Camphor freezing-point depression

Expensive special thermometers are usually needed for determinations of freezing-point depression and boiling-point elevation but, when camphor is used, a common lab thermometer may be employed. A student mixes 0.1032 g... 

PROBLEM 11.25 A solution of 0.250 g of naphthalene (mothballs) in 35.00 g of camphor lowers the freezing point by 2.10°C. What is the molar mass of naphthalene The freezing-point-depression constant for camphor is 37.7 (°C kg)/mol. 

C7H4O C]4H802 95. a. 303 9 g/mol b. No, codeine could not be eliminated since its molar mass is in the possible range including the uncertainty c. We would like the uncertainty to be 1 g/mol. We need the freezing-point depression to be about 10 times what it was in this problem. Two possibilities are (1) make the solution ten times more concentrated (may be solubility problem) or (2) use a solvent with a larger Kf value, e.g., camphor. 

Again, Kf values can be calculated from 7 , AHr, and Mi for the solvent Some results. are shown in Table 5.4. The agreement with the direct determination of Kf from freezing-point depressions is very satisfactory. The very large value of Kf for camphor means that this substance is. frequently a very suitable solvent for molecular weight determinations. 

Reserpine is a natural product isolated from the roots of the shrub Rauwolfia serpentina. It was first synthesized in 1956 by Nobel Prize winner R. B. Woodward. It is used as a tranquilizer and sedative. When 1.00 g reserpine is dissolved in 25.0 g camphor, the freezing-point depression is 2.63X Kf for camphor is 40.x kg/mol). Calculate the molality of the solution and the molar mass of reserpine. 

Camphor (CioHigO) melts at 179.8 C, and it has a particularly large freezing-point-depression constant, Kf = 40.0 °C/m. When 0.186 g of an organic substance of unknown molar mass is dissolved in 22.01 g ofUquid camphor, the freezing point of the mixture is found to be 176.7 °C. What is the molar mass of the solute ... 

The observed melting point of camphor is often low. Look up the molal freezing-point-de-pression constant K for camphor and calculate the expected depression of the melting point of a quantity of camphor that contains 0.5 molal impurity. Hint Look in a general chemistry book under "freezing-point depression" or "colligative properties of solutions."... 

III. Depression of the Freezing-point of Camphor (Rast s Method). 

A convenient small apparatus for fused solvents was devised and used by Eykman. The depression of freezing-point of camphor was used by A. Jouniaux and modified into a micro-method by K. Rast. ... 

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