Question

A certain liquid X has a normal boiling point of 118.40 C and a boiling point elevation constant K,-240 С kg-mol-1. A solution is prepared by dissolving some benzamide (C,H,NO) in 150. g of X. This solution boils at 120.6 C. Calculate the mass of C,H,NO that was dissolved Be sure your answer is rounded to the correct number of significiant digits.

Answer 1

Answer : The mass of benzamide is, 0.166 grams

Explanation :

Formula used for Elevation in boiling point :

`\Delta T_b=i* k_b* m`

or,

`T_b-T^o_b=i* k_b* (w_2* 1000)/(M_2* w_1)`

where,

`T_b` = boiling point of solution =
`120.6^oC`

`T^o_b` = boiling point of liquid X =
`118.40^oC`

`k_b` = boiling point constant of liquid X =
`240^oC/m`

m = molality

i = Van't Hoff factor = 1 (for non-electrolyte)

`w_2` = mass of solute (benzamide ) = ?

`w_1` = mass of solvent (liquid X) = 150 g

`M_2` = molar mass of solute (benzamide ) = 121.14 g/mol

Now put all the given values in the above formula, we get:

`(120.6-118.40)^oC=1* (240^oC/m)* ((w_2)* 1000)/(121.14g/mol* (150g))`

`w_2=0.166g`

Therefore, the mass of benzamide is, 0.166 grams