2022 WAEC GCE Chemistry Objectives And Essay Questions And Answer

2022 WAEC GCE Chemistry Objectives And Essay Questions And Answer

2022 WAEC GCE Chemistry Objectives And Essay Questions And Answer

Chemistry 1 (Objective) – 10:30am – 11:30pm
Chemistry 3 (Alternative to Practical Work) – 1:00pm – 2:30 pm

1. The Number of Hydroxonium ions produced by one moleculeof Ann acid in aqueous Solution is it’s

  • A. Acidity
  • B. Basicity
  • C. Concentration
  • D. pH

ANSWER: B ( Basicity)

2. When an acid anhydride dissolves in water, the solution formed would have pH

  • A. Lower than 7
  • B. Equal to 7
  • C. Higher than 7
  • D. Equal to 14

ANSWER: A (lower than 7)

3. A solution of pH 7 is.

  • A. Acidic
  • B. Dilute
  • C. Neutral
  • D. Saturated

ANSWER: C (Neutral)

4. Which of the following statements is NOT correct?

  • A. The average kinetic energy of a gas is directly proportional to its temperature
  • B. At constant tempearture, the volume of a gas increases as the pressure increases
  • C. The pressure of a gas is inversely proportional to its volume
  • D. The temperature of a gas is directly proportional to its volume
  • E. The collisions of molecules with each other are inelastic

5. Zinc Oxide is a

  • A. Basic Oxide
  • B. Acidic Oxide
  • C. Amphoteric Oxide
  • D. Neutral Oxide
  • E. Reactive Oxide

6. When sodium chloride and metallic sodium are each dissolved in water

  • A. both processes are exothermic
  • B. both processes are endothermic
  • C. the dissolution of metallic sodium is endothermic
  • D. the dissolution of metallic sodium is exothermic
  • E. the dissolution of sodium chloride is explosive

7. The periodic classification of elements is an arrangement of the elements in order of their

  • A. Atomic Weights
  • B. Isotopic Weights
  • C. Molecular Weights
  • D. Atomic Numbers
  • E. Atomic Masses

8. In the reaction between sodium hydroxide and sulphuric acid solutions, what volume of 0.5 molar sodium hydroxide would exactly neutralise 10cm3 of 1.25 molar sulphuric acid?

  • A. 5cm3
  • B. 10cm3
  • C. 20cm3
  • D. 25cm3
  • E. 50cm3

9. Which of the following pH value indicates strong acidity..

  • A. 1.5
  • B. 6.7
  • C. 7.5
  • D. 10.0

10. Fine Chemical have the following except

  • A. They are chemically pure
  • B. They are produced by batch process
  • C. They are produced in large quantity because of high applicability
  • D. They are produced in small quantity because of limited applicability

Essay

1. (a) (i) What is Faraday’s first law of electrolysis?
(i) Faraday’s first law of electrolysis states that the mass(m) of an element discharged during electrolysis is directly proportional to the quantity of electricity(Q) passing through it.

(ii) -Strong electrolytes conduct large currents while Weak electrolytes do not conduct current readily.
– Strong electrolytes ionize completely while weak electrolytes ionize only slightly.
(b) Ethyne burns in air to give a smoky and luminous flame (complete combustion)

(c) (i) If an organic compound contains carbon atoms joined by double or triple covalent bonds. The compound is said to be an unsaturated hydrocarbon.
(ii) CH3COOH(aq) + CH3OH(aq) <–> CH3COOCH3(l) + H2O(l)
(iii) Methyl ethanoate
(d) By removing the main product continuously

(e) Number of moles of Zn dust = Mass/molars mass = 3.75/65 =0.0077
Reacting mole ratio of Zn to H2 is 1:1
: No of moles of H2 produced =0.0677 moles
1 mole = 6.02×10²³ molecules
0.0577moles of hydrogen produces
=6.02×10²³ x0.0577
=0.347×10²³ molecules
Or 3.47×10²² molecules.
(f) Flooding
(g) (i) Reaction C
(ii) Zinc (from + 2 to + 4)

(h) (i) – Each spectral line is caused by one electron
– Electrons can exist only in a circular orbit of definite quantum energy.

(ii) It could not account for the spectrum at note complicated atoms

(i) (i)Temperature of the reacting system
(ii)Pressure of the reacting system
(iii)Concentration of the reacting system

(j) (i) Both liberate carbon(iv) oxide
(ii) One produce a chloride salt, the other produces an ethanoate salt.

2. (a) (i) What is the structure of the atom as proposed by Rutherford?
(ii) Distinguish between the atomic number and the mass number of an element.
(iii) Explain briefly why the relative atomic mass of chlorine is not a whole number.

