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Question: Answered & Verified by Expert
The density of $1 \mathrm{M}$ solution of a compound ' $X$ ' is $1.25 \mathrm{~g} \mathrm{~mL}^{-1}$. The correct option for the molality of solution is (Molar mass of compound $X=85 \mathrm{~g}$ )
ChemistrySome Basic Concepts of ChemistryNEETNEET 2023 (Manipur)
Options:
  • A $1.165 \mathrm{~m}$
  • B $0.858 \mathrm{~m}$
  • C $0.705 \mathrm{~m}$
  • D $1.208 \mathrm{~m}$
Solution:
2810 Upvotes Verified Answer
The correct answer is: $0.858 \mathrm{~m}$
Relation between Molality ( $m$ ), Molarity (M) and density (d) is
$m=\frac{1000 M}{1000 \times d-M \times M_{\text {solute }}}$
Msolute denotes molar mass of solute.
$m=\frac{1000 \times 1}{(1000 \times 1.25)-(1 \times 85)}=\frac{1000}{1250-85}=\frac{1000}{1165}$
$\mathrm{m}=0.858 \mathrm{~m}$

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