NABTEB GCE 2023 CHEMISTRY (ESSAY & OBJ) ANSWERS

NABTEB GCE 2023 CHEMISTRY (ESSAY & OBJ) ANSWERS – EXAMKING.NET
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CHEMISTRY-OBJ
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CHEMISTRY (ESSAY)-ANSWERS
INSTRUCTION: ANSWER FOUR(4) QUESTIONS ONLY
(1ai)
– Oxidation: Oxidation is the process in which an atom, ion, or molecule loses electrons.

– Reduction: Reduction is the process in which an atom, ion, or molecule gains electrons.

(1aii)
A. Electrolyte: An electrolyte is a substance that, when dissolved in a solvent (usually water), produces ions and is capable of conducting an electric current. Electrolytes are essential for many electrochemical processes.

B. Non-electrolyte: A non-electrolyte is a substance that, when dissolved in a solvent, does not produce ions and does not conduct an electric current.

C. Conductor: A conductor is a material that allows the flow of electric current. In the context of electrolytes, conductors are substances that can carry an electric current due to the movement of ions.

(1aiii)
(A)Electrolyte Example: Sodium chloride (NaCl)
(B) Non-electrolyte Example: Glucose (C₆H₁₂O₆)
(C) Conductor Example: Copper (Cu)

(1b)
(i) Action on acidified potassium tetraoxomanganate (VII)
(ii) Action on acidified potassium heptaoxo-dichromate (VI)

(1ci)
Equation: 2HCl(aq) + Mg(OH)₂(aq) —-> MgCl₂(aq) + 2HO₂(l)
No. of moles of Mg(OH)₂ which reacted = Mass/Molar mass
= 5/24+2(17)
= 5/58 = 0.0862 moles
No. of moles of HCl required for neutralisation = (2/1) × (5/58)
= 10/58
= 0.1724 moles
Concentration of HCl = no. of moles/Volume
= (0.1724/450) × 1000 mol/dm³
= 0.383 mol/dm³

(1cii)
– Nature of reactants
– Surface area of reactants
– Temperature of reaction mixture
– Concentration of reactants

(1d)
(i) Electrolysis is used to electroplate objects with a thin layer of metal
(ii) It is employed in the extraction of reactive metals like aluminum and sodium from their ores.
(iii) It converts electrical energy into chemical energy during the charging process of batteries
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(2a)
(i) At the Anode (oxidation):
Oxygen Gas (O₂)

(ii) At the Cathode (reduction): Hydrogen Gas (H₂)

(2b)
(i) Dative bond: A dative bond is formed when one atom donates a pair of electrons to another atom. It’s like one atom lending a helping hand to another. An example is the formation of the ammonium ion (NH₄⁺), where a lone pair of electrons from an ammonia molecule (NH₃) is donated to a hydrogen ion (H⁺) to form NH₄⁺.

(ii) Metallic bond: A metallic bond occurs in metals when the outer electrons of metal atoms are shared among neighboring atoms. This creates a “sea” of delocalized electrons that move freely throughout the metal. An example is the metallic bond in copper (Cu), where the outer electrons of copper atoms are shared among neighboring copper atoms.

(iii) Hydrogen bond: A hydrogen bond is like a special attraction between a hydrogen atom and an electronegative atom, such as oxygen, nitrogen, or fluorine. It’s like a little tug of attraction between molecules. An example is the hydrogen bonding between water molecules, where the hydrogen atom of one water molecule is attracted to the oxygen atom of another water molecule.

(iv) Ionic bond: An ionic bond is like a strong attraction between positively and negatively charged ions. It’s like a magnet pulling oppositely charged ions together. An example is the ionic bond in sodium chloride (NaCl), where a sodium ion (Na⁺) donates an electron to a chlorine ion (Cl⁻) to form NaCl.

(2ci)
Quantity of electricity required = It
= 1.0 × t
= t coulombs
Cu²⁺(aq) + 2e⁻ = Cu(s)
2 × 96,500C liberates 64g of Cu
t Coulombs liberates 2.3g of Cu
Therefore:
t = 2 × 96500 × 2.3/64
t = 6935.9375secs
t = 1.9266 hours of 115.6 minutes

(2cii)
(i) Liquids do not have a fixed shape and take the shape of their container, while solids have a definite shape.
(ii) Liquids have a definite volume, but it can change with temperature and pressure while Solids also have a definite volume.
(iii) In liquids, the particles are close together but can move around and slide past each other While In solids, the particles are tightly packed and vibrate in fixed positions.

(2ciii)
A mole of a substance is defined as the amount of that substance that contains the same number of entities (atoms, molecules, ions, etc.) as there are in 12 grams of carbon-12.
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(3ai)
The strength of an acid refers to its ability to donate protons (H +) in a solution. Strong acids completely decompose in water, releasing a high concentration of H + ions, while weak acids only partially decompose, resulting in a lower concentration of H + ions.

(3aii)
Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain an equal number of molecules.

(3aiii)
The Avogadro constant, also known as the Avogadro number, is the number of atoms, ions, or molecules in one mole of a substance.
The value of the Avogadro constant is approximately
6.0221×10²³mol-1

(3bi)
– Element C; Sulphur
– Element D; Magnesium

(3bii)
MgS (Magnesium Sulphide)

(3biii)
(i) It is ionic in nature
(ii) It has a high melting point.
(iii) It is readily soluble in water

(3biv)
Ionic bonding

(3ci)

(3cii)
(i) Gas particles are in constant, random motion: Gas particles are constantly moving in straight lines until they collide with other particles or the walls of their container. These collisions are elastic, meaning there is no net loss of energy.

(ii) Gas particles are negligible in size: The size of gas particles is considered to be very small compared to the distance between them. This assumption allows us to treat gases as point masses.