(b) (i) What is meant by first ionization energy?
(ii) List three properties of electrovalent compounds
(iii) Consider the following pairs of elements:
9F and 17CL;
12Mg and 20Ca.
Explain briefly why the elements in each pair have similar chemical properties.

(c) Explain briefly the following terms using an appropriate example in each case
(i) homologous series;
(ii) heterolytic fission.

(d) State the indicator(s) which could be used to determine the end-point of the following titrations:
(i) dilute hydrochloric acid against sodium hydroxide solution;
(ii) dilute hydrochloric acid against ammonium hydroxide solution;
(iii) ethanoic acid against sodium hydroxide solution.

(e) A solid chloride E which sublimed on heating reacted with an alkali F to give a choking gas G. G turned moist red litmus paper blue.  Identify E, F and G.

ANS: (a) (i) The atom has a small/ tiny positively charged centre /nucleus with electrons surrounding the space around the centre.
(ii) Atomic number of an element is the number of protons/electrons in an atom of the element while the mass number is the sum of the protons and neutrons in the atom of the element.
(iii) Chlorine atom is made up of a mixture of isotopes and the relative atomic mass of chlorine is the average of its isotopic masses.

(b) (i) Is the (minimum) energy required to remove one mole of an electron from one mole of gaseous atom (to form one mole gaseous charged ion
(ii) High melting /boiling point;
Ability to conduct electricity in the molten state or in solution;
Solid at room temperature;
Soluble in water or polar solvents /insoluble in non-polar solvents.
(iii) Atoms of the elements in each pair have the same number of electrons in their outer-most shell therefore similar chemical properties.

(c) (i) Is a family of organic compounds:
– where successive members differ by –CH2 of the molar mass of 14;
– with similar chemical properties;
– which conform to the same general formula;
– which show a gradation of physical properties;
– which have the same general method of preparation. e.g  alkanes, alkenes , alkanols.
(ii) Is a process in which a (covalent) bond is broken in such a way that the electron pair is completely transferred to one of the atoms (resulting in the formation of ions)
H ÷ CI     →      H+ + Cl-/ HCl ® H+ + Cl-
(d)(i) Methyl orange/ methyl red/ phenolphthalein;
(ii) Methyl orange/ methyl red;
(iii) Phenolphthalein.
(e) E   –   NH4Cl
F  –  NaOH, KOH, or Ca (OH)2,  Li OH, CsOH, Ba(oH)2, Mg(OH)2
G  –   NH3.

3. (a) (i) Define saturated solution.
(ii) The solubility of KN03 at 20°C was 3.00 mol dm-3 If 67.0g of KN03 was added to 250cm3 of water and stirred at 20°C, determine whether the solution formed was saturated or not at that temperature.

(b) (i) Distinguish between the dative bond and covalent bond.
(ii) Explain why sugar and common salt do not conduct electricity in the solid-state.
(iii) State the type of intermolecular forces present in
I. hydrogen fluoride;
II. argon.
(iv) Consider the compounds with the following structures:
S – H —-N and 0 – H —–N
In which of the compounds is the hydrogen bond stronger? Give a reason for your answer.

(c) (i) State Dalton’s Law of Partial Pressure.
(ii) If 200cm3 of carbon(IV) oxide were collected over water at 18°C and 700 mmHg, determine the volume of the dry gas at s.t.p.[ standard vapour pressure of water at 18°C = 15 mmHg]

ANS: (a) (i) Is a solution that contains the maximum amount of solute it can dissolve at a given temperature (in the presence of undissolved solute).
(ii) Solubility of KN03 in in g dm-3 = 3.00 x 101 = 303
.. 1000cm3 of saturated solution = 303g
250cm3 of the solution = 303 x 250 
1000
= 75.8 g
Since the quantity of KN03 added (67.0) to 250 cnr’ of water is less than the maximum amount required to form a saturated solution, then the solution is unsaturated.

(b)(i) In a dative bond, only one of the participating atoms/ species donated electrons to be shared by both atoms while in a covalent bond both participating atoms/ species contribute equally to the electrons being shared.
(ii) Sugar is covalent while common salt (NaCl) is electrovalent/ ionic. Electrical conductivity (in compounds) depends on the presence of mobile ions.
(iii) The intermolecular forces present in hydrogen fluoride and argon were hydrogen bond and van der Waal’s forces respectively.
(iv) 0 – H —- N has a stronger hydrogen bond because oxygen is more electronegative and smaller in size than sulphur.

