Chemistry 2023

Objective Questions

Which of the following laws or theory cannot be explained by the application of the kinetic theory of gases?

A) Dalton's atomic theory B) Charles' law C) Gay-lussac's law D) Boyle's law

Correct Answer: A) Dalton's atomic theory

The primary component of natural gas is

A) Butane B) Ethane C) Methane D) Propane

Correct Answer: C) Methane

Thermal cracking of alkanes usually

A) Involves decomposition B) Is an exothermic process C) Produces only small alkanes D) Requires hydrogen

Correct Answer: A) Involves decomposition

Carbon is deposited in the exhaust pipes of cars because of

A) Contamination of petrol with diesel B) Presence of carbon petrol C) Presence of additives in petrol D) Incomplete combustion of petrol

Correct Answer: D) Incomplete combustion of petrol

How many moles of copper would be deposited by passing 1 Faraday of electricity through a CuCl₂ solution?

A) 2 B) 1 C) 0.5 D) 0.25

Correct Answer: C) 0.5

Alkenes can be manufactured by

A) Addition of hydrogen to unsaturated vegetable oils B) The cracking of hydrocarbons C) Polymerization reactions D) The combustion of alkanes

Correct Answer: B) The cracking of hydrocarbons

Petrochemistry is an example of

A) Pure chemistry B) Applied chemistry C) Biochemistry D) Environmental chemistry

Correct Answer: B) Applied chemistry

Species that occur in a reaction pathway but not in the overall reaction are known as

A) Products B) Inhibitors C) Reactants D) Intermediates

Correct Answer: D) Intermediates

Which of the following statements is correct?

A) An alkane with 49 carbon atoms contain 100 hydrogen atoms B) Addition reactions occur between alkanes and chlorine C) Butane has a lower boiling point than propane D) Pentane has five isomers

Correct Answer: A) An alkane with 49 carbon atoms contain 100 hydrogen atoms

The best indicator to use for the titration of ethanoic acid with sodium hydroxide is

A) Methyl red B) Methyl orange C) Phenolphthalein D) Screened methyl orange

Correct Answer: C) Phenolphthalein

The reduction half equation of the following reaction is:
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

A) Zn(s) → Zn²⁺(aq) + 2e⁻ B) CuSO₄(s) + H₂O(l) → Cu²⁺(aq) + SO₄²⁻(aq) C) Cu²⁺(aq) + 2e⁻ → Cu(s) D) Cu²⁺(aq) + e⁻ → Cu(s)

Correct Answer: B) CuSO₄(s) + H₂O(l) → Cu²⁺(aq) + SO₄²⁻(aq)

If 100 cm³ of a saturated solution of sodium tetraoxosulphate (VI) at 30°C contains 10.5 g of the salt, what would be its solubility at this temperature? [Na₂SO₄ = 142]

A) 0.74 mol dm⁻³ B) 2.15 mol dm⁻³ C) 0.60 mol dm⁻³ D) 0.57 mol dm⁻³

Correct Answer: A) 0.74 mol dm⁻³

An example of a crystalline substance that does not possess water of crystallization is

A) Potassium trioxonitrate B) Sodium trioxocarbonate (IV) C) Iron (II) tetraoxosulphate (VI) D) Sodium tetraoxosulphate (VI)

Correct Answer: A) Potassium trioxonitrate

The salt solution formed from a reaction between ethanoic acid and sodium hydroxide solution would be

A) Basic B) Acidic C) Neutral D) Amphoteric

Correct Answer: A) Basic

Which of the following reactions represents the hydrolysis of an alkanoate?

A) CH₃COOH + OH⁻ ⇌ CH₃COO⁻ + H₂O B) CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O C) CH₃COOC₂H₅ + H₂O ⇌ CH₃COO⁻ + CH₃CH₂OH D) CH₃COOCH₂CH₃ + H₂O ⇌ CH₃COOH + CH₃CH₂OH

Correct Answer: C) CH₃COOC₂H₅ + H₂O ⇌ CH₃COO⁻ + CH₃CH₂OH

Which of the following statements about the collision theory is correct?

