2022 WAEC Chemistry Past Question Paper

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2022 WAEC Chemistry Past Question Paper [Objective Test – Paper 1]

Instruction: Answer all the questions. Do all rough work on this question paper

The by-product of fermentation of sugar is
- A. carbon(IV) oxide
- B. ethanoic acid
- C. propanol.
- D. propan-1,2,2- triol.
Which of the following sugars is a product of the condensation of monosaccharides?
- A. Galactose
- B. Maltose
- C. Glucose
- D. Fructose
The cleaning effect of soap is low in acidic water because of
- A. the formation of unionized fatty acid.
- B. increase in the pH of the soap molecules.
- C. anti-biodegradable effect of hydrogen ions
- D. the hardness of the acidic water.
The following compounds are condensation polymers except
- A. nylon
- B. protein
- C. starch
- D. polyethene
What amount of electricity is required to deposit one mole of aluminium from a solution of AlCl₃?
- A. One Faraday
- B. One sampere
- C. Three Faradays
- D. Three amperes
Which of the following compounds would react rapidly with bromine?
- A. Benzene
- B. Hexane
- C. Hexene
- D. Hexanol
Alkanols can be manufactured from alkenes by the initial reaction of alkenes with
- A. bromine in tetrachloromethane
- B. concentrated tetraoxosulphate (VI) acid.
- C. aqueous potassium tetraoxomanganate (VII)
- D. sodium hydroxide solution
Which of the following statements about the standard hydrogen electrode is not correct?
- A. The hydrogen gas is at a pressure of 1 atmosphere
- B. A solution containing 1 mol dm^-3 of H⁺_(aq) ions is used
- C. A platinum electrode is used
- D. The temperature is kept at 20⁰C
If 60g of M combines with 24g of oxygen, what would the empirical formula of the oxide be? [0 = 16.0, M = 120]
- A. MO
- B. MO₂
- C. MO₃
- D. MO₄
The products of the electrolysis of dilute sodium chloride using carbon electrodes are Anode/Cathode
- A. chlorine and sodium
- B. oxygen and hydrogen
- C. chlorine and hydrogen
- D. hydrogen and oxygen
Determine the quantity of electricity used when a current of 0.20 amperes is passed through an electrolytic cell for 60 minutes.
- A. 12 C
- B. 120 C
- C. 360 C
- D. 720 C
Oxochlorate (I) acid is used as a bleaching agent because it is
- A. a weak acid
- B. a reducing agent
- C. an oxidizing agent
- D. a strong acid
The IUPAC name for CH₃CHCH₃CHCLCHCH₃CH₂CH₃ is
- A. 2, 4 – dimethyl – 3 – chlorohexane
- B. 3, 5 – dimethyl – 4 – chlorohexane
- C. 4 – chloro -3, 5 – dimethylhexane
- D. 3 – chloro -2, 4 – dimethylhexane.
A colourless gas with a pungent smell is evolved when dilute hydrochloric acid is added to a sample of a salt. The gas evolved could turn
- A. acidified K₂Cr₂ O₇ solution colourless
- B. acidified KMnO₄ solution colourless
- C. Fe(NO₃)₂ solution green
- Pb(NO₃)₂ paper black
If 5.0g of marble reacts with 25.0cm³ hydrochloric acid, which of the following combination has the fastest reaction rate?
- A. Marble chips and 2.0 mol dm^-3 HCL_(aq)
- B. Marble chips and 2.0 mol dm^-3 HCL_(aq)
- C. Powered marble and 2.5 mol dm^-3 HCL(aq)
- C. Powered marble and 2.0 mol dm^-3 HCL(aq)
Increasing the temperature generally
- A. decreases the solubility of a solid in a liquid but increases the solubility of a gas in a liquid
- B. increases the solubility of a solid in a liquid but decreases the solubility of a gas in a liquid
- C. increases the solubility of both a solid and gas in a liquid
- D. decreases the solubility of both a solid and a gas in a liquid.
A white precipitate was formed when BaCl_2(aq) was added to an aqueous solution of a salt X. The precipitate dissolved in dilute HCL with rapid effervescence. Salt X is likely to contain
- A, SO₄^2- ions
- B. SO₃^2- ions
- C. NO₃^–ions
- D. CO₃^2- ions
Before a reaction could take place, the should be
- A. ionization of reactant particles
- B. breakage of bonds of products
- C. breakage of bonds of reactants
- D. ionization of product particles
Consider the following reaction equation: CaO + SiO₂ → CaSiO₃ Silicon(IV) oxide is acting as
- A. a basic oxide
- B. a reducing agent
- C. an acidic oxide
- D. an oxidizing agent
Which of the following acids would form normal salt only?
- A . Tetraoxosulphate (IV) acid
- B. Trioxonitrate (V) acid
- C. Tetraoxophosphate (V) acid
- D. Trioxosulphate (IV) acid
