WAEC SSCE - Chemistry - 1995 (Objective)

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Question 2 Report

What is the percentage by mass of copper in copper in copper (l) oxide (CU₂O)? [O = 16; CU =64]

88.9%

80.0%

66.7%

20.0%

11.1%

Answer Details

To determine the percentage by mass of copper in copper (I) oxide (Cu2O), we need to calculate the molar mass of Cu2O, which is the sum of the atomic masses of the elements in the compound. Molar mass of Cu2O = 2Cu + O = (2 x 64) + 16 = 144 g/mol The molar mass of copper in Cu2O is 2 x 64 = 128 g/mol The percentage by mass of copper in Cu2O is: (128 g Cu / 144 g Cu2O) x 100% = 88.9% Therefore, the correct answer is 88.9%.

Read lesson note on Stoichiometry And Chemical Reactions (WAEC)

Stoichiometry And Chemical Reactions

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Question 3 Report

The function of limestone in the extraction of iron in the blast furnace is

removal of the earthly impurities

decomposition of the iron ore

conversion of iron (lll) to iron (ll) compounds

generation of heat for the process

conversion of coke to carbon(ll)oxide

Answer Details

The function of limestone in the extraction of iron in the blast furnace is to remove impurities from the iron ore. During the extraction process, iron ore is heated with coke (a form of carbon) and air to produce molten iron, which is then drained from the bottom of the furnace. However, the iron ore contains impurities such as silicon dioxide (SiO2), which is acidic in nature and can corrode the lining of the furnace. Limestone (calcium carbonate, CaCO3) is added to the blast furnace to act as a flux, which neutralizes the acidic impurities and forms a slag, a waste material that can be easily removed from the furnace. Thus, the function of limestone is to purify the iron ore by removing the impurities and prevent the corrosion of the furnace lining.

Read lesson note on Acids, Bases And Salts (JAMB)

Acids, Bases And Salts

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Question 4 Report

Which of the following is hydrocarbons is unsaturated?

Ethane

Benzene

Propane

2 - methylbutane

2,2,4-trimethylpentane

Answer Details

The hydrocarbon that is unsaturated is benzene. A hydrocarbon is considered unsaturated when it contains at least one double or triple bond between carbon atoms, which means that it has fewer hydrogen atoms per carbon atom than a saturated hydrocarbon. Benzene is an unsaturated hydrocarbon with a ring structure and alternating double bonds between carbon atoms. The other options, ethane, propane, 2-methylbutane, and 2,2,4-trimethylpentane, are all saturated hydrocarbons, which means they only have single bonds between carbon atoms and are fully saturated with hydrogen atoms.

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 5 Report

Fructose and glucose are classified as carbohydrates because they

are crystalline white solids

are energy -giving substances

are naturally occurring organic compounds

contain carbon oxygen and hydrogen

conform to the general formula C_x(H₂O)_y

Basic Biochemistry And Synthetic Polymers

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Question 6 Report

Which of the following species is always present in acidified water?

NH⁺₄

O ^2-

HCI

H³O⁺

HNO₃

Answer Details

The species that is always present in acidified water is H³O⁺. When water is mixed with an acid, it produces H⁺ ions, which react with water to form H³O⁺ ions. These ions are responsible for the acidic properties of the solution. Therefore, out of the given options, H³O⁺ is the correct choice.

Read lesson note on Periodic Chemistry (Ghana Only) (WAEC)

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Question 7 Report

The following salts dissolve readily in cold water except

CaCI₂

PbSO₄

(NH₄)₂SO₄

Na₂CO₃

Na₂SO₃

Answer Details

Among the given options, the salt that does not dissolve readily in cold water is PbSO₄. This is because PbSO₄ is an ionic compound with a high lattice energy, meaning that its ions are held together by strong electrostatic forces of attraction. These forces of attraction make it difficult for the PbSO₄ crystals to break apart and dissolve in water. Therefore, PbSO₄ is considered insoluble in water. The other options, such as CaCI₂, (NH₄)₂SO₄, Na₂CO₃, and Na₂SO₃, readily dissolve in cold water due to their ionic nature and low lattice energy.

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)

Acids, Bases And Salts (Ghana Only)

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Question 8 Report

Sodium chloride cannot conduct electricity in the solid state because it

is a normal salt

is highly soluble in water

is an electrovalent compound

does not have any effect on litmus

does not contain mobile ions

Answer Details

Sodium chloride (NaCl) cannot conduct electricity in the solid state because it does not contain mobile ions. In the solid state, the sodium (Na) and chloride (Cl) ions are held tightly in a lattice structure, and cannot move freely to conduct an electric current. When dissolved in water, NaCl dissociates into its ions, which are free to move and conduct electricity. Therefore, NaCl is an example of an ionic compound that conducts electricity only when dissolved in water or melted.

