Question

calculate the melting point in Celsius of a solution that is 4.37% benzene (C6H6 molar mass 78.108 g/mol) by mass in carbon tetrachloride. the normal melting point of CCl4 is -22.9 Celsius and Kf= 29.9 C/m

thank you!

Answer 1

Percentage concentration(w/w) = (Amount of solute/ amount of solution ) X 100

For 1000 gram of CCl4

4.37 = (Amount of benzene/Amount of benzene + 1000 g) X 100

Amount of benzene = 45.697 g

Number of moles of benzene = Amount of benzene/mw of benzene= 45.697 g/78.108g/mole = 0.585 moles

Molality of benzene solution = Number of moles of benzene / Amount of CCl4 inKg

                                               = 0.585 mole/1 kg = 0.585 m

Depression in melting point = Kf X m

For given problem

Depression in melting point solution = 29.9 celsius/m X 0.585 m = 17.5 celsius

Depression in melting point solution = melting point of CCl4 – Melting point of solution

Melting point of solution = -22.9 celsius – 17.5 celsius = -40.4 celsius   Answer