A solution of glucose `("molar mass"= 180g mol^(-1))` in water is labelled as 10% (by mass). What would be the molarity and molality of the solution? Given that the density of the solution is `1.2g mL^(-1)`.

Explanation

10% ( by mass ) solution of glucose means that 10 g of glucose in present in 100 g of solution or in 90 g water .
(i) Calculation of molaltiy .
Mass of glucose = 10 g
Moles of glucose `= (10)/(100) = 0.0556`
(Molar mass of glucose = 180)
Mass of water = 90g
`therefore ` Molality ` = ("Moles of glucose")/("Mass of water") xx 1000`
` = (0.0556)/(90) xx 1000 = 0.618 m`
(ii) Calculation of molarity
Moles of glucose = 0.556
Volume of solution ` = ("Mass")/("Density")`
` = (100)/(1.20) = 83.3 mL`
Molarity = `("Moles of glucose")/("Vol.of solution") xx 1000`
`= (0.0556)/(83.3) xx 1000` = 0.667 M.