Read lesson note on Acids, Bases And Salts (JAMB)

Acids, Bases And Salts

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Question 9 Report

The following alkanols will yield alkanoic acids on reacting with excess acidified K₂Cr₂O₇ except

CH₃CH₂OH

(CH₃)₂CHCH₂OH

(CH₃)₃CCH₂OH

(CH₃)₃COH

CH₃CH₂CH₂CH₂OH

Answer Details

The alkanols that will yield alkanoic acids on reacting with excess acidified K₂Cr₂O₇ are primary and secondary alkanols. Tertiary alkanols do not undergo oxidation. Therefore, the correct answer is (CH₃)₃COH, which is a tertiary alcohol and cannot be oxidized to an alkanoic acid.

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 10 Report

Alums are classified as

simple salt

acid salts

anhydrous salts

double salts

basic salts

Answer Details

Alums are classified as double salts. Double salts are compounds that contain two different cations and one anion, held together by ionic bonds. In the case of alums, they are double salts of a monovalent cation (such as potassium or ammonium), a trivalent cation (such as aluminum or chromium), and a sulfate anion. The general formula for alums is M^+M^3+(SO4)2·12H2O, where M^+ is a monovalent cation and M^3+ is a trivalent cation. Alums are commonly used as mordants in dyeing and in various industrial processes.

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)

Acids, Bases And Salts (Ghana Only)

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Question 11 Report

What mass of copper will be deposited by the liberation of Cu²⁺ when 0.1F of electricity flows through an aqueous solution of a copper (ll) salt? [Cu = 64]

64g

32g

12.8g

6.4g

3.2g

Electrolysis

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Question 12 Report

A positive brown ring test indicates the presence of

NO ₃

Fe ³⁺

SO ^2-₃

CU⁺

NO^- ₂

Answer Details

The positive brown ring test indicates the presence of nitrate ions (NO₃). The test is done by adding freshly prepared iron(II) sulfate (FeSO₄) solution and concentrated sulfuric acid (H₂SO₄) to the test solution. If nitrate ions are present in the solution, a brown ring will form at the junction of the two liquids. This occurs because nitrate ions reduce Fe²⁺ ions to Fe³⁺ ions, which then react with the sulfuric acid to form Fe(HSO₄)₂ which appears as the brown ring.

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)

Acids, Bases And Salts (Ghana Only)

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Question 13 Report

The following statements about graphite are correct except that it

is used as a lubricant

has a network structure

contains mobile free electrons

is good conductor

is an allotrope of carbon

Metals And Their Compounds

Chemical Bonds (Nigeria Only)

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Question 14 Report

Which of the following is an alloy of mercury?

Stainless steel

Soft solder

Coinage bronze

Amalgam

Duralumin

Answer Details

The alloy of mercury is amalgam. An amalgam is a type of alloy that consists of mercury as one of the components. Amalgams are usually used in dentistry to fill cavities. When mercury is mixed with other metals like silver, tin, or copper, it forms a soft, pliable material that can be easily shaped to fill the cavity. Once the amalgam hardens, it becomes a durable and long-lasting filling. Therefore, the correct answer is Amalgam.

Read lesson note on Metals And Their Compounds (JAMB)

Metals And Their Compounds

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Question 15 Report

Which of the following cannot be deduced from the electronic configuration of a transition metal?

Possession of magnetic property

Ability to form complex ions

Position in the Periodic Table

Variable oxidation states

Physical properties of the metal

Structure Of The Atom (Ghana Only)

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Question 16 Report

If a solid has a low melting point and dissolves readily in benzene, it would probably

contain strong electrostatic forces of attraction

conduct electricity in the molten state

dissolve in water

have covalent bonding

absorb moisture on exposure to air

Answer Details

If a solid has a low melting point and dissolves readily in benzene, it would probably have covalent bonding. Covalent compounds are those that are held together by sharing of electrons between atoms, and they typically have low melting points and do not conduct electricity in either the solid or molten state. Benzene, a nonpolar solvent, readily dissolves covalent compounds, which explains why the solid in question dissolves readily in it. Strong electrostatic forces of attraction are associated with ionic compounds, which typically have high melting points and are soluble in polar solvents like water.

