1.

A5.25% solution of a substance is isotonic with a 1.5% solution of urea (molar mass = "60 g mol"^(-1)) in the same solvent. If the densities of both the solutions are assumed to be equal to "1.0 g cm"^(-3), molar mass of the substance will be

Answer»

`"210.0 g MOL"^(-1)`
`"90.0 g mol"^(-1)`
`"115.0 g mol"^(-1)`
`"105.0 g mol"^(-1)`

Solution :Isotonic solutions have the same MOLAR concentration. Hence,
Molar conc. Of the SUBSTANCE = Molar conc. Of urea
`(52.5gL^(-1))/(M)=(15gL^(-1))/("60 g mol"^(-1))`
`("100 g solution = 100 mL as d = 1 g mL"^(-1))`
`therefore""M=(52.5xx60)/(15)="210 g mol"^(-1)`


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