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Electrolysis Flashcards

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1
Q

How does electrolysis work?

A

Electrolysis is the decomposition of a compound into the elements that produce it. This only occurs in subsances that conduct electricity.

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2
Q

What is a positively charged ion called? And what is a negative one called?

A

Cation - positively charged ion
Anion - negatively charged ion

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3
Q

What is the electrode that attracts positively charged ions called?

A

Cathode

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4
Q

What is the charge of an anode?

A

Positive

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5
Q

What is the electrode that attracts negatively charged ions called?

A

anode

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6
Q

What is the charge of a Cathode?

A

Negative

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7
Q

What is the electode that attracts negative ions called?

A

anode

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8
Q

How does Cu²⁺ form copper in electrolysis?

(2 points)

A
  • When voltage is applied, the Cu²⁺ ions are attracted to the cathode.
  • When they touch the cathode, they gain two electrons to form the copper metal.
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9
Q

What happens at the cathode?

A

The metal forms

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10
Q

Explain Oxidation and Reduction in terms of electrolysis.

(HINT: OxidAtion, reduCtion)

A

Oxidation: electrons are lost. This happens at the anode.
Reduction: electrons are gained. This happens at the cathode.

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11
Q

What is an aqueous solution?

A

A solution where the solvent is water.

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12
Q

What happens at the cathode in the electrolysis of an aqueous solution?

A

H⁺ (hydrogen) is produced if the metal is more reactive/higher up on the reactivity series than hydrogen.
The metal ions will form if it is less reactive/further down in the reactivity series than hydrogen.

(e.g, copper)

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13
Q

What happens at the anode in the electrolysis of an aqueous solution?

A

If there are Halide ions present, the respective halides will form.

If there are no halides, oxygen (NOT HYDROXIDE) will form.

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14
Q

What are the half equations for the electrolysis of lead bromide (PbBr₂)?

A

anode, oxidation:
Pb⁺² + 2e⁻ → Pb
cathode, reduction:
2Br⁻ → Br₂ + 2e⁻

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15
Q

Is the electron a product or a reactant in the half equation or a non metal? And why?

A

Product. It has an overall negative charge and needs to loose electrons to become stable.

If the electron is a product the substance is gaining electrons.

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16
Q

Is the electron a product or reactant in the half equasion for a metal?

A

Reactant. It has an overall positive charge and needs to gain electrons to become stable.

If the electron is a reactant the substance is loosing electrons.

17
Q

What two ions form when water is involved in electrolysis? And what electrode are they attracted to?

A

Hydrogen ions: Cathode.
Hydroxide ions: Anode.

18
Q

What is the BALANCED half equation for when oxygen forms at the anode?

A

4OH⁻ → O₂ + 2H₂O + 4e⁻

19
Q

Electrolysis can be used to extract copper from a solution of copper (II) sulfate. Suggest how oxygen is also produced.

A

Oxygen is produced through discharge of hydroxide ions from the water.

20
Q

State two reasons why we use graphite electrodes in the electrolysis of ionic compounds.

A
  • good conductors of electricity
  • inert/unreactive
21
Q

In the extraction of aluminium from aluminium oxide by electrolysis the positive electrode is made of carbon and needs to be regularly replaced. Explain why.

A

The oxygen may react with the carbon anode to form carbon dioxide.

22
Q

How can we test for Hydrogen?

(2 marker)

A
  • squeaky pop test (1 mark)
  • a lighted splint is exposed to the hydrogen. If it makes a squeaky pop then hydrogen is present in thr solution (1 mark)
23
Q

How can we test for oxygen?

(2 marker)

A
  • relight test (1 mark)
  • a lighted splint is exposed to the solution. If oxygen is present then the splint will reignite. (1 mark)
24
Q

Why is the remaining electrolyte an alkali solution after electrolysis has occured in an aqueous solution?

A

There are excess OH- ions (which are alkali)

25
Q

Write the balanced equation for when Hydrogen is discharged/formed in electrolysis.

A

2H⁺ + 2e⁻ -> H₂

26
Q

What is electroplation and why is it sometimes used in electrolysis?

A
  • Electroplation is when a layer of a metal is put on a different metal.
  • This is done to improve the physical appearance of the metal
  • It can also be used to prevent corrosion of the electrodes
27
Q

How can we test for chlorine at the anode?

(2 marker)

A

Litmus paper test (1 mark)
Dampen the litmus paper with water. Expose the litmus paper to chlorine. The paper will be bleached if chlorine is present. (1 mark)

28
Q

How do we know if Bromine has formed at the anode?

A

A brown gas will form due to the high temperatures reached in the process.

29
Q

Reduction is -
Oxidation is -

A

Reduction is - the gain of electrons
Oxidation is - the loss of electrons

30
Q

What are the two elements in brass?

A

Copper and Zinc

31
Q

What happens at the negative electrode?
What happens at the positive electrode?
Identify in terms of reduction or oxidation

A

Reduction occurs at the negative electrode
Oxidation occurs positive electrode

32
Q

Why is magnesium extracted using electrolysis instead of carbon?

A

Magnesium is more reactive than carbon, and therfore carbon cannot be used to extract it.

33
Q

Why is extracting metals through electrolysis so expensive?

A

Lots of energy is required to…
- heat the solution
- produce the elecric current

34
Q

What is the first step to undergo electrolysis when extracting aluminum?

A

The aluminum should be mixed with cryolite, so as to reduce the melting point.

35
Q

When extracting aluminum with electrolysis, the anodes are replaced often. Why is this?

A

The oxygen molecules (from aluminum oxide) react with the carbon anode to produce carbon dioxide.

36
Q

Recite the steps of the electrolysis practical.

A
  • Pour 50cm³ of the molten/aqueous solution into a beaker
  • Place a petri dish over the beaker. It should have 2 holes, each of which are for either electrode
  • Insert the carbon-graphite elecrodes through the holes in the petri dish.
  • Ensure the electodes do not touch. (it would produce a short-circuit)
  • Attach crocodile leads to the rods and plug them into a low-voltage power supply and select 4 Volts

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