Solutions

1. Solutions L

2. Solutions • Mixture of substances (2+) • State of matter depends on the solvent • Solute: substance that is dissolved • Solvent: substance that does the dissolving

4. Properties of solutions • Homogeneous • Cannot be filtered • Transparent • Can be separated by evaporating the solvent

5. Solubility • Soluble – if a substance can be dissolved in the solvent • AKA: Miscible • Insoluble – if a substance can not be dissolved in the solvent • AKA immiscible • Solubility -- How much solvent can be dissolved in a solute at a given temp and pressure

6. Like Dissolves Like! • Polar compounds dissolve polar compounds • Water is the universal solvent because of its polarity • Non-polar compounds dissolve non-polar compounds • Benzene can dissolve plastic because both are non-polar

7. Solvation

8. Rate of solubility • Since solubility occurs when molecules collide, increasing the rate of collisions will increase how much quickly the solute dissolves • Stirring • Increasing solute surface area • Increasing temperature • Since the molecules of solvent have to move between the molecules of solute energy is absorbed (endothermic process)

9. Factors that effect solubility • Temperature • Effects solid solubility mainly • Direct relationship with solubility • Pressure • Effects gaseous solubility mainly • Solubility increases as pressure around the solute increases • Soda is bottled at a higher pressure, when opened it begins to effuse out.

10. Solubility curves • Graph assumes a 100g sample of water, if you had 200g just double the values • Different phases dissolve differently • Solids • Higher solubility at higher temp. • (+) slopes • Gases • Higher solubility at lower temps • (-) slopes

11. Solubility curves-think of it like a party • Saturated – on the line • “We’re out of seats, no one can come in till someone leaves.” • Unsaturated – below the line • Coach L’s usual party itinerary • “We got room come on it!” • To calculate how much more can fit in find out how much under the line you are on the Y-axis • Supersaturated – above the line • “I’ve hired a bouncer!” • Excess is precipitate • Solid falls out of solution • To calculate: find how much you are over on the Y-axis and subtract till you get to the line

12. Molarity • Concentration – how much stuff do you have in a set space • Molarity -- Concentration of molecules in a solution Molarity (M) = molsolute Lsolution • You are usually given grams so you have to convert • You are usually given milliliters so you have to convert

13. Example: • What is the molarity of a solution of 100L of water and 36g of hydrochloric acid 36g HCl X (1mol HCl/36g HCl) = 1mol HCl 1mol HCl/100L H2O = 0.01M HCl

14. Practice • How many grams of CaCl2 would be dissolved in 1.0L of a 0.10M solution of CaCl2? • A Liter of 2M NaOH solution contains how many grams of NaOH? • How many grams of CaCl2 would need to dissolved in 500mL of water to make a 0.20M solution of CaCl2? • 11g CaCl2 • 80g NaOH • 11g CaCl2

15. Dilutions • Since the number of Moles doesn’t change when we change the volume we can find the new concentration with the following formula M1V1 = M2V2 • Ex: what volume, in milliliters of 2.00M calcium chloride (CaCl2) stock solution would you use to make a 0.50L of 0.300M calcium chloride solution?

16. what volume, in milliliters of 2.00M calcium chloride (CaCl2) stock solution would you use to make a 0.50L of 0.300M calcium chloride solution? M1V1 = M2V2 M1 = 2.00 M CaCl2 V1 = ? L of 2.00M CaCl2 M2 = 0.300M CaCl2 V2 = 0.50L of 0.3M CaCl2 2M (V1) = 0.3M (0.5L) 2M (V1) = 0.3M (0.5L) 2M2M V1 = 0.075 L V1 = 75mL

17. Practice • What volume of a 3.0M KI solution would you use to make 0.300L of a 1.25M KI solution? • How many milliliters of a 5.0M H2SO4 stock solution would you need to prepare 100mL of a 0.25M H2SO4 • If you dilute 20.0mL of a 3.5M solution to make 100mL of solution, what is the molarity of the dilute solution? • 125mL • 5.0mL • 0.70M

18. Colligative Properties of solutions • Physical properties of solutions that are effected by the number of particles in solutions but NOT by the identity of dissolved particles in solution. • Ionic compounds have a greater effect on colligative properties then covalent compounds • Dissociation factor(df) • How many ions does the compound form? • For non-electrolytic compounds (covalent compounds) the df is always one (1). • For ionic compound the df is the number of ions that form that compound. • Effect: • Vapor pressure • Boiling point • Freezing point

19. Vapor pressure • number of solvent particles exposed to surface, less enter gas phase • Lower vapor pressure

20. Boiling Point • Increases because fewer particles on the surface are contributing to the vapor pressure (takes more energy to raise the vapor pressure) • Dependent on vapor pressure • Kb = difference in temp. of solution and pure solvent

21. Freezing point • When kinetic energy can no longer overcome attraction • Decreases because solute particles get in the way of attractive forces, cause the more energy to need to be lowered for phase change

22. Calculating the effect of solute on freezing points and boiling points DT = m(df)K Where DT = change in BP or FP (°C) m = molarity or concentration of solution df = dissociation factor K = constant for solvent (given)

23. What is the freezing point of a 0.40m solution of sucrose in ethanol, if ethanol’s normal freezing point is -114.1°C? DT = m(df)K • m = 0.40m • df = 1 • K = 1.99 °C/m DT = 0.40m (1) 1.99°C/m DT = 0.796°C New freezing piont = -114.1°C – 0.796°C = -114.896°C