Find the molality of the thiosulphate (Na2S2O3) solution, if the density of a 3M thiosulphate (Na2S2O3) solution is 1.2g/mL.
A
4.13m
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B
2.57m
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C
3.85m
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D
5.46m
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Solution
The correct option is A4.13m 3M solution means 3 moles of sodium thiosulphate is present in 1L of the solution.
Mass of (Na2S2O3) in solution = 3×molarmass
Molar mass of (Na2S2O3=158g/mol)
Mass of solute = 3×158=474g
Since, Density = massvolume
Mass of solution =1.2g/mL×1000mL=1200g Mass of solvent = mass of solution - mass of solute =1200−474=726g Molality(m)=number of moles of solutemass of solvent in kg×1000 Molality=3726×1000=4.13m