New
New
Year 11
Edexcel
Foundation

Electrolysis of molten salts

I can explain why salts can be electrolysed when in their liquid state, and describe the reactions taking place.

New
New
Year 11
Edexcel
Foundation

Electrolysis of molten salts

I can explain why salts can be electrolysed when in their liquid state, and describe the reactions taking place.

Lesson details

Key learning points

  1. A solid ionic compound cannot conduct electricity.
  2. Salts are ionic compounds which can be electrolysed when they are in the molten state.
  3. Gases may be formed at the electrodes.
  4. Freely moving ions can reach the electrodes and undergo oxidation or reduction.
  5. A non-metal always forms at the positive electrode, and a metal forms at the negative electrode.

Common misconception

Students often think that during electrolysis the charge carriers are electrons and not ions.

Revisit the structure of ionic compounds in the solid and liquid states. Point out that there are no delocalised electrons. The electrons are associated with ions and so are unable to move through the electrolyte. Ions can move in the liquid state.

Keywords

  • Molten - the term used to describe a liquid substance formed by heating ionic compounds and metal ores.

  • Anode - A positively charged electrode, in an electrolysis cell, to which the anions are attracted.

  • Cathode - A negatively charged electrode, in an electrolysis cell, to which the cations are attracted.

  • Anion - A negatively charged ion

  • Cation - A positively charged ion

Demonstrate or show a video of the electrolysis of molten zinc chloride. Point out that the bulb only lights up when all the solid has melted.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.
What is an ion?
Correct answer: an atom that has gained extra electrons
Correct answer: an atom that has lost some electrons
an atom that has gained extra protons
an atom with extra neutrons
an atom that has lost some protons
Q2.
When metal atoms react to form ions they ...
Correct answer: lose electrons.
gain electrons.
Correct answer: form positive ions.
form negative ions.
become a noble gas.
Q3.
Which of the following elements form negatively charged ions?
Correct answer: chlorine
magnesium
sodium
Correct answer: oxygen
neon
Q4.
How does a sodium atom become a sodium ion (Na⁺)?
it gains one electron
Correct answer: it loses one electron
it gains one proton
it loses a proton
it gains a neutron
Q5.
What is the total charge of an ionic compound?
+1
+2
Correct answer: 0
-1
-2
Q6.
What is electrolysis?
Correct answer: a process of using electricity to break down ionic compounds into their elements
a process of using heat to break down ionic compounds into their elements
a process of using pressure to break down ionic compounds into their elements
a process of using electricity to break down molecules into their elements
a process of using heat to break down molecules into their elements

6 Questions

Q1.
What happens when molten calcium chloride is electrolysed?
Correct answer: the Cl- ion is attracted to the anode
the Cl- is attracted to the cathode
the Ca2+ is attracted to the anode
Correct answer: the Ca2+ is attracted to the cathode
Q2.
What state must salts be in to conduct electricity for electrolysis?
gaseous
Correct answer: molten
Correct answer: dissolved
solid
Q3.
What is produced at the cathode during the electrolysis of molten sodium chloride?
chlorine gas
sodium chloride
Correct answer: sodium metal
Q4.
Why can molten salts conduct electricity?
the atoms are free to move
the electrons are free to move
Correct answer: the ions are free to move
Q5.
What happens to cations during electrolysis?
Correct answer: they gain electrons
they lose electrons
they remain unchanged
they gain protons
they lose protons
Q6.
What is the overall charge of the products formed during electrolysis?
+1
-1
Correct answer: 0
+2
-2