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  4. An aqueous solution of ethanol has density 1.025 g / mL and molarity 8 M. Calculate molality of this solution:

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Q. An aqueous solution of ethanol has density $1.025 \,g / mL$ and molarity $8 \,M$. Calculate molality of this solution:

Some Basic Concepts of Chemistry

Solution:

$8 \,M$ means 8 moles of ethanol in $1 L$ of solution

8 mole means $46 \times 8=368 g$ of ethanol

Let us consider one litre of this solution-

So, mass of solution $=1025\, g$

Mass of water $=1025-368=657 \,g$

$8 M =\frac{x g }{46 \times 12}=368 g / mol$

Molality $=\frac{368}{46 \times 657}=12.17 \,m$