Chapter 13 Water and Its Solutions

1. Chapter 13 Water and Its Solutions Section 13.2 Solutions and Their Properties

2. Solubility Submicroscopic interactions between water and solutes determines how much solute it dissolves Ionic substances are soluble in water Electrical conductivity is observed when ionic compounds are dissolved in water Ex: Salt

3. DISSOCIATION (ionic compounds) The process by which charged particles in an ionic solid separate from one another Water molecules are polar- have a positive and negative end Water molecules are attracted to ionic compounds that have dissociated into both positive and negative charged ions  Examples: H20 NaCl(s) → Na+ (aq) + Cl- (aq) H20 SrCl2(s) → Sr+ (aq) + 2Cl- (aq)

5. Covalent Compounds Water is also good at dissolving covalent compounds Ex: Sucrose (table sugar) The molecules are simply separated by water molecules, No dissociation occurs Water dissolves both ionic and covalent substances, however, it does NOT dissolve everything

6. “Like dissolves Like” Dissolving occurs when similarities exist between the solvent and the solute Examples: Water can dissolve salt because water is polar and it tends to dissolve ionic substances Water can dissolve sugar because water has hydrogen bonding and tends to dissolve substances that are polar Oil and water are an example of two substance that do not mix Oil is a mixture of nonpolar covalent compounds

7. Solubility Guidelines See guidelines and answer the following… Which is insoluble? LiCl, NaCl, AgCl or KCl Which is soluble? Barium Sulfate or Potassium Sulfate Which is insoluble? Potassium Carbonate or Zinc Carbonate Which is soluble? Ammonium hydroxide or magnesium hydroxide

8. Solution concentration Relative amount of solute and solvent Represented by [ ]

9. Concentrated versus Dilute Concentrated- large amount dissolved in water (high concentration) Dilute- little amount dissolved in water (low concentration)

10. Unsaturated versus Saturated UNSATURATED SOLUTION- amount of solute dissolved is less than the max that could be dissolved in the solution SATURATED SOLUTION- solution which holds the max amount of solute per amount of the solution under the given conditions

11. Unsaturated versus Saturated SUPERSATURATED SOLUTION contain more solute than the usual max amount Unstable- cannot permanently hold the excess solute in solution and may release it suddenly Usually created at elevated temperatures (higher solubility), then slowly cooled Produce a large amount of crystalline solid if a small amount of solute is added (ex. Fudge) http://education-portal.com/academy/lesson/solubility-and-solubility-curves.html#lesson

12. Solubility Curve Below the line soln is unsaturated On or above the line soln is saturated Supersaturated? Example - How many grams of KCl can dissolve in 100g of water at 30C?

13. Unsaturated versus Saturated Temp has a significant effect on solubility The solubilities of MOST solutes increase with increasing temperature

14. HEAT OF SOLUTION Heat taken in or released in dissolving process For most solutes, the process of dissolving is an endothermic process – heat is written as a reactant Example: NH4NO3 However, the dissolving of some solutes is exothermic – process releases heat Example: CaCl2

15. Concentration Unit Molarity = moles of solute/ liter of solution M = moles / liter or mol/L Concentration example: 0.15 M NaCl = 0.15 moles of sodium chloride per liter of solution

16. To make a quantitative aqueous solution Need to know three things: 1) Concentration 2) Amount of solute 3) Total volume of solution needed http://education-portal.com/academy/lesson/calculating-molarity-and-molality-concentration.html#lesson

17. Steps to Quantitative Solution Preparation 1. Weigh the solute 2. Transfer solute to a volumetric flask 3. Add enough water to dissolve solute (mix). 4. Bring the solution volume up to the calibration mark on the flask 5. Solution is shaken, stored and labeled

18. Sample Solution Preparation Practice Problems p. 462 #7) How would you prepare 1.00 L of a 0.400 M solution of CuSO4? Cu = 63.5 g/mol S = 32.1 g/mol 4 O = 16 x 4 = 64.0 g/mol CuSO4 = 159.6 g/mol 1.00 L soln x 0.400 m CuSO4 x 159.6 g CuSO4 1 L solution 1 mol CuSO4 = 63.8 g CuSO4 dissolve 63.8 g CuSO4 in 1.00 L solution

19. Sample Solution Preparation Practice Problems p. 462 #8) How would you prepare 2.50 L of a 0.800 M solution of KNO3? K = 39.098 g/mol N = 14.007 g/mol 3 O = 15.999 x 3 = 47.997 g/mol KNO3 = 101.102 g/mol 2.50 L soln x 0.800 molKNO3x 101.102 g KNO3 1 L solution 1 mol KNO3 = 202.2 g KNO3 dissolve 202.2 g KNO3 in 2.50 L solution

20. Calculating Molarity Practice Problem p. 463 12) What is the molarity of a soln that contains 14 g Na2SO4 dissolved in 1.6 L soln? Na = 2 x 22.990 g/mol= 45.98 S = 32.066 g/mol 4 O = 15.999 x 4 = 63.996 g/mol Na2SO4 = 142.042 g/mol 14 g Na2SO4 x 1 mol Na2SO4 = 0.062 mol Na2SO4/ L 1.6 L soln 142.04 g Na2SO4 or 0.062 M Na2SO4

21. Calculating Molarity Practice Problem #13) What is the molarity of a soln that contains 7.4 g NH4Cl dissolved in 820 mL soln? N = 14.007 g/mol 4 H = 4 x 1.008 = 4.032 g/mol Cl= 35.453 g/mol NH4Cl = 53.492 g/mol 7.4 g NH4Cl x 1 mol = 0.17 mol NH4Cl/ L 0.820 L soln 53.492 g NH4Cl or 0.17 M NH4Cl

22. Freezing-Point Depression A solution has a lower FP than the corresponding pure solvent (less than 0ºC) The amount that the FP is depressed relative to 0ºC depends on the concentration of the solute An ionic solute produces greater depression of FP than a covalent one because it dissociates into ions (more ions to interfere with the freezing process) Ex: Ice cream, salt on sidewalks in winter

23. Boiling-Point Elevation BP of a solution is higher than the BP of a corresponding pure solvent (greater than 100ºC) Solute interferes with the ability of the solvent particles to escape the liquid state – higher temperature is required to allow boiling The higher the concentration of solute particles, the greater the boiling-point elevation Ex. Anti-freeze

24. OSMOSIS The flow of solvent molecules through a selectively permeable membrane (higher solute to lower solute concentration) Selectively permeable – allows certain materials to pass through them

25. Solutions of Gases in Water The solubility of a gas in a liquid depends on the pressure of the gas pushing down on the liquid The higher the pressure, the more soluble the gas For solns of gases in liquids, gas solubility decreases as temp. increases (soda fizzes more when warm)

26. COLLOIDS Mixtures that are between true solutions and heterogeneous mixtures Contain particles that are evenly distributed through a medium and remain distributed over time – do not settle out Colloid particles are 10-100x larger than typical ions or molecules dissolved in solutions

27. COLLOIDS Light moving through a colloid is partially scattered and reflected by the dispersed particles- light scattering effect is called TYNDALL EFFECT The light becomes visible and broadens. This occurs because colloid particles are about the same size as the wavelength of visible light (400 to 700 nm)

28. Name Color Solubility CuCO3 blu/grn Insol Na2SO4 colorless Sol NaNO3 colorless Sol PbCO3 wht Insol BaCO3 wht Insol CuI brn/wht insol I2 brn Insol PbI2 yellow insol BaI2 colorless sol PbSO4 wht insol BaSO4 wht insol