Unit: Solutions

Types of Mixtures

Recall Heterogeneous mixture-non-uniform composition Heterogeneous mixture-non-uniform composition Homogeneous mixture-uniform composition Homogeneous mixture-uniform composition –AKA a solution

Classification of Matter MATTER Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous MixtureCompoundElement MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes

Solution A solution is a mixture that is so well mixed that is the same throughout, even down to the molecules. And those molecules can be separated physically A solution is a mixture that is so well mixed that is the same throughout, even down to the molecules. And those molecules can be separated physically Ex: carbonated water, coke, rubbing alcohol, 14-carat gold, air Ex: carbonated water, coke, rubbing alcohol, 14-carat gold, air

Parts of a Solution Solution-Homogeneous mixture of two or more substances in a single phase Solution-Homogeneous mixture of two or more substances in a single phase Solvent-dissolving medium Solvent-dissolving medium –What something is being dissolved into Solute-substance dissolved Solute-substance dissolved –If filtered, would pass through filter paper

Mixtures that are NOT solutions: Suspensions A temporary mixture in which the solvent particles are so large that they settle out unless the mixture is constantly stirred or agitated. A temporary mixture in which the solvent particles are so large that they settle out unless the mixture is constantly stirred or agitated. Particles can be separated using filter paper Particles can be separated using filter paper Example-muddy water Example-muddy water

Mixtures that are NOT solutions: Colloids A mixture that has larger particles. The particles come in clusters, not single molecules (like in solutions) and they don’t settle (like in suspensions) A mixture that has larger particles. The particles come in clusters, not single molecules (like in solutions) and they don’t settle (like in suspensions) Examples: mayonnaise, egg whites, milk Examples: mayonnaise, egg whites, milk

Colloids vs solutions Tyndall effect-scattering of light by colloidal particles is a transparent medium Tyndall effect-scattering of light by colloidal particles is a transparent medium –Can be used to distinguish between colloids and solutions

Types of Mixtures SolutionsColloidsSuspensions HomogenousHeterogeneousHeterogeneous Particle size: molecular (smallest) Particle size: Slightly larger in clusters Particle size: larger particles (often visible) Do not separate on standing Particles settle out Cannot be separated by filtration Can be separated by filtration Do not scatter light Scatter light (Tyndall effect) May scatter light, but are not transparent Table 13-3, page 398

Solutions Recall-A homogenous mixture of 2 or more substances in a single phase Recall-A homogenous mixture of 2 or more substances in a single phase –Doesn’t settle –Cannot be filtered –Does not exhibit Tyndall effect Solutes can be classified according to whether they yield molecules or ions in solution Solutes can be classified according to whether they yield molecules or ions in solution

Electrolytes When an ionic compound dissolves in water, the cations and anions separate from each other When an ionic compound dissolves in water, the cations and anions separate from each other Ions are free to move and make it possible for an electric current to pass through the solution Ions are free to move and make it possible for an electric current to pass through the solution Electrolyte-a substance that dissolves in water to give a solution that conduct electricity Electrolyte-a substance that dissolves in water to give a solution that conduct electricity –Examples-any soluble ionic compound

Nonelectrolytes A solution containing only neutral solute molecules does not conduct electric current because it does not contain any mobile charged particles. A solution containing only neutral solute molecules does not conduct electric current because it does not contain any mobile charged particles. Nonelectrolyte-a substance that dissolves in water to give a solution that does not conduct an electric current. Nonelectrolyte-a substance that dissolves in water to give a solution that does not conduct an electric current. –Example-sugar

Electrolyte vs. Nonelectrolyte Strong Electrolyte Non- Electrolyte solute exists as ions only - + salt - + sugar solute exists as molecules only - + acetic acid Weak Electrolyte solute exists as ions and molecules View animation online.animation

Electrolyte or Nonelectrolyte? SO 2 SO 2 Calcium carbonate dissolved in water Calcium carbonate dissolved in water Glucose Glucose KCl KCl Tap water Tap water Distilled water Distilled water Gatorade Gatorade

The Solution Process

Factors Affecting Dissolution Rate 3 major factors affect how quickly a solute can be dissolved 3 major factors affect how quickly a solute can be dissolved –Surface area of solute The more surface area that is available for contact with the solvent, the more quickly a solute will go into solution The more surface area that is available for contact with the solvent, the more quickly a solute will go into solution Example-sugar cube vs. granulated sugar Example-sugar cube vs. granulated sugar –Agitation of solution Increases contact of solvent with solute, speeding up dissolution Increases contact of solvent with solute, speeding up dissolution –Temperature of solvent Increases the kinetic energy of the solvent particles, so collisions between the solvent & solute are more frequent & more forceful. Helps to separate the solute particles & disperse them more quickly. Increases the kinetic energy of the solvent particles, so collisions between the solvent & solute are more frequent & more forceful. Helps to separate the solute particles & disperse them more quickly.

Solubility Why is there a limit to how much solute you can dissolve in a solvent? Why is there a limit to how much solute you can dissolve in a solvent? Solution equilibrium-physical state in which the opposing processes of dissolution & crystallization of a solute occur at equal rates. Solution equilibrium-physical state in which the opposing processes of dissolution & crystallization of a solute occur at equal rates. –Even though nothing appears to be happening in a solution at equilibrium, solute particles are re-entering the solid phase at the same rate others are leaving it.

Saturated vs. Unsaturated Saturated solution-a solution that contains the maximum amount of dissolved solute Saturated solution-a solution that contains the maximum amount of dissolved solute –If more solute is added to the solution, it will settle to the bottom of the container & does not dissolve. Unsaturated solution-a solution that contains less solute than a saturated solution under the existing conditions. Unsaturated solution-a solution that contains less solute than a saturated solution under the existing conditions.

