Correct WAEC Chemistry Questions and Answers 2023 (100% Sure) Theory & Obj Solution

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  1. CHEMISTRY SOLUTION

    ERN
    1A
    A transmission element is a component that transfers data or energy from one point to another.

    1bi. Element D-288 forms a doubly charged cation.
    1bii. The soluble trioxocarbonate (IV) is CO32-.

    1C.

    The general decrease in the first ionization energies of the period in the periodic table is due to the increase in atomic radius and the decrease in effective nuclear charge.

    1d.

    -methane (CH4)
    -propane (C3H8).

    1e.

    Alkanols are stronger bases than water because they have a higher tendency to donate a proton (H+) to an acid. This is because the alkyl group in alkanols is electron-donating, which increases the electron density on the oxygen atom in the hydroxyl group (-OH).

    1f. The major raw materials used in the Solvay process are
    -salt (NaCl)
    -limestone (CaCO3)
    -ammonia (NH3).

    1g. Geometric isomerism is a type of stereoisomerism that arises when two or more compounds have the same molecular formula and connectivity, but differ in the spatial arrangement of their atoms due to restricted rotation around a double bond or ring.

    1h. Water gas is a better fuel than producer gas because it has a higher calorific value and a higher percentage of hydrogen gas.

    1hi. Heat of combustion is the amount of heat energy released when one mole of a substance undergoes complete combustion with oxygen under standard conditions.

    1ji. Faraday’s second law of electrolysis states that the amount of substance produced at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte. It can be expressed mathematically as:
    m = (Q * M) / (n * F)

    1jii. To calculate the amount of silver deposited, we can use Faraday’s law of electrolysis, which states that:
    m = (Q * M) / (n * F)
    Plugging in the values, we get:
    m = (10920 C * 107.87 g/mol) / (1 * 96500 C/mol)
    m = 12.17 g
    Therefore, the amount of silver deposited when 10920 coulombs of electricity is passed through a solution of a silver salt is 12.17 grams.

  2. 1a. Transition elements are the elements in the central block of the periodic table, from groups 3 to 12. They are characterized by having partially filled d orbitals in their outer electron shells, which gives rise to their unique properties, such as variable oxidation states, colored compounds, and complex formation.

    (c) The general increase in the first ionisation energies across a period in the periodic table is due to the increasing effective nuclear charge experienced by the outermost electrons. As the atomic number increases, the number of protons in the nucleus increases, which attracts the negatively charged electrons more strongly and increases the energy required to remove them. Additionally, the decreasing atomic radius also contributes to the increase in ionisation energy, as the outermost electrons are held more tightly by the smaller, denser nucleus.

    2bi.:

    1) Gas particles have negligible volume compared to the volume of the container.
    2) Gas particles do not interact with each other.

    2bii. Real gases do not obey these postulates because they have non-zero molecular volumes and exhibit intermolecular forces of attraction. In real gases, the volume of the gas molecules and their interactions with each other become significant at high pressures and low temperatures, causing deviations from the ideal gas law. These deviations can be accounted for using corrections such as the van der Waals equation of state.

  3. Number 3
    3a.
    The empirical formula of the compound with 52.2% C, 13.1% H, and 34.7% O and a vapor density of 23 is C2H6O.

    3aii
    The empirical formula C2H6O has a molar mass of 2(12.01 g/mol) + 6(1.01 g/mol) + 16.00 g/mol = 46.08 g/mol.

    The vapor density of the compound is 23, which is half of its molar mass. Therefore, the molar mass of the compound is 46.08 g/mol x 2 = 92.16 g/mol.

    To find the molecular formula, we need to divide the molar mass of the compound by the molar mass of the empirical formula:

    92.16 g/mol ÷ 46.08 g/mol = 2

    The molecular formula is therefore twice the empirical formula:

    C4H12O2

    Therefore, the molecular formula of the compound is C4H12O2.

    3aiii.
    (I)the functional group present in the compound is carboxylic acid and alcohol. The compound reacts with sodium metal, indicating the presence of a carboxylic acid group.

    ii. The structural formula of glucose is:

    HOCH2(CHOH)3CHO

    And the structural formula of fructose is:

    HOCH2(CHOH)3CO.

    3b.

    Chemical equation for the production of ethanol from cooked cassava is (C6H10O5)n + nH2O → nC6H12O6 → 2nC2H5OH + 2nCO2.

    3ci.
    When aluminium is exposed to air, it forms a thin layer of aluminium oxide on its surface that protects it from reacting with water. This layer reacts with water to form a different compound that also protects the metal from further reaction with water. This is why aluminium does not react with water in a way that produces hydrogen gas.

    3cii. To make pure aluminium chloride crystals, mix aluminium with hydrochloric acid, evaporate water, cool, crystallize, clean, and dry.

    3d. To separate water from CuSO4, heat the aqueous solution until water evaporates, leaving solid CuSO4.
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    Completed

  4. *CONTINUATION OF NUMBER 2*

    2ci. The compound is called hexane-1,2,3,4,5,6-hexol, also known as sorbitol.

    2cii.
    -mannitol
    -dulcitol.

    2ciii. Sorbitol is made from starch by a process called hydrogenation. First, starch is broken down into glucose. Then, the glucose is treated with hydrogen gas and a metal catalyst to turn it into sorbitol. Finally, the sorbitol is purified and separated.

    2civ.
    C6H12O6 + H2 → C6H14O6
    In this equation, glucose (C6H12O6) reacts with hydrogen gas (H2) in the presence of a metal catalyst to produce sorbitol (C6H14O6).

    2cv.

    Alpha-amylase
    glucoamylase

    COMPLETED.

    Number 3
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