Summary notes for CIE IGCSE Chemistry Topic 5: Electricity and chemistry
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Course
Chemistry
Institution
GCSE
Complete revision notes for Topic 5 of the CIE IGCSE Chemistry course: Electricity and chemistry. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Define electrolysis as the breakdown of an ionic compound, molten or in aqueous solution,
by the passage of electricity
What sort of compound can conduct electricity?
YES:
Molten ionic compounds
Aqueous ionic compounds
When an electric current is passed through a molten/aqueous ionic compound the
compound decomposes or breaks down
NO:
Covalent compounds cannot conduct electricity hence they do not undergo electrolysis.
Ionic compounds in the solid state cannot conduct electricity either since they have no free
ions that can move and carry the charge.
Electrolysis key terms
Electrode is a rod of metal or graphite through which an electric current flows into or out of
an electrolyte
Electrolyte is the ionic compound in molten or dissolved solution that conducts the
electricity
Anode is the positive electrode of an electrolysis cell
Anion is a negatively charged ion which is attracted to the anode
Cathode is the negative electrode of an electrolysis cell
Cation is a positively charged ion which is attracted to the cathode
, DC (direct current) defines which electrode is the cathode and which is the anode.
State the general principle that metals or hydrogen are formed at the negative electrode
(cathode), and that non-metals (other than hydrogen) are formed at the positive electrode
(anode)
Describe electrolysis in terms of the ions present and reactions at the electrodes in the
examples given
KEY DIFFERENCE between molten ionic compounds and aqueous ionic compounds. Aqueous
solutions also contain H+ and OH– ions from the water, so the product produced at each
electrode depends on the relative reactivity of H+ and OH– vs. the ions in the ionic
compound.
Positive electrode (anode)
OH– ions and non-metal ions (anions) are attracted to the positive electrode
Two possible products:
o Oxygen
o Non-metal gas
Either OH– or non-metal ions will lose electrons and oxygen gas or gas of non-metal in
question is released, e.g. chlorine, bromine, nitrogen
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