Unit 8 Solution Chemistry Chapters 12 & 13

Chapter 12 SOLUTIONS

Chapter 12 – Section 1: Types of Mixtures A mixture is two or more substances which are mixed together but not chemically combined. Mixtures can be solid, liquid or gas.

Heterogeneous Mixtures Chapter 12 – Section 1: Types of Mixtures Heterogeneous Mixtures A heterogeneous mixture consists of visibly different substances.

Chapter 12 – Section 1: Types of Mixtures Homogeneous Mixtures A homogeneous mixture has the same uniform appearance and composition.

Chapter 12 – Section 1: Types of Mixtures Solutions A solution is a homogeneous mixture of two or more substances in a single phase. Solvent – the dissolving medium. Solute – the substance being dissolved. Solutions may exist as gases, liquids, or solids. Alloys – solid solutions in which the atoms of two or more metals are uniformly mixed (i.e. brass, 14 K gold.)

Chapter 12 – Section 1: Types of Mixtures Suspensions A suspension is a mixture in which the particles are so large that they settle out unless the mixture is constantly stirred or agitated. Particles in a suspension are over 1000 nm in diameter—1000 times as large as atoms.

Chapter 12 – Section 1: Types of Mixtures Colloids A colloid is a mixture in which the particles are intermediate in size between those in solutions and suspensions. Many colloids look like solutions because their particles cannot be seen. But colloids exhibit the Tyndall effect – the scattering of light by colloidal particles. (example: a headlight beam on a foggy night.)

Solutions, Colloids, and Suspensions Chapter 12 – Section 1: Types of Mixtures Solutions, Colloids, and Suspensions The table below shows a comparison between the properties of solutions, colloids and suspensions (from pg. 404. in your book.)

Chapter 12 – Section 1: Types of Mixtures Electrolytes Electrolyte – a substance that conducts electricity when it is dissolved in water.

Dissolving a Solid in a Liquid Chapter 12 – Section 2: The Solution Process Dissolving a Solid in a Liquid The following 3 factors affect the rate at which a solid dissolves in a liquid : Surface area – a solute dissolves faster if surface area is increased. Agitating a solution – shaking or stirring makes dissolving faster. Increased temperature – most substances dissolve faster in hot water. Visual Concept

Saturated, Unsaturated, and Supersaturated Solutions Chapter 12 – Section 2: The Solution Process Saturated, Unsaturated, and Supersaturated Solutions A saturated solution contains the maximum amount of dissolved solute. A solution that contains less than the maximum amount of solute is unsaturated. A supersaturated solution contains more than the maximum amount of solute that can be dissolved under existing conditions.

Chapter 12 – Section 2: The Solution Process Solubility Solubility – the amount of a substance that will dissolve in a specific amount of solvent at a certain temperature. (example: The solubility of sugar is 204 g per 100 g of water at 20°C.) Solubility varies greatly between different types of compounds.

Solute-Solvent Interactions Chapter 12 – Section 2: The Solution Process Solute-Solvent Interactions “Like dissolves like” Polar solvents will dissolve polar solutes. Non-polar solvents will dissolve non-polar solutes. Liquids that dissolve in one another are miscible. Liquids that don’t dissolve each other are immiscible. Miscible Immiscible

Chapter 12 – Section 2: The Solution Process Solubility of a Gas There are 2 main factors that affect the solubility of a gas in a liquid: Temperature – decreasing the temperature generally increases the solubility of a gas. Pressure – Increasing the pressure increases the solubility of a gas. Effervescence – The rapid escape of a gas from a liquid due to a decrease in pressure. Visual Concept

Properties of Solutions Chapter 12 – Section 2: The Solution Process Properties of Solutions Solution equilibrium – state in which the opposing processes of dissolution and crystallization occur at the same rates. Enthalpy of solution – the amount of energy absorbed as heat by the solution when a specific amount of solute dissolves in a solvent. A negative enthalpy of solution means that energy is released.

Chapter 12 – Section 3: Concentration of Solutions The concentration of a solution is a ratio of solute to solvent. Concentrated means that there is a relatively large amount of solute in a solvent. Dilute means that there is a relatively small amount of solute in a solvent.

