Can someone help me with these chem questions? with the solutions and answers !

Question

Can someone help me with these chem questions? with the solutions and answers ! Thank you :)

1.) Note from the 'Introduction' that the freezing-point-depression constant, Kfp, for any solvent can be calculated as long as the heat of fusion, Hfus, and freezing point of the solvent is known. Calculate the freezing-point-depression constant (in SI units) for carbon tetrachloride, CCl4, given that its heat of fusion is 2.5 kJ/mol and its freezing point is 250.3 K.

2.) The 'Introduction' contains a diagram showing the relative entropies of a pure solvent in its solid and liquid states compared to the entropy of a solution of that solvent. Draw a similar diagram that also includes the entropy of the vapor phase of the solvent. Based on this diagram, which would have the larger entropy change: vaporization of the solution, or vaporization of the pure solvent? Explain how this would effect the boiling point of the solution relative to the boiling point of the pure solvent.

3.) A student dissolved 3.2 g of an unknown solute in 20.0 mL of water. The measured freezing point was –2.1 oC . The measured freezing point of the pure solvent was -0.2 oC. Assume the density of water is 0.998 g/mL. What is the freezing point and freezing point depression of the solution? What is the molality, m, of the original solution? (m= moles solute/kg of solvent) What is the molar mass of the unknown solute? (Hint: Start by using the definition of molality to solve for moles of solute.)

Explanation / Answer

Answer 1:

Freezing point constant is given by Kf = RTf2M/dHfus

So, dHfus = 2.5kJ/mol = 2500kJ/mol

R = 8.314J/kmol

Tf = 250.3K

M = 153.82g/mol

So, Kf = [8.314 x 250.32 x 153.82 ]/2500 = 32048.26 K/m

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