CP Chapter 15/16 Solutions What Are Solutions?

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1 CP Chapter 15/16 Solutions What Are Solutions? What is a solution? A solution is uniform that may contain solids, liquids, or gases. Known as a mixture Solution = + o Solvent The substance in abundance in the solution A solvent dissolves the solute. (dissolving ) o Solute The substance dissolved in the solvent Characteristics of Solutions Soluble The solute s ability to in a solvent Insoluble The solute is able to dissolve in a solvent Immiscible Two liquids that can be mixed together, but shortly after you stop mixing them Miscible Two liquids that are in each other Solvation in Aqueous Solutions Solvation The process of solute particles with solvent particles to form a solution Aqueous solution A solute dissolved in Rules for Solvation dissolves Polar molecules dissolve molecules molecules dissolve non-polar molecules Factors that Affect Rate of Solvation Need to increase between solute and solvent molecules 1. Agitating the mixture ( ) New collisions between solute and solvent will occur 2. Increasing the surface of the solute (Crushing the solute) Greater surface area allows more collisions to occur 3. Increasing the of the solvent Increases kinetic energy of molecules and more frequent collisions occur 4. Increasing the (For gases) Increases the rate of collision between particles. Solubility Solubility The amount of solute that will dissolve in a given amount of solvent at a specified temperature and pressure. Solubility is usually expressed in grams of solute per 100 g of solvent or in. Saturated solution contains the amount of dissolved solute for a given amount of solvent at a specific pressure and temperature. Unsaturated solution contains dissolved solute for a given temperature and pressure than a saturated solution 1

2 Supersaturated solution contains dissolved solute than a saturated solution at the same temperature Factors That Affect Solubility Temperature o Most substances as temperature increases solubility o are the exception and solubility tends to decrease as temperature increases, because they are moving quickly escaping the solvent Pressure o The solubility of a gas in any solvent increases as the above the solution increases, keeping the gas from escaping in the solvent Example 1: If the solubility of NaCl at 25 o C is 36.2 g/100 g H2O, what is the maximum mass of NaCl can be dissolved in g of H2O at the same temperature? Example 2: If the solubility of KNO3 at 20 o C is 79 grams in 250 grams of water, what is solubility in grams per liter? Henry s Law Henry s Law states that at a given temperature the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) Example 3: The solubility of a gas is 0.35 g/l at 25.0 kpa of pressure. What is the solubility when the pressure is increased to 115 kpa? Electrolytes Electrolytes are compounds that or ionize in water to form a solution that conducts an electric current Ionic compounds are because they dissociate into ions Ex: NaCl(s) Na + + Cl Electrolytes dissociate into individual ions and conduct an current 2

3 Strong and Weak Electrolytes A strong electrolyte conducts a current and the compound has completely dissociated into ions o NaCl A weak electrolyte conducts a current because only part of the solute exists as ions. o NH3 (Ammonia) A nonelectrolyte does dissociate or form ions, thus does not conduct a current. o Most molecular compounds are nonelectrolytes o Sucrose (sugar) Percent by mass Solution Concentrations Solution = Solute + Solvent Example 1: An aquarium must contain 13.6 g NaCl per g of water. What is the percent by mass (m/m) of NaCl in the solution? Example 2: You have a g of a KCl solution. If the percent by mass of the solute, KCl is 1.25% (m/m), how many grams of solute are in the solution? How many grams of solvent are in the solution? Percent by volume Example 3: What is the percent by volume (v/v) of ethanol in a solution that contains 45 ml of ethanol dissolved in 145 ml of water? 3

4 Example 4: If you have ml of a 35.0% aqueous solution of ethanol, what volume of ethanol and water are in the solution? Parts Per Million (ppm) 1 ppm = 1 mg/l Example 5: If 25 grams of a chemical is dissolved in 75 grams of water, what is the concentration of the chemical in parts per million (ppm). Example 6: Suppose 17 grams of sucrose is dissolved in 183 grams of water. What is the concentration of sucrose in ppm? Example 7: 150 ml of an aqueous sodium chloride solution contains g NaCl. Calculate the concentration of NaCl in parts per million (ppm). 1 ppm = 1 mg/l Example 8: Convert % NaCl by mass into parts per million of NaCl. 4

5 Molarity Unit for molarity Example 1: Calculate the molarity of 1.75 L solution containing 3.45 moles of CaCl 2. Example 2: Calculate the molarity of an 855 ml solution containing 2.75 moles of NaNO3. Example 3: A L of IV solution contains 5.10 g of glucose. What is the molarity of this solution? The molar mass of glucose is g/mol. Example 4: How many moles of HCl are in a 0.85 L of a 0.50 M solution? Example 5: How many moles of NaNO3 are in 655 ml of a 3.45 M solution? Preparing Molar Solutions Example 1: How many grams of CaCl2 would be dissolved in a 2.5L of a 0.10 M solution of CaCl2? 5

6 Example 2: How many grams of NaOH are in 2.5 L of 4.0 M NaOH solution? Example 3: How many grams of NaOH are in 350 ml of a 2.3 M solution? Diluting Solutions Example 1: What volume, in milliliter of 2.00M CaCl2 stock solution would you use to make 0.50L of M calcium chloride solution? What volume in milliliters of a 12.0 M HCl solution would you use to make 2.50 L of a 2.00 M HCl solution? Colligative Properties The physical properties of solutions that are different than the physical properties of a pure solvent. These depend only upon the number of particles in a solution. o Vapor pressure lowering o Boiling point increasing o Freezing point lowering o Put in order from least to greatest colligative properties. Then explain. Ex 1: H2O (l) H2O (l) Ex 2: NaCl(s) Na + (aq) + Cl - (aq) (2 moles of ions) Ex 3: C6H12O6 (s) C6H12O6 (aq) (1 mole) 6