What is the partial pressure of oxygen at s.t.p. in a gaseous mixture containing 100cm³ of oxygen and 900 cm³ of nitrogen gas?
- A. 1.0 atm
- B. 0.1 atm
- C. 9.0 atm
- D. 0.9 atm
Graphite is used as a dry lubricant due to the presence of
- A. mobile electrons
- B. free electrons
- C. octahedral structures
- D. layered structures
Which of the following gases is alkaline?
- A. NO₂
- B. CO₂
- C. NH₃
- D. N₂0
Which of the following statements about an equilibrium system is correct?
- A. Forward and backward reactions occur at the same rate.
- B. The concentrations of reactants must equal that of the products
- C. The concentrations of reactants and products can be changes by adding a catalyst.
- D. The concentrations of reactants and products are not affected by a change in temperature.
Consider the following reaction equation: N_2(g) + 3H_2(g) ⇌ 2NH_3(g); H = -92kJ. Increasing the temperature of the reaction would
- A. Shift the equilibrium to the right
- B. increase the yield of ammonia.
- C. decrease the amount of hydrogen
- D. decrease the yield of ammonia.
When air in a syringe is compressed such that there is no change in temperature, the
- A. air liquefies
- B. pressure increases
- C. intermolecular space increases.
- D. density decreases
Which of the following statements about liquids is/are true? I.) Liquids maintain their volume at constant temperature. II.) Liquids have fixed shape. III.) Liquids do not diffuse. IV.) Change in pressure affects volume of liquids.
- A. I only
- B. IV only
- C. I and IV only
- D. II and III ONLY
A hydrogen chloride gas reacted with oxygen gas to yield water and chloride gas. The mole ratio of the hydrogen chloride gas to water is
- A. 1:3
- B. 2:1
- C. 3:1
- D. 4:1
What number of moles of oxygen would exert a pressure of 10 atm at 320 K in an 8.2 dm³ cylinder? [R = 0.082 atm dm^-3 mol^-1 K^-1]
- A. 0.32
- B. 1.52
- C. 3.13
- D. 31.25
If 50cm³ of a saturated solution of KN0₃ at 40^OC contained 5.05g of the salt, its solubility at the same temperature would be [KNO₃ = 101]
- A. 1.0 mol dm^-3.
- B. 1.5 mol dm^-3.
- C. 2.0 mol dm^-3.
- D. 5.0 mol dm^-3.
Which of the following elements would displace copper from a solution of copper ions?
- A. Silver
- B. Gold
- C. Lead
- D. Mercury
What is the percentage composition of carbon in Ca(HCO₃)₂? [ Ca = 40.0, O = 16.0, C = 12.0, H = 1.0]
- A. 22.2 %
- B. 14.8 %
- C. 7.4 %
- D. 3.7 %
Which of the following bond types is intermolecular?
- A. Covalent bond
- B. Hydrogen bond
- C. Ionic bond
- D. metallic bond
The maximum number of covalent bonds formed by nitrogen is
- A. 1.
- B. 2.
- C. 3.
- D. 4
The IUPAC name of the compound CH₃CH(CH₃)CHCH₂ is
- A. 2 – methyl but – 1 – ene
- B. 2 – methyl but – 2 – ene
- C. 3 – methyl but – 1 – ene
- D. 3 – methyl but – 2 – ene
Ionization energy increases across the period in the periodic table because
- A. atomic number increases.
- B. effective nuclear charge increases.
- C. mass number decreases
- D. screening effect decreases.
Which of the following properties indicate that an element is a metal. It (I) reacts with oxygen to form an acidic oxide. (II) forms ionic chlorides. (III) has variable oxidation states. (IV). displaces hydrogen from dilute HCL.
- A. I and III only
- B. I and II only
- C. II and IV only
- D. I, II, III and IV
The electron configuration of carbon atom in its excited state is
- A. 1s²2s²2p_x²2P_y⁰
- B. 1s²2s²2p_x¹2p_y¹
- C. 1s²2s¹2p_x¹2py¹2p_z¹
- D. 1s¹2s²2p_x¹2p_y¹2p_z¹
An oxide has the following properties. It (I). is a white powder. (ii) react with HCL. (III) reacts with NaOH (IV) in insoluble in water. The oxide is
- A. alkaline
- B. amphoteric
- C. acidic
- D. nuetral
Which of the following statement about atoms of a metal is correct? They
- A. readily accept electrons
- B. are soft
- C. are held together by covalent bond
- D. are held together by a sea of electron cloud
Which of the following sketches is a graphical representation of Boyle’s law?
The atom with the electron configuration 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁴ is in
- A. period 4, p- block
- B. period 3, p- block
- C. period 4, d-block
- D. period 3, d-block
Electropositivity of elements across the periodic table normally
- A. remains constant down the group
- B. increases across the period
- C. decreases across the period
- D. decreases down the group
Consider the following table

