(a) Consider the following compounds: (i) What is the relationship between the compounds labeled A and B? (ii) Name each of compounds A and B. (iii) Will the chemical properties of compounds A and B be the same? (iv) Give the reason for the answer stated in 2(a)(ii).
(b)(i) Give two characteristic features of boiling, (ii) What would be the effect of each of the following conditions on the boiling point of water? I. Addition of crystals of sodium chloride. II. Reduction of the atmospheric pressure. (iii) State one way in which boiling differs from evaporation.
(ii) Consider the following reaction equation: MgO + 2HCI ? MgCl\(_2\) + H\(_2\). 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]. (e) State three physical properties of metals.
(a) Compounds A and B
- (i) Relationship: A and B are geometric (cis-trans) isomers. They have the same molecular formula and the same atoms joined in the same order, but differ in the spatial arrangement of the groups about the carbon-carbon double bond.
- (ii) Names: Compound A is trans-1,2-dichloroethene; Compound B is cis-1,2-dichloroethene.
- (iii) Chemical properties: Yes, the chemical properties of A and B are the same.
- (iv) Reason: They contain the same functional group (the carbon-carbon double bond) and the same type of atoms connected in the same way, so they undergo the same chemical reactions.
(b)(i) Two characteristic features of boiling
- Boiling takes place at a specific, constant temperature (the boiling point) at which the vapour pressure of the liquid equals the atmospheric pressure.
- Boiling takes place throughout the whole body of the liquid, with bubbles of vapour forming within it.
(b)(ii) Effect on the boiling point of water
- I. Addition of sodium chloride crystals: it increases the boiling point of the water.
- II. Reduction of atmospheric pressure: it lowers the boiling point of the water.
(b)(iii) One difference between boiling and evaporation
Boiling occurs throughout the whole liquid at a fixed temperature, whereas evaporation occurs only at the surface of the liquid and at all temperatures.
(c)(i) Unsaturated versus saturated solution
An unsaturated solution can still dissolve more solute at a given temperature and contains no undissolved solute, whereas a saturated solution cannot dissolve any more solute at that temperature and is in contact with undissolved solute.
(c)(ii) Making a saturated solution dissolve more solute
- By increasing the temperature of the solution.
- By increasing the volume of the solvent.
(c)(iii) One factor affecting solubility of a solid in a liquid
Temperature (also the nature of the solute and the nature of the solvent).
(d)(i) The mole
The mole is the amount of a substance that contains as many elementary particles as there are atoms in 12 g of carbon-12, that is, \(6.02 \times 10^{23}\) particles.
(d)(ii) Mass of magnesium oxide
\[ MgO + 2HCl \to MgCl_2 + H_2O \]
Moles of HCl \(= \dfrac{25.0}{1000} \times 0.1 = 2.5 \times 10^{-3}\,\text{mol}\).
From the equation, 2 mol HCl react with 1 mol MgO, so moles of MgO \(= \dfrac{2.5 \times 10^{-3}}{2} = 1.25 \times 10^{-3}\,\text{mol}\).
Molar mass of MgO \(= 24.0 + 16.0 = 40.0\).
\[ \text{Mass of MgO} = 1.25 \times 10^{-3} \times 40.0 = 0.05\,\text{g} \]
(e) Three physical properties of metals
- They are malleable and ductile.
- They are lustrous (shiny) and good conductors of heat and electricity.
- They have high melting and boiling points.
