WAEC SSCE - Chemistry - 1995

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]

Détails de la réponse

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.

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)

Détails de la réponse

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.

Which of the following is an alloy of mercury?

Détails de la réponse

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.

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]

Détails de la réponse

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

Détails de la réponse

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.

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

Détails de la réponse

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.

The following statements about graphite are correct except that it

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

Détails de la réponse

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."

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

Détails de la réponse

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.

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

Détails de la réponse

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%.

The following salts dissolve readily in cold water except

Détails de la réponse

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.

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

Détails de la réponse

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.

Which of the following molecules is linear in shape?

Détails de la réponse

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.

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

Détails de la réponse

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.

Sodium chloride cannot conduct electricity in the solid state because it

Détails de la réponse

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.

Alums are classified as

Détails de la réponse

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.

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

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

Détails de la réponse

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."

A positive brown ring test indicates the presence of

Détails de la réponse

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.

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)

Détails de la réponse

From the balanced chemical equation, it is observed that 1 mole of Zinc reacts with 2 moles of Hydrochloric acid to produce 1 mole of Hydrogen gas. Therefore, 0.6 mole of Hydrochloric acid would react with 0.3 mole of Zinc and produce 0.3 mole of Hydrogen gas. So the answer is (c) 0.3 mole.

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

Détails de la réponse

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.

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

Détails de la réponse

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.

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

Détails de la réponse

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.

Fructose and glucose are classified as carbohydrates because they

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A WEAK ACID IS ONE WHICH

Détails de la réponse

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.

The gas produced when a mixture of sodium propanoate and soda lime is heated is

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

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

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Which of the following is hydrocarbons is unsaturated?

Détails de la réponse

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.

(a) Name the device used for producing an electric current from a chemical

(b) Copy and complete the table below.

Détails de la réponse

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(a) State the type of reaction involved in the conversion of:

(i) proteins.to amino acids:

(ii) ethanol to ethene;

(iii) benzene to bromobenzene

(b) Write an equation to show that ethene reasts with hydrogen in the presence of finely divided nickel.

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(a)(i) Explain the term pH

(ii) If sodium hydroxide solution were added to a solution of a strong acid, what would happen to the pH of the solution?

(b) Give one example of each of the following:

(i) acidic oxide

(ii) acid salt.

Détails de la réponse

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(a) List two differences between solids and liquids.

(b) The graph below is the heating curve for a solid X. Use the graph to answer Questions (i) — (iii) below.

(i) What is the melting point of X?

(ii) If the vapour of X is cooled, at what temperature will it start to condense?

(iii) (I) As X is heated, state what happens to the: I. frequency of collision of molecules of X;

(II) value of the entropy of the system.

Détails de la réponse

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(a)(i) Explain what is meant by saturated solution

(ii) Describe in outline, a suitable procedure for preparing a saturated solution of sodium trioxonitrate(V) at 30°C.

(ii) State two techniques that can be used to recover crystals of sodium trioxonitrate(V) from its saturated solution.

(b) 1.0dm\(^3\) of an aqueous solution at 90°C contains 404g of potassium trioxonitrate(V) and 245g of potassium trioxochlorate (V).

(i) Determine which of the two salts will separate out when the solution is cooled to 60°C. N = 14. O = 16, CI = 35.5, K = 39; Solubility of KNO\(_3\) in water at 60\(^o\)C = 5.14 mol.dm\(^{-3}\), Solubility of KCIO\(_3\) in water at 60°C = 1.61 mol.dm\(^{-3}\)

(ii) Calculate the mass of salt that will separate out at 60°C

(c)(i) List two salts which cause hardness of water.

(ii) Explain why temporary hardness of water result in the furring of kettle.
 

Détails de la réponse

a)(i) Saturated solution: A saturated solution is a solution that has dissolved the maximum amount of solute at a given temperature and pressure, where any additional solute will remain undissolved at the bottom of the container.

a)(ii) Preparation of saturated solution: To prepare a saturated solution of sodium trioxonitrate(V) at 30°C, a known mass of the solute is added to a fixed volume of solvent (water) at 30°C, and stirred continuously until no more solute dissolves, and some amount remains undissolved.

a)(iii) Recovery techniques: Two techniques that can be used to recover crystals of sodium trioxonitrate(V) from its saturated solution are cooling the solution, which will cause the excess solute to crystallize out, and evaporation of the solvent, which will leave the solute behind as crystals.

b)(i) Separation of salts: To determine which of the two salts will separate out when the solution is cooled to 60°C, we need to compare the solubility of each salt at 60°C with the concentration of each salt in the solution at 90°C. The solubility of KNO3 in water at 60°C is higher than the solubility of KCIO3 in water at 60°C, so KNO3 will remain in solution while KCIO3 will separate out.

b)(ii) Calculation of mass: To calculate the mass of salt that will separate out at 60°C, we need to use the solubility data and the concentration of KCIO3 in the solution. The amount of KCIO3 in the solution at 90°C is 245g, which is equal to 245/122 = 2.01 mol. At 60°C, the solubility of KCIO3 is 1.61 mol.dm-3, so the maximum amount of KCIO3 that can remain in solution is 1.61 mol. Therefore, the amount of KCIO3 that will separate out is 2.01 - 1.61 = 0.40 mol. The molar mass of KCIO3 is (39+35.5+3x16) = 122g/mol, so the mass of KCIO3 that will separate out is 0.40 x 122 = 48.8g.

c)(i) Salts causing hardness of water: Two salts that cause hardness of water are calcium carbonate (CaCO3) and magnesium sulfate (MgSO4).

c)(ii) Temporary hardness of water: Temporary hardness of water is caused by the presence of dissolved calcium and magnesium bicarbonates, which can decompose upon heating, leading to the formation of insoluble calcium and magnesium carbonates. These carbonates deposit as a layer of scale (furring) on the inside of kettles and other hot water equipment.

