Solid Covalent Non-Metals cannot conduct electricity because they do not have free electrons since all of them are taken to form bonds.

Some liquids conduct electricity

Electrolysis- The process in which an electrical current flows through a liquid compound or solution. During the process, the breakdown of an ionic compound (that can be molten or in aqueous solution)

→ To test electricity in liquids, we use an apparatus called Electrolytic Cell.

Key terms used in a simple electrolytic cell

• Electrode is a rod of metal or graphite through which an electric current flows into or out of an electrolyte;

• Electrolyte is the ionic molten compound or the aqueous solution that conducts the electricity;

• Anode is the positive electrode of an electrolysis cell;

• Cathode is the negative electrode of an electrolysis cell;

• Cation is a positively charged ion which is attracted to the cathode;

• Anion is the negatively charged ion which is attracted to the anode.

→ PANIC- Positive (is) Anode, Negative Is Cathode

Charge Transfer

During Electrolysis, current needs to flow around the circuit.

In order for this to occur, charge must be transfered around the circuit by charge carriers (the ions and electrons)

The power supply provides the Cathode with a supply of electrons causing it to become negatively charged.

Positive ions (cations) in the elctrolyte move towards the cathode where they gain electrons (cathode gives electrons to cations).

Negative ions (anions) in the electrolyte move towards the anode where they lose electrons (the anions give electrons to the anode)

The electrons move from the anode back towards the power supply and then towards the cathode.

→ Electrons are the charge carriers in the external circuit

→ Ions are the charge carriers in the electrolyte.

Electrolysis of Molten compounds

• A binary ionic compound is made of just two elements joined together by ionic bonding.

• When these compounds undergo electrolysis they always produce their corresponding elements.

To predict the products made at each electrode, firts identify the ions:

The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode;

Therefore, the cathode product will always be the metal, and the products formed at the anode will always be the non-metal (usually a gas).

Electrolysis of Solutions

Chemical reactions

• Electrolyses of ionic solutions also produces a chemical change;

• But the products obtained are different, because water itself produces ions.

To predict the products made at each electrode, we must follow these general principles:

• Metals or hydrogen are released at the negative electrode (cathode);

• Non-metals are formed at the positive electrode (anode). The exception is hydrogen;

• The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode;

Therefore the cathode product will always be the metal or hydrogen gas, and the product formed at the anode will always be the non-metal.

• During this reaction only a few water molecules decompose to produce 2 ions: H+ and OH- (most of the molecules will remain intact). These ions will compete with the ions from the salt to be discharged at the electrodes, but at each electrode, only one type of ion gets discharged.

• The ions that will win this battle and be discharged at the electrode will be the ones that are less reactive.

• The most reactive ions tend to stay as ions and will not be discharged at the electrodes.

If the metal is above hydrogen in the reactivity series, then hydrogen will be produced, and bubbling will be seen at the cathode.

The metal ion will remain at the solution.

The ions produced by the decomposition of the water moleculess are H+ and OH-. These ions will compete to be discharged with the other ions in the solution, but at each electrode, just one type of ion gets discharged.

Who wins this battle? In the first place, we must identify which ions are present

→ For cations, the ions that will win this “battle” and be discharged at the electrode will be the ones that are less reactive. The most reactive ions tend to stay as ions in the solution and will not be discharged at the electrodes

→For anions, it depends of several details:

• If there are halides, are the halides that will be discharged (react at the anode) and a halogen is produced;

• If there are no halides, are the hydroxide ions that will be discharged, producing water and oxygen.

• The more concentrated ion will tend to get discharged over a more dilute ion

If a concetrated halide solution is being electrolysed, the halogen forms at the anode.

If a dilute halide solution is being electrolysed, water and oxygen are formed

example: if in the solution there are 2 kinds of cations, such as H+ and Cu2+, Hydrogen is more reactive than copper, so hydrogen ions will remain in the solution and copper ions will be discharged to form metal atoms.

example: if in the solution there are 2 kinds of anion, such as OH- and any halogen (Cl-,Br-,I-), the halogens ions will give up electrons to the anode more easily, so hydroxide ions will remain in the solution and the halogens ions will form molecules (will be released as a gas).

→ At the anode, negatively charged ions lose electrons, so they are oxidised.

→ At the cathode, the positively charged ions gain electrons, so they are reduced.

→ Ionic half equations show the oxidation and the reduction of the ions involved.

→ It is important to make sure the charges are balanced.

OIL RIG - Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons

Chemical reactions can be used to produce electrical energy.

By using a fuel cell, it is possible to convert chemical energy into electrical energy.

A Hydrogen-Oxygen fuel cell uses the reaction between hydrogen and oxygen to produce electrical energy.

Hydrogen is used as fuel in rocket engines and in fuel cell to power some cars.

A Hydrogen Fuel Cell is an electrochemical cell in which a fuel (hydrogen) donates electrons at one electrode and oxygen gains electrons at the other electrode.

The hydrogen-oxygen fuel cell produces electricity by combining both elements, releasing energy and water. So, the products are not pollutants.

The overall equation for the reaction within a hydrogen fuel cell is:

hydrogen + oxygen —→ water

2H2 + O2 —→ 2H2O

• The air entering provides oxygen

• The fuel entering is hydrogen

• The only chemical product made is water

Aplications of electrolyses:

→ Manufacture of Aluminium

→ Manufacture of Chlorine, Hydrogen and Sodium Hydroxide

→ Electroplating

→ Hydrogen fuel cells

Manucture of Aluminium - is an industrial electrolyses of molten aluminium oxide (pg 258)

Manufacture of Chlorine, Hydrogen and Sodium Hydroxide - is and industrial electrolyses of Brine (sodium chloride solution) (pg 261)