Laboratory Assistant Dairy / CFP — KCMMF Ltd — 2016 — Official Paper — Kerala PSC PYQ Practice with Answers

Correct answer (Option A):\nMolarity is defined as the number of moles of solute dissolved per litre of solution.\nFormula: Molarity = Moles of solute / Volume of solution in litres\nMoles of NaOH = Mass / Molar mass = 4 g / 40 g/mol = 0.1 mol\nVolume = 1 L\nMolarity = 0.1 mol / 1 L = 0.1 M\nOption A is correct.\n\nWhy others are wrong:\nOption B (1 M) would require 40 g of NaOH.\nOption C (0.5 M) would require 20 g of NaOH.\nOption D (10 M) would require 400 g of NaOH.\n\nStudy tip:\nAlways remember that the molar mass of Sodium Hydroxide (NaOH) is approximately 40 g/mol (Na=23, O=16, H=1).

Correct answer (Option B):\nAccording to Le Chatelier's principle, increasing the pressure of a gaseous system at equilibrium shifts the equilibrium in the direction that has fewer moles of gas.\nIn this reaction, the reactant side (left) has 1 mole of gas, while the product side (right) has 2 moles of gas.\nTherefore, an increase in pressure shifts the equilibrium to the left.\nOption B is correct.\n\nWhy others are wrong:\nOption A is incorrect because pressure changes shift equilibrium positions rather than terminating reactions.\nOption C is incorrect because gaseous reactions with unequal moles are sensitive to pressure modifications.\nOption D is incorrect because shifting right increases the total moles, which opposes the pressure increase.\n\nStudy tip:\nLe Chatelier's principle states that a system at equilibrium responds to stress by shifting in a direction that minimizes that stress.

Correct answer (Option D):\nColligative properties are properties of solutions that depend solely on the total number of solute particles (molecules or ions) present in a given volume of the solvent, regardless of their chemical identity.\nExamples include relative lowering of vapor pressure, elevation of boiling point, depression of freezing point, and osmotic pressure.\nOption D is correct.\n\nWhy others are wrong:\nOptions A, B, and C are incorrect because colligative properties depend on particle count ratio, not on the mass or chemical type of the solute/solvent particles directly.\n\nStudy tip:\nWhen electrolytes dissociate into multiple ions (like NaCl into 2 particles), they alter the colligative properties more than non-electrolytes due to higher total particle counts.

Correct answer (Option B):\nSpecific conductance (conductivity) is the conductance of a unit volume of solution.\nUpon dilution, the total number of current-carrying ions per unit volume (per cm³ or per m³) decreases, leading to a reduction in the specific conductance.\nOption B is correct.\n\nWhy others are wrong:\nOption A is incorrect because equivalent and molar conductances increase on dilution, not specific conductance.\nOptions C and D are incorrect because the relationship is a continuous decline as ions spread out over a larger volume.\n\nStudy tip:\nRemember the distinction: Molar conductance increases on dilution due to an increase in total volume and ion mobility, whereas specific conductance decreases because ion density decreases.

Correct answer (Option B):\nGiven: Hydroxide ion concentration [OH⁻] = 0.001 M = 10⁻³ M\nStep 1: Calculate pOH\npOH = -log[OH⁻] = -log(10⁻³) = 3\nStep 2: Calculate pH using the relationship pH + pOH = 14\npH = 14 - pOH = 14 - 3 = 11\nOption B is correct.\n\nWhy others are wrong:\nOption A (3) is the pOH value, not the pH value.\nOptions C and D are mathematically incorrect based on standard logarithmic water dissociation relationships.\n\nStudy tip:\nAlways cross-check if the question provides hydrogen ion concentration [H⁺] or hydroxide ion concentration [OH⁻] to avoid mixing up pH and pOH.