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GCSE chemistry > Electrolysis > Flashcards

Electrolysis Flashcards

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1
Q

What is electrolysis?

A

A process that uses electrical current from a DC supply is used to decompose electrolytes.

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2
Q

What are electrolytes?

A

Ionic compounds that are melted or dissolved in water, and the ions are free to move, and thus the solution will conduct electricity.

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3
Q

What are electrodes?

A

When a voltage is applied across an electrolyte, the charged ions are attracted to the electrode of the opposite charge.

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4
Q

What charge is the cathode?

A

Negative

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5
Q

What charge is the anode?

A

Positive

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6
Q

What happens when an ion touches an electrode, what happens?

A

Electrons are transferred, meaning ions are converted to elements as they gain or loose electrons.

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7
Q

What can electrolysis be used for?

A

extract reactive metals from molten ores, such as aluminium which is more reactive than carbon.

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8
Q

What happens at the anode when extracting reactive metals such as aluminium?

A

Oxygen forms at the carbon anode, and reacts with the carbon to form CO2.
The anode is usualy made of carbon because it is cheap and a good conductor

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9
Q

What happens at the cathode when extracting reactive metals such as aluminium?

A

Aluminium is formed

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10
Q

What are the disadvantages of electrolysis?

A
  • Lots of energy is needed to melt the ionic compound and produce the electric current
  • All the energy costs a lot of money
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11
Q

What are the electrode products and observations during the electrolysis of sodium sulfate?

A
  • Produces hydrogen at the cathode and oxygen at the anode
  • Graphite electrodes
  • Formation of hydrogen at cathode can be detected using a lit splint, and a squeaky pop can be heard
  • The oxygen gas produced at the anode can also be detected using a glowing splint. The splint will relight in oxygen gas.
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12
Q

What are the electrode products and observations during the electrolysis of molten lead bromide?

A
  • forms lead (metal) at the cathode and bromine (non-metal) at the anode.
  • Graphite electrodes
  • Lead bromide → lead + bromine
  • We know lead is present if a shiny metal forms around the cathode.
  • Bromine is observed as a brown gas because of the high temperatures reached in the process.
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13
Q

What are the electrode products and observations during the electrolysis of dilute sulphuric acid?

A
  • When concentrated sulfuric acid is electrolysed, hydrogen is produced from the acid and oxygen from the water.
  • produces hydrogen gas at the cathode and oxygen at the anode.
  • Graphite electrodes
  • The formation of hydrogen at the cathode can be detected using a lit splint. A squeaky pop is heard.
  • The oxygen gas produced at the anode can also be detected using a glowing splint. The splint will relight in oxygen gas.
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14
Q

What are the electrode products and observations during the electrolysis of copper chloride solution?

A
  • produces copper at the cathode and chlorine gas at the anode.
  • Graphite electrodes
  • The chlorine gas can be detected by its smell. It also bleaches damp litmus paper.
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15
Q

What are the electrode products and observations during the electrolysis of concentrated aqueous sodium chloride?

A
  • hydrogen is formed instead of sodium, because of the water.
  • Applying electricity across aqueous sodium chloride produces hydrogen gas at the cathode and chlorine gas (non-metal) at the anode.
  • The electrodes are inert graphite or platinum.
  • The formation of hydrogen at the cathode can be detected using a lit splint. A squeaky pop is heard.
  • The chlorine gas can be detected by its smell. It also bleaches damp litmus paper.
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16
Q

During the electrolysis of aqueous solutions, what is formed at the anode?

A

It depends whether halide ions are present or not. If there are halide ions, the respective halogen forms. If not, oxygen forms.

17
Q

During the electrolysis of aqueous solutions, what is formed at the cathode?

A

It depends on the reactivity of the metal. Hydrgogen is produced if the metal is more reactive than hydrogen. The metal is produced if the metal is lower than hydrogen in the reactivity series.

18
Q

What do half equations show?

A

The reaction happening at the electrodes.

19
Q

What type of reaction happens at the anode?

A

Oxidation - loss of electrons by negatively charged ions

eg: 2Br- → Br2 + 2e-

20
Q

What type of reaction happens at the cathode?

A

Reduction - gain of electrons by positively charged ions

eg: Pb2+ + 2e- → Pb

21
Q

What happens in the electrolysis of copper sulfate using inert electrodes?

A
  • Impure copper is attatched at the anode
  • Cu2+ ions go into the electrolyte solution of copper sulphate, and they will be attracted to the cathode, and pure copper will form.
22
Q

What is the half equation for the electrolysis of copper ions using inert electrodes?

A

Cu2+(aq) + 2e- → Cu(s)

23
Q

What are the results of the electrolysis of copper sulphate using inert electrodes?

A

Impurities of the anode will fall to the bottom of the beaker
When the mass of the cathode is constant, the purification process is complete

24
Q

How do you measure the mass of copper formed at the cathode over time on inert electrodes?

A
  • Record the initial mass of the electrodes - the cathode must be cleaned for copper to stick to it
  • Use a variable resistor to keep current constant
  • Wash electrodes to remove any copper sulphate, using a volatile solvent such as propanone to make them dry faster
  • Final mass - initial mass = change in mass
25
Q

What are the products of copper sulphate solution electrolysis using inert electrodes?

A

Cathode - pure copper forms

Anode - oxygen forms

26
Q

Describe how you would conduct an experiment to investigate the electrolysis of copper sulphate solution using inert electrodes.

A

1 - Pour some copper sulfate solution into a beaker.
2 - Place two graphite rods into the copper sulfate solution. Attach one electrode to the negative terminal of a dc supply, and the other electrode to the positive terminal.
3 - Completely fill two small test tubes with copper sulfate solution and position a test tube over each electrode as shown in the diagram.
4 -Turn on the power supply and observe what happens at each electrode.
5 - Test any gas produced with a glowing splint and a burning splint.
6 - Record your observations and the results of your tests.

27
Q

Describe how you would conduct an experiment to investigate the electrolysis of copper sulphate solution using copper electrodes.

A

1 - Pour some copper sulfate solution into a beaker.
2 - Measure and record the mass of a piece of copper foil. Attach it to the negative terminal of a dc supply, and dip the copper foil into the copper sulfate solution.
3 - Repeat step 2 with another piece of copper foil, but this time attach it to the positive terminal.
4- Make sure the electrodes do not touch each other, then turn on the power supply. Adjust the power supply to achieve a constant current as directed by your teacher.
5 - After 20 minutes, turn off the dc supply.
6 - Carefully remove one of the electrodes. Gently wash it with distilled water, then dip it into propanone. Lift the electrode out and allow all the liquid to evaporate. Do not wipe the electrodes clean. Measure and record the mass of the electrode.
7 - Repeat step 6 with the other electrode. Make sure you know which is which.
8- Repeat the experiment with fresh electrodes and different currents.

28
Q

What would be the observations when conducting the electrolysis of copper sulphate solution using copper electrodes?

A

The gain in mass by the negative electrode is the same as the loss in mass by the positive electrode. So the copper deposited on the negative electrode must be the same copper ions that are lost from the positive electrode.

Current used is directly proportional to the mass gained by the cathode.

29
Q

Safety precautions of the core practical?

A

Copper sulfate solution
- Causes skin and serious eye irritation - Wear gloves and eye protection

Propanone

  • Highly flammable liquid and vapour - Keep away from naked flames
  • may cause drowsiness or dizzines - use it in a fume cupboard

GCSE chemistry (9 decks)

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