1. Gas-Solution Properties Gas Solubility Henry’s Law Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

2. 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.

3. 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.

4. 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?

5. 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

6. 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

7. 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

8. 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)

9. 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?

10. 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.

11. 7/16/2015 Henry’s Law Applications  Carbonated beverages  Diver’s bends m dissolved gas = k · P gas

12. 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?

13. 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?

14. 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?