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Chemistry: Module 5 > 5.1.3 Acids, Bases & Buffers > Flashcards

5.1.3 Acids, Bases & Buffers Flashcards

1
Q

Define a Brønsted- Lowry acid

A

Proton donor

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2
Q

Define a Brønsted-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 answers) Name and formula

A

H+ (hydrogen ion) or more accurately,
H3O+ (oxonium ion) as protons react with H2O to form it

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6
Q

What ion causes a solution to become alkaline?

A

OH- (hydroxide ion)

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7
Q

Write an equation for ionisation of water? (2)

A

2H2O (l) <=> H3O+ (aq) + OH- (aq)
H2O (l) <=> H+ (aq) + OH- (aq)

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8
Q

Give an example of a monobasic acid

A

HCl

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9
Q

Give an example of a dibasic acid

A

H2SO4

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10
Q

Give an example of a tribasic acid

A

H3PO4

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11
Q

Write equation for reaction between ethanoic acid and water. Identify the acid pairs.

A

CH3COOH + H2O <=> CH3COO- + H3O+
acid 1. base 2. base 1. acid 2

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12
Q

Define strong acid

A

Acid that dissociates completely

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13
Q

Give some examples of strong acids

A
  • Hydrochloric acid
  • Sulfuric acid
  • Nitric acid
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14
Q

What is the difference between concentrated and strong?

A

Concentrated means how many mol per dm^3, strong refers to amount of dissociation

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15
Q

Define weak acids

A

An acid that only partially dissociates

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16
Q

Give some examples of weak acids

A

Methanoic acids, 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 symbol of acid dissociation constant?

A

Ka

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19
Q

Write acid dissociation constant expresson

A

For acid HA, HA <=> H+ + A-
Ka = [H+][A-]/ [HA]

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20
Q

What does a larger Ka mean?

A

Larger Ka= greater extent of dissociation

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21
Q

Write equation to convert Ka into pKa

A

pKa = -log10Ka

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22
Q

Write equation to convert pKa into Ka

A

Ka = 10^-pKa

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23
Q

What is relationship between pKa and strength of the acid?

A

Smaller the pKa, stronger the acid

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24
Q

Write equation to convert concentration of H+ into pH

A

pH = -log10[H+]

25
Write equation to convert pH into [H+]
[H+] = 10^-pH
26
Why is a pH scale useful compared to [H+]?
pH scale allows a wide range of H+ concentration to be expressed as simple positive values
27
What is relationship between pH and [H+]?
High pH means a small [H+]
28
If two solutions have a pH difference of 1, what is the difference in [H+]?
A factor of 10
29
[H+] of a strong acid is equal to what?
[H+] = [HA]
30
Write equation to calculate [H+] of weak acids
[H+] = (square root of) Ka x [HA]
31
What assumption is made when calculating pH of weak acids
It is assumed that the concentration of acid at equilibrium is equal to concentration of acid after dissociation. This is because only very little of the acid dissociates.
32
Write expression for ionic product of water, Kw
Kw = [H+][OH-]
33
Whag is units for Kw?
mol^2dm^-6
34
What is value of Kw at 298k/ 25°c?
1x10^-14
35
What physical factors affect value of Kw? How do they affect it?
Temperature only- if temperature is increased, the equilibrium moves to the right so Kw increases and the pH of pure water decreases
36
Indices of [H+] and [OH-] add up to what?
-14
37
Define the term strong base
Base that dissociates 100% in water
38
Give examples of some strong bases
NaOH KOH Ca(OH)2
39
Give an example of a weak base
Ammonia
40
Write equation to calculate [H+] of strong bases
[H+]= Kw/ [OH-]
41
Define a buffer solution
A mixture that minimises pH change on addition of small amounts of acid or base
42
What are 2 ways in which buffers can be made?
- weak acid and its conjugate base - weak acid and a strong alkali
43
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 the H+
44
In which direction does equilibrium shift when an alkali is added ti 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
45
Write equation used to calculate [H+] of buffer solutions
[H+] = Ka x ([HA]/[A-])
46
Which buffer system maintains blood pH at 7.4? What happens acid/alkali is added?
H+ + HCO3- <=> CO2 + H2O Add OH- -> reacts with H+ to form H2O then shifts equilibrium to left to restore H+ lost Add H+ -> equilibrium shifts to the right, removing excess H+
47
What is a titration?
The addition of an acid/base of known concentration to a base/acid to determine concentration. An indicator is used to show that neutralisation has occurred, as is a pH meter.
48
Define the term equivalence point
The point at which the exact volume of base has been added to just neutralise the acid or vice versa
49
What is the end point?
The point at which the pH changes rapidly
50
What are the properties of a good indicator for a reaction? (3)
- Sharp colour change (not gradual)- no more than one drop of acid/alkali needed for colour change - End point must be the same as the equivalence point otherwise titration gives wrong answer - Distinct colour change so it is obvious when the end point has been reached.
51
What indicator would you use for a strong acid- strong base titration?
Phenolphthalein or methyl orange, but phenolphthalein is usually used as clearer colour change
52
What indicator would you use for a strong acid-weak base titration?
Methyl orange
53
What indicator would you use for a strong base-weak acid titration?
Phenolphthalein
54
What indicator would you use for a weak acid-weak base titration?
Neither methyl orange or phenolphthalein is suitable, as neither give a sharp change at the end point
55
What colour is methyl orange in acid? In alkali?
Red in acid; yellow in alkali
56
What colour is phenolphthalein in acid? In alkali?
Colourless in acid; red in alkali
57
What colour is bromothymol blue in acid? In alakli?
Yellow in acid and blue in alkali
58
Describe how to use a pH meter?
- Remove the pH probe from storage solution and rinse with distilled water - Dry the probe and place it into the solution with unknown pH - Let the probe stay in the solution until it gives a settled reading

Chemistry: Module 5 (7 decks)

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