(a) (i) State the important points put forward in Dalton’s atomic theory.
(ii) How does the theory explain the law of multiple proportion?
(b) (i) Name three commercially useful products that may be obtained by chemical transformation of vegetable oils.
(ii) With the aid of equations, describe the chemical reaction involved in the transformations stated in (b)(i).
(c) Certain properties of Beryllium (Be) and its compounds differ from those of Magnesium (Mg) and its compounds, but rather resembles those of Aluminium and its compounds. Explain briefly why this is so.
(d) Write balanced equation for the reaction between iodine and aqueous sodium trioxothiosulphate(VI).
Explanation
(a) (i) – All elements consist of atoms which are indivisible
– Atoms can neither be created nor destroyed
– The atoms of an element are all alike but differ from those / atoms of other elements
– When atoms combine with other atoms they do so in simple ratios – All chemical changes result from the combination or separation of atoms
(ii) If A and B form more than one compound, since the atoms are indivisible, combination will be in (simple) integral ratios, as mass of atom of each element is fixed.
(b) (i) – soap – margarine – propan – 1,2,3 – triol / glycerine
Alkaline hydrolysis gives soap / propan-1,2,3-triol
(c) Atomic radii increases down the group and decreases across the period hence the size of Beryllium (Be) is about the same as the size of Aluminium (Al). The charge densities of Be(^{2+}) and Al(^{3+}) cause almost the same effect. OR
Periodic properties increase / decrease from left to right and decrease / increase down the group in the periodic table. A diagonal relationship / similar properties exist between a pair of diagonally adjacent elements in the second and third periods ofthe periodic table as in the case of Be and Al.
(d) I(_2) + 2Na(_2)S(_2)O(_3) → 2NaI + Na(_2)S(_4)O(_6)