What would you observe when zinc is added to a solution of iron( II ) sulphate? Write the chemical reaction that takes place.

Zinc is placed above iron in the reactivity series of metals. Zinc is more reactive than iron, hence it displaces the iron metal to form zinc sulphate when added to iron II sulphate. The colour of the solution fades from green to colourless due to the formation of zinc sulphate and greyish black iron metal is deposited. A single displacement reaction takes place. The chemical reaction is as follows: Zn s + FeSO 4 aq Pale green → ZnSO 4 aq Colourless + Fe s

Oil and fat containing food items are flushed with nitrogen. Why?

The condition produced by aerial oxidation of fats and oils in food marked by unpleasant smell and taste is called rancidity. So, oxygen from the air reacts with food substances and spoil them. On the other hand, nitrogen is an inert gas and does not easily react with most substances like noble gases. This is because it contains a triple bond between two nitrogen atoms and therefore it needs a lot of energy to break those bonds and participate in a chemical reaction. Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack, the rancidity of oil and fat containing food items can be prevented.

What does one mean by exothermic and endothermic reactions? Give examples.

The chemical reactions that release energy in the form of heat or light are called exothermic reactions. Example of exothermic reaction: When sodium metal is mixed with chlorine gas, it yields sodium chloride salt and a large amount of energy. Hence, it is an exothermic reaction. Na s + 1 2 Cl 2 g → NaCl s + 411 kJ The chemical reactions that absorb energy or require energy in order to proceed are called endothermic reactions. Example of endothermic reaction: White silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride in the presence of sunlight which results in the formation of silver and chlorine. Energy is absorbed from sunlight during the reaction. Hence, it is an endothermic reaction. 2 AgCl s → sunlight 2 Ag s + Cl 2 g

Translate the following statement into a chemical equation and then balance it. Hydrogen sulphide gas burns in the air to give water and sulphur dioxide.

A balanced equation is an equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charges is the same for both the reactants and the products. The balanced chemical equation for the reaction of hydrogen sulphide gas in air is: 2 H 2 S g Hydrogen sulphide + 3 O 2 g Oxygen → 2 H 2 O l Water + 2 SO 2 g sulphur dioxide

Translate the following statement into a chemical equation and then balance it. Hydrogen gas combines with nitrogen to form ammonia.

A balanced equation is an equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charges is the same for both the reactants and the products. The balanced chemical equation for the reaction of hydrogen with nitrogen to form ammonia is: 3 H 2 g + N 2 g → 2 NH 3 g