IISER IAT Chemistry: Quantitative and Structural Reasoning
Core quantitative toolkit
IISER IAT Chemistry mixes numerical physical chemistry with structural organic and periodic inorganic questions. For numericals, write a balanced equation, convert to moles, identify the limiting reagent, then carry concentration into equilibrium, pH, or electrochemistry. For organic, assign hybridization and geometry first, then look for the highest-priority functional group and stereocentres. For inorganic, use periodic trends (atomic radius, ionization enthalpy, electronegativity) and VSEPR before memorized exceptions.
Worked example
Find the pH of 0.10 M acetic acid (Ka = 1.8×10⁻⁵). Let x = [H⁺]. Ka = x²/(0.10 − x). Assume x << 0.10: x² ≈ 1.8×10⁻⁶, so x ≈ 1.34×10⁻³ M. Check the approximation: 1.34×10⁻³/0.10 = 1.34%, under 5%, so it is valid. pH = −log(1.34×10⁻³) = 2.87. The degree of dissociation is α = x/0.10 = 1.34%.
Traps that cost marks
- Reporting pH to too many decimals; pH from a concentration with two significant figures is usually given to two decimal places.
- Using Ka as if it were [H⁺], or forgetting that dilution changes α but not Ka.
- Applying Le Chatelier to a catalyst; a catalyst changes rate, not position.
- Assigning R/S without checking the lowest-priority group orientation.
- Giving oxygen a −2 oxidation state in peroxides or superoxides.
- Ignoring the 5% approximation check in weak-acid problems.