An unknown compound contains only carbon, hydrogen, and oxygen. Combustion analysis of the compound gives mass percents of 31.57% C and 5.30% H. The molar mass is determined by measuring the freezing point depression of an aqueous solution. A freezing point of -5.20°C is recorded for a solution made by dissolving 10.56 g of the compound in 25.0 g water. Determine the empirical formula, molar mass, and molecular formula of the compound. Assume that the compound is a nonelectrolyte.
2007-11-09 09:02:56 · 2 answers · asked by softball_linz_06 1 in Science & Mathematics ➔ Chemistry
From the freezing point depression, and from the freezing point depression constant of water, you can work out the molar mass.
Find the empirical formula as follows:
By mass, C:H:O :: 31.57:5.30:63.13
By number of atoms, :H:O :: 31.57/12.0 : 5.30/1.0 :63.13/16.0
Work out that last line, and divide by the smallest.
Finally, the molecular formula must be an exact multiple of the empirical formula, and must have the correct molar mass.
2007-11-10 00:41:33 · answer #1 · answered by Facts Matter 7 · 0⤊ 0⤋
mass ethanol = 75.0 mL x 0.79 g/mL=59.3 g moles ethanol = 59.3 g/ 46.069 g/mol=1.29 Molarity = 1.29 mol / 0.250 L=5.15
2016-04-03 04:23:20 · answer #2 · answered by ? 4 · 0⤊ 0⤋