Solutions and Solubility

1. Chemistry Solutions and Solubility

2. Mixtures • Heterogeneous Mixtures—particles that are large enough to be seen without a microscope; made of materials that are dissimilar • Homogenous Mixtures—particles are molecule-sized and uniform throughout

3. Solutions are Homogenous Mixtures • Solution=a homogeneous mixture of two or more substances uniformly dispersed throughout a single phase. • Can a solution be a solid? Yes! Brass is a solution of zinc and copper atoms!

4. Solvents and Solutes • When most people use the word solution, they usually refer to a homogenous liquid mixture. • Solute= the substance that is dissolved in the solvent • Solvent=the substance in which the solute is dissolved Huh??????

5. Dissolve the Solute in the Solvent • When mixing a liquid solution, the liquid material is the solvent and what is dissolved in the liquid is the solute. • The most common liquid solutions are aqueous solutions—in these, the solvent is water. In the solution shown, what is the solvent? What is the solute?

6. Concentration • In a solution, the solute is distributed evenly throughout the solvent. • Any part of the solution has the same ratio of solvent: solute. • This ratio is the concentration.

7. Calculating Concentration • Concentration of a substance can be measured in different units: • Ppm=parts per million • Molarity=moles of solute/liters of solution Persistent Organic Chemicals such as PCBs bio-accumulate. This diagram shows the degree of concentration in each level of the Great Lakes aquatic food chain for PCBs (in parts per million, ppm). The highest levels are reached in the eggs of fish-eating birds such as herring gulls.

8. Molarity • Molarity=a concentration unit of a solution expressed as moles of solute dissolved per liter of solution

9. How to Prepare Solutions • 1. Determine the molar mass of the solute (the substance you will be dissolving) • 2. Convert the desired molarity to grams, using molar mass. • 3. Add the correct number of grams of the solute to a small amount of liquid. • 4. After dissolving, add the rest of the liquid to reach the desired amount.

10. Preparing an Aqueous Solution

11. Preparing 1.0 L of a .5 M Solution • To make .5 Molar Solution of a substance, you will need .5 moles of the substance you are dissolving. • How will you get .5 moles of Glucose: C6H12O6? • 1. Figure out the molar mass of Glucose C = 12 X 6 = 72 H = 1 X 12 = 12 O = 16 X 6 = 96 Total molar mass of Glucose = 180 g/mol

12. Preparing 1.0 L of a .5 M Solution • To make .5 Molar Solution, you will need .5 moles of the substance you are dissolving. • How will you get .5 moles of Glucose: C6H12O6? • Total molar mass of Glucose = 180 g/mol • Conversion: • .5 mol Glucose 180 g. Glucose 90g 1 mol Glucose

13. Preparing 1.0 L of a .5 M Solution • 90g of Glucose is .5 moles. • To make 1.0 L of .5 Mol Glucose, you will need a total of 1.0 L of solution. • Add 90g of Glucose to 500 mL of Water, and mix. • Finally, add enough additional water to make a total of 1 Liter.

14. Now You Try! • How will you prepare a 0.85 M solution of sodium chloride (NaCl)? You will need 100 mL of this solution.

15. Calculating with Molarity • What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl?

16. Calculating with Molarity • What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl? • First, don’t freak out!!!

17. Calculating with Molarity • What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl? • 1. Convert the mass of KCl into moles of KCl by using the molar mass. 85.0 g KCl 1 molKCl 1.14 molKCl 74.55 g KCl

18. Calculating with Molarity • What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl? • 2. Convert the volume in milliliters into volume in Liters: 400.0mL 1 Liter 0.4000 Liters 1,000 mL

19. Calculating with Molarity • What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl? • Molarity is the moles of solute divided by the volume of the solution. • 1.14 molKCl = 2.85 mol/L = 2.85 M KCl • 0.4000 L

20. Now You Try! • If 18.25 g HCl is dissolved in enough water to make 500.0 mL of solution, what is the molarity of the HCl solution? • 1. Convert mass to moles • 2. Convert mL to Liters • 3. Molarity is moles divided by volume in Liters Remember not to Freak Out! http://www.bozemanscience.com/solutions-molarity

21. What factors affect how fast a substance dissolves? • Agitation • Temperature • Particle size of solute Which dissolves faster? Sugar by itself; sugar being stirred Which dissolves faster? Sugar in cold water; sugar in hot water Which dissolves faster? Fine-grain sugar; large crystal sugar Why????

