(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 th...

(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.