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NEET CHEMISTRYSome Basic Concepts of ChemistryMedium

Question

The density of a 2 M2 \text{ M} aqueous solution of NaOHNaOH is 1.28 g/cm31.28 \text{ g/cm}^3. The molality of the solution is: [molecular mass of NaOH=40 g mol1NaOH = 40 \text{ g mol}^{-1}]

A

1.20 m1.20 \text{ m}

B

1.56 m1.56 \text{ m}

C

1.67 m1.67 \text{ m}

D

1.32 m1.32 \text{ m}

Step-by-Step Solution

  1. Understand Molarity: A 2 M2 \text{ M} solution contains 2 moles of solute (NaOHNaOH) in 1 Litre (1000 mL1000 \text{ mL}) of solution .
  2. Calculate Mass of Solution: Mass=Density×Volume\text{Mass} = \text{Density} \times \text{Volume} Mass of solution=1.28 g/mL×1000 mL=1280 g\text{Mass of solution} = 1.28 \text{ g/mL} \times 1000 \text{ mL} = 1280 \text{ g}
  3. Calculate Mass of Solute (NaOHNaOH): Mass=Moles×Molar Mass\text{Mass} = \text{Moles} \times \text{Molar Mass} Mass of NaOH=2 mol×40 g/mol=80 g\text{Mass of } NaOH = 2 \text{ mol} \times 40 \text{ g/mol} = 80 \text{ g}
  4. Calculate Mass of Solvent (Water): Mass of Solvent=Mass of SolutionMass of Solute\text{Mass of Solvent} = \text{Mass of Solution} - \text{Mass of Solute} Mass of Solvent=1280 g80 g=1200 g=1.2 kg\text{Mass of Solvent} = 1280 \text{ g} - 80 \text{ g} = 1200 \text{ g} = 1.2 \text{ kg}
  5. Calculate Molality (mm): Molality is defined as moles of solute per kilogram of solvent . m=Moles of SoluteMass of Solvent (kg)m = \frac{\text{Moles of Solute}}{\text{Mass of Solvent (kg)}} m=21.21.666... mm = \frac{2}{1.2} \approx 1.666... \text{ m} Rounding to two decimal places, the molality is 1.67 m1.67 \text{ m}.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Some Basic Concepts of Chemistry. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYSome Basic Concepts of Chemistrydensityaqueoussolutionmolalitysolution

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