Ch 12.1 Types of Mixtures

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.

Solutions may exist as gases, liquids, or solids, and may also be combinations. Solute StateSolvent StateExample Gas Oxygen in Nitrogen GasLiquidCO 2 in Water Liquid Alcohol in Water LiquidSolidMercury in Silver & Tin SolidLiquidSugar in Water Solid 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.

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

Ch 12.2 The Solution Process

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 Gaseous Solutes

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.

Factors Affecting Solubility Pressure affects the solubility of: Gaseous Solutes

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.

Ch 12.3 Concentrations of Solutions

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?

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

Calculate the molality of a solution prepared by dissolving 10.0g of NaCl in 600.g of water. Calculate the molality of a solution prepared by dissolving 10.0g of NaCl in 600.g of water. Calculating Molality of a Solution m = mol of solute kg of solvent kg of solvent 10.0g NaCl  mol NaCl = mol of NaCl kg of water kg of water g  kg = 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? How many moles of sodium fluoride are needed to prepare a 0.40m NaF solution that contains 750.0g of water? mol NaF= 0.40 mol x 0.75 kg = 0.30 mol NaF kg kg m = mol of solute kg of solvent kg of solvent

Chapter 13: Ions in Aqueous Solutions and Colligative Properties

Section 1: Compounds in Aqueous Solutions

Dissociation When an ionic compound dissolves in water, the ions separate. To find how many moles of ions are produced, we write a balanced dissociation equation and look at the coefficients in front of the ions. NaCl  Na + + Cl - 1 mol of Sodium Ion and 1 mol of Chloride Ion These are like decomposition reactions.

Example 1 Write the equation for the dissolution of aluminum sulfate, Al 2 (SO 4 ) 3, in water. How many moles of Al ions and SO 4 ions are produced by dissolving 1 mol of Al 2 (SO 4 ) 3 ? What is the total number of moles of ions produced? Al 2 (SO 4 ) 3  2Al SO mol Al 3+ and 3 mol SO 4 2- Total moles = = 5 moles

Precipitation Reactions GENERAL SOLUBILITY GUIDELINES 1. Lithium, sodium, potassium, and ammonium compounds are soluble in water. 2. Nitrates, acetates, and chlorates are soluble. 3. Most chlorides, bromides, and iodides are soluble, except those of silver, copper, mercury and lead.

Precipitation Reactions GENERAL SOLUBILITY GUIDELINES CONT… 4. Most sulfates are soluble, except those of barium, strontium, lead, calcium, silver, and mercury. 5. Most carbonates, phosphates, and silicates are insoluble, except those of lithium, sodium, potassium, and ammonium. 6. Most hydroxides and sulfides are insoluble, except those of calcium, strontium, barium, lithium, sodium, potassium, and ammonium.

Example 3 Look at the solubility chart to determine if the following are Soluble or Insoluble? Sodium Carbonate Calcium Phosphate Cadmium Nitrate Ammonium Sulfide

Example 3 Look at the solubility chart to determine if the following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Cadmium Nitrate Ammonium Sulfide

Example 3 Look at the solubility chart to determine if the following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium PhosphateInsoluble Cadmium Nitrate Ammonium Sulfide

Example 3 Look at the solubility chart to determine if the following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium PhosphateInsoluble Cadmium NitrateSoluble Ammonium Sulfide

Example 3 Look at the solubility chart to determine if the following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium PhosphateInsoluble Cadmium NitrateSoluble Ammonium SulfideSoluble

Electrolytes and Nonelectrolytes Electrolyte: a compound that conducts an electric current when it is in an aqueous solution or in the molten (liquid) state. All ionic compounds are electrolytes because they dissociate into ions. Nonelectrolyte: a compound that does not conduct an electric current in either aqueous solution or the molten state.

Strong Electrolyte: nearly all the ionic compound exists as separate ions. Weak Electrolyte: only a fraction of the ionic compound exists as separate ions.

Section 2: Colligative Properties of Solutions

Colligative Properties Colligative Properties depend on the concentration of solute particles, not on the identity of the solute.

Freezing-Point Depression. This is the difference in the freezing points of pure solvent and a solution. It changes according to the molality concentration of the solution.  t f = K f molality K f for water = -1.86°C/m

Example 6 What is the freezing-point depression of water in a solution of g of sucrose, C 12 H 22 O 11, in 200 g of water? What is the actual freezing point of the solution? Find molality of the sugar solution. Multiply the K f (of water) by the molality. Take normal freezing point 0°C + Δt f.

Boiling-Point Elevation This is the difference in the boiling points of pure solvent and a solution. It changes according to the molality concentration of the solution.  t b = K b molality K b for water = 0.51°C/m

Example 7 What is the boiling-point elevation of a solution made from 20.1 g of a nonelectrolyte solute and grams of water? The molar mass of the solute is 62.0 g/mol.

Electrolytes & Colligative Properties When electrolytes are dissolved in a solvent, the effects are greater than that of nonelectrolytes. This is because more moles of solute particles are formed when the compounds dissolve.