Set 18 Chemistry [Paper] 2

1 SECTION A : ( 60 MARKS) Answer three questions from this section. 1. When 20cm3 of a gaseous alkyne P, , was exploded with 135cm3 of excess oxygen and on cooling to room temperature, the residual gas occupied a volume of 105cm3. When the residual gas was passed through concentrated sodium hydroxide solution, the volume decreased by 80cm3. (a) (i) Write the equation for combustion of P. (01½ marks) (ii) Determine the molecular formula of P. (03½ marks) (b) Write the st ructural formulae and names of possible isomers of P. (03 marks) (c) P reacts with sodium metal in presence of liquid ammonia to form compound Q. Identify; (@01 mark) (i) P (ii) Q (d) P was bubbled through ammoniacal silver nitrate solution. (i) State what was observed (0½ mark) (ii) Write equation for the reactio n (01 mark) (e) Write equation and suggest a mechanism for the reaction between; (i) P and a solution of bromine in tetrachloromethane (03½ marks) (ii) Q and 1 -bromopropane (02 marks) (f) With the aid of an equation, describe how P reacts with wat er. (3) 2. Some of the elements of group (II) of the periodic table are beryllium, magnesium, calcium, strontium and barium. (a) Write a general outermost electron configuration for the elements (01 mark) 2 (b) The table below shows the variation in first ionization energy and melting points of gr oup II elements. Element Be Mg Ca Sr Ba Atomic number 4 12 20 38 56 First ionization energy 899 738 589 549 502 Melting point(K) 1553 923 1123 1043 993 (i) On the same axes, plot graphs of first ionization energy and melting points of the elements against atom ic number. (6 ms) (ii) Explain the shapes of each of th e graphs in (b) (i) …