(a) State three characteristic properties of
(i) electrovalent compounds;
(ii) alpha particles
(iii) catalysts
(b)(i) Write the electronic configuration of silicon (atomic number 14) and state the group to which it belongs in the Periodic Table.
(ii) State the type of chemical bonding between silicon and oxygen in SiO\(_2\)
(iii) A chip used in a microcomputer contains 5.72 x 10\(^{-3}\)g of silicon, calculate the number of silicon atoms in the chip.
[Si = 28; Avogadro constant = 6.02 x 10\(^{23}\) mol\(^{-1}\)]
(c) An element X belongs to the same group as sodium but is more reactive.
(i) Suggest with reason whether X would be a reducing or oxidizing agent.
(ii) What would be a suitable method of storing X in the laboratory?
(iii) Describe briefly what would be observed if a small piece of X were dropped into a trough of cold water which had been coloured with red litmus.
(iv) Write an equation to show how the oxide of X would react with dilute HCI.
(v) Suggest the likely colour of the salts of X
Explanation
(a)(i) Characteristic properties of electrovalent compounds.
- They do not contain molecules
- They dissolve in water to form electrolyte
- They have high melting or boiling point
- They are mostly inorganic compounds
(ii) Alpha particles: They are positively charged
- They have low penetrating power
- They exert a very powerful ionizing effect upon any gas through which they pass.
(iii) Catalysts : Catalysts remain unchanged in chemical nature and in mass at the end of a reaction.
- Catalysts alter the rate of a chemical reaction
- They are specific in action
- Catalysts cannot initiate or start a reaction
- They have no effect on the equilibrium of a reversible reaction.
(b)(i) \(_{14}\)Si - 1S\(^2\)2S\(^2\) 2P\(^6\)3S\(^2\)3P\(^2\). Silicon belongs to group four in the periodic table.
(ii) Bond between silicon and oxygen is covalent.
(iii) 1 mole of silicon has a mass of 28 and 6.02 x 10\(^{23}\) atom, in 5.72 x 10\(^{-3}\) g.
= \(\frac{5.72 \times 10^{-3}}{28}\) x 6.02 x 10\(^{23}\)
= 1.2298 x 10\(^{20}\).
(c)(i) X is a good reducing agent because it will react with water to liberate hydrogen.
(ii) X is best stored under oil.
(iii) X will react with cold water to liberate hydrogen gas. It is a violent reaction.
(iv) X\(_2\)O + 2HCI \(\to\) 2XCI + H\(_2\)O.
(v) The likely colour of the salt of X is white.