exothermic reaction between an acid and an alkali or between an acid and a base to produce salt and water.

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14
Q

What happens when an acid reacts with water?

A

It dissociates or ionises.

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15
Q

How can the reaction of acid with water be written?

A

HA (aq) + H2O (l) H3O+ (aq) + A- (aq)orHA (aq) H+ (aq) + A- (aq) It can be shown with or without water, both representations are correct.

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16
Q

What is a strong acid?

A

One that dissociates completely in aqueous solution. It is a good proton donor and has a weak conjugate base.

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17
Q

Where does the position of equilibrium lie for the dislocation of an acid?

A

A long way to the right, there is very little tendency for the conjugate base to pick up a proton to re form the acid.

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18
Q

What is an example of a strong acid dissociating?

A

Hydrochloric acid HCl (aq) ——> H+ (aq) + Cl- (aq)

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19
Q

What is a weak acid?

A

One that dissociates partially aqueous solution.

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20
Q

What is an example of a weak acid dissociating?

A

Ethanoic acidCH3COOH (aq) —–> CH3COO- (aq) + H+ (aq)

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21
Q

What happens the stronger the acid?

A

It dissociates more and the weaker its conjugate base.

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22
Q

What is a strong base?

A

Strong bases are group 1 hydroxides and ionise completely in aqueous solution.

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23
Q

What is an example of a strong base dissociating in water?

A

Sodium hydroxide NaOH (aq) —-> Na+ (aq) + OH- (aq)

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24
Q

What happens when a weak base reacts with water?

A

It accepts a proton from the water and ionises according to the equation:B (aq) + H2O (l) BH+ (aq) + OH- (aq)

