1. Solutions Chapter 15

2. Mixtures Heterogeneous mixture- unevenly mixed substance (separation can be seen) Homogeneous mixture- evenly mixed substance (no separation can be seen)

3. Suspensions ~Small but visible particles suspended or floating in a gas or liquid (heterogeneous mixture) Like a snow globe or dust or “shake before using” the particles are too big to float forever without being stirred If a suspension sits, the particles will settle Can be filtered out

4. Colloids or Colloidal Suspension ~mixture that appears uniform unless under a high powered microscope. Particles are a little larger than the wavelength of light Extremely light particles float almost indefinitely. Milk, blood, smoke These can be separated in a centrifuge

5. Tyndall Effect ~Scattering of light by a colloid or suspension Both a colloid and a suspension have particles larger than the wavelength of light, so when light shines through it should be deflected every which way. This will make the beam of light visible.

6. Solutions Particles are smaller than the wavelength of light. Therefore, it will not scatter light. With solutions, no separation can be seen even under a high powered microscope. Cannot be separated by any filter or by a centrifuge. Can be separated by boiling/ melting points. salt water, metal alloys, air

7. Tyndall Effect Colloid/suspension solution

8. Parts of a solution Solvent- what the substance is dissolved in Solute- what is being dissolved Water is called the “universal solvent” because it dissolves a lot of substances and is very common. Water solutions are called aqueous.

9. Mass and volume In a solution, mass is conserved, however, volume is not. That is to say, the mass of a solution = mass of the solute + solvent. The volume of a solution may not equal the volume of the solute +solvent.

10. Example It is easy to think of sand and water (not a solution, but it works for the general concept) If you mix a liter of sand and a liter of water you get… A mixture that is more than one liter but less than 2 liters. Now this applies to solutions, if you mix 1 L of water with.5 liter of Na 2 CO 3 the resultant solution is more than 1 L but less than 1.5 L

11. Density of solutions Increasing the mass of the solution and not increasing the volume comparatively will increase the density. Dissolving solids into water almost always increases the density. How much the density increases, depends on how much is dissolved.

12. Solution misconceptions Solutions don’t have to be a solid in a liquid. carbonated water is CO 2 dissolved in water, streams have dissolved O 2 in them. The solvent doesn’t have to be water or even a liquid. Alloys (two or more metals) are a solution as is air. Several things dissolve in oils.

13. Gases Gases dissolved in water tend to decrease the density of the solution. Again the volume of the solution does NOT increase anywhere near the volume of the gas + water, but it does increase at a greater rate than the mass.

14. Liquids Liquids may increase or decrease the density of the solution dependent on whether they are more or less dense than the solvent. Rubbing alcohol will decrease the density of a water solution, where acetic acid will increase the density of a water solution.

15. Coke v. Diet Coke Coke cans sink in water, diet coke floats. That means a coke can is more dense than water, diet coke is less dense. Aluminum is more dense than water, but there is head space, a little air pocket, at the top of the can. Diet Coke (and all diet beverages) use artificial sweeteners like Nutrasweet. Nutrasweet is 200x sweeter than sugar, so you need to dissolve less in the solution, making it less dense

16. Molarity Problems Molarity = mol/L Molarity = moles of solute / Liters of solution

17. Concentration ~How much solute is present in a solution compared to the solvent. Molarity (M)- moles of solute per liter of solution. M = mol/L 2.1 M AgNO 3 means 2.1 mol of AgNO 3 for every one liter of solution

18. Other measures of concentration Name Abbrev. What it is molalitymmol solute/kg solvent parts per millionppmg solute/g solvent x 10 6 parts per billionppbg solute/g solvent x 10 9 mole fractionxmol solute/mol solution percent by mass%g solute/g solution x 100 percent by volume%mL solute/mL solvent x100

19. Molarity problems How many moles of HCl are in 125 mL of 2.5 M HCl? 2.5 mol HCl 1 L of soln..125 L of soln =.31 mol HCl

20. Here we go What concentration solution would be prepared if 39 g of Ba(OH) 2 were mixed in a 450 mL solution? What concentration solution would be prepared if 39 g of Ba(OH) 2 were mixed in a 450 mL solution? 39 g Ba(OH) 2 1 mol Ba(OH) 2 171.316 g Ba(OH) 2 =.2276 mol Ba(OH) 2.2276 mol Ba(OH) 2.45 L of solution M = mol/L =.51 M Ba(OH) 2

21. More For a lab in this chapter, I need to make.60 L of 3.0 M NaOH, what mass of NaOH did I need?

22. Molarity Problems A 0.24 M solution of Na 2 SO 4 contains 0.36 moles of Na 2 SO 4. How many liters were required to make this solution?

23. Getting tougher AgNO 3 + BaCl 2  AgCl + Ba(NO 3 ) 2 Balance the equation. If 1.2 L of.50 M AgNO 3 is reacted completely, what molarity solution of Ba(NO 3 ) 2 will be created if the volume increased to 1.5 L?

24. Homework Problem HNO 3 + Zn  H 2 + Zn(NO 3 ) 2 If you have.45 L of 2.1 M HNO 3 and you react it completely what volume of H 2 gas will you produce at STP? Solve for moles of H 2, then use Avogadro’s law to get a volume at STP.

25. Solubility and cleaning

26. Vocabulary Soluble/miscible- will dissolve in a solvent Insoluble/immiscible- will not dissolve in a solvent ~Both of these terms require a solvent For example vitamin A is a fat soluble vitamin, meaning it will dissolve in oils (fat) However it is insoluble in water Water soluble (vitamin C) vitamins dissolve in water but are insoluble in oils.

