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Question

The density of lake water is 1.3 g/cc. and it contains 69 g of Na+ ions per kg of water. What is molality of Na+ ion in the lake?

A
1 m
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B
3 m
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C
2 m
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D
4 m
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Solution

The correct option is A 3 m
Lake water contains 69 g of Na+ per kg of water.

moles of Na+=weightmolecular weight=6923=3 moles

Mass of solvent (water)=100069=931 g

Molality (M)=Moles of soluteMass of solvent (g)×1000

M=3931×1000

M=3.22 m

M3 m

Hence, the correct option is B

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