Answer: 18 grams
Explanation:
Elevation in boiling point:
[tex]\Delta T_b=i\times k_b\times m[/tex]
[tex]T_b-T^o_b=i\times k_b\times \frac{w_2\times 1000}{M_2\times w_1}[/tex]
where,
[tex]T_b[/tex] = boiling point of solution = [tex]62.60^oC[/tex]
[tex]T^o_b[/tex] = boiling point of chloroform = [tex]61.2^oC[/tex]
[tex]k_b[/tex] = boiling point constant of chloroform = [tex]3.88^oC/m[/tex]
m = molality
i = Van't Hoff factor = 1 (for non-electrolyte)
[tex]w_2[/tex] = mass of solute (hexachlorophene ) = x g
[tex]w_1[/tex] = mass of solvent (chloroform) = 125 g
[tex]M_2[/tex] = molar mass of solute (hexachlorophene ) =406.9
Now put all the given values in the above formula, we get:
[tex](62.60-61.2)^oC=1\times (3.88^oC/m)\times \frac{(xg)\times 1000}{406.9\times (125g)}[/tex]
[tex]1.40^oC=1\times (3.88^oC/m)\times \frac{(xg)\times 1000}{406.9\times (125g)}[/tex]
[tex]x=18g[/tex]
Therefore, the mass of hexachlorophene that must be added is 18 grams
