1. Solutions

2. Water Think back to the structure of water: The charges on water can attract other “things” which makes water the universal solvent.

3. Water Also, because of the different charges water molecules can bond to one another. This hydrogen bonding gives water many of its unique properties.

4. Properties of Water Hydrogen bonding causes water to have some unique properties: high surface tension high specific heat low vapor pressure high heat of vaporization

5. Evidence of Surface Tension Evidence of water's surface tension can be seen where the water strider's legs dent but do not break through the water's surface. The attraction of polar water molecules to each other helps create water's strong surface tension.

6. Beading The water molecules beneath the surface are pulled in all directions. The molecules at the surface are pulled together and in. This creates a tighter arrangement of molecules at the surface and the round shape of a drop of water.

7. Alcohol vs. Water Alcohol has one O–H bond which is polar but a large portion of the molecule is made up of C–H bonds which are nonpolar. Alcohol molecules do not attract each other as strongly as water molecules and have a weaker surface tension.

8. Water of Hydration Hygroscopic a compound that removes water from the environment (hydrates) Desiccant a hygroscopic substance that removes water from the atmosphere to keep the environment dry used as a drying agent (shoes, electronics) Deliquescent substances that remove so much water from the air that it turns into a solution, ZnCl 2

9. Solutions Solutions are homogeneous mixtures Solute is the dissolved substance Seems to “disappear” or “take on the state” of the solvent Solvent is the substance the solute dissolves in Does not appear to change state Solutions in which the solvent is water are called aqueous solutions Water is often called the universal solvent When in question, the solvent is the substance that you have more of.

10. The Solution Process - Solvation When ionic compounds dissolve in water they dissociate into ions ions become surrounded by water molecules - hydrated When solute particles are surrounded by solvent molecules we say they are solvated Solvation of molecular compounds  dissolving Solvation of ionic compounds  dissociation Solvation rate affected by: Agitation, temperature, particle size

13. Solubility When one substance (solute) dissolves in another (solvent) it is said to be soluble When one substance does not dissolve in another they are said to be insoluble Rule of Thumb: Like dissolves like (polarity) There is a limit as to how much solute can dissolve in a solvent. this is called solubility Ex.  at 20 o C 64.2 g NiCl 2 in 100 g H 2 O  g/L with a gas solute and liquid solvent

15. Solution Composition A saturated solution contains as much solute as will dissolve at that temperature (solubility curve) An unsaturated solution does not contain as much solute as will dissolve at that temperature (under solubility curve) A supersaturated solution contains more dissolved solid than a saturated solution can hold at that temperature. (above solubility curve)A supersaturated solution Obtained by dissolving a solid to saturation limit at an elevated temperature and then cooling the solution. Supersaturated Solutions are unstable.

16. Reading Solubility Curves: The amounts shown will result in saturated solutions of a salt at a given temperature. Which of the salts shown is the least soluble in water at 10°C? 30 grams of KCl are dissolved in water at 45°C. How many more grams are needed to make the solution saturated at 80°C? A saturated solution of NaNO 3 in 300 g of water is cooled from 50°C to 10°C, how many grams of the salt will precipitate from the solution? 20 grams 345-240 = 105 g

17. Describing Solutions - Qualitatively A concentrated solution has a high proportion of solute to solution – lots of solute A dilute solution has a low proportion of solute to solution – little solute A saturated solution has the maximum amount of solute that will dissolve in the solvent Depends on temp An unsaturated solution has less than the saturation limit A supersaturated solution has more than the saturation limitsupersaturated adding a seed crystal will initiate the crystallization of this supersaturated solution

19. Solutions & Solubility The solubility of the solute in the solvent depends on the temperature Higher Temp = Larger solubility of solid in liquid Lower Temp =Larger solubility of gas in liquid The solubility of gases depends on the pressure of the gas above the solution Higher pressure = Larger solubility Henry’s Law: S1P1S1P1 = S2P2S2P2 Ex: A gas has a solubility of 0.77 g/L at 3.5 atm. What is the solubility at 1.00 atm.?

20. As the temperature increases, the number of grams of carbon dioxide that can dissolve in water decreases.

22. Mentos + Soda Although the candies seem smooth, they have microscopic rough spots. The carbon dioxide molecules in the soda attach to these rough spots or nucleation points on the surface of the candies. The carbon dioxide builds up into bubbles and the increased pressure pushes the gas and the soda out of the bottle.

23. Describing Solutions Quantitatively Solutions have variable composition To describe a solution accurately, you need to describe the components and their relative amounts Concentration = amount of solute in a given amount of solution Occasionally amount of solvent

24. Solution Concentration Molarity (M) moles of solute per 1 liter of solution used because it describes how many particles of solute in each liter of solution If a sugar solution concentration is 2.0 M, 1 liter of solution contains 2.0 moles of sugar, 2 liters = 4.0 moles sugar, 0.5 liters = 1.0 mole sugar, etc. molarity = moles of solute liters of solution

25. Examples - Molarity 1.An aqueous solution has a volume of 2.0 L and contains 36.0 g of glucose (C 6 H 12 O 6 ). What is its molarity? 2.If you want to make 250. mL of a.500 M solution of copper (II) chloride in water, how many grams of solute will you need?

