Chemistry Questions

# Chemistry Questions - Mole Fraction(x Consider a solution...

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Mole Fraction (x): Consider a solution that contains 1.00 mol (46.1 g) of ethanol, C2H5OH in 9.00 mol (162 g) of water. What are the mole fractions? Ethanol X ethanol = 1/(1 + 9) = 1/10 Water X water = 9/(1 + 9) = 9/10 What percent: what is the weight % of alcohol in this alcohol water mixture? Weight % = [46.1/(46.1 + 162)] * 100 = 22.15% Using Henry’s Law: the Henry’s Law constant in water at 25 is 4.48e10 ̊ -5 M/mm Hg. What is the concentration of CO 2 in water when the partial pressure is 0.33 atm? S g = kP g k = 4.4848e10 -5 M/mm Hg Pg = 0.33 atm = 250.8 mm Hg S g = (4.4848e10 -5 M/mm Hg ) * (250.8 mm Hg ) = .011235 M = 1.1e10 -2 M Using Raoult’s Law: Suppose 651 g of ethylene glycol, HOCH2CH2OH, is dissolved in 1.50 kg of water. What is the vapor pressure of the water over the solution at 90 C = 525.8 mm Hg ̊ P solvent = X solvent P solvent X solvent = mole fraction 651 g/(62 g/mol) = 10.5 mol 1500 g/(18 g/mol) = 83.33 mol X solvent = 83.33/(83.33 + 10.5) = 0.888 P solvent = X solvent (525.8) = 466.96 Boiling Point Elevation: What quantity (in grams) of ethylene glycol, HOCH2CH2OH, must be added to 125 g of water to raise the boiling point by 1.0 C? (molal boiling point elevation constant for water: 0.512 C/m) Practice Test 1 Practice Test 2 Freezing Point Depression. In the Northern United States, summer cottages are usually closed up for the winter. When doing so, the owners “winterize” the plumbing by putting antifreeze in the

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toilet tanks, for example. Will adding 525 g of HOCH 2 CH 2 OH to 3.00 kg of water ensure that the water will not freeze at -25 C? (molal freezing point depression concstant for water. -1.86 C/m) ̊ ̊ Δ T f = K f m 525 g/ (62.1 g/mol) = 8.45 mol glycol m = (mol of solute)/(kg of solvent) = 8.45 mol glycol / 3 kg H 2 O = 2.82 m Δ T f = K f m = (-1.86 C/m)(2.82 ̊ m ) = -5.24 C/m ̊ Practice Test 3 1) The osmotic pressure of a solution is directly proportional to both the ______ and the _____. Π = MRT = cRT concentration (molarity) temperature 2) Osmosis of solvent from one solution to another can continue until both solutions are hypotonic/hypertonic/isotonic(circle the correct one), which means they have the same _____. isotonic concentration 3) A so-called protozoan (a single-celled animal) that normally lives in the ocean is placed in fresh water. Will it shrivel or burst? Explain briefly. Burst, because lots of fresh water will flow into the cell. 4) Pure antifreeze freezes at -11.5 C. A solution made by adding a small amount of water to ̊ antifreeze has a lower/higher (circle the correct one) freezing point than pure antifreeze. Lower, solvent = antifreeze, solute = water 5) Assign a type of colloid (foam, aerosol, gel, emulsion) to each of the following so-called colloidal dispersions: a) clouds and fog _____ b) shaving cream, whipped cream _____ c) marshmallow _____ d) mayonnaise, face cream _____ e) cheese, butter _____ a) aerosol
b) foam c) foam d) emulsion e) gel 6) You make a saturated solution of sugar in water at 25 C. No solid is present in the beaker ̊ holding the solution. What can be done to increase the amount of dissolved sugar in the solution?

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Chemistry Questions - Mole Fraction(x Consider a solution...

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