RP3 Electrolysis

Question 1

how do you set up a general electrolysis experiment?

Answer 1

• place the positive and negative electrodes in a beaker containing a molten or dissolved ionic compound
• connnect both electrodes to a power supply with wires

Question 2

how could you investigate what happens when an aqueous solution of CuCl2 is electrolysed?

Answer 2

• half fill a beaker with aqueous CuCl2
• place a lid on the beaker and insert the electrodes into the solution through holes in the lid (electrodes must not touch)
• connect the electrodes to a low voltage power supply
• switch the power supply on to 4V
• turn off the power after a few minutes and record any observations

Question 2

what forms at the cathode and the anode in electrolysis?

Answer 2

cathode: metals or hydrogen
anode: non-metals

Question 2

what would you observe at each electrode when copper chloride solution is electrolysed?

Answer 2

positive electrode: bubbles of gas (chlorine)
negative electrode: electrode coated with a brown solid (copper)

Question 2

why must the positive electrode (anode) be regularly replaced?

Answer 2

the positive electrode is made of carbon and will react with oxygen to produce carbon dioxide

Question 2

what would you observe at each electrode when copper chloride solution is electrolysed?

Answer 2

positive electrode: bubbles of gas (chlorine)
negative electrode: bubbles of gas rapidly produced (hydrogen)

Question 3

in the electrolysis of NaCl hydrogen is produced at the cathode. why is sodium not produced?

Answer 3

hydrogen is produced because sodium is more reactive than hydrogen.
sodium remains in the solution.

Question 3

write half equations for the reactions that occur at the electrodes when aqueous CuCl2 is electrolysed

Answer 3

cathode: Cu2+ + 2e- –> Cu
anode: 2Cl2- –> Cl2 + 2e-

Question 4

write half equations for the reactions that occur at the electrodes when aqueous NaCl is electrolysed

Answer 4

cathode: 2H+ + 2e- –> H2
anode: 2Cl- –> Cl2 + 2e-

Question 5

how could you test that chlorine gas was produced at the anode?

Answer 5

the gas produced will bleach damop litmus paper - it will turn white

Question 6

how could you test the hydrogen gas was produced at the anode?

Answer 6

the gas produced will make a squeaky pop with a lighted splint

Question 7

how could you test that oxygen was produced at the anode?

Answer 7

the gas produced will relight a glowing splint