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25
What happens the stronger the base?
The stronger the base the better it is at accepting a proton and the weaker its conjugate acid.
26
What are example of weak bases?
Ammonia NH3Amines RNH2 R2NH R3N
27
What is important when distinguishing experimentally between solution of strong and weak acids?
You must compare solutions of equal concentrations.
28
How can you distinguish between strong acids and weak acids?
Strong acids conduct electricity bettie than solutions of weak acids.Strong acids dissociate more therefore there is a higher concentration of (H+) ions in solution,Strong acids have a lower pH than weak acids.Strong acids react more violently with metal or carbonates - more rapid fizzing.
29
How can you distinguish between strong bases and weak bases?
Solutions of strong bases have a higher pH and are better conductors than solutions of weak bases.
30
What is the equation for pH?
-log10[H+(aq)]
31
What are the units for pH?
pH has no units.
32
What is the equation for finding the concentration of hydrogen ions?
[H+(aq)] = 10^(-pH)
33
What happens to the concentration of H+ ions when the pH increases by one unit?
A 10 fold decrease in the H+ concentration is required to increase the pH by one unit - every time a solution of strong acid is diluted by a factor of 10 the pH goes up by 1 unit.
34
How does water dissociate?
H2O (l) H+ (aq) + OH- (aq)
35
What is the equilibrium constant for the dislocation of water?
Kw = [H+(aq)][OH-(aq)]
36
Why is the concentration of water not included in the expression for Kw?
Because it is the solvent and its concentration is essentially constant.
37
What is Kw known as and what is its value?
The ionic products constant for water and has a value of 1.0x10^-14 at 25 degrees Celsius.
38
In any aqueous solution at 25 degrees celsius what is equal to 1.0x10^-14?
The product of H+ concentration and OH- concentration is 1.0x10^-14
39
When is the only time [H+] equals [OH-]?
In a neutral solution or in pure water.
40
What is the concentration of H+ ions compared to OH- in an acidic solution?
[H+] > [OH-]
41
What is the concentration of H+ ions compared to OH- in an alkaline solution?
[OH-] > [H+]
42
What information do the acid and base dissociation constants give?
The strength of acids and bases.
43
Using the equation HA (aq) H+ (aq) + A- (aq) what is the equation for Ka?
Ka = [A-(aq)] [H+(aq)] / [HA(aq)]
44
How are Ka and pKa related?
pKa = -logKaKa = 10^(-pKa)
45
What does a larger value for Ka indicate?
A stronger acid.
46
What does a smaller value for pKa indicate?
A stronger acid.
47
How does Kw vary with temperature?
The ionisation of water is endothermic and therefore the degree of ionisation increases as temperature increase. This means that the pH of water decreases s temperature increases (higher contraction of H+ (q) at higher temperature).
48
What is the equivalence point?
The point at which equivalent number of moles of acid and alkali have been added.
49
What are the difference in initial pH for the pH curves for a strong and weak acid?
The initial pH is higher for a weak acid since it only dissociates partially, initial pH for a strong acid is lower because it fully dissociates.
50
What are the difference in volume of NaOH required for exact reaction for the pH curves for a strong and weak acid?
The volume of NaOH required for each reaction is the same because the same volume of and concentration of acid is used.
51
What are the differences in the steep parts of the curve for the pH curves for a strong and weak acid?
For a week acid the steep part is more in the alkaline region since the base is stronger than the acid.The steep part of the curve for a strong acid is equally in the acidic and alkaline regions.
52
What are the difference in equivalence point for the pH curves for a strong and weak acid?
The pH equivalence point > 7 for a weak acid because the base is stronger than the acid.The pH equivalence point = 7 for a strong acid because the base and the acid are both strong.
53
What are the difference in final pH for the pH curves for a strong and weak acid?
The final pH is the same for both because the same alkali was used.
54
What is the pH at equivalent point for a strong acid strong base titration?
7
55
What is the pH at equivalent point for a strong acid weak base titration?
Below 7
56
What is the pH at equivalent point for a weak acid strong base titration?
Above 7
57
What is the pH at equivalent point for a weak acid weak base titration?
Depends on the relative strength of the acid and base.
58
What is important about the shape of the pH curve for a weak acid weak titration?
There is no steep part.
59
How is the pKa of the acid found on the pH curve for a weak acid strong base titration?
By the Ph at the half equivalence point.
60
What is an indicator?
Weak acids or weak bases which exhibit different colours depending on the pH, the ionised and unionised forms have different colours.
61
What is the equation of an indicator that is a weak acid?
HIn (aq) H+ (aq) + In- (aq)Colour 1 colour 2
62
What happens when more H+ is added to the indicator?
The position of equilibrium will shift to the left to use up as far as possible the H+ that has been added, the indicator will appear as colour 1.
63
What happens when more alkali is added to the solution?
The indicator changes to colour 2. When we add alkali the OH- from the alkali reacts with the H+ on the right hand side of the equilibrium to produce water. The position of equilibrium thus shifts to the right to replace the H+ as far as possible.
64
What is the pH range of an indicator?
The pH range over which intermediate colours of the indicator can be seen.
65
What is the end point of a titration?
The point at which the indicate changes colour.
66
How should the correct indicator be chosen?
So that the pH range of the indicator occurs entirely within the very steep art of the pH curve.
67
How should the correct indicator be chosen if the pH curve has not been given?
Use the pH at equivalence point as a guide.
68
What indicator should be used for a strong base strong acid titration with an equivalence point of pH seven?
Most common indicators used are methyl red.
69
What indicator should be used for a strong acid weak base titration with an equivalence point of below pH seven?
Indicators with pKa less than 7 such as bromocresol green.
70
What indicator should be used for a strong base weak acid titration with an equivalence point of above pH seven?
Indicators with pKa greater than 7 such as phenolphthalein.
71
What indicator should be used for a weak base weak acid titration with an equivalence point that depends on the relative strength of the acid and base?
Indicators cannot be used - the pH cure does not show a really steep part and a gradual change in colour ill be seen.
72
How can you determine whether a solution of a particular salt is acidic, alkaline or neural.?
If the salt has been made from an acid and base, if the acid is stronger the pH will be acidic, but if the base is stronger the pH will be basic.
73
If the salt has been made from a strong acid and strong base what will the pH of the salt solution be?
7
74
What are examples of a strong acid strong base salt?
NaOH
75
If the salt has been made from a strong acid and weak base what will the pH of the salt solution be?
Less than 7
76
What are examples of a strong acid weak base salt and how do the NH4+ ions dissociate?
NH4ClNH4+ (aq) NH3 (aq) + H+ (aq)
77
If the salt has been made from a weak acid and strong base what will the pH of the salt solution be?
Greater than 7
78
What are examples of a weak acid strong base salt and how do the CH3COO- ions dissociate?
CH3COONaCH3COO- (aq) + H2O (l) CH3COOH (aq) + OH- (aq)
79
If the salt has been made from a weak acid and weak base what will the pH of the salt solution be?
Depends on acid and base.
80
What are examples of a weak acid weak base salt and how do the CH3COO- and NH4+ ions dissociate?
CH3COONH4 CH3COO- (aq) + H2O (l) CH3COOH (aq) + OH- (aq)NH4+ (aq) NH3 (aq) + H+ (aq)
81
Why is a solution of CH3COONa alkaline?
Because CH3COO- is the conjugate base of a weak acid and therefore a reasonably strong base.
82
Why is a solution NH4Cl acidic?
Because NH4+ is the conjugate acid of a weak base and therefore is a reasonably strong acid.
83
What pH are 3+ ions in solution and why?
Acidic, the high charge density of ion causes the water molecule to be sufficiently polarised for H+ to dissociate.
84
What is a buffer solution?
One which resists changes in pH when small amounts of acid or alkali are added.
85
What does a buffer solution contain?
Two components and must always contain something to react with any acid added and something to react with any base added.
86
What is an acidic buffer solution?
A solution of a weak acid (HA) and the salt/conjugate base of that weak acid.
87
What is the equilibrium that exists in the acidic buffer solution?
HA (aq) H+ (aq) + A- (aq)
88
What happens if acid is added to the buffer solution?
A- (aq) + H+(aq) -----> HA (aq)
89
What happens if alkali is added to the buffer solution?
HA(aq) + OH-(aq) -----> A-(aq) + H2O (l)
90
Why do small changes in the concentration of HA and A- not change the position of the original equilibrium?
Because large amounts of HA and A- are present and hence the pH remain approximately constant.
91
What is a basic buffer solution?
Contains a weak base and the salt of that weak base.

A Level Chemistry (2 decks)

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