Electrolysis

Electrode - an electrical conductor which carries charge to or from a liquid undergoing electrolysis. Electrolysis Electrolysis is the break-down of a substance by electricity Electrolyte - a molten or aqueous solution through which an electrical current can flow. Lead bromide

Electrolysis experiments Electrolysis only happens in: - molten ionic liquids or - aqueous solutions containing ions. There must be a complete circuit. A lamp or ammeter shows that electricity is flowing around the circuit. This slide shows the basic equipment needed for electrolysis. If you have an interactive white board or the image is projected onto a normal white board, a student could be selected to label the diagram. A heat arrow could be added to show a molten electrolysis (which reiterates that ionic compounds have high melting points). No heat arrow is needed for solution electrolysis (which reiterates that many ionic compounds are soluble in water). It is important to reinforce that a circuit must be complete. This could be extended by a teacher drawing a wire between the 2 electrodes, which would make a short circuit, and posing the question as to whether electrolysis would happen. It would not, as the electricity would flow through the wire rather than the solution as the wire would have less resistance. It is vital that the electrodes are below the liquid surface, or again the circuit would not be complete. Please note that the circuit symbol for a lamp may be different, see your specification. Question to support this slide: Question 8 on page 117.

At the electrodes Anode (+) Cathode (-) (positive electrode) Negative ions go here (anions). As non-metal ions are negative, they go to the anode. Ions lose electrons. They are oxidised and become neutral atoms (which react together to form molecules). Cathode (-) (negative electrode) Positive ions go here (cations). As metal ions are positive, they go to the cathode. Ions gain electrons. They are reduced and become neutral atoms. This is an animated slide: when you click the left-hand mouse button once, the cathode statement will appear; click the button again and the contrasting anode statement will appear. This animation can be removed to have all text displayed by going into Slide Show, Custom Animation, then by highlighting each piece of text in turn and clicking (left-hand mouse key) Remove. This slide is colour-coded: red for anything which is positive (anode and cation); blue for anything which is negative (cathode and anion); and green for anything neutral. Questions to support this slide: Question 5 on page 117. Question 6 on page 117. Question 16 on page 138. Question 18 on page 139. Question 19 on page 139. Question 20 on page 139.

Electrode Observation Deduction Anode (+ve) Bubbles seen; smells like a swimming pool; bleaches litmus paper Chlorine gas is being given off Cathode (-ve) A pink solid forms on the electrode; black ppt is formed Copper solid is being deposited onto the electrode

Electrode Observation Deduction Anode (+ve) Brown gas is being formed Bromine vapour is produced Cathode (-ve) A silvery liquid forms underneath Molten lead is being formed