Ch 12.1 Types of Mixtures

Chapter 12.1 Standard 6.a.: Students know the definitions of solute and solvent. Objectives: We will distinguish between heterogeneous and homogeneous mixtures We will compare the properties of suspensions, colloids, and solutions.

Heterogeneous vs. Homogeneous Mixtures Heterogeneous Mixture: mixture does not have a uniform composition. Ex: Milk and soil Homogeneous Mixture: entire mixture has the same or uniform composition. Ex: Salt water

Solutions Soluble: capable of being dissolved. Ex. Sugar is soluble in water. Sugar and water create a solution, or a homogeneous mixture of two or more substances in a single phase. Solvent: the thing that does the dissolving. Solute: the thing that is being dissolved.

Copper in Nickel (alloy) Solutions may exist as gases, liquids, or solids, and may also be combinations. Solute State Solvent State Example Gas Oxygen in Nitrogen Liquid CO2 in Water Alcohol in Water Solid Mercury in Silver & Tin Sugar in Water Copper in Nickel (alloy)

Suspensions Suspension: When the particles in a solvent are so large that they settle out unless the mixture is constantly agitated. Ex: Muddy water The particles in a suspension can be separated by passing the mixture through a filter.

Colloids Particles that are intermediate in size between those in solutions and suspensions form mixtures called colloids. These are also known as emulsions and foams and cannot be separated using a filter. Ex. Mayonnaise and Milk Tyndall Effect: when light is scattered by the particles in a colloid. *Table 3 on page 404 lists the properties of solutions, colloids, and suspensions.

Solutes: Electrolytes vs. Nonelectrolytes Electrolyte: a substance that dissolves in water to give a solution that conducts an electric current. Nonelectrolyte: a substance the dissolves in water to give a solution that doesn’t conduct an electric current.

Chapter 12.1 Standard 6.a.: Students know the definitions of solute and solvent. Objectives: We will distinguish between heterogeneous and homogeneous mixtures We will compare the properties of suspensions, colloids, and solutions.

Homework Ch 12.1 pg 406 #1-4, 6

Ch 12.2 The Solution Process

Chapter 12.2 Standard 6.c.: Students know temperature, pressure, and surface area affect the dissolving process. Objectives: We will list the 3 factors that affect that rate of dissolution. We will compare the effects of temperature and pressure on solubility.

Factors Affecting Dissolution Rate The compositions of the solvent and the solute determine whether a substance will dissolve. Three factors that affect dissolving rate: Stirring (agitation) Temperature Surface area of the dissolving particles.

Solubility Solution Equilibrium: the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates. Solubility tells us how much solute can dissolve in a certain amount of solvent at a particular temperature and pressure to make a saturated solution. Expressed in grams of solute per 100 grams of solvent

Saturated Solution: the solution cannot hold any more solute. Unsaturated Solution: the solution could still dissolve more solute. Supersaturated Solution: the solution is holding more than it should at the given temperature, and if you messed with the solution by shaking it or adding even one more crystal of solute, the whole thing would crystallize rapidly.

Solubility Values: amount of substance required to form a saturated solution with a specific amount of solvent at a specified temperature. Solubility of sugar is 204 grams per 100 grams of water at 20°C.

Solute-Solvent Interactions “Like dissolves Like” Polar will dissolve other polar molecules and Nonpolar dissolves other nonpolar. Hydration: when water is used to dissolve an ionic solution.

Liquid Solutes and Solvents Miscible: two liquids that can dissolve in each other. Immiscible: the liquids don’t mix. Ex. Oil and vinegar

Factors Affecting Solubility Temperature affects the solubility of: Solid Solutes Liquid Solutes Gaseous Solutes Pressure affects the solubility of:

Temperature Gas dissolved in a Liquid: as the temperature increases, the solubility decreases. Example: Warm soda loses its carbonation. Solid dissolved in a Liquid: as the temperature increases, the solubility increases. Example: Sugar in hot tea versus iced tea.

Pressure Gas dissolved in Liquid: As pressure increases, solubility increases. Example: Soda is carbonated under high pressure. Solid dissolved in Liquid: As pressure increases, solubility does not change! Since you cannot compress solids and liquids, pressure has no effect on solubility.

