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Chapter 16 Cracolice Custom Combo Redux.Key The Characteristics of a Soln Goal 1 Define the term solution, and, given a description of a substance, determine if it is a solution. The Characteristics of a Soln Solution (as used in chemistry) A homogenous mixture. A sample of matter containing two or more substances that has a uniform appearance and uniform properties throughout. The Characteristics of a Soln Solid solution examples: Steel, brass, bronze Liquid solution examples: Alcohol in water, sugar water, coffee Gaseous solution examples: An air sample, any mixture of gases Solution Terminology Goal 2 Distinguish among terms in the following groups: solute and solvent; concentrated and dilute; solubility, saturated, and supersaturated; miscible and immiscible. Solution Terminology Solute The substance present in a relatively small amount in a solution; the solid or gas when a substance in that state is dissolved in a liquid to make a solution. Solvent The substance present in a relatively large amount in a solution; the liquid when a solid or gas is dissolved to make a solution. Solution Terminology Concentrated Solution Has a relatively large quantity of a specific solute per unit amount of solution. Dilute Solution Has a relatively small amount of a specific solute per unit amount of solution. Solution Terminology Solution Terminology Solubility A measure of how much solute will dissolve in a given amount of solvent at a given temperature. Saturated A solution whose concentration is at the solubility limit for a given temperature. Unsaturated A solution whose concentration is less than the solubility limit for a given temperature. Solution Terminology Supersaturated A solution whose concentration is greater than the normal solubility limit. Generally means that the solution is not stable, and that the solute will ppt out with any slight initiation. Solution Terminology Solution Terminology Miscible Soluble (usually used only in reference to solutions of liquids in liquids). Immiscible Insoluble (usually used only in reference to solutions of liquids in liquids). Solution Terminology The Formation of a Solution Goal 3 Describe the formation of a saturated solution from the time excess solid solute is first placed into a liquid solvent. Goal 4 Identify and explain the factors that determine the time required to dissolve a given amount of solute or to reach equilibrium. The Formation of a Solution The water molecule is polar. A polar molecule is one with an asymmetrical distribution of charge, resulting in positive and negative poles. The Formation of a Solution Dissolving an Ionic Solute in Water When a soluble ionic compound is placed in water: The negative ions at the surface of the solute are pulled from the crystal because of their attraction to the positive region of the water molecules. The Formation of a Solution Solution Terminology An Ionic Compound, CuCl2, in Water The Formation of a Solution Development of Equilibrium in Forming a Saturated Solution Dissolving rate: If temperature is held constant, the rate of dissolving per unit of solute surface is constant. Crystallization rate: The rate per unit of surface area increases as the solution concentration at the surface increases. Dynamic equilibrium: Dissolving rate is equal to crystallization rate. The Formation of a Solution The Formation of a Solution The time required to dissolve a given amount of solute— or to reach equilibrium, if excess solute is present— depends on several factors: 1. Surface area. A finely divided solid has more surface area per unit of mass and therefore dissolves more rapidly. 2. Stirring or agitating the solution. This prevents concentration build-up at the solute surface, reducing the crystallization rate and maximizing the net dissolving rate. 3. Temperature. Particle movement is more rapid at higher temperatures, speeding up all physical processes. Determination of Solubility Goal 5 Given the structural formulas of two molecular substances, or other information from which the strength of their intermolecular forces may be estimated, predict if they will dissolve appreciably in each other, and state the criteria on which your prediction is based. Determination of Solubility The extent to which a particular solute dissolves in a given solvent depends on three factors: 1. The strength of intermolecular forces within the solute, within the solvent, and between the solute and the solvent 2. The partial pressure of a solute gas over a liquid solvent 3. The temperature Determination of Solubility Intermolecular Forces Solubility, a macroscopic property, depends on intermolecular forces at the particulate level. If forces between molecules of A are about the same as the forces between molecules of B, A and B will probably dissolve in one another. Like dissolves like. Determination of Solubility H-Bonding Between Methanol and Water -δ H-bond +δ -δ Determination of Solubility Partial Pressure of Solute Gas Over Liquid Solution