1. 1 Properties of solutions Solutions are homogenous mixtures that may be solid, liquid, or gaseous The compositions of the solvent and the solute determine if a substance will dissolve 3 factors that effect rates solubility 1.Stirring aka (agitation) 2.temperature 3.surface area of dissolving particles These factors involve the contact of the solute with the solvent.

2. 2 Stirring or agitation Stirring affects only the rate which a solid solute dissolves and it does NOT influence the amount of solute that will dissolve. Ex: What happens when you take a teaspoon of sugar and place it in the water?

3. 3 Temperature High temperatures increase the kinetic energy of water molecules therefore they move faster Fast movement of the solvent molecules leads to an increase of the force of the collision between the solvent and the solute. Ex:Sugar dissolves much more rapidly in hot tea then in ice tea.

4. 4 Particle Size The rate a solute dissolves at depends on the size of the solute particles. The dissolving process is a surface phenomenon. More surface of the solute that’s exposed the faster it dissolves Ex:Granulated sugar dissolves faster than a sugar cube The smaller particles in granulated sugar expose a much greater surface area to the water molecules

5. 5 Solubility Definitions Saturated solution-contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure. Solubility- the amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution. Solubility is often expressed in grams of solute per 100g of solvent. Unsaturated solution-a solutions that contains less solute that a saturated solution at a given temperature and pressure.

6. 6 Solubility definitions Some liquids are infinitely soluble in each other Ex: water and ethanol- any amount of these liquids will dissolve in each other Miscible- two liquids if dissolved in each other in all proportions Ex: ethylene glycol and water mix in all proportions Immiscible- liquids that are insoluble in one another Water and diethyl are partially miscible.

7. 7 Factors Affecting Solubility Temperature affects the solubility of a solid, liquid and gaseous solutes in a solvent. Temperature and pressure affect the solubility of gaseous solutes.

8. 8 Temperature and Solubility Solubility of most solid substances increases as the temperature of the solvent increases. Ex: Mineral deposits in hot springs result from the cooling of the hot saturated solution of minerals that emerge from the spring The solution cools in the air and cannot contain the same concentration of the minerals at higher temps. This results in the minerals precipitating Solubility decreases with temperature with only a few substances Ex: ytterbium sulfate

9. 9 Temp. and Solubility Continued Supersaturated solution-contains more solute that it can theoretically hold at a given temperature. Crystallization of a supersaturated solution can be initiated if a very small crystal called a seed crystal of the solute is added. Ex:Rock Candy Excess solute deposits on the surface of a seed crystal can be rapid Crystallization can occur if the inside of the container is scratched

10. 10 Temperature and Solubility Continued What would happen to lake water if we dumped hot water into it? Solubility of gases in liquid solvents is opposite of solids Most gases are greater in cold water than in hot. Ex: Oxygen is less soluble in water if the temperature of the solution rises.

11. 11 Pressure and Solubility Henry’s Law- at a given temperature the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquids. Gas above the liquid increases the solubility of the gas increases When the pressure of a gas decreased the solubility of the gas decreases. Change in pressure has little affect on the solubility of solid and liquids but influences the solubility of gases. Gases- solubility increases as the partial pressure of the gas above the solutions increases Ex:Soda

12. 12 Solubility Curves Describes if a solution is unsaturated, saturated, or supersaturated. If you are above the curve then the solution is supersaturated If you are on the curve the solution is saturated If you are below the curve then the solution is unsaturated Usually solubility measured in grams of solute per 100 g of H 2 O is on the y-axis and either temperature or pressure is on the x-axis

13. 13 This curve is showing the solubility of multiple substances. Which curve does not look like the rest? Why? For NaNO 3 describe the solution at A,B, and C A B C

14. 14 Molarity Molarity – number of moles of solute dissolved in one liter of solution Quantitative measure of concentration M means molar 3M NaCl is 3 molar sodium chloride solution

15. 15 Calculating molarity There are 2 moles of KCl in 4 liters of solution. What is the molarity of the solution? (1 step problem) Mole of solute = 2 moles Volume of solution = 4 L

16. 16 Calculating Molarity A solution contains 9 g of NaCl in exactly 1 L of solution. What is the molarity of the solution? (2 step problem) Convert mass to moles then calculate molartiy m = 9g  (9g) / (58.5 g/mole) = 0.15 mol V= 1L

