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Chemistry > Topic 4: Chemical changes > Flashcards

Topic 4: Chemical changes Flashcards

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1
Q

What is the pH scale?

A

A measure of how acidic or alkaline a solution is

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2
Q

What can be used to measure of pH of a solution? [2]

A
  1. Universal indicator
  2. pH probe
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3
Q

What do acids produce in aqueous solutions?

A

H⁺ ions

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4
Q

What do alkalis produce in water?

A

OH⁻ ions

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5
Q

What is an alkali?

A

A base that dissolves in water

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6
Q

What happens in a neutralisation reaction between an acid and an alkali?

A

Hydrogen ions react with hyroxide ions to produce water

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7
Q

What is a strong acid?

A

Completely ionised in aqueous solution (all acid particles dissosiate to release H⁺ ions)

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8
Q

What is a weak acid?

A

Only partially ionised in aqueous solution (small proportion of acid particles dissosiate and release H⁺ ions)

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9
Q

What is pH a measure of?

A

The concentration of H⁺ ions in a solution

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10
Q

For every decrease of 1 on the pH scale, how much does the concentration of H⁺ ions increase by?

A

A factor of 10

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11
Q

3 examples of strong acids

A
  1. Sulfuric acid
  2. Hydrochloric acid
  3. Nitric acid
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12
Q

3 examples of weak acids

A
  1. Ethanoic acid
  2. Citruc acid
  3. Carbonic acid
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13
Q

Why is a pH probe better to use than universal indictor?

A

Removes human judgement, making results more reliable

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14
Q

What is the neutralisation word equation?

A

Acid + base —> salt + water

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15
Q

What are the 3 common acids?

A
  1. Sulphuric acid
  2. Hydrochloric acid
  3. Nitric acid
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16
Q

What are the 2 common bases?

A
  1. Sodium hydroxide
  2. Calcium carbonate
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17
Q

What type of reaction do weak acids form?

A

Reversible reactions

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18
Q

Why does equilibrium lie to the left in a weak acid reaction?

A

Only a few particles release H⁺ ions

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19
Q

What is the equation for an acid + a metal oxide?

A

Acid + metal oxide —> salt + water

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20
Q

What is the equation for an acid + metal hydroxide?

A

Acid + metal hydroxide —> salt + water

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21
Q

What is the equation for an acid + metal carbonate?

A

Acid + metal carbonate —> salt + water + carbon dioxide

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22
Q

What is the colour change of litmus? acid —> alkali

A

Red —> blue

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23
Q

What is the colour change of methyl orange? acid —> alkali

A

Red —> yellow

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24
Q

What is the colour change of phenolphthalein? acid —> alkaline

A

Colourless —> pink

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25
Q

What is the equation for an acid + metal?

A

Metal + acid —> salt + hydrogen

26
Q

What is the equation for a metal + water?

A

Metal + water —> metal hydroxide + hydrogen

27
Q

How can you investigate the reactivity of metals? [2]

A
  1. Rate at which hydrogen bubbles are produced
  2. Temperature change
28
Q

What is oxidation?

A

Gain of oxygen

29
Q

What is reduction?

A

Loss of oxygen

30
Q

What happens in a reduction reaction?

A

A metal is separated from its oxide

31
Q

Which metals can be reduced using carbon?

A

Metals below carbon on the reactivity series

32
Q

Why can some metals be reduced using carbon?

A

Carbon can take the oxygen from metals which are less reactive than carbon itself, leaving behind a pure metal

33
Q

Why are metals such as gold only ever found as the metal itself?

A

They are too unreactive to react with things like oxygen

34
Q

What do metals above carbon on the reactivity series have to be reduced by?

A

Electrolysis

35
Q

What is the problem with electrolysis?

A

Very expensive

36
Q

What gas is produced if a metal is reduced?

A

CO₂

37
Q

What is oxidation in terms of electrons?

