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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3. (b) (iii) Three methods to prevent the rusting of iron are: • Painting or greasing the iron surface to create a barrier against oxygen and water. • Galvanizing, which involves coating iron with a layer of zinc. Zinc acts as a sacrificial metal. • Sacrificial protection, where a more reactive metal (like magnesium or zinc) is connected to the iron, corroding instead of the iron. • Electroplating with a less reactive metal like chromium or tin. (iv) The oxidation number of iron in the product Fe_2O_3 · xH_2O is: Step 1: Identify the neutral components. Water (H_2O) is a neutral molecule and does not affect the oxidation state of iron. Step 2: Determine the oxidation state of oxygen in Fe_2O_3. Oxygen typically has an oxidation state of -2. Step 3: Set up an equation for the sum of oxidation states in Fe_2O_3. Let the oxidation state of iron be x. 2(x) + 3(-2) = 0 2x - 6 = 0 2x = 6 x = +3 3. (c) (i) Arrangement of metals in order of increasing reactivity and extraction by electrolysis: Order of increasing reactivity: Au < Sn < Zn < Mg < Ca < Na. Metals extracted by electrolysis (highly reactive metals): Na, Ca, Mg. (ii) Zinc is said to be amphoteric because it reacts with both acids and strong bases to form salts and hydrogen gas. Example with acid: Zn(s) + 2HCl(aq) ZnCl_2(aq) + H_2(g) Example with base: Zn(s) + 2NaOH(aq) + 2H_2O(l) Na_2Zn(OH)_4 + H_2(g) (sodium zincate) 3. (d) (i) Oxidation in terms of electron transfer is the loss of electrons by an atom, ion, or molecule. (ii) Determine the moles of electrons transferred: Step 1: Use Faraday's constant to convert coulombs to moles of electrons. Given: 1 F = 96500 C and 1 F = 1 mole of electrons. Step 2: Calculate the moles of electrons. Moles of electrons = Total charge (C)Faraday's constant (C/mol) Moles of electrons = 4825 C96500 C/mol Moles of electrons = 0.050 mol (iii) Calculate the number of copper (II) ions discharged: Step 1: Write the half-reaction for the discharge of copper (II) ions. Cu^2+(aq) + 2e^- Cu(s) This shows that 2 moles of electrons are required to discharge 1 mole of Cu^2+ ions. Step 2: Determine the moles of electrons from the given Faraday value. Given: 0.250 F = 0.250 moles of electrons. Step 3: Calculate the moles of Cu^2+ ions discharged. Moles of Cu^2+ = Moles of electrons2 = 0.250 mol2 = 0.125 mol Step 4: Calculate the number of Cu^2+ ions using Avogadro's constant. Number of ions = Moles × Avogadro's constant Number of ions = 0.125 mol × (6.02 × 10^23 mol^-1) Number of ions = 7.525 × 10^22 ions 4. (a) (i) Esterification is a chemical reaction in which an alcohol and a carboxylic acid react to form an ester and water, typically in the presence of an acid catalyst. (ii) Saponification is the hydrolysis of an ester (usually a fat or oil) with a strong base (like sodium hydroxide) to produce a soap (a salt of a fatty acid) and an alcohol (glycerol). 4. (b) (i) The general molecular formula of alkynes is C_nH_2n-2. (ii) For ethylethanoate (CH_3COOCH_2CH_3): • Molecular formula: Count all atoms. There are 4 carbon atoms, 8 hydrogen atoms, and 2 oxygen atoms. So, the molecular formula is C_4H_8O_2. • Empirical formula: Find the simplest whole-number ratio of atoms. Divide the subscripts by their greatest common divisor (which is 2). So, the empirical formula is C_2H_4O. (iii) The structure of 1, 1, 2, 2-tetrabromoethane: ` Br Br | | H --- C ---- C --- H | | Br Br ` (iv) Equation for the reaction of ethanol with sodium: 2CH_3CH_2OH(l) + 2Na(s) 2CH_3CH_2ONa(aq) + H_2(g) 4. (c) (i) Type of process/reaction involved in each stage: • Stage I: Fractional distillation • Stage II: Cracking • Stage III: Addition reaction (specifically, halogenation) • Stage IV: Addition polymerization (ii) Identify X and Y: • From Stage III, X + Y forms 1,2-dichloroethane (CH_2Cl-CH_2Cl). This is an addition reaction, so X must be an alkene and Y must be chlorine. • From Stage IV, nX forms a polymer (-CH_2-CH_2-CH_2-CH_2-)_n. This polymer is poly(ethene), meaning X is ethene. • Therefore, X is ethene (CH_2=CH_2) and Y is chlorine (Cl_2). (iii) The IUPAC name of the product obtained in stage III is 1,2-dichloroethane. (iv) Reaction conditions for stage IV (polymerization of ethene): • High temperature (e.g., 200-300^) • High pressure (e.g., 1000-3000 atm) • Catalyst (e.g., Ziegler-Natta catalyst or peroxide initiator) 4. (d) (i) Palm wine froths or foams because yeast present in the palm sap ferments the sugars into ethanol and carbon dioxide gas. The escaping carbon dioxide gas creates the froth or foam. (ii) Palm wine tastes sour after some days because bacteria (specifically Acetobacter) in the presence of air oxidize the ethanol in the wine into ethanoic acid (acetic acid), which is responsible for the sour taste. 3 done, 2 left today. You're making progress.