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Read lesson note on Atomic Structure And Bonding (JAMB)

Rates Of Chemical Reaction

Solubility

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Question 17 Report

Copper (ll) tetraoxosulphate (VI) is often added to swimming pools because it

prevents the growth of algae

coagulates suspended particles

neutralizes dissolved gases in water

reacts with any excess chlorine present

increases the amount of dissolved oxygen

Answer Details

Copper (II) tetraoxosulphate (VI) is often added to swimming pools because it prevents the growth of algae. Algae can grow in the warm, moist environment of swimming pools and can make the water appear green and murky. Copper (II) tetraoxosulphate (VI) is a powerful algicide that can prevent the growth of algae in swimming pools. When added to the water, it releases copper ions which are toxic to algae and prevent their growth. Copper (II) tetraoxosulphate (VI) is a safe and effective way to keep swimming pools clean and clear.

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Oxidation And Reduction

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Question 18 Report

The most suitable method for preparing lead (ll) chloride is by

action of dilute HCI on PbSO ₄

acts of dilute HCI on lead

action of dilute HCI on PbCO₃

bubbling chlorine into a solution of Pb(NO₃)₂

mixing aqueous solutions Pb(NO₃)₂ and NaCI.

Answer Details

The most suitable method for preparing lead (II) chloride is by mixing aqueous solutions of Pb(NO₃)₂ and NaCI. When aqueous solutions of lead nitrate and sodium chloride are mixed, a white precipitate of lead (II) chloride is formed. The other options mentioned in the question are not suitable for preparing lead (II) chloride. For example, the action of dilute HCl on PbSO₄ will produce lead (II) sulfate, not lead (II) chloride. Similarly, the action of dilute HCl on lead will produce lead (II) chloride, but it is not the most suitable method for preparing lead (II) chloride. Therefore, the correct answer is "mixing aqueous solutions Pb(NO₃)₂ and NaCI."

Read lesson note on Periodic Chemistry (Ghana Only) (WAEC)

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Question 19 Report

Which of the following molecules is linear in shape?

CH₄

H₂O

NH₃

H₂S

CI₂

Answer Details

The shape of a molecule is determined by its electronic geometry, which depends on the arrangement of the atoms and the number of electron pairs around the central atom. A molecule is considered linear if it has two atoms and no lone pairs of electrons on the central atom. Based on this definition, the molecule that is linear in shape is CI₂ because it has two chlorine atoms and no lone pairs of electrons on the central atom. All the other molecules listed have lone pairs or more than two atoms, which means they are not linear in shape.

Read lesson note on Atomic Structure And Bonding (JAMB)

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Question 20 Report

Which of the following is not correct of the reaction represented by the equation below? 2C_(s) + O_2(g) → 2CO_(g); ∆H = - xKJ

there is an increase in entropy ;

There is anincrease in gaseous volume

Carbon (lV) oxide is produced

The oxidation number of carbon increases from 0 to +2

The reaction is exothermic

Kinetic Theory Of Matter And Gas Laws

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Question 21 Report

What is the amount (in mole) of hydrogen gas that would be produced if 0.6 mole of hydrochloric acid reacted with excess zinc according to the following equation? Zn_(s) + 2HCI_(aq) → ZnCI_2(aq) + H_2(g)

0.1 mole

0.2mole

0.3 mole

1.0 mole

2.9 moles

Answer Details

According to the balanced chemical equation, 1 mole of zinc reacts with 2 moles of hydrochloric acid to produce 1 mole of hydrogen gas. Zn_(s) + 2HCI_(aq) → ZnCI_2(aq) + H_2(g) Therefore, if 0.6 mole of hydrochloric acid is used, it will react with 0.3 mole of zinc to produce 0.3 mole of hydrogen gas. Thus, the amount of hydrogen gas produced is 0.3 mole. Therefore, the correct option is: 0.3 mole.

Read lesson note on Stoichiometry And Chemical Reactions (WAEC)

Stoichiometry And Chemical Reactions

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Question 22 Report

Consider the reaction represented by the equation below: XO + YO → X + YO₂ In the reaction, YO acts as

an acidic oxide

a basic oxide

a reducing agent

a weak base

an oxidizing agent

Answer Details

In the given chemical equation, XO is being reduced, and YO is being oxidized. An oxidizing agent is a substance that causes another substance to be oxidized, while a reducing agent is a substance that causes another substance to be reduced. YO is being reduced, which means it is causing the reduction of XO. Thus, YO is acting as a reducing agent.