A

Loss of electrons

38
Q

What is reduction in terms of electrons?

A

Gain of electrons

39
Q

What is electrolysis?

A

Splitting up with electricity

40
Q

What is an electrolyte?

A

A molten or dissolved ionic compound

41
Q

Is the cathode positive or negative?

A

Negative

42
Q

What kind of ions move to the cathode?

A

Positively charged ions

43
Q

Is the anode negative or positive?

A

Positive

44
Q

What kind of ions move to the anode?

A

Negatively charged ions

45
Q

THINK: electrode? reduced/oxidised? released as?

Describe what happens when lead bromide (a simple ionic compound) is electrolysed in a molten state [2]

A
  1. Lead is attracted to the cathode, reduced and falls to the bottom as pure lead
  2. Bromine is attracted to the anode, oxidised and is released as bromine gas
46
Q

In electrolysis, which way do electrons travel?

A

Anode —> cathode

47
Q

Why are the electrodes in electrolysis usually made from inert carbon?

A

Inert carbon is unreactive, so will not interfere with the reaction

48
Q

In electrolysis, why does the compound you’re trying to separate need to be molten or dissolved?

A

So the ions are free to move and can conduct electricity

49
Q

Draw and check on back

Draw an electrolysis set-up? [5]

A
  1. Beaker
  2. Electrolyte
  3. Anode and cathode
  4. Wire
  5. Battery (small line towards cathode)
50
Q

When would a metal be extracted from its ore by electrolysis? [2]

A
  1. If the metal is too reactive to be reduced with carbon
  2. If the metal reacts with carbon itself
51
Q

What ore is alumunium extracted from?

A

Bauxite

52
Q

What steps have to be taken before aluminium oxide can be electrolysed? [3]

A
  1. Purify aluminium oxide from bauxite
  2. Mix aluminium oxide with cryolite - to lower the melting temperature
  3. Melt it to make it molten
53
Q

Why is cryolite mixed with aluminium oxide before electrolysis?

A

To lower the melting temperature

54
Q

THINK: electrode? reduced/oxidised? released as?

Describe what happens when aluminium oxide (a metal ore) is electrolysed in a molten state [2]

A
  1. Aluminium is attracted to the cathode, reduced and falls to the bottom as pure metal
  2. Oxygen is attracted to the anode, oxidised and is released as oxygen gas
55
Q

Write and check

Write the half equations for the electrolysis of aluminium oxide [2]

A
  1. Al³⁺ + 3e⁻ —> Al
  2. 2O²⁻ —> O₂ + 4e⁻
56
Q

Why must the positive electrode (anode) be continually replaced?

A

It is made from carbon so it will start to react with oxygen to produce carbon dioxide

57
Q

Why is electrolysis expensive?

A

It requires a large amount of energy

58
Q

In aqueous solutions, what else is present as well as the ions from the compound? [2]

A
  1. Hydrogen ions
  2. Hydroxide ions
59
Q

What is the general rule at the cathode in aqueous solutions?

A

Hydrogen gas will be produced if the metal ion is more reactive than hydrogen

60
Q

What is the general rule at the anode in aqueous solutions?

A

If no halide ions are present, then the hydroxide ions will be discharged as oxygen and water

61
Q

Describe what happens when a solution of copper sulfate is electrolysed [2]

A
  1. Copper and hyrogen ions are attracted to the cathode. Copper is less reactive than hydrogen so it is discharged and coats the electrode
  2. Sulfate and hydroxide ions are attracted to the anode. No halide is present so hydroxide ions are discharged as oxygen and water
62
Q

Describe what happens when a solution of sodium chlorine is electrolysed [2]

A
  1. Sodium and hydrogen ions are attracted to the cathode. Sodium is more reactive than hydrogen so hydrogen gas is produced
  2. Chloride and hydroxide ions are attracted to the anode. A halide is present so chlorine gas is produced

Chemistry (10 decks)

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