Electrolysis

When Calcium Chloride solution is electrolysed, what products are formed at the negative Cathode and the positive Anode?

Specify which product is oxidised and which is reduced.

[4 mark]

Visual Mark Scheme Breakdown

• Ions in Calcium Chloride?

  Cl negative ion (since it gains an electron)

  Ca positive ion (since it loses an electron)

• Ions in Water?

  Solution means dissolved in Water.

  Water splits up into H+ and OH-

• Which electrode is each ion attracted to?

  Negative ions (OH- and Cl-) are attracted to the positive Anode.

  Positive ions (Ca2+ and H+) are attracted to the negative Cathode.

• Which ion wins at the Cathode?

  At the negative electrode (Cathode), the LESS reactive ion wins.

  Hydrogen is less reactive than Calcium so H+ wins.

• So what product is formed at the Cathode?

  H+ ions gain negative electrons at the Cathode.

  So Hydrogen gas is formed at the Cathode. (1 mark)

  According to OIL RIG, Reduction is Gain of electrons.

  So Hydrogen has been Reduced. (1 mark)

• Which ion wins at the Anode?

  At the positive electrode (Anode), if there is a Halide ion (Group 7), it wins. Otherwise OH- wins.

  Cl is in group 7 so it wins.

• So what product is formed at the Anode?

  H+ ions gain negative electrons at the Cathode.

  So Chlorine gas is formed at the Anode. (1 mark)

  According to OIL RIG, Oxidation is Loss of electrons.

  So Chlorine has been Oxidised. (1 mark)