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ELECTRICITY AND CHEMISTRY YEAR 10 NOTES

The following are things required for you to know.

Define electrolysis as…
● The breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity

Describe the electrode products and the observations made during the
electrolysis of:

molten lead(II) bromide, concentrated hydrochloric acid,
concentrated aqueous sodium chloride, dilute sulfuric acid between inert
electrodes (platinum or carbon)

Make sure you remember the following.

● When you have a ionic solution (NOT a molten ionic compound),

your solution will contain:

the ions that make up the ionic compound, and the ions in water
● (OH- and H+)
● at the cathode- negative electrode (-), the following ions move there:
○ hydrogen (from H+in water) is produced UNLESS the + ions in the ionic
compound are from a metal less reactive than hydrogen
○ if the metal is less reactive, it will be produced instead
● at the anode- the positive electrode  (+):
○ oxygen (from OH in water) will be produced UNLESS the ionic compound
contains halide ions (Cl-, Br-, I-)
○ if there are halide ions, the halogen will be produced instead (e.g. Cl2)

CASE STUDY

● Electrolysis of:
○ Molten lead (II) bromide
■ Pb2+ since it is positive moves to cathode, Pb (s) is produced (not in solution so these are
the only + ions present)
■ Br- since it is negative moves to anode, Br2(l) is produced (not in solution so these are the
only – ions present)

CASE 2
○ Concentrated hydrochloric acid

IONS CONTAINED

■ H+
ions go to cathode, H2(g) is produced (H+is present in both
water and HCl)
■ Cl- ions go to anode,

Cl2(g) is produced (Cl- are halide ions), Chlorine ions are preferentially discharged compared to OH ions in a concentrated solution.

CASE 3

○ Sodium chloride solution
■ H+ions go to cathode,

H2(g) is produced (Na is more reactive than
hydrogen THEREFORE HYDROGEN IS PREFERENTIALLY DISCHARGED)
■ Cl-  ions go to anode,

Cl2(g) is produced (Cl- are halide ions and are preferentially discharged more than OH ions of water)

○ Dilute sulfuric acid. [Ions present H+ and SO4 From sulfuric acid, and H+ AND OH from WATER]
■ H+to cathode,

H2 (g) is produced (these are the other ions present in sulfuric acid H2SO4)
■ OH to anode, O2
(g) is produced (SO4
2- ions are not halide ions)

Relate the products of electrolysis to the electrolyte and
electrodes used,

aqueous copper(II) sulfate using carbon electrodes and using copper
electrodes (as used in the refining of copper)

● Electrolysis of copper (II) sulfate solution
o Cu+ions go to cathode, Cu (s) is produced (Cu is less reactive than
hydrogen)
o OH ions go to anode, O2(g) is produced (SO4
2- ions are not halide ions)Copper electrodes:
● set up:
o anode is made of impure copper (that you are purifying)
o cathode is made of pure copper
o the solution is copper sulfate
● what happens:
o Cu2+ ions from the anode move to the cathode, where they gain electrons
and are discharged as pure copper
o impurities form as sludge below the anode
● the cathode will increase in mass as it gains pure copper, whilst the anode will
lose mass as copper ions are lost (they replace the ones from the CuSO4 solution
that go to the cathode) and so are impurities

Carbon electrodes :
● at the cathode Cu (s) is produced (Cu is less reactive than hydrogen)
● at the anode O2
is produced (SO4
2- ions are not halide ions)
● this leaves H
+ and SO4
2- ions in the solution, which will react to form H2SO4
-sulfuric acid The solution therefore will have a lower pH.

Describe electrolysis in terms of the ions present and
reactions at the electrodes in the examples given

● During electrolysis, positively charged ions (cations) move to the negative
electrode (cathode), and negatively charged ions (anions) move to the positive
electrode (anode).
● Ions are discharged at the electrodes producing elements.