Substance	Melting point/ ⁰C	Boiling point/^OC
P	-78	-25
Q	-8	40
R	-6	150
S	44	380

Which of the substances is a liquid at room temperaturw and rapidly evaporates on exposure to air?

A. P
B. Q
C. R
D. S

45. Which of the following oxides is amphoteric?
- A. Carbon (II) oxide
- B. Nitrogen (IV) oxide
- C. Lead (II) oxide
- D. Calcium oxide
46. Which of the following processes occur during fractional distillation of petroleum?
- A. Condensation and diffusion
- B. Diffusion and evaporation
- C. Diffusion and sublimation
- D. Evaporation and condensation
47. If the molar mass of X(HCO₃)₂ is 162g mol^-1, determine the relative atomic mass of X. [H = 1.0, C = 12.0, O = 16.0]
- A. 40
- B. 48
- C. 61
- D. 101
48. Charcoal is used in the decolourization of sugar because of its
- A. absorption property
- B. amorphous property
- C. oxidizing property
- D. adsorption property
49. The first defination of an element was made by
- A. J. Dalton
- B. A. Lavoisier
- C. R. Boyle
- D. J. J. Thompson
50. Which of the following scientists formulated the law of conservation of mass?
- A. A. Lavoisier
- B. J. Dalton
- C. R. Boyle
- D. J. Proust

OBJECTIVE ANSWERS [WAEC past questions and answers on Chemistry 2022]

1-10: ABACCABBCD
11-20: DCDBCCDCDB
21-30: BDCADAABCA
31-40: CBDCCDCBBD
41-50: CACCCDADCA

THEORY ANSWERS [2022 WAEC Chemistry Past Question Paper]

Question 1

(a) (i) An electron electron pair acceptors [2marks]

(ii) AlCl₃, BCl₃, H₂O, H⁺, Transition metal ions [1mark]

(1a) (i) An electron electron pair acceptors [2marks]
(ii) AlCl₃, BCl₃, H₂O, H⁺, Transition metal ions [1mark]

(1b) Is the addition of NaCl (1) to the reaction mixture (1) in soap production to facilitate the precipitation of soap (1) from the mixture [3marks]

(1c)
Reagent – AgNO₃ in NH_3(aq) / Ammoniacal silver trioxonitrate (v)
Condition – Heat [2marks]

(1d) Is the fraction of a given isotope (1) in a mixture of isotopes of the same element (1) OR
The % of an isotope with a specific atomic mass (1) found in a naturally accruing sample of an element (1).

(1e) (i) because the element is/has

unreactive
stable
inert
a noble gas
completely filled outermost shell

(ii) Because of a weak forces between the molecules (1) hence not much heat (1) is needed to break the forces (1) [3marks]

(1f)
(Conc) HNO₃ produces brown fumes (1) (of NO₂) when copper tunings are added (1) to it / copper (II) salt is added but H₂S0₄ will not react with the copper tuning / copper (II) salt (1).
When Concentrated H₂SO₄ is added to sugar (1) it chars (1) the sugar but Concentrated HN0₃ will not (1)
Add BaCl₂ solution to each acid (1) white precipitate indicates H₂SO₄ (1) no precipitate indicates HNO₃ (1) Any 1 x 3 = 3marks

(1g) Any 2 x 1 = 2marks

Electrochemical cell	Electrolytic cell
– the node is negative/ cathode is positive	– anode is positive / cathode is negative
– chemical energy is converted to electrical energy	– electrical energy is converted to chemical energy
– the two half cells are in separate containers and connected by a salt bridge	– the two half cells are in the same container
– reaction is spontaneous	– non-spontaneous
– current is generated from within the cell	– current is generated from external source / battery

[WAEC past questions and answers on Chemistry 2022]

