Question

a). Calculate the boiling point elevation constant (Kb) for cyclohexane, given that Tvap = 354 K and ΔHvap = 29.97 kJ/mol. The density of cyclohexane is 779.00 kg/m^3.

b.) Calculate the boiling point of cyclohexane when 150.0 g of naphthalene are dissolved in 100.0 mL of cyclohexane.

Answer 1

Kb= boiling point elevation constant = RT_b²M/deltaHV*100

R= 8.314 J/mole.K. Tb= 354, Molar mass of cyclohexane = 84, deltaHV= 29.97Kj/mol= 29.97*1000 j/mol

Kb= 8.314* (354)²*84/ 29.97*1000*100 = 0.34 K kg/mole.

2. Molar mas of napthalene= 128, moles of napthalee = 150/128= 1.171

densitt of cyclohexane = 779 kg/m3= 0.779 g/cc

Mass of cyclohexane = 100*0.779= 77.9 gm= 77.9/1000 =0.0779 kg

Moles of solute/ kg of solvent = 1.171/0.0779 =15.03

Boilng point elevation = kb*m= 0.34*15.03 = 5.12

Boiling point= 354+5.12= 359.12 K