C2: Electrolysis

For electrolysis, you must know the 4 state symbols:

(s) = solid

(l) = liquid

(g) = gas

(aq) = aqueous solution

When an ionic substance is melted or dissolved in water, the ions are free to move about within the liquid or solution

electrolysis = passing an electric current through ionic substances that are molten or in solution to break them down into elements

During electrolysis, atoms become ions

The positively charged ions move to the negative electrode(Cathode)

The negatively charged ions move to the positive electrode (Anode)

For the atoms to become ions, electrons are either lost (oxidation) or gained (reduction) by the atoms. For you to remember this just use OIL RIG:

O = oxidation

I = is

L = loss (of electrons)

R = reduction

I = is

G = gain (of electrons)

1. The electrodes are made of copper. The impure copper is at the anode (positive electrode) and the pure copper is at the cathode (negative electrode).

2. The copper ions (Cu2+) move from the electrolyte to the cathode (negative electrode) where they then gain 2 electrons (reduction) to form copper.

3. The copper atoms in the impure copper at the anode (positive electrode) lose two electrons (oxidation) to form copper ions (Cu2+). These electrons dissolve in the electrolyte.

4. As the copper ions are released at the positive electrode (anode) the impurities are set free and collect at the bottom.

The reaction at each electrode can be shown using half equations

At the negative electrode (cathode):

Cu2 (aq) + 2e- > Cu (s) (reduction)

At the positive electrode (anode):

Cu (s) > Cu2 (aq) + 2e- (oxidation)

This shows that the purification of copper is a redox reaction as both oxidation and reduction have happened in the same reaction

1. The electrolyte is the Sodium Chloride Solution (Brine). The negative chloride ions (Cl-) form the electrolyte are attracted to the positive electrode (anode) Here, each Cl- loses an electron to form Cl atoms (oxidation), which then form molecules of Chlorine gas (Cl2).

2. At the cathode (negative electrode) the H+ ions gain electrons to make Hydrogen atoms (reduction) which then form hydrogen molecules (H2).

3. Na+ and OH- ions are left behind, which form a solution of sodium hydroxide (NaOH)

4. The products produced are chlorine gas, hydrogen gas and sodium hydroxide

The half equations for the electrolysis of brine (sodium chloride solution) are:

At the positive electrode (anode):

2Cl- (aq) > Cl2 (g) + 2e (reduction)

At the negative electrode (cathode):

2H+ (aq) + 2e > H2 (g) (oxidation)

This shows that the electrolysis of brine (sodium chloride solution) is a redox reaction as both oxidation and reduction occured in the smae reaction

Hydrogen:

• used in the maufacture of margarine
• used to produce hydrochloric acid which is used in cleaning materials, manufacturing food and medicine as well as cosmetics

Chlorine:

• used in water and sewage treatment
• used in the maufacture of textiles and solvents, drugs to treat heart disease, leukaemia and arthiritis

Sodium hydroxide:

• purifies petroleum and matural gas
• degreases metals
• water and sewage treatment
• used to manufacture paper, aluminium and soaps/detergents