|AP Chemistry -- Freezing Point Depression
an aqueous solution of sodium chloride starts to freeze, why don't the
ice crystals contain ions of the salt?
||Explain why a
nonvolatile solute dissolved in water makes the system have a lower
freezing point than pure water.
glycol, C2H6O2, is used in some
antifreeze mixtures. Protection against freezing to as low as -40oC
a) How many moles of solute are needed per kilogram of water to ensure this protection?
b) The density of ethylene glycol is 1.11 g/mL. To how many millilitres of solute does your answer to part a) correspond?
(formula weight 92), is essentiually a nonvolatile liquid that is very
soluble in water. A solution is made by dissolving 46.0 g of
glycerol in 250 g of water. Calculate the
a) its freezing point.
b) its vapor pressure at 25oC. (At this temperature the vapor pressure of water is 3.17 kPa)
||A solution of
12.00 grams of an unknown molecular compound dissolved in 200.0 g of
benzene at 3.45oC. Calculate the formula weight of the
calls for the use of the dichromate ion, Cr2O72-,
as an oxidizing agent for isopropyl alcohol, C3H8O.
The oxidation is done in acid, and the chief product is acetone, C3H6O.
a) Write the balanced, net ionic equation for this oxidation.
b) The dichromate ion is available when needed only as sodium dichromate dihydrate. In theory, how many grams of this substance are needed to oxidize 25.0 g of isopropyl alcohol according to the balanced equation.
c) The amount of acetone actually isolated was 16.4 g. Calculate the percentage yield.
d) The reaction produces a volatile by-product. When a sample with a mass of 8.654 mg was burned in oxygen, it was converted into 22.368 mg of carbon dioxide and 10.655 mg of water, the sole products. Calculate the percentage composition of this by-product and determine its empirical formula.
e) A solution prepared by dissolving 1.338 g of this by-product in 115.0 g of benzene had a freezing point of 4.87oC. Calculate the formula weight of the by-product and write its moleculear formula.