(c)(i) the total pressure exerted by a mixture of gases that do not react chemically is equal to the sum of the individual partial pressures of the gases in the mixture.
(ii) pressure of the dry gas (P 1) = 700 – 15 = 685 mmHg
VI = 200cm3, TI = 18°C = 273 + 18 = 291K, P2 = 760 mmHg,
T2 = 273
P1V1 = P2V2
T1         T2
V2 = P1V1T2   =
P2T1

= 685 x 200 x 273
   760 x 291

= 169.1cm3

4. (a) (i) Define nuclear fission
(ii) A certain natural decay series starts with and ends with. Each step involves the loss of an alpha or a beta particle. Using the given information,  deduce how many alpha and beta particles were emitted.
(b) Consider the equilibrium reaction represented by the following equation: A2(g)  +  3B2(g)    2AB3(g);    H   =  +  kJmol-1
Explain briefly the effect of each of the following changes on the equilibrium composition;
(i)  increase in the concentration of B;
(ii) decrease in pressure of the system;
(iii) addition of catalyst.
(c) The lattice energies of three sodium halides are as follows:

Compound

NaF

NaBr

NaI

 Lattice energy/kJmol-1 890 719 670

Explain briefly the trend.

(d) State the property exhibited by nitrogen (IV) oxide in each of the following reactions:
(i) 4Cu  +  2NO2        4CuO + N2;
(ii) H2O+ 2NO2        HNO3   + HNO2

(e) Iron is manufactured in a blast furnace using iron ore (Fe2O3), coke and limestone.
Write the equation for the reaction(s) at the:
(i) top of the furnace;
(ii) middle of the furnace;
(iii) bottom of the furnace.
(f) (i) Name two products of destructive distillation of coal.
(ii) Give one use of each product in 3(f)(i).

5. Copy and complete the following table:

Oxide of nitrogen Oxidation state of nitrogen Colour of gas Solubility in water Action on damp blue litmus paper
N2O + 1 Insoluble
NO Colourless
NO2

(i) Mention one compound that makes water
I. temporarily hard;
II. permanently hard.
(ii) State one method that could be used to remove
I. only temporary hardness;
II. permanent hardness.
(iii) Write an equation to show the removal of:
I. temporary hardness;
II. permanent hardness.
(c) (i) List three sources of water pollution.
(ii) Mention two ways by which water pollution can be controlled.
(d) state the function of each of the following substances in the purification of water for town supply:
I. sodium aluminate (III) (NaAIO2);
II. lime (calcium hydroxide);
III. calculated mount of iodine;
IV. sand bed.

6. (a) (i) What is meant by atomicity?
(ii) Mention one element in each case which is
I. monatomic,
II. diatomic,
III. tetratomic.
(iii) Write the orbital electron configuration of
I. 20Ca,
II. 9F.
a. In which group does each of the elements belong?
b. How many unpaired electrons are present in 9F?
c. How many electrons are present in 20Ca2+?

(b) (i) Write a balanced equation for the thermal decomposition of KCƖO3.
(ii) Mention the catalyst that could be used to increase the rate of reaction in 6(b)(i).
(ii) If 5.0 g of KCƖO3 was decomposed by heat, determine the volume of oxygen produced at s.t.p.
[Molar gas volume at s.t.p. = 22.4dm3, K = 39,  Cl = 35.5, O = 16]

(c) (i) Mention the products formed when each of the following substances is heated strongly:
I. ZnCO3;
II. CuSO4.5H2O.
(ii) State the colour change observed when each of the residues in 1(d)(i) above is allowed to cool.

7. (a) Describe briefly how each of the following aqueous solutions could be identified in the laboratory:
(i) Ammonium trioxocarbonate (IV);
(ii)Ammonium chloride.
(b) Arrange the following compounds in order of increasing boiling point and give reasons for your answer: CS2,  NaF and CO2.
(c) List two gases each that are:
(i) acidic;
(ii) highly soluble in water;
(iii) oxidized by acidified KMnO4(aq).
(d) In a tabular form, compare the elements silicon and sulphur under the following properties:
(i) metallic character;
(ii) physical state;
(iii) conduction of electricity.
(e) A cuboid piece of sodium metal measures 3 cm x 4 cm x 10 cm. If the density of sodium is 0.971 g cm-3, calculate the number of atoms in the sodium metal.
[ Na = 23; Avogadro constant = 6.02 x 1023 mol_1 ]

waec chemistry answer

8. (a)  (i) Define standard electrode potential.
(ii) State two factors that affect the value of standard electrode potential.
(iii) Give two uses of the values of standard electrode potential.
(iv) Draw and label a diagram for an electrochemical cell made up of
Cu2+/Cu;   = + 0.34
Zn2+/Zn;   = – 0.76
(v) Calculate the e.m.f of the cell in 8(a)(iv) above
(b) (i)  In terms of electron transfer, define
I. oxidation;
II. oxidizing agent.
(ii) Balance the following redox reaction: MnO4-    +  I- H+   I2Mn2+

(c) Classify each of the following oxides as basic, amphoteric, acidic or neutral:
(i) Carbon (II) oxide;
(ii) Sulphur(IV) oxide;
(iii) Aluminium oxide;
(iv) Lithium oxide.

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