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GCSE Chemistry LTS > Chapter 6 Electrolysis > Flashcards

Chapter 6 Electrolysis Flashcards

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1
Q

What happens to the ions in ionic compounds when they are dissolved in water?

A

When ionic substances dissolve the ions are free to move about.

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2
Q

What word do we use to describe ionic substances that have been dissolved in water?

A

We describe ionic substances dissolved in water as aqueous (aq).

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3
Q

What happens to the ions in ionic compounds when the compound is melted?

A

When ionic substances are molten the ions are free to move about.

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4
Q

What is electrolysis?

A

Electrolysis breaks down a substance using electricity.

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5
Q

What needs to be placed in molten or aqueous ionic substances for electrolysis to take place?

A

Electrodes are placed in a solution of an ionic compound or in a molten ionic compound.

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6
Q

What is the positive electrode called?

A

The positive electrode is called the anode.

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7
Q

What is the negative electrode called?

A

The negative electrode is called the cathode.

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8
Q

When electricity is passed through molten or aqueous ionic substances how do the ions behave?

A

Positive ions move towards the cathode (negative electrode) and negative ions move towards the anode (positive electrode).

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9
Q

What are electrodes usually made from and why?

A

The electrodes are usually made of graphite. Graphite conducts electricity but will not react with the ions.

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10
Q

What is an electrolyte?

A

The substance being broken down by electrolysis is called the electrolyte.

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11
Q

What happens to ions when they discharge?

A

Ions become discharged (lose their charge) at the electrodes and become elements.

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12
Q

Write the half equation for the discharge of chloride ions. Where does this happen? (HIGHER ONLY)

A

At the anode (positive electrode) non-metals lose electrons and become elements. We write this as a ‘half equation”.
Example:

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13
Q

What word do we use to describe the loss of electrons by non-metal ions?

A

When non-metal ions lose electrons we say they are ‘oxidised’.

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14
Q

What is reduction?

A

Oxidation is the loss of electrons.
Reduction in the gain of electrons.
OIL RIG

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15
Q

Write the half equation for the discharge of copper(II) ions. Where does this happen?

A

At the cathode (negative electrode) metals gain electrons and become elements. We write this as a ‘half equation”.
Example:

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16
Q

What term do we use to describe metal ions gaining electrons?

A

When metal ions gain electrons we say they are ‘reduced’.

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17
Q

Where in the reactivity series will you find the metals that are capable of being deposited on electrodes?

A

Only metals lower than hydrogen in the reactivity series will be deposited on the cathode when electrolysing a solution.

18
Q

What is produced at the cathode during the electrolysis of metal ions that are more reactive than hydrogen? What is formed at the anode?

A

Electrolysis involving metal ions more reactive than hydrogen in the reactivity series results in hydrogen gas being produced at the cathode (negative electrode) and oxygen being produced at the anode (positive electrode).
Example:

19
Q

Write the half equation for the formation of hydrogen at the cathode.
(HIGHER ONLY)

A

When the metal ions are more reactive than hydrogen the reaction at the cathode is:
2H+(aq) + 2e- → H2(g)

20
Q

Write the 2 half equations for the possible products at the anode when electrolysing ionic compounds with metals more reactive than hydrogen.
(HIGHER ONLY)

A

When the metal ions are more reactive than hydrogen the reaction at the anode depends on the concentration of halide ions in the electrolyte. If the concentration is high then a halide gas will form if it is low then oxygen gas will form.
2Cl-(aq) → Cl2(g) +2e-
Or
4OH-(aq) → 2H2O(l) + O2(g) + 4e-

21
Q

If there are 2 possible products as an electrode how do you know which one is actually formed?

A

If there are 2 elements that could be produced at an electrode it is always the less reactive element formed.

22
Q

What is the order at which ions are discharged (lose their charge) at the anode?

A

The order at which ions are discharged (lose their charge) an the anode is:
halide ion > hydroxide (OH-) > all other negatively charged ions

23
Q

Why is oxygen produced at the anode?

A

Oxygen is produced at the anode due to the breakdown of water by electrolysis.
H2O(l) → H+ + OH-
4OH-(aq) → 2H2O(l) +O2(g) + 4e-

24
Q

How are reactive metals extracted from their ores?

A

Electrolysis can be used to extract metals from their ores.

25
Q

Give 5 uses for aluminium.

A

Aluminium is an important metal. It is used to make: pans, overhead power cables, aeroplanes, cooking foil, drink cans, window and door frames, bicycles frames and car bodies.

26
Q

In what form is aluminium found in bauxite?

A

Aluminium is found in the form of aluminium oxide in the ore bauxite.

27
Q

Why does bauxite need to be processed?

A

Bauxite has impurities in it so once mined it must be processed to remove the impurities.

28
Q

Why can we not extract aluminium from its oxide using carbon?

A

Aluminium is more reactive than carbon so cannot be extracted from aluminium oxide using carbon.

29
Q

Can metals less reactive than carbon be extracted using electrolysis?

A

Metals less reactive than carbon can also be extracted using electrolysis but they don’t have to be.

30
Q

What is the formula for aluminium oxide?

A

Aluminium oxide has the formula Al2O3.

31
Q

Why do we mix aluminium oxide with cryolite during extraction?

A

Aluminium oxide is mixed with cryolite for electrolysis to lower the melting point from 2050°C to 850°C.

32
Q

Describe the electrolysis of aluminium oxide in detail. Include a diagram and the products at the electrodes.

A

Molten aluminium oxide is electrolysed to produce aluminium at the cathode. At the anode oxygen gas is produced. This oxygen gas reacts with the carbon electrode to produce carbon dioxide gas.

33
Q

Write the half reactions for the electrolysis of aluminium oxide. (HIGHER ONLY)

A

The half reactions for the electrolysis of aluminium oxide are:

34
Q

Why do the carbon anodes in the extraction of aluminium need to be regularly replaced?

A

At the anode the oxygen produced is constantly reacting with the carbon that the anode is made from. This means that the carbon anodes gradually burn away and need to be replaced regularly.

35
Q

Why is it worth using so much energy to extract aluminium from its ore?

A

The electrolysis of aluminium oxide requires huge amounts of energy and is only done due to the value of the aluminium metal produced.

36
Q

How can we test for the presence of chlorine gas at the cathode?

A

Blue litmus paper can be used to test for the presence of chlorine gas (Cl2) at the anode. If chlorine is present it will change from blue to colourless. We say it has ‘bleached’ the litmus paper.

37
Q

How can we test for the production of oxygen gas at the anode?

A

We can test for the presence of oxygen at the anode by seeing if it relights a glowing splint. If it does then oxygen gas has been produced.

38
Q

What is the formula for carbonate?

A
39
Q

What is the formula for the sulfate ion?

A
40
Q

What is the formula for the nitrate ion?

A
41
Q

What is the formula for the ammonium ion?

A
42
Q

What is the formula for hydroxide?

A

GCSE Chemistry LTS (15 decks)

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