Chapter 11 Solutions and their Properties. Solutions. A mixture is a combination of 2 or more substances. There are 3 types of mixtures, namely:
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Solutions and their Properties
A solution is made up of 10.0 ml ethyl alcohol (C2H5OH, d=0.785 g/ml) dissolved in 50.0 ml water. Calculate for the following concentrations:
1. % m/m, 2. X solute, 3.Molarity, 4. molality
mass solute = 10.0ml x 0.785g/ml = 7.85g
mass solvent = 50.0ml x 1.00g/ml = 50.0g
moles solute = 7.85g x 1 mol solute/46g = 0.171 mols
moles solvent = 50.0g x 1 mol solvent/18g = 2.78 mols
% m/m = 7.85g/57.85g x 100 = 13.7%
X = 0.171 / (0.171 + 2.78) = 0.0579
M = 0.171mol / 0.060L = 2.85M
m = 0.171mol / 0.050kg = 3.42m
11.70 Vinyl Chloride has a Henrys Law constant of 0.091 mol/(L.atm) at 25oC. What is the solubility of vinyl chloride in water in mol/L at 25oC and a pressure of 0.75 atm.
11.72 Fish generally need an O2 concentration in water of at least 4 mg/L for survival. What partial pressure of oxygen above the water in atmospheres at 0 oC is needed to obtain this concentration? The solubility of O2 in water at 0 oC and 1 atm partial pressure is 2.21 x 10-3 mol/L.
11.13 What is the vapor pressure in mm Hg of a solution prepared by dissolving 5.00 g benzoic acid (C7H6O2) in 100.00 g ethyl alcohol (C2H6O) at 35oC? The vapor pressure of pure ethyl alcohol at 35oC is 100.5 mm Hg.
11.14 How many grams NaBr must be added to 250 g of water to lower the vapor pressure by 1.30 mm Hg at 40oC. Assuming complete dissociation? The vapor pressure of water at 40oC is 55.3 mm Hg.
11.36 The following phase diagram shows a very small part of the solid/liquid phase transition boundaries for two solutions of equal concentration. Substance A has i=1, and substance B has i=3.
Deicing roads – the addition of soluble solute to ice lowers its melting point thereby melting it. Table salt (NaCl) or MgCl2 is used to deice roads. MgCl2 has the advantage of a higher van’t Hoff’s factor.
Reverse Osmosis – the addition of pressure on the salt solution side results in water diffusing through a semi-permiable membrane producing pure water.
Fractional distillation – used in refineries to separate different grades of hydrocarbons from oil.
Physiological effects – differences in salt concentrations inside and outside the cell causes the cell to shrink (crenate) or explode (lysis).