QUESTION 1

(a) What key terms best matches the following statements or definitions?

i. Atoms of the same element having the same atomic number but different mass numbers.

ii. Sub-atomic particle of negligible mass orbiting around the nucleus of an atom.

iii. The process by which a soluble solid can be separated from a liquid.

iv. The amount of substance which contains the same number of particles as there are atoms in exactly 12 grams of carbon-12.

v. Elements of the periodic table having high melting and boiling points and forming coloured salts.

vi. Compound formed when a reactive metal reacts with a non-metal by transferring electrons to form oppositely charged particles.

vii. Very strong forces of attraction that occur between molecules of a compound having a hydrogen atom bonded to a highly electronegative atom.

viii. The energy change that occurs during a chemical reaction.

ix. Process by which metal ions in a solution are moved by an electric current to coat an electrode.

x. Substance that increases the rate of a reaction without actively taking part in the reaction.

(b) 15.3 g of aluminium reacted with 13.6 g of oxygen gas (O2) to form an oxide.

i. Express this in moles.

ii. How many moles of oxygen gas will react with one mole of X?

iii. What is the simplest formula for the oxide?

QUESTION 2

(a) In green parts of plants, the sugar (C₆H₁2O₆) and oxygen (O₂) are developed from carbon dioxide (CO₂) and water (H₂O) according to the following reaction:

6CO₂(g) + 6H₂O(l) chlorophyll C₆H₁2O₆(s) + 6O₂(g) light

The sugar from ripe fruit changes to ethanol (C2H5OH) and carbon dioxide under the influence of wine fermentation yeasts:
C₆H₁2O₆(s) Yeasts 2C₂H₅OH(l) + 2CO₂(g)

You conduct an experiment in the laboratory, where you produce wine by fermenting pulpy apricots for 15 days. The wine formed during the reaction is separated from the fruit residue and the ethanol produced is removed using various separation techniques.

i. Describe with the aid of diagrams two techniques would you use to separate ethanol from the fermentation mixture in the laboratory?

ii. How you would test for the gas liberated during the fermentation process?

Describe your observations

iii. Describe your observations and write down the products that would form if the ethanol collected in a. above was:

1. heated in a test tube

2. ignited.

b. With the need for renewable energy sources, ethanol is being considered as an alternative. Ethanol has a standard enthalpy of combustion of -1370.7 kJ/mol.

i. Define the term standard enthalpy of combustion.

ii. Write a balanced chemical equation for the complete combustion of ethanol.

iii. Is the combustion of ethanol an endothermic or an exothermic process?

iv. Given your answer to iii, what can you say about the entropy of the reactants and products of the above process?

QUESTION 3

(a) A 0.382 g sample of magnesium was mixed with 2.652 g of nitrogen gas (N₂). A chemical reaction took place, and the only product was magnesium nitride (Mg₃N₂). After the reaction was complete the mass of unreacted nitrogen was found to be 2.505 g.

i. Write a balanced equation for this reaction.

ii. What mass of magnesium nitride was produced?

iii. Calculate the percentage composition by mass of magnesium and nitrogen in magnesium nitride.

iv. What mass of magnesium would be present in 27.35 g of magnesium nitride?

v. If you only had 3.726 g of nitrogen gas available, what is the maximum mass of magnesium that you could convert into magnesium nitride?

(b) Baking soda (NaHCO₃) is often used as an antacid. It neutralizes excess hydrochloric acid (HCl) in the stomach to form sodium chloride, water and carbon dioxide.

Milk of magnesia, which is an aqueous suspension of magnesium hydroxide (Mg(OH)₂), is also used as an antacid, which neutralizes hydrochloric acid to form magnesium chloride and water.

i. Write balanced chemical equations for the reaction of baking soda and milk of magnesia with hydrochloric acid.

ii. Which is the more effective antacid per gram?

QUESTION 4

(a) One of the reactions that occur in the catalytic converter in the exhaust system of a car engine is

2???? ?? + 2???? ?? ↔ ??₂ ?? + 2????₂ ?? Δ?? = -745 ??????????-1

This reaction, which converts two poisonous gases into two harmless gases, is a dynamic equilibrium. The temperature in the catalytic converter is high.

i. What do you understand by the term dynamic equilibrium?

ii. State Le Chatelier's Principle.

iii. State and explain what would happen to the equilibrium if the temperature in the catalytic converter is lowered

iv. The gases from the engine are however not cooled before entering the converter. Suggest a reason why.

v. Discuss the benefits of using a catalyst in the above system in terms of:

1. The equilibrium involved

2. The kinetics of the reaction.

b. Chlorine is used for the manufacture of many familiar materials; hydrochloric acid is the cheapest industrial acid, sodium chlorate (I) is used as bleach and disinfectant. Chlorine and sodium hydroxide are produced during electrolysis in a membrane cell.

i. What electrolyte is used?

ii. State the gaseous products formed at the electrodes.

At the anode:

At the cathode:

iii. Write the chemical equation for the overall reaction that occurs in the membrane cell.

iv. Give one piece of evidence that the reaction in part iii. Above cannot occur without electrolysis