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Electrolysis 2
Sodium hydroxide and chlorine are used to make bleach.

Electrolysis 2

Electrolysis is a process you need to understand for GCSE Chemistry. This is the second of two quizzes on the subject but what exactly is electrolysis and how was it discovered? Electrolysis is a method of using a direct electrical current to cause a chemical reaction. It was discovered by accident in 1800 when the scientist William Nicholson and surgeon Anthony Carlisle attempted to reproduce the experiment in which Italian scientist Alessandro Volta created the world's first battery. Instead of using frog's legs to test whether electricity was produced, they were using a device developed by Nicholson, similar to the gold leaf electroscope. To get a better contact between the wires from their battery and the measuring device, they used a drop of water. When they noticed that a gas was bubbling off from this water, they investigated further and were astonished to find that when they passed the electric current from their battery through river water there was a reaction - a gas bubbled off from both wires they had dipped into their sample. That was the first time electrolysis was seen.

1.
When an electrical current is passed through brine (sodium chloride solution), three products are formed. They are...
chlorine gas, hydrogen gas, sodium chloride solution
chloride ions, hydrogen gas, sodium hydroxide solution
chlorine gas, hydrogen gas, sodium hydroxide solution
chlorine gas, hydrogen ions, sodium hydroxide solution
All three have important uses in the chemical industry
2.
The third product from the electrolysis of brine is sodium hydroxide. This is NOT used to...
make bleach
make paper
make soap
make margarine
Hydrogen is used for hydrogenating oils to produce margarine
3.
Copper can be purified using electrolysis. Pick the correct combination of components for the electrolytic cell.
Cathode: Impure copper
Anode: Pure copper
Electrolyte: Copper sulfate
Cathode: Pure copper
Anode: Impure copper
Electrolyte: Copper sulfate
Cathode: Pure copper
Anode: Pure copper
Electrolyte: Copper sulfate
Cathode: Impure copper
Anode: Pure copper
Electrolyte: Water
Copper ions in solution are attracted to the cathode, where they are deposited as copper atoms
4.
What gas forms at the positive electrode during the extraction of aluminium?
Hydrogen
Chlorine
Nitrogen
Oxygen
This oxygen reacts with the carbon of the positive graphite electrodes forming carbon dioxide and as a result, they have to be replaced frequently
5.
Which of the following is NOT a use for chlorine?
Kill bacteria
Make bleach
Make PVC
Control pH
The use of chlorine to disinfect drinking water in Victorian Britain had a profound effect on health, reducing the number of people catching water borne bacterial diseases like cholera
6.
Aluminium ore (bauxite) must be dissolved in molten cryolite before it can be electrolysed. Why?
Raise the melting point
Lower the melting point
Increase its viscosity
Reduce its viscosity
Cryolite melts at less than 1000°C, bauxite melts at over 2000°C
7.
Choose the correct half equations for the electrolysis of brine.
Anode 2Cl- → Cl2 + 2e-
Cathode 2H+ + 2e- → H2
Anode Cl- → Cl2 + e-
Cathode 2H+ + e- → H2
Anode 2Cl- → Cl2 + 2e-
Cathode Na+ + e- → Na
Anode Cl- → Cl + 2e-
Cathode H+ + e- → H2
Both chlorine and hydrogen are diatomic molecules
8.
The hydrogen produced by the electrolysis of brine is NOT used to...
make margarine
make bleach
make hydrochloric acid
make hydrogen chloride gas
Sodium hydroxide and chlorine are used to make bleach
9.
Pick the correct half equations for the electrolysis of copper sulfate using copper electrodes.
Cathode: Cu(s) → Cu2+(aq) + 2e-
Anode: Cu2+(aq) + 2e- → Cu(s)
Cathode: Cu2+(aq) + 2e- → Cu(s)
Anode: Cu(s)→ Cu2+(aq) + 2e-
Cathode: Cu(s) → Cu+(aq) + e-
Anode: Cu2+(aq) + 2e- → Cu(s)
Cathode: Cu(s) → Cu2+(aq) + 2e-
Anode: Cu+(aq) + e- → Cu(s)
Remember, in a pair of half equations, everything needs to be balanced, just like in any symbol equation
10.
If graphite electrodes are used instead of copper in the electrolysis of copper sulfate, the equation that shows what happens at the anode is...
H2O → H+ + O2 + e-
Cu2+ + 2e- → Cu
2H2O → 4H+ + O2+ 4e-
Cu → Cu 2+ +2e-
Graphite is carbon and is a conductor of electricity and can therefore be used for making electrodes
You can find more about this topic by visiting BBC Bitesize - Electrolysis

Author:  Kate Gardiner

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