Answer to Question #297920 in General Chemistry for Phia

Question

How many grams of Lactic acid (C6H10O5) should be dissolved in 650g of cyclohexane (C6H12) to raise the boiling point to 84.910C? The normal boiling point of cyclohexane is 810C and its molal boiling point is 2.75 0C/m.

Answer 1

The formula of lactic acid is not C₆H₁₀O₅, it is C₃H₆O₃. Moreover, it is unlikely to be well soluble in cyclohexane. Anyway, the solution below will be provided for the formula as given in the task (C₆H₁₀O₅).

$\Delta{T}=k_b\times{m}$ , where m is the molality. Solving for m,

$m=\frac{\Delta{T}}{k_b}=\frac{84.91\degree{C}-81\degree{C}}{2.75\degree{C}/m}=1.42\frac{mol\ C_6H_{10}O_5}{kg\ C_6H_{12}}$

The molar mass of C₆H₁₀O₅ is 162.14 g/mol

$mass(C_6H_{10}O_5)=0.650\ kg(C_6H_{12})\times\frac{1.42\ mol\ C_6H_{10}O_5}{1\ kg\ C_6H_{12}}\times\frac{162.14\ g\ C_6H_{10}O_5}{1\ mol\ C_6H_{10}O_5}=150\ g$

Answer: 150 g