A) All collisions bring about reactions B) Rate of reaction is proportional to the number of effective collisions C) Collision of molecules will split the molecules to react D) Ineffective collision brings about chemical reaction

Correct Answer: B) Rate of reaction is proportional to the number of effective collisions

Why are H₂SO₄ and CaCl₂ not suitable for drying ammonia gas?

A) Are corrosive B) Are poisonous C) React with the gas D) Pollute the gas

Correct Answer: C) React with the gas

Which of the following equations does not illustrate correctly one of the reactions of chlorine?

A) Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O B) Cl₂ + 2NaF → 2NaCl + F₂ C) Cl₂ + 2NaOH → NaCl + NaClO + H₂O D) H₂S + Cl₂ → 2HCl + S

Correct Answer: C) Cl₂ + 2NaOH → NaCl + NaClO + H₂O

How many unpaired electrons are present in ₂₆Fe³⁺?

A) 2 B) 3 C) 4 D) 5

Correct Answer: D) 5

Going down Group II in the periodic table normally

A) Shielding effect decreases B) Melting point increases C) Ionization energy increases D) Electronegativity increases

Correct Answer: B) Melting point increases

Which of the following elements has its valence electrons in the S-orbital?

A) Sodium B) Carbon C) Phosphorus D) Aluminium

Correct Answer: A) Sodium

The periodic property that is used to determine whether a covalent molecule is polar or not is

A) Atomic radius B) Electron affinity C) Electronegativity D) Ionization energy

Correct Answer: C) Electronegativity

The following steps are scientific methods except

A) Analysis B) Open-mindedness C) Experimentation D) Problem identification

Correct Answer: B) Open-mindedness

Isoelectronic species have the same number of

A) Electrons B) Neutrons C) Protons D) Ions

Correct Answer: A) Electrons

An element X has two isotopes, ⁶⁵X₃₀ and ⁶⁶X₃₀ with relative abundance of 60% and 40% respectively. The relative atomic mass of X is

A) 66.00 B) 65.50 C) 65.00 D) 65.40

Correct Answer: D) 65.40

The pair of compounds that belongs to the same homologous series is

A) C₂H₆ and C₄H₁₀ B) C₃H₈ and C₃H₆ C) C₂H₄ and C₄H₁₀ D) C₄H₁₀ and C₅H₁₀

Correct Answer: D) C₄H₁₀ and C₅H₁₀

A consequence of global warming is

A) Flooding B) Water pollution C) Air pollution D) High humidity

Correct Answer: A) Flooding

Which of the following gases has the lowest rate of diffusion? [H = 1.0, C = 12.0, N = 14.0, O = 16.0]

A) Nitrogen B) Methane C) Ammonia D) Oxygen

Correct Answer: D) Oxygen

The gas that is less dense than air is

A) Carbon (IV) oxide B) Nitrogen C) Chlorine D) Oxygen

Correct Answer: B) Nitrogen

Which of the following equimolar solutions has the highest conductivity?

A) CH₃COOH(aq) B) H₂CO₃(aq) C) H₂SO₄(aq) D) NaOH(aq)

Correct Answer: C) H₂SO₄(aq)

What takes place at the cathode during electrolysis?

A) Anions lose electrons B) Anions are oxidized C) Cations are discharged D) Cations are oxidized

Correct Answer: C) Cations are discharged

How many grammes of NaOH (s) would be needed to produce 100.0 cm³ of a 0.20 mol dm⁻³ NaOH(aq)? (NaOH = 40.0)

A) 0.02 g B) 0.80 g C) 20.0 g D) 800.0 g

Correct Answer: B) 0.80 g

The formation of a bond between hydrogen and a highly electronegative atom results in

A) Polarity B) Dipole C) Metallic bond D) Electrovalent bond

Correct Answer: A) Polarity

The molecule that has a non-polar covalent bond is

A) H₂O B) HCl C) NH₃ D) Cl₂

Correct Answer: D) Cl₂

Which of the elements in the table below would react more readily with chlorine?

