Solutions Solution: A homogenous mixture consisting of ions or molecules -Assignment: Ch 15 Questions & Problems : 5, (15b,d), (17a, c), 19, 21, 23, 27, (33b,c), 39, (43c,d),45b, 47, (49b,d), (55a,b), 57, 59 Solvent: The major component of a solution. Usually H 2 O Solute: The minor components of a solution. Aqueous solution: solution with water as the solvent Experiment 11 Various Types of Solutions Part 2 filtration 4 1
Solubility of Ionic Substances Ionic substances break up into individual cations and anions. Solubility of Polar Substances Ethanol is soluble in water because of the polar OH bond. 5 7 Solubility of Ionic Substances Polar water molecules interact with the positive and negative ions of a salt. Solubility of Polar Substances Why is solid sugar soluble in water? 6 8 2
How Substances Dissolve A hole must be made in the water structure for each solute particle. The lost water-water interactions must be replaced by water-solute interactions. Concept Check Which of the following solutes will generally not dissolve in the specified solvent? Choose the best answer. (Assume all of the compounds are in the liquid state.) like dissolves like Polar + Polar Nonpolar + nonpolar 9 a) CCl 4 mixed with water (H 2 O) b) NH 3 mixed with water (H 2 O) c) CH 3 OH mixed with water (H 2 O) d) N 2 mixed with methane (CH 4 ) 11 Substances Insoluble in Water Nonpolar oil does not interact with polar water. Solutions Concentration: A measure of the amount of solute dissolved in solution. Water-water hydrogen bonds keep the water from mixing with the nonpolar molecules. Concentration = Solute Solution Grams, molecules, moles Volume (L, cm 3 ) 10 3
Solutions Concentration: A measure of the amount of solute dissolved in solution. Qualitative measures of concentration Concentration = Solute Solution Concentrated relatively large amount of solute Solubility The solubility of a solute is limited. Saturated solution contains as much solute as will dissolve at that temperature. Unsaturated solution has not reached the limit of solute that will dissolve. 15 Solutions Concentration: A measure of the amount of solute dissolved in solution. Solubility Solubility: The maximum amount of solute to dissolve in a solvent at a given temperature. Units---- g/ml or g/l Concentration = Solute Solution dilute relatively small amount of solute Soluble: Said of a solute that has appreciable solubility. 4
Solubility Precipitate: Solute that comes out of solution. Exercise What is the percent-by-mass concentration of glucose in a solution made my dissolving 5.5 g of glucose in 78.2 g of water? 6.6% [5.5 g / (5.5 g + 78.2 g)] 100 = 6.6% glucose 19 Solubility % mass of solute Mass percent = 100% mass of solution grams of solute Mass percent = 100% grams of solute + grams of solvent 18 Molarity = Solutions M moles of solute Liters of solution Molarity: A unit of concentration expressed in moles solute per liter of solution. Units: Moles/L or M Solution A is 1 moles/l and Solution B is 4 moles/l or Solution A is 1 M and Solution B is 4 M Solution A is 1 molar ad solution B is 4 molar 5
Exercise You have 1.00 mol of sugar in 125.0 ml of solution. Calculate the concentration in units of molarity. 8.00 M 1.00 mol / (125.0 / 1000) = 8.00 M 21 Exercise Consider separate solutions of NaOH and KCl made by dissolving 100.0 g of each solute in 250.0 ml of solution. Calculate the concentration of each solution in units of molarity. NaOH 39.998 g/mol KCl 74.55 g/mol 10.0 M NaOH [100.0 g NaOH / 39.998 g/mol] / [250.0 / 1000] = 10.0 M NaOH 5.37 M KCl [100.0 g KCl / 74.55 g/mol] / [250.0 / 1000] = 5.37 M KCl 23 Exercise A 500.0-g sample of potassium phosphate is dissolved in enough water to make 1.50 L of solution. What is the molarity of the solution? 1.57 M Concentration of Ions For a 0.25 M CaCl 2 solution: CaCl 2 Ca 2+ + 2Cl Ca 2+ : 1 0.25 M = 0.25 M Ca 2+ Cl : 2 0.25 M = 0.50 M Cl. 500.0 g is equivalent to 2.355 mol K 3 PO 4 (500.0 g / 212.27 g/mol). The molarity is therefore 1.57 M (2.355 mol/1.50 L). 22 24 6
Concept Check Which of the following solutions contains the greatest number of ions? a) 400.0 ml of 0.10 M NaCl. b) 300.0 ml of 0.10 M CaCl 2. c) 200.0 ml of 0.10 M FeCl 3. d) 800.0 ml of 0.10 M sucrose. Dilutions The process of adding water to a concentrated or stock solution to achieve the molarity desired for a particular solution. Dilution with water does not alter the numbers of moles of solute present. Moles of solute before dilution = moles of solute after dilution M 1 V 1 = M 2 V 2 25 27 To Make a Standard Solution Weigh out a sample of solute. Transfer to a volumetric flask. Add enough solvent to bring the volume to the mark on flask. Diluting a Solution Transfer a measured amount of original solution to a flask containing some water. Add water to the flask by bringing volume to the mark (with swirling) and mix by inverting the flask. 26 28 7
Exercise What is the minimum volume of a 2.00 M NaOH solution needed to make 150.0 ml of a 0.800 M NaOH solution? 60.0 ml M 1 V 1 = M 2 V 2 (2.00 M)(V 1 ) = (0.800 M)(150.0 ml) 29 8