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AQA - A level Chemistry > Acids and bases > Flashcards

Acids and bases Flashcards

1
Q

What is meant by a Bronsted-Lowry acid?

A

Proton donor

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2
Q

What is meant by a Bronsted-Lowry base?

A

Proton acceptor

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3
Q

What is meant by a strong acid?

A

Fully dissociates

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4
Q

What is meant by a weak acid?

A

Partially dissociates

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5
Q

Definition of PH

A

pH = -log10[H+]

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6
Q

Definition of [H+]

A

[H+] = 10-pH

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7
Q

Definition of the ionic product of water (Kw)

A

Kw = [H+][OH-]

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8
Q

What equation should be used when calculating the pH of a strong acid?

A

pH = -log10[H+]

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9
Q

What equation should be used when calculating the pH of a weak acid?

A

Ka = [H+]2 / [HA]
Rearrange to get [H+]

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10
Q

What equation should be used when calculating the pH of a buffer?

A

Ka = [H+][A-] / [HA]
Rearrange to get [H+]

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11
Q

metal + acid ……

A

salt + hydrogen

e.g. HCl (aq) + Na (s) —> NaCl (aq) + 1/2 H2 (g)

hydrochloric acid + sodium —> sodium chloride + hydrogen

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12
Q

metal oxide + acid ……

A

salt + water

e.g. 2HNO3 (aq) + K2O (aq) —> 2KNO3 (aq) + H2O (l)

nitric acid + potassium oxide —> potassium nitrate + water

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13
Q

acid + metal hydroxide …..

A

salt + water

e.g. H3PO4 (aq) + 3NaOH (aq) —> Na3PO4 (aq) + 3H2O (l)

phosphoric acid + sodium hydroxide —> sodium phosphate + water

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14
Q

acid + metal carbonate …..

A

salt + water + carbon dioxide

e.g. H2SO4 (aq) + Na2CO3 (s) —> Na2SO4 (aq) + CO2 (g) + H2O (l)

sulfuric acud + sodium carbonate —> sodium sulfate + carbon dioxyde + water

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15
Q

ammonia + acid ….

A

salt

e.g. NH3 (aq) + HCl (aq) —> NH4Cl (aq)

ammonia + hydrochloric acid —> ammonium chloride

e.g. NH3 (aq) + H3PO4 (aq) —> (NH4)3 PO4 (aq)

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16
Q

What is a monoprotic acid?

A

only one H+ ion released e.g. HCl

17
Q

What is a diuretic acid?

A

two H+ ions released e.g. H2SO4

18
Q

What does smaller pH mean in terms of [H+]

A

Higher concentration of [H+]

19
Q

What are the 4 main examples of strong acids?

A
  • HCl
  • H2SO4
  • HNO3
  • H3PO4
20
Q

Where does the position of equilibrium for strong acids usually lie?

A

entirely to right side

21
Q

Where does the position of equilibrium for weak acids usually lie?

A

More to the left side

22
Q

How to find pKa from Ka?

A

pKa = -log10Ka

23
Q

How to find Ka from pKa?

A

Ka = 10-pKa

24
Q

What is the Kw value for water?

A

1 x 10-14 mol2dm-6

25
Q

Why is water always neutral?

A

[OH-] = [H+]

26
Q

How can [H+] be found from Kw?

A

Kw = [H+]2

27
Q

How can Kw] be found from [H+]?

A

[H+] = square root of Kw

28
Q

Strong bases…

A
  • fully dissociate
  • to release OH- ions
29
Q

Where does the position of equilibrium for strong bases usually lie?

A

entirely on right side

30
Q

Equation to find [H+] of strong alkalis

A

[H+] = Kw / [OH-]

31
Q

Suggest why pure water is not alkaline

A

[H+] = [OH-]

32
Q

Explain why [H2O] is not shown in the Kw expression

A

[H2O] is (almost) constant

33
Q

A student has an unknown weak acid of unknown concentration and a bottle of 0.5 mol dm-3 NaOH.
Explain, using brief practical details, how you would determine the Ka of the weak acid. [6]

A
  • Measure 25 cm3 of acid into a beaker/conical flask using volumetric pipette.
  • Use a pH probe to measure the initial pH
  • Add 1cm3 NaOH from a burette swirl and record the pH
  • Repeat until the NaOH is in excess
  • Plot a graph of pH against vol NaOH added in cm3
  • Use the vertical section to find the volume of NaOH needed for neutralisation
  • The half neutralisation point is half the volume of neutralisation.
  • Read off the pH at the half neutralisation point.
  • At half neutralisation ka = [H+]/pKa=pH
  • Ka = 10-pH
34
Q

write equation to show how ethanoic acid behaves as a weak acid in it’s reaction with water

A

CH3COOH —> CH3COO- + H+

35
Q

write equation when pure ethanoic acid reacts with pure nitric acid where ethnic acid acts as a base

A

CH3COOH + HNO3 —. CH3COOH2+ + NO3 2-

36
Q

explain why chloroethanoic acid is stronger than ethanoic acid

A
  • electronegative chlorine withdraws electrons
  • weakens O-H bond
37
Q

explain why data books do not usually contain Ka values for strong acids

A
  • strong acids completely dissociate
  • ka for strong acids is very large
38
Q

state how buffer solution made

A

add excess weak acid to alkali

39
Q

state how buffer solution resists changes in PH

A

CH3COO- from salt reacts with H+

AQA - A level Chemistry (25 decks)

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