Element	Ionization energy (KJ mol^-1 x 10^-3
W	12.0
X	21.0
Y	106.0
Z	200.0

A) W and X only B) W and Z only C) X and Z only D) Y and Z only

Correct Answer: A) W and X only

The relative molar mass of a gaseous hydrocarbon is 30. Determine its vapour density.

A) 15 B) 30 C) 60 D) 45

Correct Answer: A) 15

Consider the following reaction equation:
2SO₃(g) → 2SO₂(g) + O₂(g), ΔH = +198 kJ/mol
Which of the following statements about the reaction is correct?

A) 198 kJ of energy is given off B) The reaction is exothermic C) The reaction container would feel warm D) 198 kJ of energy is absorbed

Correct Answer: D) 198 kJ of energy is absorbed

Which of the following properties does not give evidence of the kinetic theory of matter?

A) Evaporation B) Diffusion C) Polymerization D) Melting

Correct Answer: C) Polymerization

A compound that could be dried by using conc. tetraoxosulphate (VI) acid and not by calcium oxide is likely to be

A) An alkaline gas B) A neutral salt C) A deliquescent salt D) An acid anhydride

Correct Answer: D) An acid anhydride

Positive ions in a sea of electrons are found in

A) Covalent bonds B) Dative bonds C) Ionic bonds D) Metallic bonds

Correct Answer: D) Metallic bonds

Dilute trioxonitrate (V) acid does not produce hydrogen when it reacts with metals because

A) It is a strong oxidizing agent B) It reacts with the product C) There is no visible reaction D) It is highly corrosive

Correct Answer: A) It is a strong oxidizing agent

How many moles are there in 3.0 g of O₂? [O = 16.0]

A) 0.0093 moles B) 0.0930 moles C) 0.0625 moles D) 0.6250 moles

Correct Answer: B) 0.0930 moles

Copper (II) ions are able to participate in co-ordinate covalent bonding because they

A) Are coloured B) Have unpaired electrons C) Have vacant d-orbital D) Are positively charged

Correct Answer: C) Have vacant d-orbital

Determine the volume of 0.100 mol of HCl in 0.250 mol/dm³ of solution.

A) 200 cm³ B) 100 cm³ C) 20 cm³ D) 400 cm³

Correct Answer: B) 100 cm³

Which of the statements about gases is not correct?

A) The total kinetic energy of the gas is not affected by collision B) Molecules of the gas are in constant motion C) Gases have low densities compared to solids and liquids of equal mass D) Gases are highly soluble in water at high temperatures

Correct Answer: D) Gases are highly soluble in water at high temperatures

Arrange the following compounds in decreasing order of their boiling points:

A) NH₃, CH₄, SiH₄, HF B) CH₄, SiH₄, HF, NH₃ C) HF, NH₃, SiH₄, CH₄ D) CH₄, SiH₄, HF, NH₃

Correct Answer: C) HF, NH₃, SiH₄, CH₄

The following statements are correct except

A) Energy is released when liquids change to solids B) Particles move faster in the gaseous state than in the liquid state C) Carbon atoms in gaseous methane are further apart than those in solid diamond D) There is large decrease in the volume of a solid metal when pressure is applied to it

Correct Answer: D) There is large decrease in the volume of a solid metal when pressure is applied to it

The vapour density of an organic compound with the molecular formula C₂H₄O₂ is [H=1.0, C=12.0, O=16.0]

A) 44 B) 120 C) 65 D) 30

Correct Answer: D) 30

A mixture containing two salts of different solubility can be separated by

A) Chromatography B) Distillation C) Crystallization D) Evaporation

Correct Answer: C) Crystallization

The separation technique that is suitable for separating iodine from tetrachloromethane is

