Chemistry
AP EAMCET Chemistry carries 40 questions across physical, inorganic and organic chemistry: atomic structure, bonding, stoichiometry, thermodynamics, equilibrium, redox, s- and p-block elements, coordination compounds, hydrocarbons, haloalkanes, alcohols, aldehydes, carboxylic acids, amines, biomolecules and polymers. Many items test trends, exceptions and mechanisms rather than isolated facts.
Core rules
- pH = −log[H+]; for a weak monoprotic acid, [H+] ≈ √(Ka·C) when C/Ka > 100.
- Acidic buffer: pH = pKa + log([salt]/[acid]).
- Markovnikov addition: H adds to the carbon with more hydrogens; carbocation stability is 3° > 2° > 1° > methyl.
- Coordination: [Ni(CN)4]²⁻ is square planar and diamagnetic; [NiCl4]²⁻ is tetrahedral and paramagnetic.
- Periodic trends: atomic radius decreases across a period; electron gain enthalpy of Cl is more negative than that of F.
Worked example
Calculate the pH of 0.10 M acetic acid (Ka = 1.8 × 10⁻⁵). Let x = [H+]. Ka = x²/(0.10 − x). Since C/Ka ≈ 5.6 × 10³ > 100, x is small, so x² ≈ 1.8 × 10⁻⁶ and x ≈ 1.34 × 10⁻³ M. Then pH = −log(1.34 × 10⁻³) ≈ 2.87. The check 0.10 − 0.00134 ≈ 0.0987 confirms the approximation.
Traps
- Using pH = −log C for a weak acid, which would give 1.00 here instead of 2.87.
- Inverting the buffer ratio.
- Assuming every tetrahedral complex is paramagnetic.
- Forgetting that F has a less negative electron gain enthalpy than Cl because of small size and electron repulsion.