Supersaturated When a saturated solution is cooled, excess solute usually falls out of solution. When a saturated solution is cooled, excess solute usually falls out of solution. Sometimes excess solute doesn’t separate, and the solution contains more solute than is should be able to at that temp. Sometimes excess solute doesn’t separate, and the solution contains more solute than is should be able to at that temp. Supersaturated solution-a solution that contains more dissolved solute than a saturated solution under the same conditions. Supersaturated solution-a solution that contains more dissolved solute than a saturated solution under the same conditions.

Saturation of Solutions SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

Solubility Maximum grams of solute that will dissolve in 100 g or 100 mL of solvent at a given temperature Maximum grams of solute that will dissolve in 100 g or 100 mL of solvent at a given temperature Varies with temp Varies with temp Based on a saturated soln Based on a saturated soln –Note: rate as which dissolution occurs is not related to solubility.

Solubility Curve Shows the dependence of solubility on temperature Shows the dependence of solubility on temperature

Solubility Solids are more soluble at... Solids are more soluble at... –high temperatures. Gases are more soluble at... Gases are more soluble at... –low temperatures & –high pressures (Henry’s Law). –EX: nitrogen narcosis, the “bends,” soda

Solute-Solvent Interaction NONPOLAR POLAR “Like Dissolves Like”

Liquid Solutes and Solvents Immiscible-liquid solutes and solvents that are not soluble in each other Immiscible-liquid solutes and solvents that are not soluble in each other –Example-oil and water (nonpolar and polar) Miscible-liquids that dissolve freely in one another in any proportion Miscible-liquids that dissolve freely in one another in any proportion –Example-ethanol and water (both polar)

Effect of Pressure on Gas Solubility Henry’s law-the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid. Henry’s law-the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid. Example-carbonated beverages Example-carbonated beverages –At a bottling plant, CO 2 is forced into a solution of flavored water by increasing the CO 2 pressure to 5-10 atm and the placing the pressurized solution in a can or bottle. When the pressure is reduced to atmospheric pressure by opening the container, some of the gas rapidly comes out of solution as bubbles.

Heats of Solution Energy can be either absorbed or released during the formation of a solution. Energy can be either absorbed or released during the formation of a solution. –Dissolve KI in water  beaker feels cold –Dissolve LiCl in water  beaker feels warm Heat of solution-net amount of heat energy absorbed or release when a specific amount of solute dissolves in a solvent. Heat of solution-net amount of heat energy absorbed or release when a specific amount of solute dissolves in a solvent. Exothermic-HOS negative; energy released; beaker would feel warm Exothermic-HOS negative; energy released; beaker would feel warm Endothermic-HOS positive; energy absorbed; beaker would feel cold Endothermic-HOS positive; energy absorbed; beaker would feel cold

Concentration of Solutions

Concentration A measure of the amount of solute in a given amount of solvent or solution. A measure of the amount of solute in a given amount of solvent or solution. 2 ways to express concentration: 2 ways to express concentration: –Molarity Molarity –Molality Molality

Molarity Number of moles of solute in one liter of solution. Number of moles of solute in one liter of solution. Represented by “M” Represented by “M”

Molarity example What is the molarity of a 2.0 L solution that is made from 14.6 g of NaCl? What is the molarity of a 2.0 L solution that is made from 14.6 g of NaCl?

Molarity example What is the molarity of a HCl solution that contains 10.0 g of HCl in 250 mL of solution? What is the molarity of a HCl solution that contains 10.0 g of HCl in 250 mL of solution? Answer: 1.1M Answer: 1.1M

Molarity example How many moles of HCl exist in 500. mL of 0.50M solution of HCl? How many moles of HCl exist in 500. mL of 0.50M solution of HCl? Answer: 0.25 mol HCl Answer: 0.25 mol HCl

Molarity example To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in solution as a reactant. All you have on hand in the stock room is 5.0 L of 6.0M K 2 CrO 4 solution. What volume of the solution is needed to give you the 23.4 g of K 2 CrO 4 needed for the reaction? To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in solution as a reactant. All you have on hand in the stock room is 5.0 L of 6.0M K 2 CrO 4 solution. What volume of the solution is needed to give you the 23.4 g of K 2 CrO 4 needed for the reaction? Answer:0.020 L of 6.0M K 2 CrO 4 solution Answer:0.020 L of 6.0M K 2 CrO 4 solution

Solution Dilution The concentration calculations that we have done involved preparing a solution from scratch. We started with separate solvent and solute and figured out how much of each you would need to use. The concentration calculations that we have done involved preparing a solution from scratch. We started with separate solvent and solute and figured out how much of each you would need to use. Solutions can be prepared by diluting a more concentrated solution. For example, if you needed a one molar solution you could start with a six molar solution and dilute it. Solutions can be prepared by diluting a more concentrated solution. For example, if you needed a one molar solution you could start with a six molar solution and dilute it.

Dilution When calculating the concentration of a solution by dilution, you use: When calculating the concentration of a solution by dilution, you use: –M 1 V 1 =M 2 V 2 M 1 =initial molarity (concentrated) V 1 =initial volume M 2 =final molarity V 2 =final volume *note: number of moles stays the same

Dilution example 1 A chemist starts with 50.0 mL of a 0.40 M NaCl solution and dilutes it to mL. What is the concentration of NaCl in the new solution? A chemist starts with 50.0 mL of a 0.40 M NaCl solution and dilutes it to mL. What is the concentration of NaCl in the new solution?

Dilution Example 2 How many milliliters of water must be added to 30.0 mL of 9.0 M KCl to make a solution that is 0.50 M KCl? How many milliliters of water must be added to 30.0 mL of 9.0 M KCl to make a solution that is 0.50 M KCl?