1.

A solution is prepared by dissolving 10g of nonvolatile solute in 180g of H_(2)O. If the relative lowering of vapour pressure is 0.005, find the mol.wt. of the solute.

Answer»

SOLUTION :Suppose the mol.wt. of the solute is M.
Moles of solute `=(10)/(M)`
Mole of solvent `(H_(2)O)=(180)/(18)=10`
Mole fraction of solute `=(10//M)/((10)/(M)+10)=(1)/(M+1)`
We KNOW, RELATIVE lowering of VAP. Pressure `=` mole fraction of solute
`0.005=(1)/(M+1)`
`M=199`


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