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SOLUTIONS AND SOLVATION

SOLUTIONS AND SOLVATION. The Straight and Narrow Path to Solution. The Day of Judgement. For You will be tested on 21 February It is coming, You must be prepared. You must know your solutions You must know your Molarity You must know your way to solve the problems. MIXTURES VS COMPOUNDS.

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SOLUTIONS AND SOLVATION

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  1. SOLUTIONS AND SOLVATION The Straight and Narrow Path to Solution

  2. The Day of Judgement • For You will be tested on 21 February • It is coming, You must be prepared. • You must know your solutions • You must know your Molarity • You must know your way to solve the problems

  3. MIXTURES VS COMPOUNDS • Compounds: Chemically combined substances. • Mixtures: Physically combined substances, normally made up of two or more compounds. • Heterogeneous: Different Concentrations everywhere. It isn’t the same. • Homogeneous: Exactly the same concentrations everywhere. It’s all the same everywhere.

  4. SOLVATION • The process of dissolving a solute in a solvent • Solutes: The material that is present in smaller amounts • Solvents: The material that is present in the largest amount, can only be one in a solution • And the Solvent said unto the Solute, “Come and be Dissolved by me!” NaCl(s)  Na+(aq) + Cl-(aq)

  5. What can be Solvated • Soluble: The material can be dissolved. • Insoluble: The material can’t be dissolved • Miscible: A liquid that will dissolve • Immiscible: A liquid that will not dissolve • Solubility: How much can dissolve under the given conditions • Alloy: A metal that is dissolved in another metal.

  6. Polar in Polar • And the Like Molecules shall be dissolved by the Like Molecules, Polar unto Polar and Nonpolar unto Nonpolar each Unto it’s own kind • Unlike Molecules shall not be dissolved by Unlike Molecules, Polar SHALL NOT dissolve Nonpolar, Oil and Water Shall Not dissolve.

  7. Common Polar Solvents • Water: H2O • Ammonia: NH3 • Ethanol: CH3OH

  8. Water is Polar • As you can see, water has a positive side and a negative side.

  9. The Process • NaCl goes down into the Water The Water surrounds the NaCl pulling it apart, Na to the Negative side of water and Cl to the positive side of water and the NaCl is no more, it has been dissolved – it is one with the water. Polar unto Polar. http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

  10. NonPolar in NonPolar • The NonPolar molecules become surrounded by the NonPolar Molecules, LIKE UNTO LIKE, surrounded the Nonpolar Solute is carried away as one with the Nonpolar Solvent.

  11. Common Nonpolar Solvents • Fats • Oil • Gasoline • Covalent Compounds

  12. Electrolytes versus Nonelectrolytes • Electrolytes completely break apart and carry an electrical current. Polar • Nonelectrolytes don’t break apart and don’t carry an electrical current. NonPolar

  13. Like Dissolves Like • Polar substances are dissolved by Polar Substances • Nonpolar substances are dissolved by Nonpolar Substances. • Polar does not dissolve Nonpolar. • Nonpolar does not dissolve polar.

  14. Nonpolar will not dissolve in Polar • Iodine is NonPolar, water is Polar, so it won’t dissolve • Iodine will dissolve in Carbon Tetra Chloride which is NonPolar.

  15. TYPES OF SOLUTIONS • UNSATURATED: The solution can dissolve more solute. • SATURATED: The solution cannot dissolve more solute. • SUPERSATURATED: The solution has dissolved more solute then it should.

  16. UNSATURATED • More can be added

  17. SATURATED • The Solution cannot dissolve more:

  18. SUPERSATURATED • The solution is holding more then it should. • When more is added, a lot flows out.

  19. What a Supersaturated Looks Like • http://www.amazingrust.com/experiments/how_to/Hot-Ice.html • http://www.wonderhowto.com/how-to-make-sodium-acetate-hot-ice-w-vinegar-baking-soda-274006/

  20. Supersaturated Sodium Acetate • One application of a supersaturated solution is the sodium acetate “heat pack.”

  21. SUPERSATURATED • HOW IT HAPPENS • As a general rule: Solvents can hold a certain amount of Solute at a certain temperature • If the temperature is raised, more solute can be dissolved. • If the solution is then cooled, the solute stays dissolved. • The solution is holding more solute then it should.

  22. How solutions are measured • Concentration: How much solute there is in a given amount of Solvent. • Molarity: Moles solute/Liters solution • Molality: Moles solute/Kilograms solvent • Mass Percent: grams solute/grams solution

  23. moles solute ( M ) = Molarity liters of solution Concentration of Solute The amount of solute in a solution is given by its concentration.

