DATA SHEET 4.1 Name (continued) Section Date ns A and B as urea or glucose, and

Question

DATA SHEET 4.1 Name (continued) Section Date ns A and B as urea or glucose, and record your answers in Table 14.3. aboratory Data for Determining Molality and Solute Molar Mass for Each Solution Freezing Point Depression Constant for H20: Freezing Point Solute MolalitySolute Molar Mass Depression (C) Test Tube Solute (g/mol) 2 NaCl _A |).0 | 53148 .17 73,35 3 Unknown A |-. 4 Unknown B Based on my results, I conclude the following: Unknown A isuruw Unknown B is glutose 2 Determine the percent error of the solute molar masses you determined experimentally from the

Explanation / Answer

Depression in freezing point

3.

(a) For NaCl

molality = mass of solute/molar mass x kg of solvent

mass of solute = 0.234 g

mass of solvent = 4 x 10^-3 kg

So,

molality of NaCl solution = 0.234 g/58.44 g/mol x 4 x 10^-3 kg = 1.0 m

(b) Kf for water = 1.86 oC/m

i for NaCl = 2

So,

expected freezing point of solution = -i.Kf.m

                                                        = -2 x 1.86 x 1

                                                        = -3.72 oC

(c) experimental freezing point = -3.7 oC

percent error = (-3.72 + 3.7) x 100/-3.72 = 0.54%

Similarly one may calculate for glucose and urea.

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