The formulas for 2-methyl-2-propanol (TB), methyl acetate and propionic acid are
ID: 485252 • Letter: T
Question
The formulas for 2-methyl-2-propanol (TB), methyl acetate and propionic acid are (CH_3)_3 COH, CH_3, CO_2CH_3 and CH_3CH_2CO_2H, respectively. Methyl acetate and propionic acid are liquids at room temperature. The freezing point of TB is 25.3 degree C and the freezing point depression constant for TB is 8.20 degree C/m. a. Methyl acetate is soluble in liquid TB. Does this solubility observation surprise you? Explain. b. To a 10.00 g sample of TB was added 2.00 g of TB, Predict the freezing point of TB, and briefly justify your prediction. c. To a second 10.00 g sample of TB was added 0.250 g of methyl acetate. Predict the freezing point of the resultant solution. d. To the resultant solution in Part c above was added 0.250 g of propionic acid; the propionic acid dissolved. Predict the freezing point of the new resultant solution. e. To the resultant solution in Part d above was added 2.00 g of TB. Predict the freezing point of the new resultant solution. f. Considering your answers above, what conclusions, if any, can you draw regarding solute identity and its effect on solvent freezing point?Explanation / Answer
Solubility and freezing point
a. Methyl acetate is a polar compound which is soluble in polar TB solvent. The solubility rules say polar would dissolve in polar solvent and thus this is expected.
c. molality of solution = 0.25/74.08 x 0.01 = 0.34 m
Tb = iKfm = 1 x 8.2 x 0.34 = 2.8 oC
freezing point of solution = 25.3 - 2.8 = 22.5 oC
d. when 0.25 g propionic acid added to solution c.
molality = 0.34 + 0.34 = 0.68 m
Tb = iKfm = 1 x 8.2 x 0.68 = 5.6 oC
freezing point of solution = 25.3 - 5.6 = 19.7 oC
e. 2 g of TB added to solution d.
molality = 2(0.25/74.08 x 0.012) = 0.56 m
Tb = iKfm = 1 x 8.2 x 0.56 = 4.6 oC
freezing point of solution = 25.3 - 4.6 = 20.7 oC
f. By adding solute to TB, the freezing point of solution decreases. While adding solvent TB to the solution, the freezing point of solution goes up.
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