Question 2
(a)Consider the following compounds:
- What is the relationship between the compounds labeled A and B?
- Name each of compounds A and B.
- Will the chemical properties of compounds A and B be the same?
- Give the reason for the answer stated in 2(a)(iii).
[5 marks]
(b)
(i) Give two characteristics features of boiling.
(ii) What would be the effect of each of the following conditions on the boiling point of water?
- Addition of crystals sodium chloride.
- Reduction of the atmospheric pressure.
- State one way in which boiling differs from evaporation.
[5 marks]
(c)
(i) Differentiate between an unsaturated solution and a saturated solution.
(ii) State two ways by which a saturated solution could be made to dissolve more solute.
(iii) State one facor that could affect the solubility of a solid in liquid.
[5 marks]
(d)
(i) Define the term mole.
(ii) Consider the following reaction equation:
MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l)
What mass of magnesium oxide is needed to neutralize 25,0 cm3 of 0.1 mol dm-3 hydrochloric acid?
[O = 16.0; Mg = 24.0]
[7 marks]
(e) State three physical properties of metals.
[3 marks]
Observation
Majority of the candidates responded to this question.
A good number of the candidates responded to this question and their overall performance in the question was average.
.
In part (a), majority of the candidates failed this question because they could not write the conventional names as trans-1,2-dichloroethene and cis-1,2-dichloroethene.
In part (b), majority of the candidates could give two characteristic features of boiling and stated one way in which boiling differs from evaporation.
In part (c), majority of the candidates answered this question, but lost marks due to their inability to relate saturation to a particular temperature.
In part (d), majority of the candidates lost marks because they defined mole a number of Avogadro’s number instead of amount of substance containing Avogadro’s Number of particles of that substance.
in question d(ii), majority of the candidates could not satisfactorily respond to this question because they could not apply the principle in solving it.
In part (e), majority of the candidates stated three properties of metals.
The expected answers include:
a)
(i) They are geometric / cis-trans isomers
(ii) Compound A : Trans – 1, 2 – dichloroethene
Compound B :Cis – 1, 2 – dichloroethene
(iii) The chemical properties will be the same / Yes
(iv) because they both contain the same functional group
- They have same type of atoms connected in the same way
(b)
(i)
- boiling takes place at a specific temperature
- boiling takes place throughout the liquid
- bubbles are formed
- vapour pressure is equal to atmospheric pressure
(ii)
I. It increases the boiling point of the water
II. It lowers the boiling point of the water
(iii)
| Boiling | Evaporation |
| occurs throughout the liquid | occurs only at the surface of the liquid |
| occurs at a particular constant temperature | takes place at all temperatures |
| has no cooling effect | has a cooling effect |
| Exothermic | Endothermic |
| occurs using external source of heat / not spontaneous | occurs using internal energy / spontaneous |
| bubbles are observed | bubbles are not observed |
| not affected by humidity | affected by humidity |
| fast process | slow process |
(c)
(i)
| Unsaturated solution | Saturated solution |
| Can dissolve more solute at that temperature | Cannot dissolve any more solute at that temperature |
| Does not contain undissolved solute at that temperature | Contains undissolved solute at that temperature |
(ii) - increasing the temperature
- increasing the volume of solvent
(iii) - temperature
- nature of solvent
- volume of solvent
- nature of solute
(d)
(i) The amount of substance containing 6.02 x 1023particles of that substance / amount of substance containing as many particles as there are atoms
in 12 g of carbon – 12.
(ii) n(HCl) = 25.0 x 10-3dm-3 x 0.1 mol dm-3
n(HCl) = 2.5 x 10-3mol
from the equation of the reaction:
n(MgO) = 1
n(HCl) 2
molar mass of MgO = 24 + 16 = 40 g mol-1
mass of MgO = ½ x 2.5 x 10-3 x 40
= 0.050 g
ALTERNATIVE METHODS
(e) - are malleable
- are ductile
- are lustrous
- have high melting point / boiling
- have high tensile strength / hard / strong
- high density
- solids at room temperature except mercury
- good conductors of heat
- good conductors of electricity
- sonorous