Chemistry: Organic Reactions, Equilibrium and Electrochemistry
Chemistry in Thanawiya Amma tests organic functional groups and reactions, chemical equilibrium, electrochemistry, transition-metal chemistry, and qualitative analysis. Marks depend on correct conditions, reagents and balanced equations.
Core rules
- Alcohols oxidize to aldehydes then carboxylic acids with acidified dichromate; primary, secondary and tertiary alcohols behave differently.
- Aldehydes reduce Tollens' reagent and Fehling's solution; ketones do not.
- Carboxylic acids with alcohols form esters under acid catalysis; the reaction is reversible.
- Le Chatelier's principle predicts the shift caused by concentration, pressure or temperature changes.
- Redox equations must be balanced for atoms and charge; in acidic solution use H⁺ and H₂O.
Worked example
Find the pH of 0.01 M HCl. HCl is a strong acid and ionizes completely, so [H⁺] = 0.01 = 10^-2 M. pH = -log[H⁺] = -log(10^-2) = 2. The reasoning is that complete ionization allows direct use of the acid concentration; this would not apply to a weak acid without Ka.
Traps
- Treating a weak acid like a strong acid in pH calculations.
- Forgetting that dilution changes concentration but not the amount of solute.
- Balancing redox equations without balancing charge.
- Confusing a catalyst with an intermediate.
- Ignoring reaction conditions such as heat, acid or solvent.