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)

Predict the products of the electrolysis of a specified binary compound in the
molten state
● if ionic compounds are molten it is much more simple to predict the products of
electrolysis as there are no ions present except those in the ionic compound:
○ identify which ions there are within the ionic compound
○ the + ions will go to the cathode
○ the – ions will go to the anode

 Predict the products of electrolysis of a specified halide in
dilute or concentrated aqueous solution
● Halide ions are negative ions e.g. Cl-, Br, I-etc…

o Therefore, they go to the positive electrode (anode) and the product will
be either Cl2 or Br2 or I2 dependent on which halide ions are in the
solution
Describe the electroplating of metals
● electroplating is a method of coating objects with a metal, using electrolysis
● Negative electrode = object to be electroplated
● Positive electrode = metal to coat the object with
● Electrolyte = solution of the coating metal (with ions of the coating metal in)
● the metal ions from solution are deposited on the negative electrode, and metal
ions are released from the positive electrode to replace those lost in solution
Outline the uses of electroplating
● Coating a cheaper metal with a more expensive one e.g. silver or copper
● Silver
o E.g. Cutlery
● Copper
o E.g. Metal pan

 Construct ionic half-equations for reactions at the cathode
● This is an example of a half equation; the small number
is always the same as the 2 larger numbers within the
equation. & electrons are represented by the symbol ‘e-‘
● writing half equations for the reactions at each
electrode:
○ negative electrode: X+-> X, so ionic equation must be:X+ + e–> X, electrons gained, so positive ions are reduced
○ positive electrode: X–> X, so ionic equation must be:X–> e- + X, electrons are lost, so negative ions are oxidised
● Oxidation Is Loss (of electrons) and Reduction Is Gain (of electrons) – OIL RIG
● ANODE – loss of electrons, oxidation (positive electrode) anions come to it
● CATHODE – gain of electrons, reduction (negative electrode) cations come to it

Describe the reasons for the use of copper and (steel-cored) aluminium in
cables, and why plastics and ceramics are used as insulators
● Aluminium – good conductor of electricity, therefore is used in overhead power
cables
● Copper –good conductor of electricity, therefore is used for electrical wiring
● Plastics & ceramics do not conduct electricity – therefore they are used as
insulators
 Describe the transfer of charge during electrolysis to
include: the movement of electrons in the metallic conductor, the removal
or addition of electrons from the external circuit at the electrodes, the
movement of ions in the electrolyte
● Movement of electrons in the metallic conductor
o Electrons move in the wire
o Move from positive electrode to negative electrode
● Movement of ions in the electrolyte
o Positive ions move to negative electrode to receive electrons and are
reduced
o Negative ions move to positive electrode to lose electrons and are
oxidised

Describe the production of electrical energy from simple
cells, i.e. two electrodes in an electrolyte (this should be linked with the
reactivity series)
● This is a very similar set up to electrolysis, but isn’t the same
● you have 2 metal electrodes in an electrolyte solution and connect the 2
electrodes by a wire (outside of the solution), this creates a current of electrons
and so creates electrical energy
● More reactive metal will lose electrons, least reactive will gain them

Describe, in outline, the manufacture of: aluminium from
pure aluminium oxide in molten cryolite, chlorine, hydrogen and sodium
hydroxide from concentrated aqueous sodium chloride (starting materials
and essential conditions should be given but not technical details or
diagrams)
● Aluminium is manufactured by the electrolysis of a molten mixture of aluminium
oxide and cryolite using carbon as the positive electrode (anode).
o Aluminium oxide has a very high melting point, so it would be too
expensive to melt it, which is why it is mixed with cryolite
o the positive electrodes need to be continually replaced because oxygen is
formed, which reacts with the carbon of the positive electrodes, forming
carbon dioxide, and they gradually burn away
● Sodium chloride
o Chlorine gas forms at the positive electrode
o Hydrogen gas forms at the negative electrode
o Solution of sodium hydroxide forms
o Must use inert electrodes since the products are reactive

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Electricity & Chemistry (Multiple Choice) QP