Board-style MCQs and past-paper numericals in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
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Multiple-choice questions
Solved numericals & self-assessment (past papers)
Calculate the Rf value of a spot
A pigment spot travels 3.6 cm; the solvent front travels 8.0 cm.
Rf = distance moved by spot ÷ distance moved by solvent front
Rf = 3.6 / 8.0 = 0.45 (no units, always between 0 and 1).
Distribution (partition) coefficient
A solute distributes as 6.0 g per 100 cm³ in benzene and 1.5 g per 100 cm³ in water.
K_d = (conc. in benzene) ÷ (conc. in water) = (6.0/100) ÷ (1.5/100) = 0.060 ÷ 0.015 = 4.
The solute is 4 times more soluble in benzene than in water.
Identify the technique & mechanism
A mixture of amino acids is separated on filter paper using a solvent and located with ninhydrin.
Technique = paper chromatography; mechanism = partition (between water held in the paper and the mobile solvent). Each amino acid is identified by its Rf.