(a)(i) List the three types of particles present in atoms.

(ii) name the element which does not contain all the three particles in its atom. Mention the particle that is not present.

(b) Give the reason why:

(i) the relative atomic masses of some elements are not whole number;

(ii) relative atomic masses are used instead of the actual masses of atoms in grams;

(iii) metals are good conductors of electricity.

(c)(i) Name the type of bond present in the oxonium ion,

(ii) State one effect of the existence of intermolecular hydrogen bonding on the physical properties of ethanol.

(d)(i) Explain what is meant by water of crystallization.

(ii) When 5.0g of a compound Y was heated to constant mass, 1.8g of water vapour was given off. Determine the number of molecules of water of crystallization in one molecule of Y, given that the molar mass of its anhydrous form is 160g. [H = 1, 0 = 16]

Détails de la réponse

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(a)(i) What is isomerism?

(ii) Name the alkanol that is isomeric with methoxymethane (CH\(_3\)OCH\(_3\)).

(b)(i) Outline the laboratory:preparation of ethylethanoate. (Diagrams not required)

(ii) Write the structural formula of ethylethancqte

(iii) State two physical properties of ethylethanoate.

(c) When gas oil which consists of larger hydrocarbons was subjected to high temperature and pressure, the following reaction occurred.

C\(_{17}\)H\(_{36(l)}\) \(\to\) 3C\(_2\)H\(_{4(g)}\) + C\(_3\)H\(_{6(g)}\) + Q\(_{(l)}\)

(i) What name is given to the process indicated above?

(ii) State the importance of the process to the petroleum industry.

(iii) Find the formula of the product which Q represents in the equation above.

(iv) Mention one type of chemical industry that utilizes ethene as raw material.

(d) Consider the following compounds: CH\(_3\) — (CH\(_2\))\(_2\) —CH\(_3\); C\(_6\)H\(_5\) —CH = CH\(_2\); CH=C — CH\(_3\). State which of them:

(i) is used as a domestic fuel;

(ii) is an aromatic compound,

(iii) participates in such situation but not addition reactions;

(iv) would react with two moles of hydrogen per mole.

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(a) State three reasons why air is classified as a mixture.

(b) List two methods that can be used to separate a mixture of iodine crystals and iron filings.

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(a) Mention one process apart from respiration, which increases the amount of carbon (IV) oxide in the atmosphere.

(b)(i) State one use of sodium hydrogentrioxocarbonate (IV).

(ii) Write an equation to show the action of heat on sodium hydrogentrioxocarbonate(IV).

Détails de la réponse

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(a) What is the change in oxidation state of chromium in the reaction represented by the following equation?

3SO\(_2\) + Cr\(_2\)O\(^2_{-7}\) + 2H\(^+\)  -> 3SO\(_4^{2-}\) + 2Cr\(^{3+}\) + H\(_2\)O

(b) Use the half equations given below to deduce the equation for the reaction between iron(II) ions and heptaoxodichromate (VI) ions in acidic solution.

Fe\(^{2+}\)  --> Fe\(^{3+}\) + e\(^-\)

Cr\(_2\)O\(^{2-}_7\) + 14H\(^+\) + 6e\(^-\) ----> 2Cr\(^{3+}\) + 7H\(_2\)O.

Détails de la réponse

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What name is given to each of the following? The

(a) irregular random movement of smoke particles in air.

(b) existence of an element in various forms in the same physical-state

(c) disintegration of atomic nuclei, accompanied with radiation emission.

(d) conversion of a solid difitrunto vapour without melting.

Détails de la réponse

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(a)(i) Sketch a graph to illustrate Charles' law.

(ii) A gas occupies 500 cm\(^{ 3}\) at 2TC. calculate its volume at 40°C constant pressure.

(b) List two gases that are used as refrigerant

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(a) List three properties of a system that is in a state of chemical equilibrium.

(b) Consider reaction represented by the following equation: 3H\(_{2(g)}\) + N\(_{2(g)}\) \(\rightleftharpoons\) 2NH\(_{3(g)}\); H = 92KJ

(i) Explain the effect of increasing the temperature of the reaction on the yield of ammonia

(ii) Uses of energy profile diagram to illustrate the effect of a positive catalyst on the rate of either the forward reaction or the reverse reaction.

(c) In the extraction of aluminium from bauxite:

(i) outline the procedure used for purifying the ore;

(ii) write equation for the reaction at each electrode, during the electrolysis of the pure alumina;

(iii) state the function of molten cryolite in the electrolytic cell for the extraction.

Détails de la réponse

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(a) Mention the chemical substance manufactured starting from each of the foirownc sets of materials:

(i) sugar and yeast;

(ii) ammonia, air and water;

(iii) vegetable oil and caustic alkali.

(b) State one air pollutant generated during the manufacture of fertilizers.

Détails de la réponse

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