Chemistry 2021

Objective Questions

The hydrolysis of proteins by diluting mineral acids produces

A) sucrose B) glucose C) amino acids D) fatty acids

Correct Answer: C) amino acids

Which of the following oxide causes acid rain?

A) CO B) NO C) H₂O₂ D) NO₂

Correct Answer: D) NO₂

The ratio of carbon atoms to hydrogen atoms in a hydrocarbon is 1:2. If its molecular mass is 56, what is its molecular formula?

A) C₃H₆ B) C₄H₈ C) C₂H₄ D) CH₂

Correct Answer: B) C₄H₈

What is the relative molecular mass of the compound below

A) 137 B) 136 C) 64 D) 59

Correct Answer: B) 136

Cathodic protection of metals is based on

A) standard electrode potential of hydrogen B) its electrical conductivity C) nature of oxides formed D) relative tendencies of oxidation

Correct Answer: D) relative tendencies of oxidation

If humid air is polluted by chlorine discharged, the air can be restored by sprinkling

A) solid MnO₂ B) acidified KMnO₄ C) acidified FeSO₄ D) saturated NaCl(aq)

Correct Answer: B) acidified KMnO₄

The alkanol represented by the structure below is

A) primary and dihydric B) secondary and monohydric C) tertiary and dihydric D) secondary and dihydric

Correct Answer: A) primary and dihydric

Which of the following pairs of compounds would form a precipitate when their aqueous solutions are mixed?

A) NaCl and KNO₃ B) KCl and NaNO₃ C) K₂SO₄ and BaCl₂ D) NH₄NO₃ and CO₃

Correct Answer: C) K₂SO₄ and BaCl₂

Which of the following illustrates the variation of the rate of evolution of gas from a given length of magnesium ribbon (y-axis) with an increase in the concentration of the added (x-axis)?

A) I B) II C) III D) IV

Correct Answer: A) I

Which of the graphs illustrates the variation of the pH of a given volume of strong acid solution (y-axis) with the volume of strong base titrated against it (x-axis)?

A) I B) II C) III D) IV

Correct Answer: A) I

Which of the graphs illustrate the variation of the solubility of a salt in water (y-axis) with increase in temperature (x-axis), if the dissolution process is exothermic?

A) A B) B C) C D) D

Correct Answer: C

The formation of ethene from dehydration of ethanol can be described as

A) an addition reaction B) an elimination reaction C) an oxidation reaction D) a substitution reaction

Correct Answer:B) an elimination reaction

Which of the following gasses is highly soluble in water at room temperature?

A) ammonia B) carbon (IV) oxide C) chlorine D) nitrogen

Correct Answer:A) ammonia

A molecule of phosphorus is

A) diatomic B) triatomic C) tetra atomic D) monoatomic

Correct Answer:C) tetra atomic

The most common method of preparing insoluble salt is by

A) filtration B) decomposition C) neutralization D) double decomposition

Correct Answer:D) double decomposition

What number of moles of oxygen will exert a pressure of 10 atmosphere at 320K in an 8.2dm³ cylinder? [R = 0.082atmdm³/mol/K]

A) 0.32 B) 1.56 C) 3.13 D) 31.25

Correct Answer:C) 3.13

The basic property of salt used as drying agent is

A) efflorescence B) high melting point C) hydroscopy D) low solubility

Correct Answer:C) hydroscopy

What would be observed when aqueous ammonia is added in drops and then in excess to a solution of copper (II) ions?

A) blue precipitate is formed which is soluble in excess ammonia B) brick red precipitate is produced which is insoluble in excess ammonia C) white precipitate is formed which is soluble in excess ammonia D) green precipitate is formed which is insoluble in excess ammonia

Correct Answer:A) blue precipitate is formed which is soluble in excess ammonia

When CuSO₄(aq) is added to Pb(NO₃)₂(aq)

A) there will be no visible change B) a blue precipitate will be formed C) the resulting solution will become colourless D) a white precipitate will be formed

Correct Answer:D) a white precipitate will be formed

Consider the structure below: How many carbon atoms does the parent chain contain?

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

Correct Answer:B) 4

Under which conditions of pressure (P) and temperature (T) would the volume of an inflated balloon increase? When

A) both T and P are increased B) both T and P are decreased C) T is increased and P is decreased D) T is decreased and P is increased

Correct Answer:C) T is increased and P is decreased

The collision between ideal gas molecules are considered to be perfectly elastic because

A) they collide without losing energy B) they move randomly in a straight line C) the average kinetic energy is variable D) the distance between them is large compared to their sizes

Correct Answer:A) they collide without losing energy

Elements with high ionization energy would

A) lose electrons easily B) have large atomic radii C) have effectively nuclear charges D) have low atomic number

Correct Answer:C) have effectively nuclear charges

Which of the following statements about group VII elements is correct?

