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AQA Chemistry > 1.12 Acids & Bases > Flashcards

1.12 Acids & Bases Flashcards

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1
Q

What is a Bronsted-Lowry acid?

A

Proton donor

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2
Q

What is a Bronsted-Lowry base?

A

Proton acceptor

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3
Q

What ion causes a solution to be acidic?

A

Hydrogen ions (H⁺)

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4
Q

What ion causes a solution to be alkaline?

A

Hydroxide ions (OH⁻)

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5
Q

Write an equation for the ionisation of water.

A

H₂O (l) ⇌ H⁺ (aq) + OH⁻ (aq)

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6
Q

Derive Kw using the equation for the ionisation of water.

A

Keq = [H⁺][OH⁻] / [H₂O]
[H₂O] Keq = [H⁺][OH⁻]
[H₂O] is so large compared to [H⁺] and [OH⁻] that [H₂O] Keq can be considered to be constant
[H₂O] Keq = Kw
∴ Kw = [H⁺][OH⁻]

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7
Q

What is the value of Kw at 298K?

A

1.0 x 10⁻¹⁴

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8
Q

What physical factors affect the value of Kw?

A

Temperature only

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9
Q

How does temperature affect the value of Kw?

A

If temperature is increased, the equlibrium moves to the right so Kw increases and the pH of pure water decreases

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10
Q

Why is pure water still neutral, even if pH does not equal 7?

A

[H⁺] = [OH⁻]

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11
Q

Give an expression for pH in terms of H⁺.

A

pH = - log₁₀[H⁺]

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12
Q

What is the relationship between pH and concentration of H⁺?

A

Lower pH = higher concentration of H⁺

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13
Q

If two solutions have a pH difference of 1, what is the difference in [H⁺]?

A

A factor of 10

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14
Q

How is [H⁺] found from pH?

A

[H⁺] = 10⁻ᵖᴴ

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15
Q

How is [OH⁻] found from pH?

A

Find [H⁺]
Use Kw (1.0 x 10⁻¹⁴ ) to calculate [OH⁻]

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16
Q

What is different when finding [H⁺] from the concentration of diprotic and tripotic acids?

A

Need to multiply the concentration of the acid by the number of protons to find [H⁺]

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17
Q

What is a diprotic acid?

A

A polyprotic acid that can donate two protons or hydrogen atoms per molecules to an aqueous solution

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18
Q

What is a polyprotic acid?

A

Acids capable of losing more than a single proton per molecule in acid-base reactions

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19
Q

What is a tripotic acid?

A

A polyprotic acid that can donate three protons or hydrogen atoms per molecules to an aqueous solution

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20
Q

How is the pH of a strong alkaline solution calculated?

A

Use Kw to calculate [H⁺] from [OH⁻]
Use pH = -log[H⁺]

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21
Q

What is a strong acid?

A

An acid which fully dissociates in water to release H⁺ ions
(HX -> H⁺ + X⁻)

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22
Q

What is a strong base?

A

A base which fully dissociates in water to release OH⁻ ions
(XOH -> X⁺ + OH⁻)

23
Q

What is the difference between concentration and strength?

A

Concentrated = many mol per dm³
Strong = amount of dissociation

24
Q

What is a weak acid?

A

An acid that only partially dissociates in water to release H⁺ ions

25
Q

What is a weak base?

A

A base that only partially dissociates in water to release OH⁻ ions

26
Q

Give 3 examples of strong acids.

A

Hydrochloric acid (HCl)
Sulfuric acid (H₂SO₄)
Phosphoric acid (H₃PO₄)

27
Q

Give 3 examples of strong bases.

A

Sodium hydroxide (NaOH)
Calcium Carbonate (CaCO₃)
Sodium Carbonate (Na₂CO₃)

28
Q

Give examples of weak acids.

A

Ethanoic acid (CH₃COOH)
Any organic acid

29
Q

Give an example of a weak base.

A

NH₃

30
Q

What is Ka?

A

For acid HA: HA ⇌ H⁺ + A⁻

Ka = [H⁺][A⁻] / [HA]

31
Q

How is the pH of a weak acid found?

A

Use the equation for Ka, subbing in values for [A⁻] and [HA]
USe pH = - log[H⁺] equation to find pH

32
Q

What is a titration?

A

The addition of an acid/base of known titration to a base/acid of unknown titration to determine the concentration
An indicator is used to show that neutralisation has occurred

33
Q

Define the term equilavence point.

A

The point at which the exact volume of acid/base has been added to just neutralise the base/acid

34
Q

What generally happens to the pH of a solution around the equivalence point?

A

A large and rapid change in pH
Not in weak-weak titration

35
Q

How is the unknown concentration calculated in a titration?

A

Calculate mols of one reactant
Balanced equation to work out mols of other
Use conc = mol/vol

36
Q

What is the end point of a titration?

A

The volume of acid/alkali added when the indicator just changes colour

37
Q

Name the 3 properties of a good indicator for a titration.

A

Sharp colour change
End point same as equivalence point
Distinct colour change

38
Q

What indicator is used for a strong acid-strong base titration?

A

Phenolphthalein (or methyl orange)

39
Q

What indicator is used for a strong acid-weak base titration?

A

Methyl orange

40
Q

What indicator is used for a weak acid-strong base titration?

A

Phenolphthalein

41
Q

What indicator is used for a weak acid-weak base titration?

A

Neither methyl orange or phenolphthalein give sharp colour change

42
Q

What colour is methyl orange?

A

Red in acid
Yellow in alkali

43
Q

What pH does methyl orange change colour?

A

4-5

44
Q

What colour is phenolphthalein?

A

Colourless in acid
Red in alkali

45
Q

What pH does phenolphthalein change colour?

A

9-10

46
Q

What is the half neutralisation point of a titration?

A

Volume = half volume added at equivalence point

47
Q

What is a buffer solution.

A

A solution that resists changes in pH when small amount of acid/alkali are added

48
Q

What do acidic buffer solutions contain?

A

A weak acid and a soluble salt of that acid that fully dissociates

49
Q

Write a reaction for an acidic buffer with added acid.

A

H⁺ + A⁻ -> HA

50
Q

Write a reaction for an acidic buffer with added acid.

A

HA + OH⁻ -> H₂O + A⁻

51
Q

What do basic buffer solutions contain?

A

Weak base and soluble salt of that weak base

52
Q

How can the pH of buffer solutions be calculated?

A

Use Ka of weak acid
Sub in [A⁻] and [HA]
Calculate [H⁺] to pH

53
Q

How can the new pH of a buffer solution be calculated after an acid or base is added?

A

Calculate moles of H⁺, A⁻ & HA before acid/base added
Use equations to work out new moles of A⁻ & HA -> find [H⁺] -> pH

54
Q

What products are buffers found in?

A

Shampoos
Detergents
Maintain pH to avoid damage to skin, hair, fabrics

AQA Chemistry (8 decks)

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