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Water

Water. Water is perhaps the most important compound on our planet Water has several very important properties Surface tension* Adhesion/Cohesion* Freezing/Boiling* *All three are caused by hydrogen bonds Water is an excellent solvent!. Hydrogen bonds.

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Water

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  1. Water • Water is perhaps the most important compound on our planet • Water has several very important properties • Surface tension* • Adhesion/Cohesion* • Freezing/Boiling* *All three are caused by hydrogen bonds • Water is an excellent solvent!

  2. Hydrogen bonds • Attractions between a hydrogen on one water molecule and an oxygen on another water molecule Ocean water is a solution in which many different substances are dissolved.

  3. Solutions • Solutions form when one substance dissolves into another • Most solutions are water (aqueous) solutions • All solutions have two parts The colored crystals are the solute, and the clear liquid is the solvent.

  4. Parts of solutions • Solvent: The dissolving medium (water is the most common solvent). Usually more than 50% of the solution • Solute: The substance which actually dissolves (e.g. salt, sugar, etc.). Usually less than 50% of the solution • Electrolytes - form ions in solution • Ex.: NaCl(aq); HCl(aq) • Nonelectrolytes - NO ions in solution • Ex.: C12H22O11(aq)

  5. Electrolytes vs. Nonelectrolytes Substances which produce charged particles (ions) in solution are known as electrolytes. NaCl (s) + H2O(l) --> Na+(aq) + Cl-(aq) CaCl2(s) + H2O(l) --> Ca+2(aq) + 2Cl-(aq) Notice the mole ratio (# of particles in solution) Substances which produce uncharged particles (molecules) in solution are known as nonelectrolytes. C12H22O11(s) + H2O(l) --> C12H22O11(aq) Compare the # of particles in solution to an electrolyte.

  6. The Solution Process When an ionic solid, such as sodium chloride, dissolves in water, the water molecules hydrate the ions.

  7. The Effect of Particle Polarity on Solubility Water is a polar molecule Polar molecules and ions can be effectively hydrated by the water molecules Solutes which are nonpolar are generally not effectively hydrated by water but can be effectively dissolved by nonpolar solvents. Examples Vitamins Water Soluble - C and all the B vitamins Fat Soluble - A, D, E, K

  8. Polarity and Solubility Oil spills can be contained to some extent by using trawlers and a boom apparatus because oil and water, having different polarities, are relatively insoluble in each other.

  9. Types of solutions • Unsaturated: contain less than the maximum amount of solute • Saturated: contain the maximum amount of solute • Supersaturated: contain more than the maximum amount of solute In a saturated solution, the dissolved solute is in dynamic equilibrium with the undissolved solute.

  10. Solubility Rules • There are some general rules for the solubility of ionic compounds (SALTS) in water. • Soluble - the salt is readily soluble in water • Insoluble - the salt dissolves to such a tiny extent that it is not possible to detect it with the naked eye

  11. Solubility Rules

  12. Soluble it if contains: Li+, Na+, K+, NH4+, NO3-, C2H3O2- Cl-, Br-, I- SO42- Insoluble if it contains: Ag+, Pb2+, Hg22+ Ba 2+, Pb2+, Ca2+, Sr2+ OH-, CO32-, S2-, PO43- Solubility Rules

  13. Identifying Precipitates in Reactions Where a Solid Forms • AgNO3(aq) + KCl(aq) -->white solid • KNO3(aq) + BaCl2(aq) --> NR • Na2SO4(aq) + Pb(NO3)2(aq) --> white solid • KOH(aq) + Fe(NO3)3(aq) --> white solid

  14. Writing DR equations • AgNO3(aq) + AlCl3(aq) --> • K2SO4(aq) + BaCl2(aq) --> • Na2SO4(aq) + Pb(NO3)2 --> • KOH(aq) + Fe(NO3)3(aq) -->

  15. Factors Affecting Solubility Solubility can be increased by AGITATION SURFACE AREA OF SOLUTE Block vs. powder TEMPERATURE Increase temperature for solid solutes (generally) Decrease temperature for gaseous solutes PRESSURE (affects gaseous solutes)

  16. Factors Affecting Solubility Temperature Effects Experience tells us that carbonated beverages go flat as they get warm.

  17. Concentrated vs. Dilute Solutions Both solutions contain the same amount of solute. A concentrated solution (left) contains a relatively large amount of solute compared with the amount that could dissolve. A dilute solution (right) contains a relatively small amount of solute compared with the amount that could dissolve.

  18. Measurement of solution concentration Percent of solution m-m m-v v-v Moles of solute per volume of solution Molarity (M) = mol solute/liters soln M = mol/V

  19. Examples • Determine the molarity of a solution made by dissolving 1.5 mol NaCl in enough water to make 0.45 liters. • Determine the molarity of a solution made by dissolving 12.5 grams of sodium hydroxide in 555 mL solution. • How many grams of KCl are needed to make 2.5 liters of a 0.50 M solution? • Explain how to make 0.500 L of 3.5 M NaOH.

  20. Molarity Practice • What is the molarity of 4.5 L solution containing 14.3 moles of sodium chloride? • How many liters of a 0.25 M KOH solution can be made using 1.55 moles of solute? • How many moles of Mg(NO3)2 are needed prepare 10.0 L of a 2.00 M solution? • What is the molarity of a solution made by dissolving 13.7 g AlCl3 in water to make 275 mL solution? • How many grams of KMnO4 are required to prepare 600.0 mL of 0.25 M KMnO4? • What volume of 0.075 M Ca(NO3)2 can be prepared with 10.4 g of the solute?

  21. Dilutions When you add solvent to dilute a solution you do NOT change the amount of moles of solute Remember, M = mol/V • Molesbefore(1)=Molesafter(2) • M1V1 = M2V2 • Very useful in the lab Frozen orange juice concentrate is diluted with water prior to drinking.

  22. Dilution Examples • How much 12.0 M HCl is needed to prepare 250.0 mL of 2.5 M HCl? • If 130.5 mL of 2.00 M NaOH is diluted to 1.00 L, what is the molarity of the new solution? • How many moles of NaOH are in the solution described above? • How would you prepare 67.5 mL of 0.25 M K2CrO4 using 6.0 M K2CrO4?

  23. Solution Stoichiometry Balanced equations can be used to predict the outcomes of reactions occurring in solution EX. 50.0 mL of 1.5 M HCl reacts completely with 100.0 mL of 0.075 M NaOH. How much NaCl can be formed?

  24. Solution Stoichiometry Barium chloride solution reacts with sodium sulfate solution. What mass of barium chloride do you need to prepare 10.0 mL of 0.05 M BaCl2? What is the stoichiometric equivalent (in grams) of sodium sulfate? How much precipitate can be formed when mixing these two solutions?

  25. A water-antifreeze mixture has a higher boiling point and lower freezing point than pure water.

  26. Colligative Properties Dissolved particles effect certain properties of solutions These properties are affected by the AMOUNT of solute particles • Concentration • Electrolytic nature of solute

  27. Particle Effects Close-ups of the surface of a liquid solvent before and after solute has been added.

  28. Colligative Properties • Freezing Point Depression • Boiling Point Elevation • Osmotic Pressure - Osmotic pressure is the amount of pressure needed to prevent the solution in the tube from rising as a result of the process of osmosis.

  29. Osmosis and the effects of Osmotic Pressure Osmosis in Plants The dissolved substances in tree sap create a more concentrated solution than the surrounding ground water. Osmosis in Blood Cells Reverse Osmosis Dialysis Hypertonic Hypotonic Isotonic

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