27. Polarity of solvent molecules and compounds can either be polar or nonpolar. General rule- like dissolves like polar dissolves polar; nonpolar dissolves in nonpolar.

28. Both polar and nonpolar O HH H H H O= O- C H Methane Hydrogen is always on the outside so it has the same charge Water Hydrogen is on one side oxygen is on the other. -- ++ soap molecule This side is polar, two ends with different charges. This side is a long nonpolar branch. nonpolar polar this has a “Y” shape (3 ends)

29. Cleaning Washing is normally dissolving the “stain” material. Hard stains to get out are usually nonpolar. Dry cleaners use a nonpolar solvent (that is a liquid) that doesn’t harm most materials (tetrachloroethene) Soap is both polar and nonpolar.

30. Soap The nonpolar “tail” sticks in the stain, dissolving it. Leaving the polar “head” exposed. Many more soap molecules do this. This is called a soap micelle. So water encounters a sphere of nonpolar material with a polar “coating” on it (micelle). the water picks up the “polar” sphere and sweeps it away.

31. Soap Micelle Nonpolar part Polar part Soap molecule Nonpolar part of soap “dissolves” nonpolar stain Nonpolar stain Outside edge is polar so it “dissolves” in water

32. Emulsions This creates an emulsion (colloidal suspension of liquids) Mayonnaise is another emulsion. Mayonnaise is made up oil and vinegar (and other things) but an emulsifier allows them to mix in a colloidal suspension.

33. Polar stains Water cleans polar stains itself. Soap’s polar side does not clean polar stains. Soap only works in conjunction with water. The soap must be dissolved in the water to dissolve a nonpolar stain.

34. Hand sanitizer (Purell) vs. soap The purpose of soap is to help you remove stain material. Hand sanitizer is an alcohol based antiseptic. The purpose is to kill any bacteria present. The remains of the bacteria are still there. In a chemistry room, we need to remove any chemical that may irritate your skin. Therefore you should wash with soap and water after a lab

35. More on Soap Your body naturally secretes oil (sebum) This oil can cover a polar stain and make it difficult to clean off. Soap is very good at dissolving the oil off your skin, so you can clean what is underneath.

36. Detergents Soaps are made from naturally occurring fats and sodium hydroxide. Detergents are made from mixing crude oil products or synthetic oils and sodium hydroxide. Detergents came into heavy use during World War II when oils were in short supply.

37. Which is better? Soap will react with some ions in “hard water”, water with heavy metal ions, to form an insoluble film ~soap scum Detergents will not. Soaps tend to be better for the environment (more biodegradable) Soaps tend to be less harsh on your skin We use detergents for nonliving things, and soap for bathing.

38. Solubility ~A measure of how soluble something is. Nothing is completely soluble or completely insoluble. Increasing the temperature normally increases the amount of a solid solute a solution can hold.

39. Gases dissolved in a liquid Colder solutions hold more of a gaseous solute. Heating a solution forces gases to come out of solution (pre-boiling bubbles) Higher pressure solutions can hold more gases. ~Why a pop can fizzes when opened

40. Decompression Sickness If you dive deep into the ocean (submarine or scuba) the pressure increases More gases will dissolve in the fluids of your body. If you rise too quickly, gases dissolved in the fluids of your body will come out of solution. This painful and deadly situation is called decompression sickness or “the bends”

41. Saturation Saturated solution- solution that has all the solute it can hold. If any more is added it will not dissolve. Supersaturated solution- a soln. holding more solute than it should Made by heating a solution to dissolve more solute and then cooling it. If you disturb a supersaturated solution the solute will fall out of solution.

42. Saturation Saturated solution- solution that has all the solute it can hold. If any more is added it will not dissolve. Supersaturated solution- a soln. holding more solute than it should Made by heating a solution to dissolve more solute and then cooling it. If you disturb a supersaturated solution the solute will fall out of solution.

43. Solubility Curve Graph of grams of solute vs. temperature g of solute per 100 g of water Temperature ( o C) 0 20 40 60 80 100 100 80 60 40 20 0 KNO 3 KCl NaCl NH 3

44. Colligative Properties ~properties that depend only on the solute’s concentration rather than what the solute is All solutions will freeze at a lower temperature and boil at a higher temperature. Boiling point elevation and freezing point depression are colligative properties

45. Where it is used Road salt goes into solution with snow, ice and water on the roads and lowers the freezing point. Water below the freezing point will not freeze and runs off the road

46. Chromatography Separating a solution by capillary action ~the attraction of a liquid to the surface of a solid, why water “climbs up things” For a simple chromatography place ink on chromatography paper and place the paper in a solvent with the ink above the water line. The solvent will “climb up” and separate the ink Gas chromatography is used in breathalyzer machines to test for DUI’s

47. Conduction of Electricity to conduct electricity a substance must contain positive and negative particles that are able to move about the substance. Pure water does NOT conduct electricity ~there are no (+) and (-) particles For water to conduct electricity you must dissolve an electrolyte in it. Electrolyte- any substance that increases a solvent’s conductivity

48. What makes a good electrolyte ~something that produces ions when it dissolves NaCl is a strong electrolyte because it produces ion, sucrose C 12 H 22 O 11 is a nonelectrolyte, because it does not. HCl is a strong electrolyte, because it completely dissociates in water. Acetic acid CH 3 COOH is a weak electrolyte, because it does not.

49. Tap water Tap water is not pure water ~this is NOT necessarily a bad thing fluoride and chloride are intentionally added Electrolytes present in water make it a weak electrical conductor Which is why it is dangerous to drop electrical appliances in water