(1h)
group 1 element reacts by forming positive ions, the higher the ionization energy, the more difficult it is to lose the electron hence the lower the reactivity of the element. OR

Ionization energy decreases down group 1 elements, the lower the ionization energy, the easier to loose an electron, hence the higher the reactivity of the elements. [3marks]

(1i) Molecular formula shows the actual number of atoms of each element in a molecule. [2marks]

(1j) (i)

(1j) (i) NH₃ will deviate more [1mark]
(ii) This is because it has a larger volume and also it has a stronger intermolecular forces. [2marks]

Question 2

(2ai)
Ionization energy can be defined as the energy required to remove one electron from a mole of a gaseous atom. OR

Is the minimum energy required to convert one mole of a gas of atom into one mole of a gaseous plus 1 ions. [2marks]

2aii) ₄Be : 1s² 2s²
₅B: 1s² 2s² 2p¹ The electron to be removed from Be is in the 2s orbital which is closer to the nucleus; nuclear attraction is greater hence first ionization energy is greater but the electron to be removed from B is in the 2p orbital which is farther away from the nucleus; hence nuclear attraction is weaker; hence first ionization energy is smaller. OR 2p has less energy than 2s (1). So it is easier to remove an electron from 2p (1) as the nuclear charge is weaker in 2p (1) because 2p is further away from the nucleus (1). Hence, first ionization energy is small. 4marks

(2b)
I = 0.12A, t = 500seconds, Q = It, Q = 0.12 x 500 = 60C
m = 0.015g, 1 F =96500C
M = 48.0, Charge = ?
Using;
m = MIt/CF
C = MIt/mF
C = (48×0.12×500)/(0.015×96500) Hence charge = +2

(2ci) Alumina (Al₂O₃) mixed with molten cryolite (Na₃AlF₆)

(2cii)
(i) Abundant deposits of bauxite
(ii) Cheap source of electricity

2d) (i) Is the ability of a substance to be attracted strongly into a magnetic field. [2marks]

2dii)
(i) ₂₄Cr²⁺ – 1s²2s²2p⁶3s²3p⁶3d⁴ unpaired electron = 4
₂₄Cr⁶⁺ – 1s²2s²2p⁶3s²3p⁶ = unpaired electrons = 0

(ii) ₂₄Cr²⁺

(iii) the greater the number of unpaired electrons in the 3d – orbital (1), the greater the paramagnetism (1)

QUESTION 3

(3ai)
This can be defined as the number of particles (atoms, molecules, ions etc) present in one mole of a substance. OR Number of particles present in 12.0g of carbon – 12

(3aii)
Mass/m.m = no. of molecules/Avogadro’s number
(2.30/m.m) × (3.01×10²²/6.02×10²³)
m.m = (2.30×6.02×10²³)/3.01×10²²
m.m = 46g/mol

(3aiii)
Let Nx Oy be the formula of the oxide or 14x + 16y = 46
:. x = 1, y = 2
ie. 14(1) + 16(2) = 46
:. formula of x = NO₂

(3bi)
(i) Two layers are formed / no reaction / immiscible
(ii) There is a reaction / hydrolysis (1) with steamy fumes / white fumes

(3bii)
The reaction occurs by interaction of the lone pair of electrons of water binding to the central atom (1) (silicon or carbon) / attaching to the central atom. In silicon, the 3d – orbital is available to accept the pairs of electrons (1) but in carbon there is no vacant orbitals for bonding (1). OR Water is pola (1) hence the reaction with SiCl4 (1). But CCl4 is non polar (1) hence there is no reaction.

(3ci)
Extraction of copper
Electroplating
Purification of metals / copper

(3cii)
(i) CuSO₄
(ii) CuCl_2(aq) (iii) Cu(NO₃)₂

(3ciii)
Cu_(s) → Cu²⁺_(aq)+ 2e⁻_(aq)

(3civ)
Using; m = ZIt, t = 3min, 13 sec, = 193 sec
Z = m/It
Z = 3.2/(50×193)
Z = 3.2/9650
Z = 0.000332g/C

QUESTION 4

(4ai)
Temperature : 350 – 500⁰C/high temperature
Pressure : 150 – 1000 atm / high pressure
Catalyst: (Finely divided) Iron

(4aii)
Rate of the reaction increases (1) as particles are closer together / more particles per unit volume (1). There are more collision per second / collisions are more often

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OBJECTIVE ANSWERS [WAEC past questions and answers on Chemistry 2022]

THEORY ANSWERS [2022 WAEC Chemistry Past Question Paper]

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