Regional Mock chemistry 2007 paper 3

1. Describe briefly, indicating the scientist responsible, experiments that gave the following evida,riee7RT¬the model of an atom:
a) The atom consists of a very tiny, thickly dense positively charged nucleus, surrounded by a negatively charged electron cloud.
b) The nucleus contains a specific number of protons, positively charged particles that gives the atomic number.
c) Neutrons together with the protons in the nucleus account for the atomic weight.

 

 

2)

a) Describe how the presenceof Bromine, Nitrogen and suljhur in an organic compound can be identified.
b) An organic compound contains- carbon, hydrogen and oxygen only. On complete combustion in excess oxygen, 20.63 g of the compound yielded 57.94 g of carbondioxide and 11.85 g of water. Given that the molecular formula of the compound is the same as its empirical formula:
i) Determine the empirical formula of the substance.
ii) Suggest a plausible structure of the compound
iii) Write a chemical equation for the reaction of the compound with aqueous bromine:

 

 

3)
a) “The first member of a group in the Periodic Table of elements always shows some abnormal
chemical and physical properties fi.om all other members of the group.” Support this statement by
making reference to the first members of Groups I, It, IV and VII elements of the Periodic Table.
b) What is diagolud reAationship? Select two elements and explain how they are diagonally related.

 

 

4) a) What do you understand by the following:
i) Electronegativity.
n) An intermolecular force.
b) ” The following are electronegativity values of some elements.

 

Elements                      Na             Mg          Zn         Pb          H     Cl       O

eletronegativity         0.9           1.2             1.6          1.8        2.1    3.0  3.5

 

 

 

Use the electronegativity values to • identify and describe the bond type of each of the compounds formed between; i) Sodium and Oxygen, ii) Hydrogen and Chlorine.
For each of the co mpounds, state TWO physical properties and show how they are related to the bond type esent.
c) Identify and describe the type(s) of intermolecular forces present in the compounds formed in b(i) and b(ii) above.

 

 

5 a) For each of the reactions below, describe a suitable reaction mechanism, stating the reaction conditions and naming the major products
i) Nitrobenzene and Chloromethane
ft) 2-chloro-2-methyl propane and aqueous potassium hydroxide.
iii) Propanone and hydrogen cyanide.
iv) iodoethane and sodium hydroxide in ethanol.
b) i) Discuss the bonding and extra.stability of benzene,
ii) Using suitable examples, compare the reactivity of benzene and ethane,

 

 

6 a) . For each of Nitrogen-and Sulphur, give the formula and name of the stable compounds with the following oxidation states:
i) Nitrogen: -3, -2 and +5.
ii) – Sulphur: -2, +2 and +7.
b) Describe the ‘major stages, including the physico-chemical principles in the industrial manufacture of sulphuric acid from elemental sulphur.
c) Give’ TWO large scale uses each, of sulphuric acid and nitric acid.

 

 

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