This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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2. (a) (i) Two examples of iron ores are: • Hematite (Fe_2O_3) • Magnetite (Fe_3O_4) 2. (a) (ii) Three adverse effects of chemical products are: • Environmental pollution: They can contaminate air, water, and soil, harming ecosystems. • Health hazards: Exposure can cause various health issues, including respiratory problems, skin irritation, and long-term illnesses like cancer. • Damage to infrastructure: Corrosive chemicals can degrade materials and structures. 2. (b) (i) The alkali metals Na, Li, K in decreasing order of their melting points are: Li (180.5^) > Na (97.8^) > K* (63.5^) 2. (b) (ii) The three rules/principles of electron distribution in an atom are: • Aufbau principle • Pauli exclusion principle • Hund's rule of maximum multiplicity 2. (c) (i) • An oxidizing agent is a substance that gains electrons and causes the oxidation of another substance. • A reducing agent is a substance that loses electrons and causes the reduction of another substance. 2. (c) (ii) The ions formed when the following compounds dissociate are: I. KOH: K^+ (aq) + OH^- (aq) II. Pb(NO_3)_2: Pb^2+ (aq) + 2NO_3^- (aq) III. Na_2CO_3: 2Na^+ (aq) + CO_3^2- (aq) 2. (d) (i) I. An anode is the electrode where oxidation (loss of electrons) occurs during an electrochemical reaction. II. A cathode is the electrode where reduction (gain of electrons) occurs during an electrochemical reaction. 2. (d) (ii) Step 1: Calculate the total charge passed. The current I = 1.0 A and time t = 15 minutes = 15 × 60 s = 900 s. Q = I × t = 1.0 A × 900 s = 900 C Step 2: Determine the moles of electrons. Using Faraday's constant F = 96,500 C/mol: Moles of electrons = (Q)/(F) = 900 C96500 C/mol ≈ 0.009326 mol Step 3: Write the half-reaction for hydrogen production at the cathode. During the electrolysis of dilute tetraoxosulphate (VI) acid (H_2SO_4), hydrogen gas is produced at the cathode: 2H^+ (aq) + 2e^- H_2 (g) From the stoichiometry, 2 moles of electrons produce 1 mole of H_2 gas. Step 4: Calculate the moles of hydrogen gas produced. Moles of H_2 = (1)/(2) × Moles of electrons = (1)/(2) × 0.009326 mol ≈ 0.004663 mol Step 5: Calculate the volume of hydrogen gas at s.t.p. At s.t.p., 1 mole of any gas occupies 22.4 dm^3. Volume of H_2 = Moles of H_2 × 22.4 dm^3/mol = 0.004663 mol × 22.4 dm^3/mol ≈ 0.10445 dm^3 The volume of hydrogen produced is 0.104 dm^3. 3. (a) An energy profile diagram illustrating the effect of a catalyst on an exothermic reaction: [scale=0.8] % Axes [->] (0,0) -- (8,0) node[right] Reaction Progress; [->] (0,0) -- (0,6) node[above] Energy; % Reactants and Products at (1,5) (reactants) Reactants; at (7,1) (products) Products; % Uncatalyzed reaction [thick, blue] (1,5) .. controls (3,7) and (5,7) .. (7,1); [dashed] (1,5) -- (1,0); [dashed] (7,1) -- (7,0); [<->] (1.2,5.2) -- (3.8,6.8) node[midway, above right] E_a (uncatalyzed); % Catalyzed reaction [thick, red] (1,5) .. controls (3,6) and (5,6) .. (7,1); [<->] (1.2,5.2) -- (3.8,5.8) node[midway, below right] E_a (catalyzed); % Enthalpy change [<->] (7.3,5) -- (7.3,1) node[midway, right] ; % Labels [blue] at (4,7.3) Uncatalyzed Pathway; [red] at (4,6.3) Catalyzed Pathway; In an exothermic reaction, the energy of the products is lower than that of the reactants. A catalyst provides an alternative reaction pathway with a lower activation energy (E_a), thereby increasing the reaction rate. The overall enthalpy change () of the reaction remains unchanged. 3. (b) (i) One difference between endothermic and exothermic reactions is: • Endothermic reactions absorb heat from the surroundings, resulting in a positive enthalpy change ( > 0). • Exothermic reactions release heat to the surroundings, resulting in a negative enthalpy change ( < 0). 3. (b) (ii) Le Chatelier's principle states that if a change of condition (such as temperature, pressure, or concentration) is applied to a system in equilibrium, the system will shift in a direction that relieves the stress and re-establishes a new equilibrium. 3. (b) (iii) Three factors that affect the equilibrium position of a chemical reaction are: • Concentration of reactants or products • Temperature • Pressure (for reactions involving gases) 3. (c) (i) I. A saturated solution is a solution that contains the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature and pressure. II. A molar solution is a solution that contains one mole of solute per liter (or dm^3) of solution. Its concentration is expressed in moles per dm^3 (mol dm^-3 or M). 3. (c) (ii) Step 1: Determine the chemical formula and molar mass of sodium trioxocarbonate (IV). Sodium trioxocarbonate (IV) is Na_2CO_3. Given atomic masses: Na = 23, O = 16, C = 12. Molar mass of Na_2CO_3 = (2 × 23) + 12 + (3 × 16) = 46 + 12 + 48 = 106 g/mol. Step 2: Convert the volume from cm^3 to dm^3. Given volume = 250 cm^3. 250 cm^3 = (250)/(1000) dm^3 = 0.250 dm^3 Step 3: Calculate the number of moles of Na_2CO_3 needed. Concentration = 0.2 moldm^-3. Moles = Concentration × Volume = 0.2 moldm^-3 × 0.250 dm^3 = 0.05 mol Step 4: Calculate the mass of Na_2CO_3 needed. Mass = Moles × Molar Mass = 0.05 mol × 106 g/mol = 5.3 g The mass of sodium trioxocarbonate (IV) needed is 5.3 g. What's next?