1

Negative Ions - Bromine

Negative ions are

attracted to the

positive electrode.

The positive electrode

is called the anode.

Negative ions are

called anions. Bromine

ions are anions.

2

Electrolysis Of Molten Lead Bromide

What are the products when molten lead bromide undergoes electrolysis?

Bromine gas forms at the anode (negative bromine anions are attracted to the positive anode).

The products are liquid lead and bromine gas.

Liquid lead forms at the cathode (positive lead cations are attracted to the negative cathode).

Half equation at the anode…

2Br-(l) - 2e- Br2(g)

Half equation at the cathode…

Pb2+(l) + 2e- Pb(l)

3

Electrolysis Of Potassium Nitrate Solution

What are the products when potassium nitrate solution undergoes electrolysis?

Oxygen gas forms at the anode.

The products are oxygen gas and hydrogen gas.

Hydrogen gas forms at the cathode.

At the anode…

4OH-(aq) - 4e- 2H2O(l) + O2(g)

At the cathode…

2H+(aq) + 2e- H2(g)

4

IT: Electrodes & Ions

5

IT: Ions

6

IT: Key Words

7

Extracting Aluminium - Cathode

During the extraction of aluminium the positive aluminium ions

(Al3+) are attracted to the negative electrode.

At the negative electrode (made of graphite) each aluminium ion

gains three electrons.

What is the half equation at the negative electrode (cathode)?

Al3+(l) + 3e- Al(l)

Molten aluminium forms at the graphite cathode.

Bauxite (aluminium oxide) is an ore used in the extraction of

aluminium. It is mixed with cryolite to lower its melting point (and

thus save money).

8

Exercise: Extracting Aluminium

1. What are the electrodes made from in the extraction of aluminium from its ore?

2. What is the electrolyte used in the process?

3. To which electrode are the aluminium ions attracted?

4. How many electrons does each aluminium ion gain at this electrode?

5. What is the half-equation at the cathode?

Graphite

Cathode

Al3+(l) + 3e- Al(l)

Three

Aluminium oxide and molten cryolite

9

Some Common Ores

Metal Ore

Aluminium

Iron

Lead

Sodium

Calcium

Potassium

Magnesium

Zinc

Bauxite

Haematite

Galena

Rock salt

Limestone

Silvine

Magnesite

Calamine

10

Roasting Galena

Galena is an ore of lead, lead sulfide (PbS).

Roasting galena:

Lead sulfide(s) + oxygen(g) lead oxide(s) + sulfur dioxide(g)

2PbS(s) + 3O2(g) 2PbO(s) + 2SO2(g)

If you roast galena in air, the oxygen in the air displaces the sulfur to form lead oxide.

Heating the lead oxide with carbon:

Lead oxide(l) + carbon(s) lead(s) + carbon dioxide(g)

2PbO(l) + C(s) 2Pb(s) + CO2(g)

11

Potassium

12

Oxygen

13

Exercise: Ionic Compounds

1. What sort of structures do ionic compounds form?

2. Name some ionic compounds.

3. What holds ionic compounds together?

4. Why do ionic compounds have high melting and boiling points?

5. Why will solid ionic compounds not conduct electricity?

Giant ionic lattices

The electrostatic attraction between oppositely charged ions

The strong forces of electrostatic attraction between adjacent oppositely charged ions

In solid ionic compounds the ions are not free to move, it is only when ionic compounds are aqueous or in the molten state that they will conduct electricity because then the ions are free to move

Sodium chloride, magnesium oxide, calcium chloride

14

Fractional Distillation

Crude oil is a mixture of various organic compounds. They are separated using the fact that the different compounds have different boiling points.

To separate crude oil it is heated in a fractionating column and allowed to boil. The various compounds rise through the column and then recondense at different temperatures. The compounds recondense in different fractions. Each fraction contains molecules with a similar number of carbon atoms.

As the number of carbon atoms increase in a molecule, the boiling point of the molecule also increases.

The fractionating column is hottest at the base, so as you move up through the column and through the various fractions the number of carbon atoms in the molecules decreases.

15

Fractionating Column

16

IT: Fractional Distillation

17

Exercise: Years Left

Give two reasons why the figures above are only estimates.

18

The Alkanes

19

Burning Alkanes

What happens when you burn methane in air?

Methane(g) + oxygen(g) carbon dioxide(g) + water(g)

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

What about ethane?

Ethane(g) + oxygen(g) carbon dioxide(g) + water(g)

2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)

alkane(g) + oxygen(g) carbon dioxide(g) + water(g)

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IT: Formula

21

IT: Naming Alkanes

22

Ethane