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A-LEVEL CHEMISTRY > A7 Acids, Bases + Buffers > Flashcards

A7 Acids, Bases + Buffers Flashcards

1
Q

Define a Brønstead-Lowry acid

A

A species that donates a proton

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1
Q

Define a Brønstead-Lowry base

A

A species that accepts a proton

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2
Q

How to tell conjugate acid-base pairs

A
  • Differ by only an H+
  • Opposite sides of the equation
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3
Q

What is a monobasic acid

A

Acid that donates one proton

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4
Q

What is a dibasic acid

A

Acid that donates two protons

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5
Q

What is a tribasic acid

A

Acid that donates three protons

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6
Q

Draw a mechanism for the reaction between methanoic acid and water

A
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7
Q

Equation for pH of strong acids

A
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8
Q

Formula to work out pH from [H+]

A
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9
Q

Formula to determine pH from [H+]

A
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10
Q

Procedure to determine the pH of weak acids

A
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11
Q

What assumption is made when determining the pH of weak acids to allow [H] = [A-]

A

[H] = [A-], as dissociation of water is negligable

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12
Q

What is the limitation with the assumptions made when calculating the pH of weak acids

A

With ‘stronger’ weak acids, [HA] in equilibrium being equal to [HA] undissociated may no longer be valid

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13
Q

Formula to convert pKa to Ka

A
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14
Q

Formula to convert pKa to Ka

A
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15
Q

Steps to calculate the pH of strong bases

A
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16
Q

Why do acids still contain some OH-

A
  • Water dissociates
17
Q

Define a buffer system

A

A system that minimises pH changes on addition of small amounts of an acid or a base

18
Q

Steps to calculating the pH of a buffer system of a weak acid and salt of a weak acid

A
  • Find new concentrations of acid and salt
19
Q

Steps to calculate the pH of a buffer solution with a weak acid and a strong alkali

A
  • Find the moles left of acid remaining, and the moles of salt now present
  • Find their concentrations
20
Q

With reference to equalibrium shifts, explain what happens to a buffer solution on addition of alkali

A
  • Alkali reacts with HA
  • Equilibrium shifts RHS
  • Towards H+ and A-
21
Q

With reference to equalibrium shifts, explain what happens to a buffer solution on addition of acid

A
  • H+ reacts with A-
  • Equilibrium shifts towards LHS
  • Towards HA
22
Q

What is the equation for the buffer system in our blood

23
Q

What does the buffer system of our blood ensure

A

pH range is between 7.35 and 7.45

24
How would the pH of a buffer solution change if the volume changes
* pH remains the same * As the ratio of HA / A- remains the same
25
Where will the lower horizontal curve be on a pH curve with a weak acid
3-6
26
Where will the lower horizontal curve be on a pH curve with a strong acid
1-3
27
Where will the upper horizontal curve be on a pH curve with a weak base
8-11
28
Where will the upper horizontal curve be on a pH curve with a strong base
11-13
29
Where will the vertical line be on a pH curve with a weak acid and strong base
6-11
30
Where will the vertical line be on a pH curve with a weak acid and weak base
6-8
31
Where will the vertical line be on a pH curve with a strong acid and weak base
3-8
32
Where will the vertical line be on a pH curve with a strong acid and a strong base
3-11
33
What is the equivalence point on a pH graph
The volume of alkali added at the vertical line
34
What is true at the equivalence point on a pH graph
mol Acid = mol Base
35
How to explain that an indicator is suitable
The vertical section matches the pH range where the colour change occurs
36
How to explain the colour of an indicator at a low pH
* H+ reacts with A- so equibilbrium shifts towards LHS/RHS * Towards HA * Gives ... colour
37
How to explain the colour of an indicator at a high pH
* Alkali reacts with HA so equilibrium shifts towards LHS/RHS * Towards A- * Gives ... colour
38
How to explain the colour of an indicator at end point
* Moles of HA = Moles of A- * So final colour is a mix of the other colours
39
How can pH be measured experimentally
Using a pH probs and a data logger
40
What assumption is made when determining the pH of weak acids to allow [HA] to remain unchanged
* [HA] in equilibrium is equal to [HA] undissociated * As there is negligible dissociation of HA * [HA] in equilibrium = [HA] undissociated]

A-LEVEL CHEMISTRY (15 decks)

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