A) They are present in the same physical state B) They are strong reducing agent C) Their reactivity decreases down the group D) They exist as monoatomic molecule

Correct Answer:C) Their reactivity decreases down the group

Consider the diagram and use it to answer the question below

Which of the following cell notations represents the diagram?

A) B²⁺/B//A/A³⁺ B) A³⁺/A//B/B²⁺ C) B/B²⁺//A/A³⁺ D) A/A³⁺//B²⁺/B

Correct Answer:D) A/A³⁺//B²⁺/B

Which of the following half-reaction equations represent the reaction at the cathode?

A) A³⁺(aq) + 3e^–→ A(s) B) B²⁺(aq) + 2e^– → B(s) C) A(s) → A³⁺(aq) + 3e^– D) B(s) → B²⁺(aq) + 2e^–

Correct Answer:B) B²⁺(aq) + 2e^– → B(s)

The reactivity of fluorine is high because of

A) its high electronegativity B) the small size of the fluorine atom C) the availability of d-orbitals D) the strong F-F bond

Correct Answer:A) its high electronegativity

How many coulombs of electricity would liberate 1.08g of Ag from a solution of silver salt? [Ag = 108.0; F = 96500 C]

A) 96500 C B) 9650 C C) 965 C D) 9.65 C

Correct Answer:C) 965 C

The Bohr model of the atom proposed the existence of

A) the nucleus B) electron shells C) nucleons D) neutrons

Correct Answer:B) electron shells

At 25°C evaporation of a 100cm³ solution of K₂CO₃ to dryness gave 14g of the salt. What is the solubility of K₂CO₃ at 25°C? [K₂CO₃ = 138]

A) 0.01 mol/dm³ B) 0.101 mol/dm³ C) 1.01 mol/dm³ D) 10.0 mol/dm³

Correct Answer:C) 1.01 mol/dm³

Student X titrated 25cm³ of Na₂CO₃ with 0.1 mol/dm³ HCl using methyl orange as indicator. Student Y carried out the same exercise but he used phenolphthalein as indicator. Which of the following statements about the titration is true?

A) Hydrogen chloride gas was released in the reaction in both titration B) The titre values obtained by the titrations are equal C) The titre value obtained by X is twice that of Y D) The titre value obtained by Y is twice that of X

Correct Answer:C) The titre value obtained by X is twice that of Y

What is the concentration of a solution which contains 0.28g of KOH in 100cm³ of solution? [KOH= 56]

A) 0.01 mol/dm³ B) 0.05 mol/dm³ C) 0.10 mol/dm³ D) 0.50 mol/dm³

Correct Answer:B) 0.05 mol/dm³

What is the empirical formula of a hydrocarbon containing 0.160mol of carbon and 0.640 moles of hydrogen?

A) CH₂ B) CH₃ C) CH₄ D) C₂H₄

Correct Answer:B) CH₃

Which of the following species has the largest ionic radius?

A) S^2- B) Cl^– C) K⁺ D) Ca²⁺

Correct Answer:A) S^2-

Which of the following statements is correct about ionization energy?

A) Decreases across the period B) Results in the formation of an anion C) Causes metallic nuclei to disintegrate D) Decreases down the group

Correct Answer:D) Decreases down the group

Potassium trioxonitrate (V) can be obtained from its solution by

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

Correct Answer:C) Crystallization

An element, Q, contains 69% of ⁶³Q and 31% of ⁶⁵Q. What is the relative atomic mass of Q?

A) 63.0 B) 63.6 C) 65.0 D) 69.0

Correct Answer:B) 63.6

The following ions have the same electron configuration except ⁸O, ¹²Mg, ¹³Al, ¹⁷Cl.

A) Cl^– B) O^2- C) Mg²⁺ D) Al³⁺

Correct Answer:A) Cl^–

The region around the nucleus where electrons can be located is called

A) spectra B) an orbital C) a quanta D) a field

Correct Answer:B) an orbital

Protons and electrons are fundamentals particles because they

A) are invisible B) have different charges C) are the lightest particles D) are found in all matter

Correct Answer:D) are found in all matter

Consider the following energy profile diagram and use it to answer the question that follows.

The activation energy of the reaction is

A) E_A B) E_B C) E_C D) E_D

Correct Answer:B) E_B

The enthalpy change of the reaction is

A) E_A B) E_B C) E_C D) E_D

Correct Answer:D) E_D

The energy profile diagram illustrates

A) an endothermic reaction B) an exothermic reaction C) a spontaneous reaction D) a redox reaction

Correct Answer:B) an exothermic reaction

How many molecules of oxygen would occupy a volume of 2.24 cm³ at S.t.p.?

