Question

Data Table 3 RUN #1 RUN #2 RUN #3 Volume of used cyclohexane solvent, Vocoleane, ml 5mL 5 mL 5 mL Cyclohexane density deyclobesan 0.799 g/cm Mass of used cyclohexane solvent, (kg) 1c.11 0.012k 0-012 0-012V Freezing point depression constant, K, for cyclohexane, KF ('C. kg/mol) 20.0 The value of m-(ATF /KF), (mol/kg) for the solution of unknown in clohexane Number of moles of unknown in the sample -0.00S 0.005 7.2 x 10 xIO S - x 10-5 Mass of unknown sample, Wanknown, (g) 0.5 0.5 Molecular mass of unknown, Muskno calculated for each run in g/mol Makown, I .94310 The average molecular mass of unknown, Munk.oomn.e (gmol) Assuming that general chemical formula for the unknown is Can2H2 calculate the "n" value for the determined average molecular mass of unknown, Munknown, ave Determined chemical formula for the unknown (use the calculated above value of "n" in general formula Coa 2H2n) Note: Determine the "n" value which brings the numerical value for CaH most closely to its experimental value of Munknowa, ave. That value of "n" determined your final formula for the unknown and should be reported in data table 3.

Answer 1

The mistake that you have made here is that T degree F, are you have calculated taking the average values of T_F,1, T_F,2 and T_F,3 T degree_F, are = freezing point of pure cyclo hexane (without anything added) T degree_F = known value = 6.5 degree c [which I am using here] please check the value given in your manular you have determined separately Moles or mass can never be negative From plot, T_F,1 = -1.6, T_F,2 = -1.5, T_F,3 = -1.5 increment T_F,1 = -1.6 - 6.5 = -8.1, increment T_F,2 = -1.5 - 6.5 = 8, increment T_F,3 = -1.5 - 6.5 = 8 m_ -1 = -increment T_F,1/K_F = 8.1/20 = 0.405, m_ -2 = -increment T_F,2/K_F = 8/20 = 0.4 m_ -3 = -increment T_F.3/K_F = 8 /20 = 0.4 molality = moles/solvent in kg