9.1 Mixtures and Solutions Chapter 9: Solutions Heterogeneous mixtures are those in which the mixing is not uniform and have regions of different composition. Homogeneous mixtures are those in which the mixing is uniform and have the same composition throughout. Solutions are homogeneous mixtures that contain particles the size of a typical ion or small molecule. Solute: Solvent: Example: Colloids are homogeneous mixtures that contain particles ranging in diameter from 2 to 500 nm. Ch 9 Page 1
Problem: Classify the following liquid mixtures as homogeneous or heterogeneous. Further classify each homogeneous mixture as a solution or a colloid. Homo or Hetero solution or colloid a) orange juice (fresh squeezed) b) apple juice (canned) c) hand lotion d) tea 9.2 The Solution Process There are three types of IMFs in a solution. For a solution to form from a solute and a solvent: 1. Solvent-Solvent IMFs must be. 2. Solute-Solute IMFs must be. 3. Solute-Solvent IMF s can then. Ch 9 Page 2
General Rule of solvation: Solvation: Solutions can only form when the types of interactions are similar in kind and magnitude. Polar solvents dissolve: Non-polar solvents dissolve: Heats of Solution We had to break IMFs between We created new IMFs between Some substances dissolve exothermically (give off heat when they dissolve). Some substances dissolve endothermically (absorb heat when they dissolve). Breaking solute-solute attractions & solvent-solvent attractions (Steps 1&2 of solution process) If this takes more energy Forming solute-sovlent attractions (Step 3 of solution process) Endothermic Soln gets This releases more energy Exothermic soln gets Ch 9 Page 3
If the energy differences (to break and create IMFs) are too large, a solution will NOT form. The dissolution of a solute in a solvent is a (physical or chemical?) change since the solution components retain their chemical identities. Problem: Which of the following pairs of substances would you expect to form solutions? a) CCl 4 and water b) Gasoline and MgSO 4 c) Hexane (C 6 H 14 ) and heptane (C 7 H 16 ) d) Ethanol (C 2 H 5 OH) and heptanol (C 7 H 15 OH) Ch 9 Page 4
9.3 Solubility Solubility: The maximum amount of a substance that will dissolve in a given amount of solvent at a specified temperature. Miscible: Mutually soluble in. Saturated solution: Contains the amount of dissolved solute at equilibrium. If the solubility of NaCl in water at 20 C is 35.8g/100mL, this means: A 35.8 g of NaCl will dissolve in 100 ml of water at 20 C. Any amount above this limit simply sinks to the bottom of the container and sits there, no matter how much you stir. A saturated solution is in a state of : unsaturated saturated supersaturated solution solution solution Saturated Solutions: contains exactly the maximum amount of solute Unsaturated solutions: contains less than the maximum amount of solute Supersaturated solutions: contains more than the maximum amount of solute Ch 9 Page 5
https://www.youtube.com/watch?v=1y3bkiokcmk (start at 40 sec) 9.4 The effect of Temperature on Solubility What is the trend in the solubility of salts in water? What is the trend in the solubility of gases? This is why samples of blood gases must be stored cold after collection until analyzed. Ch 9 Page 6
9.5 The Effect of Pressure on Solubility: Henry s Law Pressure has a strong effect on the solubility of a. [None on (l) and (s)]. Henry s law: The solubility of a gas (or the concentration it will max out at) is directly proportional to the partial pressure of the gas above the solution if the temperature is constant. C = (P gas ) k C Pgas = k k is the Henry s Law constant. (Different for each gas liquid pair). Henry s law can be explained using Le Châtelier s principle. Problem: The solubility of NH 3 gas in water at an NH 3 pressure of 760. mmhg is 51.8g/100mL. What is the solubility of NH 3 if its partial pressure is reduced to 0.350 atm? Ch 9 Page 7
9.6 Units of Concentration Concentration tells us the amount of dissolved in a given amount of. Mole/Volume Concentration: Molarity Prepared as follows: Total amount of solvent added is actually: Problem: What is the molarity of a solution that contains 107 g of NaCl in 250. ml of solution? Molarity = moles solute liters solution (approach: calculate each, then divide) Ch 9 Page 8
Problem: How many moles of solute are in 125mL of 0.25M NaNO 3? Percent Concentrations (solute/solution) mass/mass percent concentration, (m/m)%: Problem: If a brass alloy contains 5.0g of Cu and 3.8g of Sn, what is the m/m % of Cu? volume/volume percent concentration, (v/v)%. Ch 9 Page 9
Problem: What is the (v/v)% of alcohol in a solution prepared by adding 37mL of alcohol to a 250. ml volumetric flask and diluting with water to the line for a total volume of 250.mL? Percent Concentration as a Conversion Factor How could we write 22% (v/v) alcohol as a conversion factor? Problem: What volume of alcohol (in ml) is needed to prepare 200. ml of 22% (v/v) alcohol? mass/volume percent concentration, (m/v)%: Problem: If 7.5 g of glucose is dissolved in enough water to give 0.050L of solution, what is the w/v %? Ch 9 Page 10
Problem: A 4.35% (m/v) KBr solution contains 53g of KBr. What is the volume of the solution? Problem: How would you prepare 2.00L of a 6.50% (m/v) CaCl 2 solution? Using percentage as a conversion factor works for all types of % concentrations. Problem: How do you make 12.5 g of a 34.2 % (m/m) solution of DMSO in acetone? Parts per Million (ppm) or Parts per Billion (ppb) Ch 9 Page 11
Molarity (M) and Stoichiometry: Volume of solution Moles of solute Problem: How many liters of a 0.625 M NaH 2 PO 4 are needed to provide 2.50 moles of NaH 2 PO 4? Ch 9 Page 12
Problem: How many grams of AgNO 3 must be dissolved to prepare 500. ml of a 0.150 M AgNO 3 solution? (molar mass = 169.88 g/mol) Problem: What is the volume (in ml) of a 1.50 M solution that contains 8.75 g of NH 3. (molar mass = 17.04 g/mol) Problem: How many milliliters of a 0.25 M nickel(ii)chloride solution are needed to supply 1.5g of nickel(ii)chloride? Ch 9 Page 13
Problem: One slice of enriched bread weighs 80.0 g and contains 75 mg of folic acid. What is the concentration of folic acid in ppm? Dilution More Solvent is added. Solute amount (moles) is constant. Since Molarity (M/L) times Volume (L) = moles (M)(V) is constant! M 1 V 1 = M 2 V 2 This can actually be made more generic C 1 V 1 = C 2 V 2 The two Cs are in the same units The two Vs are in the same units Problem: What is the final concentration if 100.0 ml of 12.0 M HCl is diluted to a final volume of 500.0 ml? Ch 9 Page 14
Problem: How much water would you add to 125 ml of 5.00 M NaCl to obtain a final concentration of 1.00 M? 9.8 Ions in Solution: Electrolytes Ionic compounds in aqueous solution can conduct electricity. Conduction occurs because negatively charged Cl anions migrate through the solution toward the positive terminal of the power source, whereas cations migrate toward the negative terminal. Ch 9 Page 15
electrolytes are substances that ionize completely when dissolved in water. electrolytes are substances that are only partly ionized in water. electrolytes are substances that do not produce ions when dissolved in water. Ch 9 Page 16