A) Solvent extraction B) Fractional distillation C) Decantation D) Filtration

Correct Answer: A) Solvent extraction

Theory Questions

a. What is a transition element?
b. Consider the electron configuration of the following elements: A=2, 8,6; B=2,8,2; C=2,8,1, D=2,8,8 State the element which forms a: i. doubly charged cation; ii. soluble trioxocarbonate (IV).
c. Explain briefly why there is a general increase in the first ionization energies of the elements across the period in the periodic table.
d. Give two examples of an aliphatic compound
e. Explain briefly why alkanols are stronger bases than water.
f. State the major raw materials used in the Solvay process
g. What is geometric isomerism?
h. Give a reason why water gas is a better fuel than producer gas.
i. Define the term heat of combustion.
ji. State Faraday's second law of electrolysis
ii. Calculate the amount of silver deposited when 10920 coulombs of electricity is passed through a solution of a silver salt. [IF = 96500 C mol-1]

a. In an experiment, 20.0 cm3 of a solution containing 4g/dm3 of sodium hydroxide was neutralized by 8.0 cm3 of dilute tetraoxosulphate (VI) acid:
i. Write a balanced equation for the reaction;
ii. calculate the concentration of the acid in mol/ dm3
b
i. State two postulates of the Kinetic theory of gases which real gases do not obey
ii. Explain briefly why real gases do not obey the postulates stated in 2(b)(i).
c. Consider the following compound:

ii. name the two structural isomers of the compound;
iii. state the chemical process involved in the preparation of the compound from starch,
iv. write the chemical equation for the steps involved in the process in 2(c)(ii).
v. name two enzymes involved in the process in 2(c)(iii)
d. Explain briefly the term structural isomerism.

a. A compound contains 52.2% C, 13.1 % H and Oxygen only. The vapour density of the compound is 23. Determine
i.) its empirical formula;
ii.) its molecular
formula, [H=1.0, C=12.0, O= 16.0]
iii). The compound reacts with sodium metal to produce hydrogen gas and when warmed with acidified KMnO4(aq) gives a solution that turns from purple to colorless. It also forms a sweet-smelling liquid when heated with ethanoic acid in the presence of concentrated H2SO4
name the functional group present in the compound;
iv). draw the structural formula of the compound.
b. Outline the chemical equations for the production of ethanol from cooked cassava.
c
i. Explain briefly why a piece of aluminum does not react with water.
ii. How can a pure sample of aluminum chloride crystals be prepared from aluminium
d. Describe how water can be separated from aqueous CuSO4

a. Starting with calcium chloride, describe briefly how a solid sample of calcium trioxocarbonate (IV) can be prepared in the laboratory.
b. With relevant equations outline the procedure for the purification of impure copper.
c. Copper reacts with concentrated trioxonitrate (V) acid:
i. write a balanced chemical equation for the reaction;
ii. state what would be observed in the reaction,
iii. state why the copper is oxidized;
iv. an excess of copper is added to 25.0 cm3 of 16.0 mol dm3 HNO3. Calculate the volume of the gas formed at s.t.p. [H=1.0, N=14.0, O= 16.0, Cu=63.0; Molar volume of gas at .s.t.p.=22.4 dm3]
di. Pure HNO3, is a colourless liquid but when exposed to air, it turns yellowish-brown in colour. Explain briefly this observation.
ii. Write a balanced equation for the laboratory preparation of hydrogen trioxonitrate (V) acid

a. Describe how iron and aluminum reacts with each of the following substances:
i. dilute H2SO4
ii. dilute HNO3
b
i. Write an equation for the burning of sulphur in air.
ii. Name the catalyst used in the contact process.
iii. In the contact process, why is an excess of air used?
iv. Why is it necessary to cool the catalyst used in 5(b)(ii)?
v. Give a reason why the air used in the contact process needs to be as clean as possible.
vi. State two reasons why SO2 should not be discharged into the atmosphere.
c
i. State the reagents and conditions used in the laboratory preparation of chlorine.
ii. State two uses of chlorine.
d
i. Name the drying agents for each of the following gases: (I)Hydrogen;
(II)sulphur (IV) oxide;
(III)Ammonia.
ii. State the components of the following
(I)Bronze;
(II). Brass.