(iii) Gas particles experience no intermolecular forces: In the Kinetic Theory of Gases, it is assumed that there are no attractive or repulsive forces between gas particles. This assumption simplifies the analysis of gas behaviour.

(3d)
(i) Roasting:
Zinc sulfide (ZnS) ore, commonly known as sphalerite, is first converted to zinc oxide (ZnO) by the process of roasting. Roasting involves heating the ore in the presence of excess air to convert the sulfide to oxide:
ZnS + O₂ —-> ZnO +SO₂

(ii) Reduction:
The obtained zinc oxide is then reduced to zinc by heating with carbon (coke) in a blast furnace:
ZnO + C —-> Zn + CO

(iii) Condensation:
The zinc vapor produced in the reduction step is then condensed into a solid form by cooling. This usually involves passing the vapor through a condenser.

(iii) Purification:
The obtained crude zinc is then subjected to a purification process to remove impurities, typically through fractional distillation or other refining methods.
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(4ai)
Vulcanisation: Vulcanisation is a chemical process in which rubber or other polymers are treated with sulfur or other vulcanising agents to improve their strength, elasticity, and durability. It involves cross-linking the polymer chains, making the material more resistant to heat, aging, and deformation.

(4aii)
Cracking: Cracking is a process in which larger hydrocarbon molecules are broken down into smaller molecules by the application of heat and/or catalysts. It is used to produce gasoline, diesel fuel, and other valuable products from heavier crude oil fractions or hydrocarbon feedstocks.

(4bi)
– Crude oil
– Natural gas
– Coal

(4bii)
Neutralisation: Neutralisation is a chemical reaction between an acid and a base, resulting in the formation of a salt and water. It involves the transfer of protons (H⁺) from the acid to the base, leading to the neutralization of their acidic and basic properties.

(4biii)
Chemical equation illustrating neutralisation: HCl(aq) + NaOH(aq) —-> NaCl(aq) + H₂O(l)

(4biv)
(i) Production of polyethylene: Ethene is a precursor for the production of polyethylene, one of the most widely used plastics.
(ii) Synthesis of ethanol: Ethene can be used in the production of ethanol through hydration, where water is added to ethene in the presence of a catalyst.
(iii) Ripening of fruits: Ethene is involved in the natural ripening of fruits. It can be used to artificially ripen fruits in controlled environments.

(4ci)
Coloured ions:
Transition elements or their ions have colored ions because of the presence of partially filled d orbitals. When light interacts with these d orbitals, electrons absorb specific wavelengths of light, resulting in the reflection of complementary colors. This absorption and reflection of light give rise to the characteristic colors of transition metal ions.

(4cii)
Formation of complex compounds:
Transition elements form complex compounds due to their ability to form coordinate bonds. The partially filled d orbitals in transition metals allow them to accept lone pairs of electrons from other molecules or ions, forming coordination complexes. These complexes are often highly stable and exhibit unique properties, such as different colors and magnetic behavior.

(4ciii)
Variable oxidation states:
Transition elements show variable oxidation states because of the availability of multiple d orbitals with different energies. The electrons in these orbitals can be easily gained or lost, allowing transition elements to exhibit a range of oxidation states. This versatility in oxidation states contributes to their ability to form a variety of compounds and participate in redox reactions.

(4civ)
Catalytic activity:
Transition elements act as catalysts due to their ability to undergo reversible oxidation and reduction reactions. The presence of multiple oxidation states and the ability to form complexes make transition metals effective catalysts. They can provide a surface for reactions to occur, stabilize reactive intermediates, and facilitate the transfer of electrons during chemical reactions.

(4d)

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(5ai)
(i) Polypropylene
(ii) Polyethylene
(iii) Ethylene Glycol

(5aii)
(i) Particulate Matter
(ii) Nitrogen Oxides (NOx)
(iii) Sulfur Dioxide (SO2)

(5bi)
The mass number of an element is the sum of the number of protons and neutrons in the nucleus of an atom. It is denoted by the letter ‘A’. In a neutral atom, the mass number is also equal to the number of electrons. On the other hand, the atomic number of an element, on the other hand, is the number of protons in the nucleus of an atom. It is denoted by the letter ‘Z’. The atomic number determines the identity of an element and is unique to each element. In a neutral atom, the atomic number is also equal to the number of electrons.

(5bii)
Isotopes of an element are atoms of the same element that have the same number of protons (and hence belong to the same element) but different numbers of neutrons. This means isotopes of an element have the same atomic number but different mass numbers.

(5biii)
(i) Deuterium
(ii) Protium

(5biv)
(i) Reduction of Iron(III) Oxide (Fe2O3):
Fe₂O₃(s) + 3C(s) —-> 2Fe(l) + 3CO(g)

(ii) Formation of Carbon Dioxide:
C(s) + O₂(g) —> CO₂(g)

(iii) Formation of Calcium Oxide (from Limestone):
CaCO₃(s) —-> CaO(s) + CO₂(g)
(iv) Formation of Calcium Silicate (Slag):
CaO(s) + SiO₂(s) —-> CaSiO₃(l)

(5ci)
(i) Acidic nature: Sulphur (IV) oxide is a non-metal oxide and can react with water to form sulfuric acid (H₂SO₄), which is a strong acid.
SO₂ + H₂O –> H₂SO₃
H₂SO₃ + H₂O –> H₂SO₄

(ii) Reducing agent: Sulphur (IV) oxide can act as a reducing agent. It is commonly used in reducing metal sulfites to metal sulfides.
SO₂ + FeS -> Fe + SO₃

(5cii)
(a) Deliquescent compound of calcium: Calcium chloride (CaCl₂)

(b) Hygroscopic compound of calcium: Calcium nitrate (Ca(NO₃)₂)
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