Electrolysis of Sodium Chloride

Electrolysis of Sodium Chloride

Aim: To investigate the electrolysis of Sodium Chloride solution of various concentrations through redox reactions.

Introduction: Electrolytic Cells consist of a single compartment (1 beaker) which holds the two electrodes which are connected to an external source of DC power. The voltage from the battery pushed electron onto the negative electrode (cathode). On the cathode, a reduction reaction occurs, while on the anode and oxidation reaction occurs.

During the reaction of a dilute solution NaCl in a Electrolytic Cell with inert electrodes (graphite), the electrons will be transferred through an external DC power source, from the anode to the cathode. This means that on the cathode, reduction of water occurs as it is less reductive than the having Na+ ions reducing into Na(s). The equation of water reducing is:

H2O + e- ---> 1/2H2+OH-

On the anode is being oxidized, as again water is more likely to oxidize than Cl+ ions into Cl(g). The equation for water oxidizing in a dilute solution of NaCl is:

H2O ---> 1/2O2(g) +2H+ + 2e-

The above two equations are true for any concentration of NaCl less than 2.0mol/L (the definition of a ‘dilute’ solution).

For a concentrated solution of NaCl (>2.0mol/L) the reduction reaction on the cathode remains the same as a dilute solution of NaCl, as water will still be more reductive than sodium. But instead of water oxidizing on the anode, Chlorine ions are oxidized to form Chlorine gas. This is because of the high concentration of the Chlorine ions in the 1/2Cl2(g) +e-

Hypothesis: If a concentrate solution of NaCl is put through electrolysis, then H2O will be reduced and Chlorine will be oxidized.

AND

If a dilute solution of NaCl is put through electrolysis, then H2O will be both reduced and oxidized.

Method/Materials: See page 43 of Practical Manual

Results:

|0.001mol/L

NaCl |0.1mol/L

NaCl |2.0mol/L

NaCl | |Observation at anode |Red |Red...