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Question 23 Report

What mass of copper will be deposited by the liberation of Cu²⁺ when 0.1F of electricity flows through an aqueous solution of a copper (ll) salt? [Cu = 64]

64g

32g

12.8g

6.4g

3.2g

Answer Details

The amount of substance that is deposited during an electrolysis reaction can be calculated using Faraday's laws of electrolysis. According to Faraday's laws, the amount of substance deposited is directly proportional to the amount of electricity that flows through the solution. The formula that relates the amount of substance to the amount of electricity is: Amount of substance = (Electricity in Coulombs) / (Faraday constant x Valency) where the Faraday constant is the amount of electric charge per mole of electrons, and the valency is the number of electrons involved in the redox reaction. For the given problem, the copper (II) ion has a valency of 2, and we are given that 0.1 F of electricity flows through the solution. The Faraday constant is 96,485 Coulombs per mole of electrons. Therefore, the amount of copper that will be deposited can be calculated as: Amount of substance = (0.1 F) / (2 x 96,485 C/mol) = 5.18 x 10^-5 mol The molar mass of copper is 64 g/mol, so the mass of copper that will be deposited is: Mass of copper = Amount of substance x Molar mass = 5.18 x 10^-5 mol x 64 g/mol = 0.00331 g ≈ 3.2 g (rounded to one decimal place) Therefore, the answer is 3.2g.

Read lesson note on Electrolysis (JAMB)

Electrolysis

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Question 24 Report

The following can be obtained directly from the destructive distillation of coal except

ammoniacal liquor

coke

producer gas

coal gas

coal tar

Answer Details

Destructive distillation is the process of heating coal in the absence of air to obtain useful products. During this process, coal is broken down into various components. Ammoniacal liquor, coal gas, coke, and coal tar are some of the products obtained from the destructive distillation of coal. However, producer gas is not obtained directly from the destructive distillation of coal. It is obtained by passing air over coke at a high temperature. Therefore, the correct option is "producer gas."

Read lesson note on Separation Of Mixtures And Purification Of Chemical Substances (JAMB)

Separation Of Mixtures And Purification Of Chemical Substances

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Question 25 Report

H₃O⁺_(aq) + OH-_(aq) → 2H₂O_(l). The heat change accompanying the process represented by the equation above is the heat of

neutralization

formation

solution

dilution

hydration

Answer Details

The heat change accompanying the given process is the heat of neutralization. This is because the reaction involves the combination of hydrogen ions (H+) from an acid (represented by the H3O+ ion) and hydroxide ions (OH-) from a base to form water molecules (H2O). This process of combining an acid and a base to form a salt and water is called neutralization. The heat released or absorbed during this process is known as the heat of neutralization.

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Energy And Energy Changes

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Question 26 Report

Metals which react with steam only when they are red-hot include

copper

sodium

calcium

gold

iron

Metals And Their Compounds

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Question 27 Report

In which of the following processes are larger molecules broken down into smaller molecules?

Vulcanization of rubber

Hydrogenation of palm oil

Hydrolysis of starch

Polymerization

Esterification

Answer Details

The process in which larger molecules are broken down into smaller molecules is called "degradation" or "cracking". Out of the given options, the process that involves larger molecules being broken down into smaller molecules is "hydrolysis of starch". Hydrolysis is a chemical reaction that involves the breaking of a bond in a molecule using water. In the case of starch, it is broken down into smaller glucose molecules by the addition of water molecules, resulting in a simpler and smaller molecule. The other processes listed involve the formation or combination of molecules rather than their breakdown.

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Read lesson note on Chemical Kinetics And Equilibrium Systems (Ghana Only) (WAEC)

Read lesson note on Periodic Chemistry (Ghana Only) (WAEC)

Solubility Of Substances (Ghana Only)

Chemical Kinetics And Equilibrium Systems (Ghana Only)

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Question 28 Report

A WEAK ACID IS ONE WHICH

IS NOT CORROSIVE

IS SLIGHTLY IONIZIED IN WATER

DOES NOT PRODUCE SALTS WITH ALKALIS

DOES NOT CONDUCT AN ELECTRIC CURRENT IN AQUEOUS SOLUTION

FORMS ACID SALTS WITH BASES

Answer Details

A weak acid is one which is slightly ionized in water. In other words, when a weak acid is dissolved in water, only a small fraction of its molecules dissociate into ions. This is in contrast to a strong acid, which dissociates almost completely into ions when dissolved in water. As a result of its weak ionization, a weak acid has a lower acidity compared to a strong acid.

Read lesson note on Periodic Chemistry (Ghana Only) (WAEC)