Electrolysis is the decomposition of a compound into its elements by an electric current. It is often used to extract metals that are high in the reactivity series and can be used to produce non-metals such as chlorine.

• The electrolyte is the compound that is decomposed, it is either a molten ionic compound or a concentrated aqueous solution of ions

• The electrodes are rods, made from either carbon or metal which can conduct electricity to and from the electrolyte

• The anode is the positive electrode or attracts anions

• The cathode is the negative electrode or attracts cations

• Cathode gets fatter

• Power supply must be direct current

Cathode: Zn2+ + 2e- => Zn

Anode: 2Cl- => Cl2 + 2e-

Overall reaction: Zn2+ + Cl2-/ZnCl => Zn + Cl2

Faraday is the quantity of electric charge carried by 1 mole of electrons or 1 mole of singly charged ions. Its value is 96500 C/ mol.

• Redox equilibrium is established when the rate of electron gain equals to the rate of electron loss

• For unreactive metals, ie Cu, the equilibrium lies further to the right •

• For reactive metals, ie V, the equilibrium lies further to the left

• The position of equilibrium differs for different combination of metals placed in solutions of their ions

• We cannot measure directly the electric potential (voltage) of the metal and metal ions in solution.

• But we can measure the difference in potential between metal/metal ions system and another system(normally standard hydrogen electrode

Electrical double layer, region of molecular dimension at the boundary of two substances across which an electrical field exists. The substances must each contain electrically charged particles, such as electrons, ions, or molecules with a separation of electrical charges (polar molecules).

The standard electrode potential for a half cell is the voltage measured under standard conditions with a standard hydrogen electrode as the other half cell

Standard conditions and requirements:

• Concentrations of ions at 1.00 mol/ dm3

• Temperature of 25 C (298K)

• Any gases should be at a pressure of 1 atmosphere( 101KPa)

• Salt bridge to allow movements of ions

• Glass bell with a hole to allow hydrogen to escape

The standard cell potential is the potential difference between the cathode and anode

• Electrode potential values give us an indication of how easy it is to reduce a substance

• The more positive (or less negative), the easier it is to reduce the ions on the left

• The more negative (or less positive), the more difficult it is to reduce the ions on the left

• The E values shows us that Cu2+ ions are easier to reduce than H+ ions( they have a more positive E value)

• Cu2+ ions are more likely to gain electrons then H+ ions

• So Cu2+ ions will accept electrons from the hydrogen half-cell and H2 will lose electrons to the copper half-cell

• The E values shows us that Cl2 ions are easier to reduce than H+ ions because they have a more positive E value

• Cl2 ions are more likely to gain electrons than the H+ ions

• So Cl2 ions will accept electrons from the hydrogen half cell and H2 will lose electrons to the chloride half cell

All the drawings are different, take note that metal and non metal electrode is exposed to both the gas and ions while ion electrode is fully exposed to the electrolyte

• If [Fe3+] is greater than 1.00mol/ dm, the value of E becomes more positive

• If [Fe2+] is greater than 1.00mol/ dm, the value of E becomes more negative

• Valid prediction if E standard difference is greater than 0.30 V

The effect of concentration and temperature on the value of E can be deduced using the nerst equation

• E is the electrode potential under non standard conditions

• Eθ is the standard electrode potential

• R is the gas constant, 8.314 J/ kmol

• T is the temperature in kelvin

• z is the number of electrons transferred in the reaction

• F is the faraday constant, 96500 C/ mol

• [oxidised] and [reduced] referes to the concentration of the oxidised form and reduced form respectively