Answer to Question #112364 in General Chemistry for Valerie

Question

What is the freezing point of a solution containing 17.98 g diphenylether (C12H10O), a nonelectrolyte, and 291.7 g acetic acid (CH3COOH)? The normal freezing point of acetic acid is 16.60 °C and Kfp for acetic acid is 3.90 °C/m.

Answer 1

$\Delta T=K_f m_l$, ΔT - temperature change (T₂-T₁), K_f - the molal boiling point elevation constant, m_l - molality or molal concentration of the solute in the solution.

n=m/M , n - chemical amount of substance(mol); m - mass of substance(g); M - molar mass of substance(g/mol).

M(C₁₂H₁₀O)=12g/mol*12+1g/mol*10+16g/mol=170g/mol

n(C₁₂H₁₀O)=17,98g/170g/mol=0,11mol

$m_l=n/m$ , n - chemical amount of substance (mol), m - solvent mass (CH₃COOH)(kg)

291,7g=0,2917kg

m_l=0,11/0,2917=0,38mol/kg

$\Delta T$ =3,90oC/m*0,38mol/kg=1,48oC

T₂=16,60oC

T₁=T₂-$\Delta T$ =16,60-1,48oC=15,12oC

Answer:15,12oC.