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Some Basic Concepts of Chemistry question

2012 · Shift 0 · Q2
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Some Basic Concepts of Chemistry question

2012 · Shift 0 · Q2

JEE MainChemistrySome Basic Concepts of ChemistryMCQ+4 / −1
The density of a solution prepared by dissolving 120 g of urea (mol. Mass = 60 u ) in 1000g of water is 1.15 g/mL. The molarity of this solution is :
  1. A
    0.50 M
  2. B
    1.78 M
  3. C
    1.02 M
  4. D
    2.05 M
View written solutionFree

Correct answer: D

  1. Calculate moles of urea

Given:

  • Mass of urea =120 g=120\,\text{g}=120g
  • Molar mass of urea =60 g mol−1=60\,\text{g mol}^{-1}=60g mol−1

n=12060=2 moln=\frac{120}{60}=2\,\text{mol}n=60120​=2mol

  1. Calculate total mass of solution
  • Mass of water =1000 g=1000\,\text{g}=1000g
  • Mass of urea =120 g=120\,\text{g}=120g

Mass of solution=1000+120=1120 g\text{Mass of solution}=1000+120=1120\,\text{g}Mass of solution=1000+120=1120g

  1. Calculate volume of solution using density

Given density of solution:

ρ=1.15 g mL−1\rho=1.15\,\text{g mL}^{-1}ρ=1.15g mL−1

So,

V=massdensity=11201.15=973.91 mLV=\frac{\text{mass}}{\text{density}}=\frac{1120}{1.15}=973.91\,\text{mL}V=densitymass​=1.151120​=973.91mL

Convert to litres:

V=0.97391 LV=0.97391\,\text{L}V=0.97391L

  1. Calculate molarity

Molarity is:

M=moles of solutevolume of solution in litresM=\frac{\text{moles of solute}}{\text{volume of solution in litres}}M=volume of solution in litresmoles of solute​

M=20.97391=2.05 MM=\frac{2}{0.97391}=2.05\,\text{M}M=0.973912​=2.05M

  1. Match with options

The correct option is:

D: 2.05 M\boxed{\text{D: } 2.05\,\text{M}}D: 2.05M​

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