UNIT 5 CHEMISTRY EXAM - (A1 INORGANIC CHEM)

1. What do metal oxides react with to produce?

2. Why are metal oxides basic?

3. What is a base?

4. What is an alkali?

1. Acid

2. They reaction to neutralise acids and have a pH greater than 7

3. A base neutralises acids

4. An alkali is a base that dissolves in water

What is the general equation for metal oxides?

Metal oxide + acid → salt + water

1. What is the formula for Alumina?

2. What happens to Alumina when you mix it with an acid or mix it with a base?

3. Why is it amphoteric?

4. What type of bonding is present in alumina?

1. Al₂O₃

2. If you mix it with an acid, it’ll act as a base, if you mix it with a base, it’ll act as an acid

3. Alumina can act as both and acid and a base (it will not dissolve)

4. Ionic bonding

What are the chemical and physical properties of alumina?

• High mpt and bpt

• Thermal conductivity- conducts when molten not aqueous

• Electrical conductivity- conducts when molten not aqueous

Explain why alumina can be used in refractories

• High mpt- can withstand high temps without melting

• chemically stable at high temps- won’t take part in the reaction

Describe the Bayer Process

1. Reaction with sodium hydroxide - reacts to make sodium aluminate which is soluble

2. Filtration - the impurities in the ore are not soluble, so the impurities can be filtered out

3. Precipitation - The reaction mixture is cooled and seeded with Al(OH)₃ which causes precipitation

4. Heating - The aluminium hydroxide is dehydrated by heating to 1000-1200 °C, to remove water and form aluminium oxide

What happens in the Hall-Héroult process?

• Extracts aluminium from aluminium oxide (Al₂O₃).

• Aluminium oxide is dissolved in molten cryolite

• Cryolite lowers the melting point of aluminium oxide, making electrolysis easier

• Electrolysis is used to separate aluminium from oxygen.

• Al³⁺ ions move towards the negative cathode and gain electrons to form molten aluminium.

• O²⁻ ions move towards the positive anode and lose electrons.

• The oxygen reacts with the carbon anodes, producing CO₂.

• Molten aluminium collects at the bottom of the cell and is removed.

1. What is the half equation for alumina?

2. Why does the Hall-Héroult process require large amounts of energy?

1. Al³⁺ + 3e⁻ → Al, 2O²⁻ → O₂ + 4e⁻

2. The alumina needs melting & electrolysis requires energy

Why is electrolysis of molten ionic compounds expensive?

• They need to be at high temperatures to melt the compounds

• Large amounts of energy is needed for electrolysis

How do you determine the products and state symbols of the electrolysis of aqueous compounds?

At the anode:

If a group 7 ion (F₂,Cl₂,Br₂,I₂) is present, it will always be produced. If not, make oxygen from OH⁻ ion.

At the cathode:

Hydrogen will be produced, unless the metal ion is less reactive (Cu, Ag, Au, Pt)