Concentration Terms — All types (molarity, molality, etc.)
Solutions
10
JEE Qs
8%
Hard
75
min
Master the step-by-step interconversion between various concentration terms using definitions, density, and molar mass rather than relying on complex, derived formulas.
🧮 Key Formulas
✅ Key Points for JEE
- 1Molarity (M) is temperature-dependent because volume changes with temperature, while Molality (m) and Mole fraction (chi) are temperature-independent as they are mass-based.
- 2Interconversion between different concentration terms (especially between mass-based and volume-based) frequently requires the density of the solution and the molar mass of the solute.
- 3Always clearly define and identify the solute, solvent, and the total solution before applying any concentration formula.
- 4Pay meticulous attention to units; ensure volume is in Liters for Molarity, mass of solvent in kilograms for Molality, and density units match mass/volume conversions (e.g., g/mL).
- 5Most concentration terms are ratios; ensure the denominator corresponds to the solution (e.g., Mass %, Volume %, Molarity, ppm) or the solvent (e.g., Molality).
⚠️ Common Mistakes
- ✕Confusing 'volume of solution' with 'volume of solvent' or 'mass of solution' with 'mass of solvent' in formulas.
- ✕Incorrectly converting units (e.g., using mL instead of L for Molarity, g instead of kg for Molality, or not converting volume to mass via density).
- ✕Neglecting the density of the *solution* when converting between mass-based concentration terms (like molality or mass %) and volume-based terms (like molarity).
- ✕Not understanding that ppm/ppb usually refers to mass/mass (w/w) unless specified as volume/volume (v/v) or mass/volume (w/v).
📝 Practice Questions
See allQ73.Consider the following cases of standard enthalpy of reaction (ΔH∘r in kJmol−1) 7 C2H6( g) + O2( g) →2CO2( g) + 3H2O(l)ΔH∘1 = −1550 2 C (graphite) + O2( g) →CO2( g) ΔH∘2 = −393.5 The magnitude of ΔH∘fC2H6( g) is _______ 1 H2( g) + O2( g) →H2O(l) ΔH∘3 = −286 2 kJmol−1 (Nearest integer).
Q70.When a non-volatile solute is added to the solvent, the vapour pressure of the solvent decreases by 10 mm of Hg . The mole fraction of the solute in the solution is 0.2 . What would be the mole fraction of the solvent if decrease in vapour pressure is 20 mm of Hg ? (1) 0.8 (2) 0.4 (3) 0.2 (4) 0.6 Q71.0.01 mole of an organic compound (X) containing 10% hydrogen, on complete combustion produced 0.9 gH2O. Molar mass of (X) is _____ gmol−1 .
Q69.Arrange the following solutions in order of their increasing boiling points. (i) 10−4M NaCl (ii) 10−4M Urea (iii) 10−3M NaCl (iv) 10−2M NaCl (1) (i) < (ii) < (iii) < (iv) (2) (iv) < (iii) < (i) < (ii) (3) (ii) < (i ) ≡(iii) < (iv) (4) (ii) < (i) < (iii) < (iv)
Q52.Density of 3 M NaCl solution is 1.25 g/mL. The molality of the solution is : (1) 1.79 m (2) 2.79 m (3) 2 m (4) 3 m
Q64.Consider a binary solution of two volatile liquid components 1 and 2. x1 and y1 are the mole fractions of component 1 in liquid and vapour phase, respectively. The slope and intercept of the linear plot of 1 vs 1 x1 y1 are given respectively as: P02−P01 (1) P0 P02−P01 (2) P0 2 , 1 , P01 P02 P02 P02 P01−P02 (3) P0 P01−P02 (4) P0 1 , 2 , P02 P02 P01 P02
Q69.Consider the given plots of vapour pressure (VP) vs temperature(T/K). Which amongst the following options is correct graphical representation showing ΔTf , depression in the freezing point of a solvent in a solution? (1) (2) (3) (4)
NCERT Chapters
- Class 12 Chemistry Ch 2: Solutions