QUESTION 1

This question has three sub-parts

(a) By showing outermost electrons only, draw dots and crosses diagrams to describe the bonding present in the following substances:

i) Ethene ii) Calcium Chloride

(b) State the following, giving an appropriate example-

i) Le Chatelier's Principle ii) Hess Law

(c) What is an Energy Profile diagram? Explain with a suitable example of your choice.

QUESTION 2

This question has two sub-parts

(a) Benzoic acid (C₆H₅COOH) and Sulphuric acid (H₂SO₄) are two different acidic substances.

Their pH values can be used to differentiate between them in aqueous solutions.

i) State one difference in terms of physical properties between them.

ii) State one difference in terms of chemical property between them.

iii) Explain what the term "pH value" means as fully as you can?

iv) Suggest suitable pH values for these two acids.

v) Give the name a substance commonly used in agriculture to control the pH of soils.

(b) A Chemist tested a sample of water and found it to contain 0.5 milligrams of Atrazine (a pesticide) in half a litre of water.

i) Suggest an appropriate analytical technique that can be used for the above.

ii) Express the above result in another unit of concentration.

iii) Describe briefly what the Chemist can do in order to be sure that any sample of water being tested is pure or no.

QUESTION 3

This question has two sub-parts

(a) Fats and proteins are natural macromolecular substances, they can be decomposed into simpler ones by heat, in the presence of acids or alkalis, being condensation polymers.
Addition polymers cannot be broken down in a similar way.

i) Draw the structure of the alcohol formed when fats are broken down.

ii) The organic product formed when a protein is broken down has 2 functional groups. Write the formulae of these groups.

iii) Give the name and draw the repeat unit structure of any addition polymer of your choice.

(b) Fresh milk gets spoiled faster when kept at ambient temperatures. Half-life studies can be used to show the relationship between temperature and spoiling of milk. As the latter gets spoiled it forms Lactic acid (2-hydroxypropanoic acid) a monobasic acid which can be titrated against standard Sodium hydroxide. Lactic acid can exist as optical isomers.

i) What do you understand by the term half-life?

ii) Calculate the Relative Molecular Mass of Lactic acid.

iii) If a 25cm³ solution of aqueous Sodium hydroxide at a concentration 0.2 mol/dm³ required 35 cm³ of Lactic acid for the titration, calculate the mass of lactic acid which was present.

iv) Draw the structural formulae of the isomers of Lactic acid.

QUESTION 4

Read the below text carefully and answer the questions which follow.
Copper metal is extracted from its ores such as Chalcopyrite (CuFeS₂) or Bornite (Cu₃FeS₃). The actual process involves different steps during which new Copper compounds are formed. In the first step, known as Roasting, Chalcopyrite is thermally decomposed into Copper (II) sulphide, Iron (II) sulphide and Sulphur at about 800 °C. In the following step, known as Smelting, one of the main reactions involves a hot mixture of Copper (l) oxide and Iron (II) sulphide which react reversibly to form Copper (I) sulphide and Iron (II) oxide. The enthalpy change for this reaction is - 82 KJ/mol. The industrially produced Copper finds many useful applications like electroplating of metallic objects and in the form of alloys.

(i) Apart from ores, state another way from obtaining Copper metal.

(ii) Calculate the percentage of Copper in the ore Bornite

(iii) With the help of a suitable diagram explain the bonding present in an alloy.

(iv) Construct a balanced chemical equation for the reaction in the Roasting step.

(v) Which of the substances involved in the above mentioned Smelting reaction gets oxidised ? Explain your answer

(vi) Which pair of compounds would be obtained in a greater proportion if a high temperature is used for the Smelting reaction. Explain your answer.

(vii) Briefly explain how a metallic frame can plated with Copper, by using a labeled diagram.

QUESTION 5

Read the below text carefully and answer the questions which follow.

Ethanoic acid is a weak acid. It is commonly used in the manufacture of vinegar. It can be synthetised industrially from Methanol and Carbon monoxide in a reactor at high temperature and high pressure in the presence of Cobalt (II) chloride. In a laboratory, these physical conditions may not be easily available. Thus, in a lab, Ethanoic acid is usually made by boiling under reflux Ethanol with an oxidising agent in presence of a mineral acid. When the solution mixture changes colour, it indicates the formation of the Ethanoic acid.

Water and ethanol form a miscible liquid pair, in order to separate them in the laboratory, fractional distillation must be performed.

(i) Construct a balanced equation for the industrial manufacture.

(ii) Suggest the role of the Cobalt (II) chloride? Give a reason for your answer.

(iii) Calculate the mass of Ethanoic acid formed if 75 dm³ of Carbon monoxide is used at Room Temperature Pressure.

(iv) Suggest why the Methanol - Carbon monoxide method may not be proper for a laboratory other than availability of conditions

(v) Describe a simple chemical test including any observations that can be made to confirm that an acid is formed as product in both methods

(vi) State the name of a suitable oxidising agent and the expected colour change for the chosen oxidising agent during the reaction.

(vii) If the Ethanoic acid is then allowed to react with the Ethanol or Methanol, a new organic compound is formed. Give the name of the family of organic compounds to which these compounds belong and write the full structural formula of any one of the two.

(viii) Explain why water and ethanol are miscible liquids.

(ix) State why the fractional distillation of mixture of ethanol and methanol is difficult?