WAEC Adapted Theory Solutions:

Question 1:

a) Contributions to the Periodic Table: - Dmitri Mendeleev: Created the first widely recognized periodic table, arranged elements by atomic mass, and predicted the existence of undiscovered elements. - Henry Moseley: Rearranged the periodic table based on atomic number rather than atomic mass, leading to the modern periodic law. (10 marks)

b) Periodic Law: The properties of elements are a periodic function of their atomic numbers. This law helps in organizing elements in the periodic table based on similar properties. (10 marks)

c) Trends in Properties: - Atomic Radius: Decreases across a period (more protons pull electrons closer) and increases down a group (more energy levels). - Electronegativity: Increases across a period (greater nuclear charge attracts electrons) and decreases down a group (increased distance from nucleus). - Ionization Energy: Increases across a period (greater attraction to nucleus) and decreases down a group (increased distance and shielding effect). (10 marks)

d) Oxidation and Reduction: - Oxidation: Loss of electrons; Reduction: Gain of electrons. - In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, Zn is the reducing agent, and Cu²⁺ is the oxidizing agent. (10 marks)

e) Balanced Redox Reaction: - Half-reactions: - Oxidation: Fe²⁺ → Fe³⁺ + e⁻ - Reduction: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O - Balanced reaction: 5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O. (10 marks)

f) Ionic Theory: Suggests that electrolytes dissociate into ions in solution. - Electrolysis of NaCl: At the anode, 2Cl⁻ → Cl₂ + 2e⁻; at the cathode, Na⁺ + e⁻ → Na. (10 marks)

g) Electrochemical Cell: A device that converts chemical energy into electrical energy (galvanic) or vice versa (electrolytic). - Example: A copper-zinc cell where Zn is oxidized and Cu is reduced, with electrons flowing from Zn to Cu. (10 marks)

h) Standard Electrode Potential: Measure of the tendency of a chemical species to be reduced, calculated by E°cell = E°(cathode) - E°(anode). - For the cell with Cu²⁺ and Zn²⁺, E°cell = +0.34 V - (-0.76 V) = +1.10 V. (10 marks)

i) Faraday’s Laws: - First Law: The mass of substance deposited is directly proportional to the quantity of electricity passed. - Second Law: The masses of different substances deposited by the same quantity of electricity are proportional to their equivalent weights. - Mass of Cu: \[ m = \frac{Q}{F} \times \text{Molar Mass} = \frac{(2 \text{ A} \times 1800 \text{ s})}{96500 \text{ C/mol}} \times 63.5 \text{ g/mol} = 0.226 \text{ g}. \] (10 marks)

WAEC Adapted Theory Solutions:

Question 1: Saturated Hydrocarbons

a) Saturated hydrocarbons are compounds that contain only single bonds between carbon atoms. The general molecular formula for alkanes is CₙH₂ₙ₊₂. (10 marks)

b) Methane (CH₄) can be prepared by the process of anaerobic decomposition of organic matter or through the reaction of sodium bicarbonate with an acid. Properties: Colorless, odorless gas; flammable; used as fuel and in the production of hydrogen. (10 marks)

Question 2: Isomerism and IUPAC Nomenclature

a) Isomerism is the phenomenon where compounds have the same molecular formula but different structural arrangements. Examples of isomers of butane (C₄H₁₀) include n-butane and isobutane. (10 marks)

b) IUPAC nomenclature rules include identifying the longest carbon chain, numbering the chain to give substituents the lowest possible numbers, and naming substituents alphabetically. (10 marks)

Question 3: Unsaturated Hydrocarbons - Alkenes

a) Alkenes are unsaturated hydrocarbons containing at least one double bond between carbon atoms. The general molecular formula is CₙH₂ₙ. Ethylene (C₂H₄) can be prepared through the dehydration of ethanol or by cracking hydrocarbons. Properties include being colorless and flammable; uses include in the manufacture of plastics and chemicals. (10 marks)

Question 4: Unsaturated Hydrocarbons - Alkynes

a) Alkynes are unsaturated hydrocarbons containing at least one triple bond between carbon atoms. The general molecular formula is CₙH₂ₙ₋₂. Ethyne (C₂H₂) can be prepared by the partial combustion of hydrocarbons. Properties include being colorless and highly flammable; uses include in welding and as a chemical building block. (10 marks)

Question 5: Aromatic Hydrocarbons

a) Benzene is an aromatic hydrocarbon with a cyclic structure and a general molecular formula of C₆H₆. It consists of six carbon atoms arranged in a ring, with alternating double bonds. (10 marks)

b) Benzene is highly stable due to resonance. It is used as a solvent and in the production of dyes, detergents, and other chemicals. Derivatives of benzene include toluene (methylbenzene) and phenol. (10 marks)

Question 6: Classification and Nomenclature

a) Hydrocarbons can be classified into saturated (alkanes) and unsaturated (alkenes and alkynes). Examples: Methane (alkane), Ethylene (alkene), and Acetylene (alkyne). (10 marks)

b) Nomenclature is crucial in organic chemistry as it provides a systematic way to name compounds, ensuring that each name reflects the structure of the compound. This avoids confusion in communication. (10 marks)