The solubility of a gaseous solute in a liquid is directly proportional to the partial pressure of the gas over the surface of the liquid. Determination of Solubility Determination of Solubility Determination of Solubility Temperature The solubility of most solids increases with rising temperature (but there are notable exceptions). The solubilities of gases in liquids generally decreases at higher temperatures. Determination of Solubility Percentage by Mass Goal 6 Given mass of solute and of solvent or solution, calculate percentage concentration. Goal 7 Given mass of solution and percentage concentration, calculate mass of solute and solvent. Percentage by Mass Solution Concentration In general, concentration is Percentage by Mass Percentage Concentration by Mass Percentage by Mass Example: A solution is prepared by dissolving 1.23 g of sodium chloride in 500.0 mL of water. What is the percentage by mass? Solution: Solve by algebra. The density of water is 1 g/mL. So, for water, mL = grams. Molarity Goal 8 Given two of the following, calculate the third: moles of solute (or data from which it may be found), volume of solution, molarity. Molarity Molarity, M Moles of solute per liter of solution: Molarity Example: How many moles of methanol are in 45.3 mL of 0.550 M CH3OH? Solution: Molarity is a PER relationship that allows you to convert between the number of particles, grouped in moles, and the volume of solution, expressed in liters. Solve with dimensional analysis. Molarity How many moles of methanol are in 45.3 mL of 0.550 M CH3OH? = 0.0249 mol CH3OH Molarity Example: Calculate the molarity of a solution made by dissolving 13.0 grams of sugar, C12H22O11, in enough water to make 4.00 × 102 milliliters of solution. Solution: Use the defining equation for molarity, Molarity Calculate the molarity of a solution made by dissolving 13.0 grams of sugar, C12H22O11, in enough water to make 4.00 × 102 milliliters of solution. 0.0950 mol C12H22O11/L = 0.0950 M C12H22O11 Molarity To prepare a solution of a specified molarity: 1. Weigh the appropriate amount of solute. 2. Add less than the total volume of solvent. 3. Mix to completely dissolve the solute. 4. Add additional solvent until the total solution volume is appropriate. Molarity Solution Concentration Dilution of Solutions Goal 9 Given any three of the following, calculate the fourth: (a) volume of concentrated solution, (b) molarity of concentrated solution, (c) volume of dilute solution, (d) molarity of dilute solution. Dilution of Solutions Concentrated solutions are diluted by adding more solvent particles. The number of solute particles remains the same before and after a dilution: Dilution of Solutions Dilution of Solutions Example: If 10.0 mL of a 16-M nitric acid solution is diluted to 1.00 L, what is the molar concentration of the dilute solution? Solution: Solve with algebra. M1 = 16 M M2 = ? V1 = 10.0 mL V2 = 1.00 L Dilution of Solutions Example: If 10.0 mL of a 16-M nitric acid solution is diluted to 1.00 L, what is the molar concentration of the dilute solution? M1 = 16 M M2 = ? V1 = 10.0 mL V2 = 1.00 L Dilution of Solutions Solution Stoichiometry Goal 10 Given the quantity of any species participating in a chemical reaction for which the equation can be written, find the quantity of any other species, either quantity being measured in (a) grams, (b) volume of solution at specified molarity, (c) (if gases have been studied) volume of gas at given temperature and pressure. Solution Stoichiometry For any reaction whose equation is known, the three steps for solving a stoichiometry problem are: 1. Convert the quantity of given species to number of particles, grouped in moles. 2. Convert the moles of given species to moles of wanted species. 3. Convert the moles of wanted species to the quantity units required. Solution Stoichiometry Solution Stoichiometry Example: Aluminum shavings are dropped into 500.0 mL of 0.77 M hydrochloric acid until the reaction is complete. How many grams of hydrogen are produced? Solution: Solve with dimensional analysis. 2 Al + 6 HCl 2 AlCl3 + 3 H2 GIVEN: 500.0 mL of 0.77 M HCl WANTED: g H2 Solution Stoichiometry Aluminum shavings are dropped into 500.0 mL of 0.77 M hydrochloric acid until the reaction is complete. How many grams of hydrogen are produced? 2 Al + 6 HCl 2 AlCl3 + 3 H2 GIVEN: 500.0 mL of 0.77 M HCl WANTED: g H2 Titration Using Molarity Goal 11 Given the volume of a solution that reacts with a known mass of a primary standard and the equation for the reaction, calculate the molarity of the solution. Goal 12 Given the volumes of two solutions that react with each other in a titration, the molarity of one solution, and the equation for the reaction or information from which it can be written, calculate the molarity of the second solution. Titration Using Molarity Titration The very careful addition of one solution to another by means of a device that can measure delivered volume precisely, such as a buret.
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