Explain three methods to prevent rusting of iron and determine the oxidation state of iron in Fe2O3.xH2O. Also, arrange metals in order of reactivity and state which are extracted by electrolysis. Exp

Water ($\text{H}_2\text{O}$) is a neutral molecule and does not affect the oxidation state of iron.

Oxygen typically has an oxidation state of -2.

Let the oxidation state of iron be $x$.

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: $\text{Zn}(s) + 2\text{HCl}(aq) \longrightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)$
Example with base: $\text{Zn}(s) + 2\text{NaOH}(aq) + 2\text{H}_2\text{O}(l) \longrightarrow \text{Na}_2[\text{Zn}(\text{OH})_4](aq) + \text{H}_2(g)$ (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:

Given: $1 \text{ F} = 96500 \text{ C}$ and $1 \text{ F} = 1 \text{ mole of electrons}$.

(iii) Calculate the number of copper (II) ions discharged:

This shows that 2 moles of electrons are required to discharge 1 mole of $\text{Cu}^{2+}$ ions.

Given: $0.250 \text{ F} = 0.250 \text{ moles of electrons}$.

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 $\boxed{\text{C}_n\text{H}_{2n-2}}$.

(ii) For ethylethanoate ($\text{CH}_3\text{COOCH}_2\text{CH}_3$):

• Molecular formula: Count all atoms. There are 4 carbon atoms, 8 hydrogen atoms, and 2 oxygen atoms. So, the molecular formula is $\boxed{\text{C}_4\text{H}_8\text{O}_2}$.
• 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 $\boxed{\text{C}_2\text{H}_4\text{O}}$.

(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:

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 ($\text{CH}_2\text{Cl}-\text{CH}_2\text{Cl}$). This is an addition reaction, so X must be an alkene and Y must be chlorine.
• From Stage IV, nX forms a polymer $(-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-)_n$. This polymer is poly(ethene), meaning X is ethene.
• Therefore, X is ethene ($\text{CH}_2=\text{CH}_2$) and Y is chlorine ($\text{Cl}_2$).

(iii) The IUPAC name of the product obtained in stage III is $\boxed{\text{1,2-dichloroethane}}$.

(iv) Reaction conditions for stage IV (polymerization of ethene):

• High temperature (e.g., $200-300^\circ\text{C}$)
• High pressure (e.g., $1000-3000 \text{ atm}$)
• 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.