  24. Properties of solutions • Colligative property: A property that changes as a result of the solution being made • Vapor Pressure Lowering: The vapor pressure of the solution goes down, the amount of substance release into the air goes down.

  25. More properties of solutions • Boiling Point elevation: Boiling point of a solution is higher then that of just the solvent. • Freezing Point depression: Freezing point of a solution is lower then that of just the solvent. • Electrolyte: A substance in a solution that allows the solution to transmit an electric current

  26. Some Definitions A solution is a mixture of 2 or more substances in a single phase. One constituent is usually regarded as the SOLVENT and the others as SOLUTES.

  27. Parts of a Solution • SOLUTE – the part of a solution that is being dissolved (usually the lesser amount) • SOLVENT – the part of a solution that dissolves the solute (usually the greater amount) • Solute + Solvent = Solution

  28. K+(aq) + MnO4-(aq) IONIC COMPOUNDSCompounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous solutions. KMnO4 in water

  29. Aqueous Solutions How do we know ions are present in aqueous solutions? The solutions conduct electricity They are called ELECTROLYTES HCl, MgCl2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions.

  30. Aqueous Solutions Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol ethylene glycol

  31. PROBLEM: Dissolve 5.00 g of NiCl2•6 H2O in enough water to make 250 mL of solution. Calculate the Molarity. Step 1: Calculate moles of NiCl2•6H2O Step 2: Calculate Molarity [NiCl2•6 H2O] = 0.0841 M

  32. USING MOLARITY What mass of oxalic acid, H2C2O4, is required to make 250. mL of a 0.0500 M solution? Step 1: Change mL to L. 250 mL * 1L/1000mL = 0.250 L Step 2: Calculate. Moles = (0.0500 mol/L) (0.250 L) = 0.0125 moles Step 3: Convert moles to grams. (0.0125 mol)(90.00 g/mol) = 1.13 g moles = M•V

  33. Learning Check How many grams of NaOH are required to prepare 400. mL of 3.0 M NaOH solution? 1) 12 g 2) 48 g 3) 300 g

  34. mol solute m of solution = kilograms solvent Two Other Concentration Units MOLALITY, m % by mass grams solute grams solution % by mass =

  35. Calculating Concentrations Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H2O. Calculate m & % of ethylene glycol (by mass). Calculate molality Calculate weight %

  36. Learning Check A solution contains 15 g Na2CO3 and 235 g of H2O? What is the mass % of the solution? 1) 15% Na2CO3 2) 6.4% Na2CO3 3) 6.0% Na2CO3

  37. Dilutions • Stock Solution: A solution of known concentration, normally saturated, used to make other solutions. • Diluting: Adding solvent to make a reduce the concentration of a solution.

  38. Dilution Equation • M1V1 = M2V2 • Mr Simms needs 250 mL of 0.150 M CuCl2 Solution. He has 3.00 M Stock Solution. How much of the stock solution does he need to use?

  39. Problem Set up • M1V1 = M2V2 • M1 = 0.150 M • V1 = 250 mL • M2 = 3.00 M • V2 = X mL

  40. Answer • (0.150 M)(250 mL) = (3.00 M)X • (0.150 M)(250 mL) = X • (3.00 M) • X = 12.5 mL • Explanation: I need to start with 12.5 mL of 3.00M Stock Solution and dilute it to 250 mL by adding 237.5 mL of Water.

  41. Boiling Point Elevation • DT = (# ions)(molality)Kb • DT = Change in Temperature, not new Temperature • (# ions) = Number of ions, NaCl has 2, MgCl2 = 3, All Covalent compounds are 1. • Molality = You should know this already • Kb = a Boiling point constant for the Solvent

  42. Example • What is the new boiling point for a 1.20 molal solution of NaI? • DT = (# ions)(molality)Kb • # ions = 2 • Molality = 1.20 molal • Kb for water = 0.512 C/m

  43. Example continued • DT = (# ions)(molality)Kb • DT = (2)(1.20)(0.512) • DT = 1.23 C • Old Boiling point = 100 • New Boiling point = 101.23

  44. Freezing Point Depression • What would the new Freezing point of the solution be? • DT = (# ions)(molality)Kf • Kf for water is 1.86 C/m • DT = (2 ions)(1.2 m)(1.86 C/m) • DT = 4.46 C • Old Freezing point of water = 0 • New Freezing point of water = 0 – 4.46 = -4.46 C

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