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Types of Solution: Concentration, Pressure, and Colligative Properties

This chapter explores the different types of solutions and their properties, including concentration, solubility, pressure, and colligative properties. It explains concepts such as molarity, molality, mole fraction, and mass percent, as well as Henry's Law and Raoult's Law.

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Types of Solution: Concentration, Pressure, and Colligative Properties

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  1. Chapter 12 Solutions suroviec Spring 2015

  2. I. Types of Solution • Most chemical reaction take place between ions/molecules dissolved in water or a solvent. • Solution: homogenous mixture of 2 or more substances in a single phase

  3. II. Molecular view of solution process • Liquids and solids held together by intermolecular attractions • Looking at specifically • Solvent-solvent • Solvent - solute • Solute – solute • 3 steps • Separate solvent molecules • Separate solute molecules • Mix together

  4. Ex. Dissolve CaCl2 (s) in H2O • What happens to the concentration of Ca2+ and Cl-? • Saturated: stable solution in which the maximum amount of the solute has been dissolved • Equilibrium in solution • Solubility: concentration of solute in equilibrium with undissolved solute in a saturated solution

  5. Examples: • CCl4 and CH4 • NaCl and CCl4

  6. III. Concentration A. Molarity: (M) Moles of solute / liter of solution • Does not tell us the EXACT amount of volume to use B. Molality: (m) Mole of solute / mass of solvent (kg) • Cannot be the same measure of a solution

  7. Example The concentration of a K2CrO4 solution is undetermined, but it was prepared from 38.3 g of K2CrO4 (MW 19.4 g/mol) and 1.00 kg of water. What is the molality? Calculate the molality of 1 L of 1.22M sucrose (MW 342.3 g/mol) solution. The density of the solution is 1.12 g/mL.

  8. C. Mole Fraction • Amount of the component we are interested divided by the total amount of all the components of the mixture Mole fraction of A (XA) =

  9. example • Consider a solution that has 1.00 mole ethanol (46.1 g) dissolved in 9.00 moles of water (162 g). Find the mole fraction of each.

  10. D. Mass Percent • Common unit of measurement for consumer products • Mass of one component divided by the total mass of the mixture multiplied by 100%

  11. Example • Consider an alcohol-water mixture that is prepared by dissolving 46.1 g of ethanol in 116.2 g of water. What is the mass percent of ethanol in the mixture?

  12. IV. Pressure, Temperature and Solubility • Solid solubility and Temperature • When a solid is dissolved an equilibrium is established • An increase in temp will shift the equilibrium

  13. B. Gas Solubility • Solubility of gasses decreases with increasing temperature • Why do fish go to bottom of lake in the summer? • Gases that dissolve to an appreciable extent in water do so in an exothermic process • So what do you need to do to get the gas out of the water?

  14. V. Pressure and Solubility A. Henry’s Law • Solubility of a gas in a liquid is directly proportional to the gas pressure • Henry’s Law • cg = kHPg • cg = molar concentration (mol/L) • kH = Henry’s law constant (mol/L · atm) • Pg =pressure of a gaseous solute (atm)

  15. Example Deep-sea diving • Solubility of gases is the concentration of gases in equilibrium with substances in gaseous state • What would happen if we increased the pressure?

  16. VI. Colligative Properties • Properties of a solution that depend only in the number of solute particles per solvent molecule and not the nature of the solute or solvent

  17. A. Raoult’s Law • Equilibrium vapor pressure: pressure of the vapor when the liquid and the vapor are in equilibrium

  18. Example • Solution contains 82.0 g of ethylene glycol in 100g of water at 22oC. (where is vapor pressure of water is 19.88 mm Hg) what is the new vapor pressure?

  19. B. Boiling Point Elevation • You have a solution of 0.200 mole of sugar in 100.0 g of benzene • The normal vapor pressure of pure benzene is 400 mmHg, what is the new vapor pressure of this solution?

  20. This vapor pressure lowering causes a BP elevation! • Normal BP is the temp at which vapor pressure =760 mm Hg • BP elevation

  21. B. BP elevation • Leads to general equation: • The melting point of water is 0oC at 1atm. If 12.15 g of ZnSO4 (MW 161.5 g/mol) are dissolved into 161.2 g of water: • What is the molality of the solution • What is the new melting point of the solution?

  22. C. Freezing Point Depression • Freezing point of a solution will be lower than of a pure solvent • General equation • Why add antifreeze to your car?

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