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Chemistry OCR(A) A Level > M5 Chapter 20 / 21 - Acids, Bases and pH / Buffers and Neutralisation > Flashcards

M5 Chapter 20 / 21 - Acids, Bases and pH / Buffers and Neutralisation Flashcards

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1
Q

Define Bronsted-Lowry acid.

A

Proton donor.

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2
Q

Define Bronsted-Lowry base.

A

Proton acceptor.

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3
Q

Define lewis acid.

A

Electron pair acceptor.

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4
Q

Define lewis base.

A

Electron pair donor.

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5
Q

What ion causes a solution to become acidic? (2)
Name and formula required.

A

H+ (Hydrogen ion)
H3O+ (Oxonium ion)

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6
Q

What causes a solution to be alkaline?

A

OH- ions (hydroxide ions)

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7
Q

Write an equation for the ionisation of water.

A

H2O <–> H+ + OH-
OR
2H2O <–> H3O+ + OH-

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8
Q

Give example of monobasic acid.

A

HCl.

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9
Q

Give example of dibasic acid.

A

H2SO4.

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10
Q

Give example of tribasic acid.

A

H3PO4.

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11
Q

Identify the acid base pairs for the reaction below.
CH3COOH + H2O <–> CH3COO- + H3O+

A

A1 B2 B1 A2

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12
Q

Define strong acid.

A

Acids that dissociate completely.

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13
Q

Give some examples of strong acids.

A

HCl
H2SO4
HNO3

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14
Q

What is the difference between concentrated and strong acid?

A

Concentrated = many mol per dm3

Strong = refers to amount of dissociation of an acid.

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15
Q

Define weak acids.

A

Acids that only dissociate partially.

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16
Q

Give some examples of weak acids.

A

HCOOH (any organic acid)

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17
Q

What is constant that is used to measure the extent of acid dissociation called?

A

Acid dissociation constant.

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18
Q

What is the symbol of the acid dissociation constant?

A

Ka

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19
Q

What does a larger Ka value mean?

A

Larger Ka = Greater the extent of dissociation.

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20
Q

Write the equation used to convert Ka to pKa.

A

pKa = -log10Ka

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21
Q

Write the equation used to convert pKa into Ka.

A

Ka = 10 to the power of -pKa

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22
Q

What is the relationship between pKa and strength of the acid?

A

Smaller the pKa, stronger the acid (inverse relationship)

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23
Q

Write the equation used to convert [H+] to pH.

A

pH = -log10[H+]

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24
Q

Write the equation used to convert pH to [H+].

A

[H+] = 10 to the power of -pH

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25
Why is a pH scale useful compared to concentration of H+?
pH scale allows for wide range of H+ concentration values to be expressed as simple positive values.
26
What is the relationship between pH and [H+]?
Higher pH means smaller [H].
27
If two solutions have a pH difference of 1, what is the difference in pH?
A factor of 10.
28
[H+] of a strong acid is equal to what?
[H+] = [HA]
29
Write the equation used to calculate the [H+] of weak acids.
[H+] = All rooted Ka x [HA]
30
What is the assumption made when calculating pH of weak acids?
Assumed the concentration of acid at equilibrium is equal to the concentration of acid after dissociation. This is because very little of the acid dissociates.
31
Write the expression for ionic product of water, Kw.
Kw = [H+][OH-]
32
What are the units for Kw?
mol2dm-6.
33
What is the value of Kw at 298K?
1.0x10-14
34
What physical factors affect the value of Kw? What impact do they have?
Temperature only If temperature is increased, equilibrium shifts right so Kw increases and the pH of pure water decreases.
35
Indices of [H+] and [OH-] always add up to what value?
-14
36
Define the term strong base.
Base that dissociates 100% in water.
37
Give some examples of strong bases.
NaOH KOH Ca(OH)2
38
Give example of weak base.
Ammonia
39
Write the equation used to calculate [H+] of strong bases.
[H+] = Kw / [OH-]
40
Define a buffer solution.
A mixture that minimises pH change on addition of small amounts of an acid or a base.
41
What are the 2 ways in which buffers can be made?
Weak acid and its conjugate base Weak acid and a strong alkali
42
In which direction does equilibrium shift when an acid is added to a buffer solution? Why?
Equilibrium shifts to the left because [H+] increases and the conjugate base reacts with the H+ to remove most of the H+.
43
In which direction does the equilibrium shift when an alkali is added to a buffer solution? Why?
Equilibrium shifts to the right, because [OH-] increases and the small concentration of H+ reacts with OH-. To restore the H+ ions HA dissociates shifting the equilibrium.
44
Write the equation used to calculate [H+] from a buffer solution.
[H+] = Ka x [HA] / [A-]
45
Which buffer system maintains blood pH at 7.40? What happens when acid/alkali is added?
H+ +HCO3- <--> CO2 + H2O Add OH-. This would react with H+ to form H2O, meaning the equilibrium would have to shift left to restore the H+ lost. Add H+. This would make the equilibrium shift right to remove excess H+.
46
What is a titration?
The addition of an acid/base of known concentration to an acid/base with to determine the concentration. An indicator is used to show the neutralisation that has occured, as is a pH meter.
47
Draw a diagram of the equipment that could be used for a titration. (8 labels)
1. Clamp stand 2. Burette 3. Acid or alkali of known concentration in burette. 4. Use pipette and filler to fill conical flask with a known volume of solution. 5. Funnel to fill the burette 6. Conical flask 7. Acid or alkali of unknown concentration 8. White tile
48
Draw the titration curve for a strong acid with a strong base added.
Proper S shape mirrored into the middle. Equivalence point pH 7.
49
Draw the titration curve for a weak acid with a strong base added.
S shape again but shifted up and starting pH value of 3. Equivalence point of pH 8.72
50
Draw the titration curve for a strong acid with a weak base added.
Curve shifted to the right. Equivalence point < 7.
51
Draw the titration curve for a weak acid with a weak base added.
weak S shape. Equivalence point is 7 but shape is much more flat.
52
Define the term equivalence point.
The point at which the exact volume of base/acid has been added to neutralise the acid/base.
53
What is the end point?
The point at which the pH changes rapidly.
54
What are the properties of a good indicator for a reaction? (3)
Sharp colour change (not gradual) End Point must be same as equivalence point otherwise titration gives the wrong answer. Distinct colour change so it is obvious when it is reached.
55
What indicator would you use for a strong acid-strong base titration?
Phenolphthalein or methyl orange Usually it is Phenolphalein because it has a clearer colour change.
56
What indictor would you use for a strong acid-weak base titration?
Methyl Orange
57
What indictor would you use for a strong base-weak acid titration?
Phenolphthalein
58
What indictor would you use for a weak base-weak acid titration?
Neither are suitable because neither give a sharp change at the end point.
59
What colour is methyl orange in acid and in alkali?
Methyl Orange: Acid = Red Alkali = Yellow
60
What colour is Phenolphthalein in acid and in alkali?
Phenolphthalein: Acid = Colourless Alkali = Red/Pink
61
What colour is bromothymol blue in acid and in alkali?
Bromothymol Blue: Acid = Yellow Alkali = Blue
62
Describe how to use a pH metre.
Remove pH probe from storage solution and rinse with distilled water. Dry probe and place into solution with unknown pH. Let the probe stay in solution until it gives a settled reading.

Chemistry OCR(A) A Level (20 decks)

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