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Gas-Solution Properties Gas Solubility Henry’s Law Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology
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7/16/2015 Solutions Reading assignment: Zumdahl: Chapter 17.1-17.3 A homogeneous mixture of two or more substances in a single phase. Solute ·The material dissolved in a solution. Solvent ·The medium into which a solute is dissolved to form a solution.
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7/16/2015 Solutions What is the solute and what is the solvent? An ounce of isopropanol (rubbing alcohol) is added to a cup of water. A drop of water is added to a cup of isopropanol. A cup of water is added to a cup of isopropanol.
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Molality One cup of isopropanol is mixed with one cup of water. isopropanol CH 3 -CHOH-CH 3 0.78 g mL -1 water 1.00 g mL -1 Molality (m) = moles of solute per kilogram of solvent What is the molality of the solution?
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7/16/2015 Henry’s Law Assumes that the gas and the solvent don’t react with each other. m dissolved gas = k · P gas
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7/16/2015 Henry’s Law The concentration of the gas in solution could also be defined in terms of mole fraction of gas in solution. m dissolved gas = k · P gas dissolved gas = k’ · P gas
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7/16/2015 Henry’s Law What are the axes? What is the slope? Does the line go through the origin? m dissolved gas = k · P gas Draw a graph that represents Henry’s Law
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7/16/2015 Henry’s Law Partial Pressure of Gas (torr) 0 0 moles of dissolved gas per kilogram of solvent (m) slope = Henry’s Law constant (k)
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7/16/2015 Solubility of Gases in Water 1 atm gas pressure above solution CH 4 O2O2 CO N2N2 He Temperature (ºC) Solubility (mmol/kg solvent) 0 0 1 2 102030 What effect does heating have on the amount of dissolved gas?
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7/16/2015 Solubility of Gases The solubility of gas in liquids usually decreases with increasing temperature. However, some gases become more soluble in organic solvents with increasing temperature.
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7/16/2015 Henry’s Law Applications Carbonated beverages Diver’s bends m dissolved gas = k · P gas
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7/16/2015 Carbonated Beverages m dissolved CO 2 = 0.034 m·atm -1 · P CO 2 Packaged under about 2 atm of CO 2 pressure. Why does a carbonated beverage go "flat" overnight?
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7/16/2015 Diver's Bends Caused by dissolved nitrogen in the blood. A diver can go deep for a short period of time, if nitrogen gas does not have a chance to equilibrate in the blood. How do the partial pressures of nitrogen and oxygen in the blood compare at 1 atm pressure and under 33 feet of water?
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7/16/2015 Physiological Implications Henry’s Law What are the problems associated with breathing pure oxygen for a sustained period? How do scuba divers avoid breathing high partial pressures of oxygen? Why is it harder to work and breathe in the mountains? Why do athletes train in the mountains?
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