Solutions

1. Solutions

2. Vocabulary • Solution: homogeneous mixture Solid – Brass, steel Liquid – Salt dissolved in water Gas – Air • Solute: substance that dissolves • Solvent: substance in which the solute dissolves

3. Vocabulary Cont’d • Insoluble: substance that cannot be dissolved • Soluble: substance that can be dissolved • Miscible: 2 liquids mix completely • Immiscible: 2 liquids that do not mix completely

4. Soluble vs. Insoluble • “Like dissolves Like” Rule: Only substances that are similar/alike will dissolve into one another • Polar and Polar (dissolve) • Nonpolar and Nonpolar (dissolve) • Polar and Nonpolar (do NOT dissolve) • Water is Polar! (IMPORTANT)

5. Water • Must be able to draw water!

6. Dissolving & Solubility • Factors that can effect the RATE (how fast/slow) dissolving: • Temperature • Stirring/Agitation • Surface Area Remember Clear Spring High (CSH) stands for Heat, Stir, Crush

7. Heat of Solution • Endothermic: energy is put into the compound (feels cold) • Exothermic: energy is released from the compound (feels hot) • The overall change is the heat of solution

8. Solubility • The maximum amount of solute that will dissolve at a specified temperature • If there are more grams of solute than can dissolve, some of the solute will fall out of solution

9. Saturation • Unsaturated: when a solution can hold more solute and it does dissolve • Saturated: when a solution cannot dissolve any more solute • Supersaturated: contains more solute than a saturated solution at the same temperature • extremely unstable and if a small amount of solute (seed crystal) is added the excess solute quickly falls out of solution (Example: hand warmers, rock candy, and cloud seeding)

10. Examples of Supersaturation

11. UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form Solubility increasing concentration

12. Solubility Curves • Know how to read this curve and answer questions • Examples + If 70 grams of NaNO3 are dissolved in water at 10°C, is the solution saturated, unsaturated, or supersaturated? + If 20 grams of NaCl are dissolved in water at 80° C, then how many more grams can be added to make a saturated solution?

14. Temperature and Solubility • Solids • Increase Temp. will Increase Dissolving (Solubility) Decrease Temp. will Decrease Dissolving (Solubility) • Gases (Different from Solids) • Increase Temp. will Decrease Dissolving (Solubility) Decrease Temp. will Increase Dissolving (Solubility)

15. Sol. Sol. To To Solids dissolved in liquids Gases dissolved in liquids As To , solubility As To , solubility

16. Water and Oxygen • Dissolved Oxygen – The amount of oxygen that is dissolved in water • If dissolved oxygen is too low, animal and aquatic life is unable to survive and the water becomes toxic • Happens commonly in lakes and ponds during the summer months

17. Pressure and Solubility (Gases) • A change in pressure on solution with a dissolved solid or liquid has very little effect on solubility. • A change in pressure on a solution with a dissolved gas has a large effect on solubility. • Solubility of a gas increases as the external pressure increases • When pressure on the outside decreases some of the gas escapes.

18. Henry’s Law • Henry’s Law – At a given temperature the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) above liquid • S1P2 = S2P1 • Show work, answer, units • Units must match • Label properly • 1=initial condition and 2=final condition • Only applies at constant temperature

19. Practice • If 0.24 g of a gas dissolves in 1.0L of water at 1.5 atm of pressure, how much of the gas will dissolve if the pressure is raised to 6.0 atm? Assume the temperature is held constant. • Answer: 0.96 g/L

20. Practice • The solubility of a gas changes from 0.95 g/L to 0.72 g/L. If the initial pressure was 2.8 atm, what is the final pressure? • Answer: 2.12 atm

21. Concentration • How much solute is dissolved in a specific amount of solvent or solution. • Can be expressed as • Percent by mass - Tuesday • Percent by volume - Tuesday • Molarity – Wednesday • Molality and Normality – We will not learn these, but they are mentioned in the book

22. Percent by Mass • (Mass of solute/Mass of solution) x 100 • Used when a solid is dissolved in a liquid • Mass of solution is equal to the mass of the solute + the mass of the solvent

23. Percent by mass problems • In order to maintain a sodium chloride concentration similar to ocean water, an aquarium must contain 30 g of NaCl per 500 grams of water. What is the percent mass of the solution? • Answer: 5.66%

24. Percent by Mass Problems • You have 150 grams of CuCl2 solution. The percent by mass of the solute is 8.0%. How many grams of CuCl2 are in solution? How many grams of solvent are in the solution? • Answer: • 12 g of CuCl2 • 138 g of water

25. Percent by Volume • Usually describes solutions where both solute and solvent are liquids • Volume of solute/Volume of solution x 100

26. Percent by Volume Problems • What is the percent by volume of ethanol in a solution that contains 50 ml of ethanol distilled in 430 ml of water? Answer: 10.42%

27. Percent by Volume Problems • If you have 30 ml of a 5% aqueous solution of H2O2, what volumes of H2O2 and water are in the solution? • Answer: • 1.5 mL of H2O2 • 28.5 mL of H2O

28. Molarity • Its unit is a M = mol/L • Moles of solute/Liters of solution

29. A 100.5 ml solution contains 5.10 grams of Glucose (C6H12O6). What is the molarity of this solution? The molar mass of glucose is 180.18 g/mol • Answer: 0.28 M

30. Calculate the molarity of 1.60 liters of a solution containing 1.55 grams of dissolved KBr. • Answer: 0.0081 M

31. Making a molar solution • Using the molarity of the solution figure out how many moles of the solute will be needed. • Using the moles of solute, convert it to grams of solute

32. How many grams of CaCl2 would be dissolved in 1.0 liters of a .10M solution? • Answer: 110.98 g CaCl2

33. How many grams of CaCl2 should be dissolved to make 500 ml of a .20M solution? Answer: 11.10 g CaCl2

34. Diluting a stock solution • Stock solution is a concentrated solution M1V1 = M2V2 • Lab: 1.0 M H2SO4 is needed • 130 students • Each set of lab partners needs 30 mL • Glassware 0.5L, 1 L, or 2L • How much should I make?

35. How many ml of a 18.0 M H2SO4 stock solution would you need to prepare 2 L of 1.0 M H2SO4? Answer: 111 mL

36. How Do You Perform This Dilution? 1. Fill a 2 liter volumetric flask half-full of distilled water. 2. Measure 111 mL of 18.0 M H2SO4 in graduated cylinder. 3. Slowly pour the acid into the water. 4. After each addition, swirl the flask to enhance mixing and to allow the exothermic heat of solution to dissipate. 5. Fill the volumetric to the “line” with distilled water. 6. Your flask now contains 2.0 L of a 1 M solution of H2SO4 that can be used for the lab.

37. Viscosity • Physical Property • Fluids resistance to flow • Fluid pours fast means LOW viscosity (example: water, coffee, tea) • Fluid pours slowly means HIGH viscosity (example: syrup, ketchup)

38. Dissolving • Ionization: The breaking up of a compound into separate ions • Electrolyte: An ionic/soluble compound whose aqueous solutions conducts electricity • Nonelectrolyte: A molecular (covalent) substance whose aqueous solutions do not conduct electricity • Precipitate: A product of a reaction that is insoluble and falls out of solution as a solid.

39. No light Dim Light Bright Light weak electrolyte strong electrolyte

40. How to Determine if a Substance is an Electrolyte or Precipitate? • Is the substance ionic or covalent? (Where are they on periodic table?) • Is the substance soluble or insoluble? (Use the solubility rules)