Chemistry: Moles, Equilibrium and Organic Logic
Chemistry in MHT-CET tests the Maharashtra State Board Class 11–12 syllabus across physical, inorganic and organic chemistry: mole concept, thermodynamics, equilibrium, electrochemistry, periodic trends, coordination compounds, hydrocarbons, alcohols, aldehydes, carboxylic acids, amines and biomolecules. MCQs favour short calculations and concept discrimination rather than long derivations.
Core rules and concepts
- Mole concept: n = m/M = N/N_A; at STP one mole of ideal gas occupies 22.4 L (273 K, 1 atm).
- Equilibrium: for a weak acid, K_a ≈ Cα²; pH + pOH = 14 at 25 °C.
- Periodic trends: atomic radius decreases across a period and increases down a group; ionisation enthalpy rises across a period.
- Organic mechanisms: SN1 proceeds via a carbocation and gives racemisation; SN2 proceeds by backside attack and gives inversion. Markovnikov addition places H on the carbon bearing more hydrogens.
Worked example
Find the pH of 0.010 M NaOH at 25 °C. [OH⁻] = 0.010 = 10⁻² M, so pOH = 2. pH = 14 − 2 = 12.
Traps that cost marks
- Applying pH = −log[H⁺] directly to a base instead of calculating pOH first.
- Forgetting that Kw changes with temperature, so pH 7 is neutral only at 25 °C.
- Counting moles of ions incorrectly for salts such as CaCl₂.
- Confusing empirical and molecular formulae.
- In organic naming, ignoring the longest chain or the lowest locant set.