(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
(a) Characteristic properties
(i) Electrovalent (ionic) compounds:
- High melting and boiling points.
- Conduct electricity when molten or dissolved in water.
- Usually soluble in water but insoluble in organic solvents.
(ii) Alpha particles:
- Positively charged (helium nuclei, 2 protons and 2 neutrons).
- Deflected by electric and magnetic fields (toward the negative plate).
- Low penetrating power (stopped by a sheet of paper) but strongly ionising.
(iii) Catalysts:
- Alter the rate of a reaction without being used up.
- Needed only in small amounts and are chemically unchanged at the end.
- Are specific and can be poisoned by impurities.
(b) Silicon
(i) Electronic configuration of Si (Z = 14): \(1s^2\,2s^2\,2p^6\,3s^2\,3p^2\), i.e. 2, 8, 4. It belongs to Group IV (Group 14).
(ii) Bonding between silicon and oxygen in SiO2: covalent (a giant covalent structure).
(iii) Number of silicon atoms:
Moles of Si \( = \dfrac{5.72 \times 10^{-3}}{28} = 2.043 \times 10^{-4}\ \text{mol} \)
Number of atoms \( = 2.043 \times 10^{-4} \times 6.02 \times 10^{23} = \mathbf{1.23 \times 10^{20}\ atoms} \)
(c) Element X (same group as Na but more reactive)
(i) X is a reducing agent. Being more electropositive than sodium, it loses its outer electron even more readily, so it reduces other species while being oxidised itself.
(ii) Store X under paraffin oil (kerosene) to keep it away from air and moisture.
(iii) If dropped into cold water coloured with red litmus, X would float and dart about on the surface, melt into a shining ball, hiss and give off a gas (hydrogen) which may ignite; the red litmus turns blue as an alkaline hydroxide is formed.
(iv) \[ X_2O + 2HCl \to 2XCl + H_2O \]
(v) The salts of X are likely to be white (colourless), as for other Group I salts.
(a) Characteristic properties
(i) Electrovalent (ionic) compounds:
- High melting and boiling points.
- Conduct electricity when molten or dissolved in water.
- Usually soluble in water but insoluble in organic solvents.
(ii) Alpha particles:
- Positively charged (helium nuclei, 2 protons and 2 neutrons).
- Deflected by electric and magnetic fields (toward the negative plate).
- Low penetrating power (stopped by a sheet of paper) but strongly ionising.
(iii) Catalysts:
- Alter the rate of a reaction without being used up.
- Needed only in small amounts and are chemically unchanged at the end.
- Are specific and can be poisoned by impurities.
(b) Silicon
(i) Electronic configuration of Si (Z = 14): \(1s^2\,2s^2\,2p^6\,3s^2\,3p^2\), i.e. 2, 8, 4. It belongs to Group IV (Group 14).
(ii) Bonding between silicon and oxygen in SiO2: covalent (a giant covalent structure).
(iii) Number of silicon atoms:
Moles of Si \( = \dfrac{5.72 \times 10^{-3}}{28} = 2.043 \times 10^{-4}\ \text{mol} \)
Number of atoms \( = 2.043 \times 10^{-4} \times 6.02 \times 10^{23} = \mathbf{1.23 \times 10^{20}\ atoms} \)
(c) Element X (same group as Na but more reactive)
(i) X is a reducing agent. Being more electropositive than sodium, it loses its outer electron even more readily, so it reduces other species while being oxidised itself.
(ii) Store X under paraffin oil (kerosene) to keep it away from air and moisture.
(iii) If dropped into cold water coloured with red litmus, X would float and dart about on the surface, melt into a shining ball, hiss and give off a gas (hydrogen) which may ignite; the red litmus turns blue as an alkaline hydroxide is formed.
(iv) \[ X_2O + 2HCl \to 2XCl + H_2O \]
(v) The salts of X are likely to be white (colourless), as for other Group I salts.