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) of the gas above the liquid. So, as the pressure of the gas above the liquid increases, the solubility of the gas increases. S1 S2 P1 P2

Calculating Solubility of a Gas If the solubility of a gas in water is 0.77 g/L at 3.5 atm of pressure, what is its solubility (g/L) at 1.0 atm of pressure and a constant temperature? P1 = 3.5 atm S1 = 0.77 g/L P2 = 1.0 atm S2 = ? g/L 0.77 g/L = S2 3.5 atm 1.0 atm S2 = 0.22 g/L

Enthalpies of Solution Solvated: when a solute particle is surrounded by solvent molecules. The formation of a solution is accompanied by an energy change, it can be released or absorbed. Enthalpy of solution: the net amount of energy absorbed as heat by the solution when a specific amount of solute dissolves in a solvent.

Chapter 12.2 Standard 6.c.: Students know temperature, pressure, and surface area affect the dissolving process. Objectives: We will list the 3 factors that affect that rate of dissolution. We will compare the effects of temperature and pressure on solubility.

Homework Ch 12.2 pg 426 #7-12

Ch 12.3 Concentrations of Solutions

Chapter 12.3 Standard 6.d.: Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, ppm, and percent composition. Objective: We will calculate the concentration of a solute, the amount of solute in a given amount of solution, and the amount of solution that contains a given amount of solute.

Concentrations of Solutions Concentration of a solution: a measure of the amount of solute that is dissolved in a given quantity of solvent. Solutions can be referred to as dilute or concentrated, but these are not very definite terms.

Molarity Molarity (M): the number of moles of solute dissolved in one liter of solution. Note: it is the total volume in liters of solution, not the liters of solvent.

Calculating Molarity of a Solution IV Saline Solutions are 0.90 g NaCl in exactly 100 mL of solution. What is the molarity of the solution? Step 1: convert mL to L (divide by 1000) Step 2: convert the grams of NaCl to moles of NaCl using molar mass. Step 3: put moles of NaCl and L of solution into the molarity equation and divide.

Finding Moles of Solute Household bleach is a solution of sodium hypochlorite (NaClO). How many moles of solute are present in 1.5L of 0.70M NaClO? Moles Solute = M x L = mol/L x L Multiply the given volume in L by the molarity expressed in mol/L.

Molality Another way to express solution concentration is Molality (m) NOT THE SAME AS MOLARITY! Molality (m) is the concentration of a solution expressed in moles of solute

m = mol of solute = 0.171 mol of NaCl = 0.285 m NaCl Calculating Molality of a Solution Calculate the molality of a solution prepared by dissolving 10.0g of NaCl in 600.g of water. 10.0g NaCl  0.171 mol NaCl 600.0 g  0.600 kg m = mol of solute kg of solvent = 0.171 mol of NaCl 0.600 kg of water = 0.285 m NaCl

Finding Moles of Solute using molality. How many moles of sodium fluoride are needed to prepare a 0.40m NaF solution that contains 750.0g of water? mol solute = m x kg of solvent m = mol of solute kg of solvent mol NaF= 0.40 mol x 0.75 kg = 0.30 mol kg

Making Dilutions Diluting a solution reduces the number of moles of solute per unit volume, but the total number of moles of solute in solution does not change. M1 x V1 = M2 x V2 Basically, you take a given amount of moles and increase the solvent which decreases the concentration but the amount of moles in the total solution is the same.

Preparing a Dilute Solution How many mL of 2.00M MgSO4 solution must be diluted with water to prepare 100.0mL of 0.400M MgSO4? Use the dilution formula and plug in the known values and then solve for the unknown. Volume can be in any unit, as long as they are both the same. (Just like gas laws). 0.400 M MgSO4 x 100.0 mL = 2.00 M MgSO4 x V2 V2 = 20.0 mL

Chapter 12.3 Standard 6.d.: Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, ppm, and percent composition. Objective: We will calculate the concentration of a solute, the amount of solute in a given amount of solution, and the amount of solution that contains a given amount of solute.

Homework Ch 12.3 pg 427 #21-23 and 27-29