Chapter 14 Section 14 2 Solution Concentration Solution

Chapter 14 Section 14. 2 Solution Concentration

Solution Concentration The concentration of a solution is a measure of how much solute is dissolved in a specific amount of solvent or solution Concentrations can be measured qualitatively and quantitatively. Qualitatively using the words: 1 - concentrated: contains a large amount of solute. 2 - dilute: contains a small amount of solute

Types of Mixtures Quantitatively using one of the following concentration ratios Concentration Description Ratio Percent by mass of solute × 100 mass of solution Percent by volume of solute × 100 volume of solution Molarity moles of solute liter of solution Molality moles of solute kilogram of solvent Mole fraction moles of solute + moles of solvent -

percent by mass: Q 1: In order to maintain a sodium chloride (Na. Cl) concentration similar to ocean water, an aquarium must contain 3. 6 g Na. Cl per 100. 0 g of water. What is the percent by mass of Na. Cl in the solution? 3. 5% Q 2: You have 1500. 0 g of a bleach solution. The percent by mass of the solute sodium hypochlorite (Na. OCl) is 3. 62%. How many grams of Na. OCl are in the solution? 54. 3 g Q 3: The percent by mass of calcium chloride in a solution is found to be 2. 65%. If 50. 0 g of calcium chloride is used, what is the mass of the solution? 1886. 79 g

Percent by volume n n n Q 1: What is the percent by volume of ethanol in a solution that contains 35 m. L of ethanol dissolved in 155 m. L of water? 18% Q 2: What is the percent by volume of isopropyl alcohol in a solution that contains 24 m. L of isopropyl alcohol in 1. 1 L of water? 2. 1% Q 3: If 18 m. L of methanol is used to make an aqueous solution that is 15% methanol by volume, how many milliliters of solution is produced? 120 m. L

Molarity n n n Q 1: A 100. 5 -m. L intravenous (IV) solution contains 5. 10 g of glucose (C 6 H 12 O 6). What is the molarity of this solution? The molar masses are, C=12’H=1’O=16 g/mol of glucose. 0. 282 M Q 2: Calculate the molarity of 1. 60 L of a solution containing 1. 55 g of dissolved KBr. (K=39, Br=80). 0. 0081 M Q 3: How much calcium hydroxide (Ca(OH )2), in grams, is needed to produce 1. 5 L of a 0. 25 M solution? (Ca=40, O=16, H=1). 28 g

How to prepare an accurate solution? Step 1: The mass of the solute is measured. Step 2: The solute is placed in a volumetric flask of the correct volume. Step 3: Distilled water is added to the flask to bring the solution level up to the calibration mark. Step 1 Step 2 Step 3

Questions n n Q 1: How many grams of Ca. Cl 2 would be dissolved in 1. 0 L of a 0. 10 M solution of Ca. Cl? 11 g Q 2: How many grams of Ca. C l 2 should be dissolved in 500. 0 m. L of water to make a 0. 20 M solution of Ca. C l? 11 g

Dilution Equation concentrated solution can be diluted by adding solvent. The number of moles of solute does not change when a concentrated solution is diluted. n Dilution Equation: M 1 V 1 = M 2 V 2 M 1 and V 1 represent the molarity and volume of the stock solution, and M 2 and V 2 represent the molarity and volume of the dilute solution. n

Questions n n Q 1: What volume, in milliliters, of 2. 00 M calcium chloride (Ca. C l 2 ) stock solution would you use to make 0. 50 L of 0. 300 M calcium chloride solution? 75 ml Q 2: If 0. 5 L of 5 M stock solution of HCl is diluted to make 2 L of solution, how much HCl, in grams, was in the solution? 91. 15 g

Molality n n n Q 1: In the lab, a student adds 4. 5 g of sodium chloride (Na. Cl) to 100. 0 g of water. Calculate the molality of the solution. 0. 77 mol/Kg Q 2: What is the molality of a solution containing 10. 0 g of N a 2 SO 4 dissolved in 1000. 0 g of water? 0. 0704 m Q 3: How much (Ba (OH)2), in grams, is needed to make a 1. 00 m aqueous solution? 171 g

Mole fraction n Mole fraction: the ratio of the number of moles of solute in solution to the total number of moles of solute and solvent. Q 1: What is the mole fraction of Na. OH in an aqueous solution that contains 22. 8% Na. OH by mass? 0. 118 If the mole fraction of sulfuric acid ( H 2 SO 4) in an aqueous solution is 0. 325, how much water, in grams, is in 100 m. L of the solution? 43. 8%

n n Questions Q 1: Explain the similarities and differences between a 1 M solution of Na. OH and a 1 m solution of Na. OH. Both solutions contain Na. OH (solute) dissolved in water (solvent). The 1 m solution contains 1 mole of Na. OH per kilogram of water; the 1 M solution contains 1 mole of Na. OH per liter of solution.

End of section 14. 2