Properties of Covalent compound
(a) Low melting points and boiling points
Because:
- Molecules held by weak intermolecular forces.
- Needs less energy to overcome these forces.
-
(b) Cannot Conduct electricity
Because:
- consists of neutral molecules.
- Do not have ions that can move freely.
(c) does not dissolve in water
(d) dissolve in organic solvents.
Properties of Ionic compound
(a) High melting points and boiling points.
Because:
- Ions held by strong electrostatic forces.
- Needs a lot of energy to overcome these forces.
(b) Conduct electricity when in molten or aqueous solution.
Because:
- In solid, ions are fixed in positions and do not move freely.
- In molten state or aqueous solution, the ions can move freely.
(c) dissolve in water
(d) does not dissolve in organic solvents.
Covalent Bond (non-metal + non-metal) Sharing of electron
[proton number: C:6, O:8]
- Electron arrangement of atom C is 2.4
- Atom C needs 4 more electron to achieve stable octet electron arrangement.
- Atom C contributes 4 electron for sharing
- Electron arrangement of atom O is 2.6
- Atom O needs 2 more electron to achieve stable octet electron arrangement
- Atom O contributes 2 electron for sharing.
- covalent compound, CO2 is formedIonic Bond (metal + non metal) Transfer of electron
[number of proton: Mg: 12, O: 8]
- Electron arrangement of magnesium atom is 2.8.2
- Magnesium atom donates 2 electron to achieve stable octet electron arrangement.
Mg → Mg2+ + 2e
- Electron arrangement of oxygen atom is 2.6
- Oxygen atom receives 2 electron to achieve stable octet electron arrangement.
O + 2e → O2-
- Mg2+ ion and O2‑ ion attract by strong electrostatic force to form ionic bond.
- Ionic compound, MgO is formed.
Heat of combustion (calculation)
An experiment was carried out to determine the heat of combustion of ethanol.
The table below shows the experimental results
| Volume of water in copper tin (cm3) |
200
|
Mass of spirit lamp before heating (g)
|
189.55
|
Mass of spirit lamp after heating (g)
|
188.80
|
Initial temperature of water (C)
|
28.5
|
Maximum temperature of water (C)
|
53.5
|
a) Calculate the number of mole of ethanol used.
b) Calculate the heat absorbed by the water.
c) Calculate the heat of combustion of ethanol.
[Specific heat capacity of solution : 4.2 J g-1 0C-1 . Density of solution : 1 g cm-3 ]
Relative atomic mass: H = 1; C = 12; O = 16]
Answer: a) 0.0163 mol b) 21 kJ c) – 1288.34 kJ mol-1
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