22. Solubility Affected by 3 Things: • Agitation: because dissolving occurs at the surface of the particle, stirring speeds up the process by continually bringing the solvent into contact with the solute. • Temperature: an increase in temperature causes particles to move faster, which leads to an increase in the frequency and force of the collisions between molecules. • Particle Size: smaller particles have a greater surface area exposed to the solvent.

23. Solubility • If you add 36.0g of NaCl to 100 g of water at 25oC, all of the 36.0g will dissolve. • But, if you add one more gram of salt and stir, no matter how vigorously or for how long, only .2g of the last portion will dissolve. Why?

24. Saturated Solutions • A saturated solution contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure. In a saturated solution, a state of dynamic equilibrium exists between the solution and any un-dissolved solute, provided the temperature stays constant.

25. Unsaturated, Saturated, Super-Saturated • Unsaturated Solution—contains less solute than a saturated solution at a given temperature and pressure • Super-Saturated Solution—contains more solute than it can theoretically hold. (How is this possible?) http://www.bozemanscience.com/solubility

26. How to Make a Super-Saturated Solution • Compare the solubility of sugar in water at different temperatures: • Solubility (g/100 g H2O): As you heat up water, notice that you can dissolve more and more sugar in the same amount of water. What will happen when the solution cools?

27. How to Make a Super-Saturated Solution • As you heat up water, you can dissolve more and more sugar in it. When this saturated solution cools, the sugar will not stay dissolved. It will then form crystals (if a small particle called a seed crystal is added first). http://www.youtube.com/watch?v=nvHrXr5Jajg

28. 3 Colligative Properties of Solutions • Colligative Properties of Solutions are those that depend on the number of particles that are dissolved, not on the identity of the dissolved particles. • 1. Vapor-pressure lowering • 2. Freezing-point depression • 3. Boiling-point elevation

29. Vapor-Pressure Lowering • Vapor Pressure=pressure exerted by a vapor that is in dynamic equilibrium with its liquid in a closed system. In the diagram at left, the liquid and the vapor are at equilibrium. At any moment an equal number of particles will evaporate and return to liquid. The vapor shown above can be measured with a certain amount of pressure.

30. Vapor Pressure Lowering • When a substance is dissolved in water, it will lower the vapor pressure. This is because each particle will form a layer of water around it (called a shell of water solvation). • This makes it less likely for water to evaporate and therefore, lowers the vapor pressure Pure water Solution Which will have a lower vapor pressure?

31. Freezing Point Depression • Freezing Point: the temperature at which a liquid turns into a solid. • When a substance freezes, the particles take on an orderly pattern. The presence of a solute disrupts the pattern because of the shells of water of solvation. • Animation: http://antoine.frostburg.edu/chem/senese/101/solutions/faq/why-salt-melts-ice.shtml

32. Freezing Point Depression The particles in this solid (ice) can easily shift into the liquid phase at the normal freezing point temperature as shown by the arrows. The particles in this solid (ice) cannot shift into the liquid phase at normal freezing point temperature because solute particles block movement from solid phase to liquid phase.

33. Freezing Point Depression • The freezing point of a solution is lower than the freezing point of the solvent alone. The difference in temperature between the two is called the freezing point depression. • The more solute you add, the greater the difference. http://science.discovery.com/tv-shows/how-do-they-do-it/videos/how-do-they-do-it-de-icing-a-plane.htm De-icing Roads with a mixture of CaCl2 and H2O. De-icing airplanes with a mixture of propylene glycol and water.

34. Boiling Point Elevation • The boiling point of a substance is the temperature at which the vapor pressure of the liquid phase equals atmospheric pressure. • Adding a solute to a liquid will lower the vapor pressure. • Because of this, it takes more energy to cause the liquid to boil.

35. Elevation of Boiling Point In System A, the liquid particle easily shift into the gas phase at the normal boiling pressure. There are no obstacles for the liquid particles to become gas. In System B, the solute particles prevent the liquid particles from escaping the system to turn into gas. This requires the liquids to possess more energy in order to become a gas.

36. Elevation of Boiling Point of Solutions Pure water - microscopic view.Normal boiling point = 100.0oC. 1.0 M NaCl solution - microscopic view.Normal boiling point = 101.0oC. There are fewer water molecules in the vapor (i.e., lower vapor pressure) above the NaCl solution than in the vapor above pure water, and the boiling point of the NaCl solution will be greater than the boiling point of pure water.