WAEC 2020
(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.
(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 factor that could affect the solubility of a solid in a liquid. (d)(i) Define the term mole .
(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) 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.
(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 factor that could affect the solubility of a solid in a liquid. (d)(i) Define the term mole .
(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.
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Correct Answer: Option
Explanation:
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 (iv) because they both contain the same functional group; - they have same type of atoms connected in the same way
b)(1)- 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.
C. (ii) -increasing the temperature; - increasing the volume of solvent (iii.) - temperature; - volume of solvent; - nature of solute; - nature of solvent
D. (i) The amount of substance containing 6.02 x 10\(^23\) particles of that Substance/amount of substance containing as many particles as there are atoms in 12g of carbon 12.
(ii) n (HCI) = 25.0 x 10 dm3 x 0.1 moldm3, n (HCI) 2.5 x 10\(^-3\) mol.
From the equation of the reaction:
Mole of HCI = 0.025 x 0.1 = 0.0025
-->mol of MgO = 0.0025 / 2 = 0.00125mol
Molar mass of MgO = 24+ 16 =40
mass of MgO= 0.00125x 40 = 0.05g
(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
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 (iv) because they both contain the same functional group; - they have same type of atoms connected in the same way
b)(1)- 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.
| 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 |
| 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 |
C. (ii) -increasing the temperature; - increasing the volume of solvent (iii.) - temperature; - volume of solvent; - nature of solute; - nature of solvent
D. (i) The amount of substance containing 6.02 x 10\(^23\) particles of that Substance/amount of substance containing as many particles as there are atoms in 12g of carbon 12.
(ii) n (HCI) = 25.0 x 10 dm3 x 0.1 moldm3, n (HCI) 2.5 x 10\(^-3\) mol.
From the equation of the reaction:
Mole of HCI = 0.025 x 0.1 = 0.0025
-->mol of MgO = 0.0025 / 2 = 0.00125mol
Molar mass of MgO = 24+ 16 =40
mass of MgO= 0.00125x 40 = 0.05g
(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