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SubjectsChemistry
सांद्रता के माप
In this Class 12 Chemistry topic from Chapter 01: Solutions, students learn how the amount of solute is expressed quantitatively in a solution. It explains common concentration measures such as mass percentage, volume percentage, parts per million, molarity, molality, and mole fraction, along with the meaning of their units and symbols. Students also learn to select the appropriate measure and apply formulas to interpret or calculate solution composition accurately.
TOPIC PRACTICE
Up to 9 questions from this page. Select your focus, then start.
Molality is the governing concentration measure defined as moles of solute divided by kilograms of solvent, not kilograms of solution. Thus, m = nsolute/mass of solvent = 0.5 mol/2 kg = 0.25 mol kg−1, written as 0.25 m. Option A results from an incorrect division, while 0.50 m ignores the 2 kg denominator and 1.00 m doubles the correct value. Therefore, option B is correct.
Molarity is defined as the number of moles of solute present in one litre of solution: M = n/V. Rearranging gives n = M × V. Substituting the given values, n = 0.02 mol L⁻¹ × 1 L = 0.02 mol. The litre units cancel, leaving moles. Therefore, option B is correct. Always ensure that volume is expressed in litres when using molarity.
Molality is defined as moles of solute divided by the mass of solvent in kilograms: m = n/mass of solvent. Rearranging gives n = m × mass of solvent. The solvent mass is already 0.100 kg, so n = 0.1 mol kg⁻¹ × 0.100 kg = 0.010 mol. The mass of the solution is not used in the molality formula. Therefore, option B is correct.
Molality is the amount of solute in moles divided by the mass of solvent in kilograms: m = n/mass of solvent. Rearranging gives n = m × mass of solvent. Substitution gives n = 0.5 mol kg⁻¹ × 0.2 kg = 0.10 mol. The solvent mass, rather than the total solution mass, must be used. Thus, option B is correct. The result also has the proper unit, mol.
Molality is defined as the moles of solute divided by the mass of solvent in kilograms: m = nsolute ÷ mass of solvent. Rearranging gives nsolute = m × mass of solvent. Therefore, nsolute = 0.2 mol kg⁻¹ × 0.25 kg = 0.050 mol. The kilogram units cancel, leaving mol. Thus, option B is correct.
Molality is defined as the number of moles of solute present in one kilogram of solvent. Therefore, m = moles of solute ÷ mass of solvent in kg = 0.1 ÷ 1 = 0.1 mol kg⁻¹, written as 0.1 m. Hence, option B is correct. The mass used must be that of the solvent, not the total solution.
First calculate the amount of solute: moles = mass ÷ molar mass = 2 g ÷ 100 g mol⁻¹ = 0.02 mol. The solution volume is 500 mL, which equals 0.500 L. Therefore, molarity = moles of solute ÷ volume of solution in litres = 0.02 ÷ 0.500 = 0.04 mol L⁻¹, or 0.04 M. Hence option B is correct.
Molarity is defined as the number of moles of solute per litre of solution. First convert the volume: 100 mL = 0.100 L. Therefore, M = moles ÷ volume in litres = 0.01 mol ÷ 0.100 L = 0.10 mol L⁻¹, or 0.10 M. Hence, option C is correct. The volume of the complete solution, not merely the solvent, must be used.
Molality is defined as moles of solute per kilogram of solvent, not per kilogram of solution. The solute amount is n = mass/molar mass = 2/100 = 0.02 mol. The solvent mass is 100 g = 0.100 kg. Thus, molality = 0.02/0.100 = 0.20 mol kg⁻¹, or 0.2 m. Therefore, option B is correct.
QUIZ COMPLETE