26. Dilution Dilution is adding solvent to decrease the concentration of a solution The amount of solute stays the same, but the concentration decreases Dilution Formula M s x V s = M d x V d Concentrations and Volumes can be most units as long as consistent

27. Examples - Dilution 1.How much stock NaCl (aq), which is 1.00 M, is required to make 100.0 mL of a 0.200 M NaCl(aq)? 2.How would you prepare 500. mL of a 0.100 M solution of MgSO 4 from a stock solution of 2.00 M MgSO 4 ?

28. Molality (m) molality (m) = mol solute kg solvent How many grams of KI must be dissolved in 500. g of H 2 O to produce a 0.600 m solution?

29. Mole Fraction mole fraction (χ) = mol solute mol solution What is the mole fraction of solute and solvent in a 0.150 m solution of KCl in H 2 O?

30. Heat of Solution Heat can be absorbed or released with ionic substances are dissolved in water. Sodium hydroxide in water becomes hot (exothermic). Calcium Chloride is found in hot packs. Ammonium nitrate in water become cold (endothermic). Found in cold packs. Vinegar and Baking Soda???

31. Heat of Solution: Water + Alcohol * When alcohol dissolves in water, water molecules “bond” to alcohol molecules and separate them from other alcohol molecules. The energy released when alcohol and water molecules attract and bond is greater than the energy required to separate alcohol molecules from each other. Since the energy released is greater than the energy absorbed, the dissolving of alcohol in water is exothermic

33. Heat of Solution: Sodium Acetate The liquid in the hand warmer is a very concentrated solution of a salt called sodium acetate. The sodium and acetate ions are ready to bond with each other and with water molecules to form a crystal. Then these ions and molecules attract and bond to each other, energy is released.

35. Vapor Pressure Depression Vapor pressure is caused by solvent evaporation Adding a non-volatile solute ALWAYS lowers the vapor pressure more solute = less solvent at surface = ↓ evaporation = ↓ vapor = ↓ vapor pressure Amount of solute is the only thing that alters this property – colligative property 1 mol glucose  1 mol glucose 1 mol NaCl  1 mol Na + and 1 mol Cl - b/c of dissociation van’t hoff factor would be 2 (count of # of “disturbing” particles in solvent)

36. Boiling Point Elevation For something to boil the vapor pressure = atmospheric pressure. Adding solute = ↓ vapor pressure = ↑ boiling point Example – adding salt to water before cooking spaghetti noodles causes that water to boil at a hotter temperature, which leads to the noodles cooking faster

37. Freezing Point Depression During freezing, the particles of a solid take on an orderly pattern. Adding solute disrupts this pattern, so even more energy must be removed for the solution to solidify. Examples – applying salt to icy roads helps prevent the water from freezing and the use of antifreeze in vehicles.

38. BPE and FPD Calculations (boiling point elevation & freezing point depression) BPE/FPD = k x m x i k = a different constant for each solvent = positive for BP (.512 kg 0 C/mol for H 2 O) = negative for FP (-1.86 kg 0 C/mol for H 2 O) m = molality i = van’t hoff factor (only matters for ionic compounds, for molecules i always = 1)

39. Examples – Colligative Calculations What is the boiling point of a solution that contains 1.25 mol of CaCl 2 in 1400. mL of H 2 O? What is the freezing point of 72.3 g of magnesium sulfate in 1350 mL of H 2 O The freezing point for H 2 O is lowered to -0.390 0 C when 3.90 g of a non-volatile molecular solid is dissolved in 475 g H 2 O. Calculate the molar mass of the substance.

40. Osmotic Pressure Elevation Osmosis is the diffusion of a solvent across a semi-permeable membrane. Osmotic pressure is the amount of pressure needed to stop osmosis. Adding more solute = ↑ flow of solvent = ↑ osmotic pressure

41. Homogeneous Aqueous Systems Two types: 1. Suspension - a mixture from which particles settle out -suspension differs from a solution because the particles of a suspension are much larger & do not stay suspended (> 1000 nm) - Particles are too large to pass through filter paper - Ex. – muddy water, gravy 2. Colloid -a mixture containing intermediate-sized particles larger than those in solutions but smaller than those in a suspension (1-1000 nm) - Particles are too large to pass through SP membrane. - Ex. – glue, paint, smoke, milk, fog

42. Tyndall Effect The scattering of visible light by colloidal particles is called the Tyndall effect. Good test to distinguish between a solution and a colloid.