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Solutions

Solutions. Solution : homogeneous mixture components are uniformly intermingled on a molecular level Solutions can be solid: brass (zinc in copper) liquid : salt water, sugar water, etc gas : Air (oxygen & others in nitrogen). Solutions. Unsaturated solution:

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Solutions

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  1. Solutions • Solution: • homogeneous mixture • components are uniformly intermingled on a molecular level • Solutions can be • solid: • brass (zinc in copper) • liquid: • salt water, sugar water, etc • gas: • Air (oxygen & others in nitrogen)

  2. Solutions • Unsaturated solution: • a solution that is capable of dissolving more solute • Saturated solution: • a solution that is in equilibrium with undissolved solid • Supersaturated solution: • a solution that contains more dissolved solute than is needed to form a saturated solution

  3. Solubility Example: Which of the following solutes would you expect to be soluble in water: CH3CH2CH3: CH3CH2OH: HCl: Vitamin A Vitamin C Remember: Substances with similar intermolecular forces tend to dissolve in each other

  4. Solubility of Gases • The solubility of a gas in a solvent depends on the nature of the solute and solvent, the temperature, and the pressure. • In general, the solubility of gases in water increases with increasing molar mass. • Larger LDF

  5. Solubility of Gases • The solubility of a gas in a solvent increases as the pressure of the gas over the solvent increases. • Henry’s Law:The solubility of a gas in a solvent is directly proportional to its partial pressure above the solution. Cg = kPg where Cg = solubility of the gas in the solution phase Pg = partial pressure of the gas k = proportionality constant (value depends on solute, solvent, and temperature

  6. Solubility Example: Calculate the concentration of CO2 in a soft drink that was bottled with a partial pressure of carbon dioxide of 3.5 atm over the liquid at 25oC. (k = 3.1 x 10-2 mol/L.atm)

  7. Solubility of Gases Example: Why does a bottle of soda bubble when the cap is first removed? • Carbonated beverages like soda are bottled under a carbon dioxide pressure slightly greater than 1 atm. • Opening the bottles, reduces the partial pressure of CO2 above the soda. • Solubility of CO2 decreases so CO2 bubbles out of the solution.

  8. Solubility of Gases • The solubility of solid solutes generally increases with increasing temperature.

  9. Solubility of Gases • The solubility of a gas in a solution decreases with increasing temperature. • Gas molecules have greater KE at higher T and can escape from the solution more easily.

  10. Concentration • Several different units can be used to express the concentration of a solute in a solution: • mass (weight) percent • parts per million (ppm) • parts per billion (ppb) • mole fraction • Molality • Molarity • Varies with temperature Independent of temperature

  11. Concentration • Mass Percent = mass of component x 100 total mass of sol’n Example: A solution is prepared by dissolving 6.8 g of NaCl in 750.0 g of water. What is the mass percent of the solute?

  12. Concentration • ppm = mass of component x 106 total mass of sol’n Example: A 10.25 g sample of lake water contains 1.28 x 10-2 mg of arsenic. What is the concentration of arsenic in ppm?

  13. Concentration • ppb = mass of component x 109 total mass of sol’n Example: A 225 g sample of lake water contains 1.2 mg of pesticide. What is the concentration of pestcide in ppb?

  14. Concentration • Mole fraction = moles of component total moles of all components Example: Calculate the mole fraction HCl present in a solution prepared by dissolving 0.25 mol HCl in 9.50 mol H2O.

  15. Concentration • Molality = m = moles of solute kg solvent Example: Calculate the molality of a solution prepared by dissolving 1.25 g of sodium chloride in 250 g of water.

  16. Concentration • Molarity = M = moles of solute L solution Example: Calculate the molarity of a solution that contains 73.0 g of HCl per 250 mL of solution.

  17. Concentration • Why does molarity vary with temperature?? • You must be able to interconvert between the different concentration units.

  18. Concentration Example: An aqueous solution of sodium hydroxide contains 4.4% NaOH by mass. Calculate the mole fraction of NaOH and the molality of the solution. To find mole fraction:

  19. Concentration

  20. Concentration To find molality:

  21. Concentration Example: Calculate the molarity of the toluene present in a 1.50 m solution of toluene (C7H8) in benzene if the solution has a density of 0.876 g/mL.

  22. Concentration Answer: 1.15 M

  23. Concentration • The dilution equation is used to calculate either • the new concentration of a solution prepared by diluting a stock solution Or • The volume of a stock solution needed to prepare a known volume of a more dilute solution C1V1 = C2V2

  24. Concentration Example: Calculate the molarity of a solution prepared by diluting 225 mL of 1.5 M KMnO4 to a total volume of 850.0 mL. Answer: 0.40 M

  25. Concentration Example: What volume of 12.0 M HCl is needed to prepare 500.0 mL of 0.60 M HCl.

  26. Concentration Example: A solution is prepared by dissolving 1.50 g of sodium chloride in enough water to give 250.0 g of solution. A 25.0 g aliquot of this solution was then diluted with water to a total mass of 100.0 g. Calculate the weight percent sodium chloride present in the final solution.

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