17. 17 Molality Molality - Concentration of solution expressed in moles of solute per kilogram of solvent Symbol is m = molal 0.5 m of NaOH would be 0.5 moles in 100kg of water

18. 18 Example What is the molality of a solution of 17.1 g of sucrose 17.1 g of C 12 H 22 O 11 Solvent mass = 125 g Step 1: Convert to proper units Step 2 calculate molality

19. 19 Remember When calculating Molarity (M) Need moles of solute Volume of solution in Liters When calculating Molality (m) Need moles of solute Mass of solvent in Kilograms

20. 20 Percent Solutions Concentration of solution in percent can be expressed in two ways 1.Ratio of volume of solute to volume of solution 2.Ratio of mass of solute to mass of solution

21. 21 Percent by volume Convenient if both solute and solvents are liquids Example: Concentrations of alcohols

22. 22 Example What is the percent by volume of ethanol in the final solution when 85 ml of ethanol is diluted to a volume of 250 ml? Vol. of ethanol 85 ml Vol of solution 250 ml %ethanol (v/v) = 85 ml / 250 ml = 34% ethanol (v/v)

23. 23 Percent by mass Convenient when solute is solid Example sugar in water

24. 24 Example You want to make 2000g of a solution of glucose water that has 2.8%(m/m) concentration of glucose. How much glucose should you use? %(m/m) = 2.8% or 0.028 Mass of solution = 2000 g Mass of glucose = ? Mass of glucose = ((%m/m)/100) x mass of solution 0.028 x 2000g = 56 g

25. 25 Colligative Properties of Solutions Topic

26. 26 Vapor-Pressure Lowering Colligative property- a property that depends only upon the number of solute particles, and not upon their identity Three important colligative properties of solutions 1.Vapor-pressure lowering 2.Boiling-point elevation 3.Freezing-point depression

27. 27 Vapor Pressure Vapor pressure- is the pressure exerted by a vapor that is in dynamic equilibrium with its liquid in a closed system Solutions that contain a solute that is nonvolatile always has a lower vapor pressure than a pure solvent. Nonvolatile-not easily vaporized Examples of nonvolatile solutes 1.Glucose 2.Sodium chloride 3.Ionic compounds When these items are dissolved in a solvent the vapor pressure of the solution is lower than the vapor pressure of the solvent

28. 28 Ionic Solutes Ionic solutes have greater effects on vapor pressure than nondissociating solutes. Examples of nondissociating solute Glucose When glucose dissolves the molecules do not dissociate Examples of ionic solutes Sodium chloride and calcium chloride These solutes will dissociate into particles The decrease in a solutions vapor pressure is proportional to the number of particles the solute makes in a solution.

29. 29 Freezing-Point Depression Freezing-point depression--- the difference in temperature between the freezing point of a solution and the freezing point of the pure solvent. The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity. Examples of freezing point depression Sprinkling salt on ice-the melted ice forms a solution with a lower freezing point than water Antifreeze- added to the water in a cars cooling system so they can withstand subfreezing temperatures

30. 30 Freezing point depression for Molecular solutes  T f =K f m Where  T f is the freezing point depression, K f if the molal freezing point depression constant and m is the molality. Only true for molecular solutes (Covalently bonded)

31. 31 Boiling-Point Elevation Boiling-point elevation--- the difference in temperature between the boiling point of a solution and the boiling point of a pure solvent. Adding nonvolatile solutes to liquid solvents decreases vapor pressure Therefore the boiling point of a solution is higher than the boiling point of a pure solvent Antifreeze protects cars from freezing in the winter and from overheating in the summer

32. 32 Boiling-Point Elevation Continued Boiling point elevation is a colligative property that depends on the concentration of particles It takes additional kinetic energy from the solvent particles to overcome the forces that keep them in the liquid The magnitude of the boiling-point elevation is proportional to the number of solute particles dissolved in the solvent Ex:Making fudge-add sugar and flavoring as water boils away the sugar in the solution increases, concentration increases the boiling point rises

33. 33 Boiling point elevation  T b =K b m Where  T b is the boiling point elevation, K b if the molal boiling point elevation constant and m is the molality. Only true for molecular solutes (Covalently bonded)