(a) Low melting points and boiling points
- Molecules held by weak intermolecular forces.
- Needs less energy to overcome these forces.
(b) Cannot Conduct electricity
- consists of neutral molecules.
- Do not have ions that can move freely.
(c) does not dissolve in water
(d) dissolve in organic solvents.
(a) High melting points and boiling points.
- Ions held by strong electrostatic forces.
- Needs a lot of energy to overcome these forces.
(b) Conduct electricity when in molten or aqueous solution.
- 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.
[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 formed
[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.
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)|
Mass of spirit lamp before heating (g)
Mass of spirit lamp after heating (g)
Initial temperature of water (C)
Maximum temperature of water (C)
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