CHAPTER 15 Solutions

Solute Solvent A solute is the dissolved substance in a solution. Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda

Concentrated vs. Dilute

Saturation of Solutions A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. A solution that contains less solute than a saturated solution under existing conditions is unsaturated. A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

Saturation and Equilibrium

Solubility Rules Reference Tables

Solubility Values Solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature The rate at which a substance dissolves does not alter the substances solubility

Factors that Affect Solubility Temperature Solubility of solids increases with temperature Solubility of gases decreases with temperature Pressure has no real effect on the solubility of liquids and solids in liquid solvents Increasing pressure increases the solubility of gases in liquids

Solubility Curves Each line represents a solute Higher curves mean that the solute is more soluble, lower curves are less soluble ABOVE the curve is SUPERsaturated, on the curve is saturated, and UNDER the curve is UNsaturated

Solubility Chart

Solubility Trends The solubility of MOST solids increases with temperature. The rate at which solids dissolve increases with increasing surface area of the solid. The solubility of gases decreases with increases in temperature. The solubility of gases increases with the pressure above the solution.

Therefore… Solids tend to dissolve best when: Heated Stirred Ground into small particles Gases tend to dissolve best when: The solution is cold Pressure is high

Review Questions

A physical change occurs when Problem 18 A physical change occurs when A a peach spoils B a bracelet turns your wrist green C a copper bowl tarnishes D a glue gun melts a glue stick

Problem 19 What substance has a melting point of -94°C and a boiling point of 65°C? a. Ethanol b. Chlorine c. Hexane d. Methanol

Problem 20 22.4 liters of a gas has a mass of 36.5 grams. What is the identity of the gas? a. Chlorine b. Hydrogen chloride c. Nitrogen d. Hydrogen

Day 2

Molarity and Dilutions

Heat of Solution The Heat of Solution is the amount of heat energy absorbed (endothermic) or released (exothermic) when a specific amount of solute dissolves in a solvent. Endothermic: absorbs heat so it feels cool Exothermic: releases heat so it feels hot

Molarity mol of solute = M L of solution The concentration of a solution measured in moles of solute per liter of solution. mol of solute = M L of solution

What is the molarity of 2.5 mol KCl in 1.0L solution? Example What is the molarity of 2.5 mol KCl in 1.0L solution? M= mol L M= 2.5mol 1L M= 2.5M

What is the molarity of 0.96g MgCl2 in 500mL of solution? Example 2 What is the molarity of 0.96g MgCl2 in 500mL of solution? M= mol L 0.96g MgCl2 1mol MgCl2 = .01 mol MgCl2 95g MgCl2 M= .01 mol MgCl2 .500L M= .02M

# of mol = molarity x L of solution Example How many moles of solute are contained in 15.25mL of a 2.1M solution of CaCl2? M = mol L # of mol = molarity x L of solution # of mol = 2.1M (.01525L) # of mol = .032 mol CaCl2

Practice Problems

What is the molarity of 1.35 mol H2SO4 in 245mL solution? M= 5.51M Practice 1 What is the molarity of 1.35 mol H2SO4 in 245mL solution? M= 5.51M

What is the molarity 9.33g Na2S in 450 mL solution? M= 0.27M Practice 2 What is the molarity 9.33g Na2S in 450 mL solution? M= 0.27M

Practice 3 How many moles of solute are contained in 125mL of a 0.050M solution of Ba(OH)2? .00625mol

Practice 4 How many grams of solute are contained in 64.3mL of a 0.0238M solution of KOH? .0859g

Practice 5 How many grams of solute are contained in 142mL of a 1.4M solution of K2SO4? 34.6g

Moles of solute in the stock solution = moles of solute after dilution Dilutions Because the # of moles of solute does not change during a dilution Moles of solute in the stock solution = moles of solute after dilution M1V1=M2V2 M1V1 is the molarity and volume of the stock solution and M2V2 is the molarity and volume of the diluted solution

Example How many milliliters of 2.55M NaOH is needed to make 125ml 0.75M NaOH? M1V1 = M2V2 V1= M2V2 M1 V1=(.75)(125) 2.55 V1= 36.76L

Practice Problems

Practice 1 How would you prepare 500mL of 3 M HCl using 6 M HCl from the stockroom? 250mL

Practice 2 How much 12 M HCl must be used to prepare 500 ml of a 1 M HCl solution? 41.67mL

Molarity and Dilution Problems Homework Molarity and Dilution Problems

Review Questions

Problem 21 Which of the following substances best illustrates polar covalent bonding? a. HCl b. NaBr c. CsF d. Cl2

Problem 22 The methane, CH4, gas molecule exhibits what type of geometric shape? a. trigonal planar b. tetrahedral c. bent or V-shaped d. trigonal pyramidal

Problem 23 Which substance would have London dispersion forces as the main type of intermolecular forces of attraction? a. H2O b. F2 c. HCl d. NaCl

Problem 24 Which of the following compounds is an exception to the octet rule? a.BH3 b.CH4 c.NH3 d.H2O