Chapter 12 – Section 3: Concentration of Solutions Molarity Molarity is the number of moles of solute in one liter of solution. The symbol for molarity is M. moles of solute Molarity (M) = liters of solution Visual Concept

Molarity Calculations Sample Problem A Chapter 12 – Section 3: Concentration of Solutions Molarity Calculations Sample Problem A You have 3.50 L of solution that contains 90.0 g of NaCl. What is the molarity of that solution? Solution: First, you need to convert from g to mol of solute. Then, plug your answer into the molarity equation: 1 mol NaCl 90.0 g NaCl = 1.54 mol NaCl 58.5 g NaCl mol solute 1.54 mol 0.440 mol/L Molarity (M) = = = L solution 3.50 L

Molarity Calculations Sample Problem B Chapter 12 – Section 3: Concentration of Solutions Molarity Calculations Sample Problem B You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain? Solution: First, write out M as moles/Liter: Then, multiply by the L of solution: mol solute 0.5 mol HCl Molarity (M) = = L solution 1 L 0.5 mol HCl 0.8 L = 0.4 mol HCl 1 L

Molarity Calculations Sample Problem C Chapter 12 – Section 3: Concentration of Solutions Molarity Calculations Sample Problem C How many grams of solute are needed to make 2.50 L of a 1.75 M solution of Ba(NO3)2? Solution: Multiply Molarity by L of solution to get mol of solute: Then, convert from mol to g by using molar mass: 1.75 mol Ba(NO3)2 2.50 L = 4.38 mol Ba(NO3)2 1 L 261.3 g Ba(NO3)2 1,140 g Ba(NO3)2 4.38 mol Ba(NO3)2 = 1 mol Ba(NO3)2

Chapter 12 – Section 3: Concentration of Solutions Molality Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent. The symbol for molality is m. moles of solute molality (m) = kilograms of solvent

Molality Calculations Sample Problem A Chapter 12 – Section 3: Concentration of Solutions Molality Calculations Sample Problem A Find the molal concentration of a solution prepared by dissolving 17.1 g of sucrose (C12H22O11) in 125 g of water. Solution: First, you need to convert from g to mol of solute. Convert g of water to kg by dividing by 1000. Then, plug the numbers into the molality equation: 1 mol C12H22O11 0.0500 mol C12H22O11 17.1 g C12H22O11 = 342.0 g C12H22O11 mol solute 0.0500 mol 0.400 mol/kg molality (m) = = = kg solvent 0.125 kg

Molality Calculations Sample Problem B Chapter 12 – Section 3: Concentration of Solutions Molality Calculations Sample Problem B How many grams of solute are needed to make a 1.50 m solution of HNO3 in 2.00 kg H2O? Solution: Multiply molality by kg of H2O to get mol of solute: Then, convert from mol to g by using molar mass: 1.50 mol HNO3 2.00 kg H2O = 3.00 mol HNO3 1 kg H2O 63.0 g HNO3 3.00 mol HNO3 = 189 g HNO3 1 mol HNO3

Ions in solutions and Colligative Properties Chapter 13 Ions in solutions and Colligative Properties

Chapter 13 – Section 1: Compounds in Aqueous Solutions Dissociation Dissociation is the separation of ions that occurs when an ionic compound dissolves. Examples: NaCl(s) → Na+(aq) + Cl-(aq) CaCl2(s) → Ca2+(aq) + 2 Cl-(aq) H2O 1 mole 1 mole 1 mole H2O 1 mole 1 mole 2 moles

Dissociation Sample Problem Chapter 13 – Section 1: Compounds in Aqueous Solutions Dissociation Sample Problem a.) Write the equation for the dissolution of aluminum sulfate, Al2(SO4)3 , in water. b.) How many moles of aluminum ions and sulfate ions are produced by dissolving 1 mol of Al2(SO4)3? c.) What is the total number of moles of ions produced by dissolving 1 mol of Al2(SO4)3? H2O Al2(SO4)3(s) 2 Al3+(aq) + SO42-(aq) 3 1 mole 2 moles 3 moles 2 moles aluminum ions & 3 moles sulfate ions 5 moles total ions

Colligative Properties Chapter 13 – Section 2: Colligative Properties of Solutions Colligative Properties Properties that depend on the concentration of solute particles but not on their identity are called colligative properties. Colligative properties include: Vapor-Pressure Lowering Freezing-Point Depression Boiling-Point Elevation

Vapor-Pressure Lowering Chapter 13 – Section 2: Colligative Properties of Solutions Vapor-Pressure Lowering A nonvolatile substance has little tendency to become a gas under existing conditions. The vapor pressure of a solvent is lower when a nonvolatile substance is added to it. This causes the solution to be liquid over a larger temperature range, lowering the freezing point and raising the boiling point.

Freezing-Point Depression Chapter 13 – Section 2: Colligative Properties of Solutions Freezing-Point Depression Freezing-Point Depression – the lowering of the freezing point of a solution compared to the pure solvent; proportional to the molal concentration of the solution.

Boiling-Point Elevation Chapter 13 – Section 2: Colligative Properties of Solutions Boiling-Point Elevation Boiling-Point Elevation – the raising of the boiling point of a solution compared to the pure solvent; proportional to the molal concentration of the solution. Visual Concept