A) 3.01 x 10²⁰ B) 3.01 x 10²⁷ C) 6.02 x 10¹⁹ D) 6.02 x 10²⁷

Correct Answer:C) 6.02 x 10¹⁹

The isotopes of neon are represented by the symbols ²⁰xNe, ²¹yNe and ²²zNe. The relationship between x, y and z is

A) x > y > z B) x < y < z C) x = y = z D) x < z < y

Correct Answer:C) x = y = z

Which of the following pairs of molecules form hydrogen bond?

A) C₂H₅OH and CH₃OH B) CH₃OH and H₂ C) H₂S and CH₄ D) NH₃ and SO₂

Correct Answer:A) C₂H₅OH and CH₃OH

Which of the following statements about elements in group VII is correct?

A) Br₂ will oxidiza Cl^– B) F₂ has the least tendency to be reduced C) Cl₂ will oxidize I^– D) I₂ is a stronger oxidizing agent than F₂

Correct Answer:D) I₂ is a stronger oxidizing agent than F₂

Electrovalent compounds normally

A) have low boiling points B) have high mobile electrons C) conduct electricity in solid state D) dissolve in polar solvents

Correct Answer:D) dissolve in polar solvents

A coordinate covalent bond could be formed between

A) NH₃ and PCl₃ B) BCl₃ and AlCl₃ C) BCl₃ and NH₃ D) H⁺ and AlCl₃

Correct Answer:D) H⁺ and AlCl₃

Which of the following scientists discovered the electron?

A) Joseph J. Thompson B) James Chadwick C) Amedeo Avogadro D) Ernest Rutherford

Correct Answer:A) Joseph J. Thompson

Theory Questions

(a) Distinguish between molecular formula and structural formula.

(b) List three factors that determine the ionization energy of an atom.

(c) State two conditions necessary for the establishment of chemical equilibrium.

(d) Consider the following table:

Element	A	B	C
Ionization energy (kJ/mol)	619	518	594

(i) State which of the elements is the strongest reducing agent.

(ii) Give a reason for your answer.

(e) State Graham’s law of diffusion.

(f) Consider the following salts:

Mg(NO₃)₂
CaCO₃
Na₂SO₄

State which of the salts is/are:

(i) readily soluble in water

(ii) insoluble in water

(g) Classify each of the following as addition or condensation polymers:

Protein
Perspex
Nylon

(h) Define atomic radius.

(i) Explain briefly why ethanol has a higher boiling point than propane although they have comparable molar masses.

(j) State three significances of pH value in everyday life.

(a)

(i) State two characteristics of a homologous series.

(ii) Explain briefly why ethane and ethene differ in their reactions.

(b) When crystals of sodium chloride were warmed with concentrated tetraoxosulphate(VI) acid:

(i) Name the gas evolved.

(ii) State two properties of the gas.

(iii) Write a balanced chemical equation for the reaction.

(c)

(i) What are hydrocarbons?

(ii) State two natural sources of hydrocarbons.

(iii) A hydrocarbon contains 83% carbon by mass. Calculate its empirical formula.

(d) Draw and label a diagram of a setup used to electroplate a copper ornament with silver.

(a) In an experiment, 25.0 cm³ of H₂SO₄ neutralized 24.0 cm³ of 0.150 mol dm^-3 KOH.

(i) Write the balanced equation.

(ii) Calculate the concentration of the acid.

(b)

(i) A burning magnesium ribbon was placed in carbon (IV) oxide.

(I) Write the equation.

(II) Explain why magnesium burns in CO₂.

(ii) Calculate the percentage by mass of nitrogen in magnesium trioxonitrate(V).

(c) Given CH₃CH₂CH=CHCOOH:

(i) State two chemical tests.

(ii) State the observations.

(d) Describe briefly how soap is manufactured.

(e) Define electronegativity.

(a)

(i) Describe the structure of graphite and diamond.

(ii) Explain their differences in hardness and conductivity.

(b)

(i) State what is achieved during aeration and sedimentation in water purification.

(ii) Name two substances that cause hardness in water.

(iii) State two methods of removing hardness.

(iv) Give one disadvantage of hard water.

(c)

(i) Describe briefly the extraction of tin.

(ii) Write equations involving oxygen and chlorine.

(a)

(i) Explain why aluminium is not affected by air.

(ii) In aluminium extraction, state:

(I) Substance used for purifying bauxite

(II) Composition of the electrolyte

(b) Show that ZnO is amphoteric using equations.

(c)

(i) List three uses of sodium trioxocarbonate(IV).

(ii) Explain why trioxonitrate(V) acid turns yellow on storage.

(iii) Describe a laboratory test for trioxonitrate(V) ions.

(d)

(i) Write equations for the preparation of hydrogen chloride.

(ii) State one use of hydrogen chloride.