electrolysis and extraction

Question 1

1:55 (Triple only) understand why covalent compounds do not conduct electricity

Answer 1

Covalent compounds do not conduct electricity because there are no charged particles (delocalised electrons) that are free to move.

Question 2

1:56 (Triple only) understand why ionic compounds conduct electricity only when molten or in aqueous solution

Answer 2

Ionic compounds only conduct electricity only when molten or in solution.

When solid the ions are not free to move.

When molten or in solution the ions are free to move.

Question 3

anion

Answer 3

negative ion

Question 4

cation

Answer 4

positive ion

Question 5

1:58 (Triple only) describe experiments to investigate electrolysis: molten compounds

Answer 5

molten compounds:

1. Solid lead bromide is heated and becomes molten so ions become free to move
2. Electrodes attached to a power source are placed in the molten lead bromide. these electrodes are made of either graphite or platinum because both conduct electricity and are fairly unreactive
3. At the anode a brown gas is given off. This is bromine gas (Br2(g)). Negatively charged bromide ions are attracted to the anode (positive electrode). At the anode, bromide ions lose electrons (oxidation) and become bromine
4. At the cathode a shiny substance is formed. This is molten lead (Pb(l) ). Positively charged lead ions are attracted to the cathode (negative electrode). At the cathode, lead ions gain electrons (reduction) and become lead atoms.

lead bromide –> lead + bromine

Question 6

1:58 (Triple only) describe experiments to investigate electrolysis: ionic solutions

Answer 6

At the cathode:

Metal ions and hydrogen ions are positively charged. Whether you get the metal or hydrogen during electrolysis depends on the position of the metal in the reactivity series:

The metal will be produced if it is less reactive than hydrogen
Hydrogen gas (H2) will be produced if the metal is more reactive than hydrogen

At the anode:

At the anode, the product of electrolysis is always oxygen gas (O2) unless the solution contains a high concentration of Cl–, Br­- or I– ions, in which case a halogen is produced, e.g. chlorine gas (Cl2), bromine gas (Br2), and iodine gas (I2).

Question 7

electrolysis of sodium chloride solution (NaCl(aq))

Question 8

electrolysis of copper sulfate solution (CuSO4(aq))

Question 9

electrolysis of sulfuric acid (H2SO4(aq))