Chapter 14 Solutions

14.1 What are solutions?

Complete the graphic organizer: matter, substance, element, compound, mixture, homogeneous(solution), heterogeneous.

Characteristics of Solutions Solutions are homogenous mixtures containing two or more substances called the solute and the solvent. The solute is the substance that dissolves. The solvent is the dissolving medium. Aqueous solutions are water samples containing dissolved substances. Ex) salt water

Characteristics of Solutions Cont. Soluble describes a substance that can be dissolved in a given solvent. Opposite: insoluble Miscible describes two liquids that are soluble in each other. Opposite: immiscible

Solutions Exist in ALL States of Matter Type of Solution Example Solvent Solute Gas in gas Air Nitrogen Oxygen Gas in liquid Soda Water Carbon Dioxide Liquid in liquid Vinegar Ethylene glycol Solid in liquid Ocean water Sodium chloride Solid in solid Steel Iron Carbon

Solvation: “Like Dissolves Like” Consider what happens when oil is poured into water. one is polar, one is nonpolar; they separate and don’t mix (immiscible liquids) Polar solutes are soluble in polar solvents. Nonpolar solvents dissolve nonpolar solutes.

Properties of Solutions Solubility is the amount of solute that will dissolve in a given amount of solvent A saturated solution contains the maximum amount of solute for a given amount of solvent at a constant temperature. An unsaturated solution contains less solute than a saturated solution. A supersaturated solution contains more than the maximum amount of solute in a saturated solution (holds more than it theoretically should)

Musical Chair Saturation Analogy When it the music stops, 6 kids try to sit in 5 chairs (supersaturated). The kids are uncomfortable, just as a supersaturated solution is comparatively unstable. When the uncomfortable extra kid gets tired of being squeezed, she stands up and vacates the chairs. This is analogous to excess solute crystallizing out of a saturated solution. Now the solution is saturated, with five kids and five chairs. What would an unsaturated situation look like?

Factors affecting solubility Solids (temperature) Gases (temperature and pressure) As a general rule, dissolved solid solutions increase in solubility as temperature increases, but gases decrease as temperature increases.

Factors affecting solution process Stirring Agitating Temperature Particle size THESE AFFECT RATE NOT AMOUNT

Henry’s Law Henrys law: S1P2=S2P1 The ratio of solubility of a gas to the pressure is a constant. As pressure increases, solubility increases.

Practice Problem If a gas has a solubility of 0.64 g/L at a pressure of 94.7 kPa, what will its solubility be at 103.5 kPa?

Homework Solubility Curves Worksheet

14.2 Solution concentration

Molarity A measure of concentration Concentration is the amount of solute that is dissolved in a given quantity of solvent while saturation compares how much is dissolved to what can be dissolved. Dilute concentration vs Concentrated

Molarity Molarity is the number of moles of solute dissolved per liter of solution. Dilutions with Molarity

Practice Problems What is the molarity of a solution if 0.400 g CuSO4 are dissolved in enough water to make 4.00L of solution? A student needs 250.0 mL of 3.00M HCl. The stock bottle says 12.0M. How much does she add?

Molality and Mole Fraction Molality is another unit of concentration and divides the moles of solute by the kilograms of solvent. Mole Fraction can be used to figure out how many moles of a substance are present in a solution.

Practice Problems If 9.00 g oxalic acid (H2C2O4) are dissolved in 250.0 g of H2O, what is the molality of the solution? What is the mole fraction of sucrose (C12H22O11) if 125.0g of sucrose are dissolved in 125g of H2O?

Percent Solutions Percent by volume Percent by mass when both components are liquids, the one with the largest volume is the solvent Percent by mass

Practice Problems What is the percent by volume of ethanol in the final solution when 85 mL of ethanol is diluted to a volume of 250 mL with H2O? How many grams of glucose would you need to prepare 2.0 L of 2.8% glucose solution?

Homework Molarity, Molarity by Dilution, and Molality worksheets

14.3 Colligative properties of solutions

Colligative Properties Colligative properties of a substance change due to having dissolved materials in it. (dissolved particles change the properties by “getting in the way”) Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure

Vapor Pressure Solvent molecules form a shell around the solute, leaving fewer molecules to vaporize (lowers the vapor pressure)

Boiling Point Elevation Additional kinetic energy must be added in order to raise the lowered vapor pressure of a solution to atmospheric pressure

Freezing Point Depression Solute disrupts the formation of a solid (more kinetic energy must be withdrawn) Adding salt to sidewalks (ice melts and forms a solution with a lower freezing point)

Colligative Properties ΔTb = Kbmi ΔTf = Kfmi where i is equal to the number of ions in the formula for an ionic compound K2SO4 i=3 (2 K+ and 1 SO42-) m is molality K is a constant for boiling or freezing.

Practice Problems What are the boiling and freezing points of a solution made by dissolving 75.0g NaCl in 500.0g of H2O?

Osmotic Pressure Osmosis is the diffusion of solvent particles across a semipermeable membrane from an area of higher solvent concentration to an area of lower solvent concentration. Semipermeable membranes are barriers with tiny pores that allow some but not all kinds of particles to cross. Example: kidney dialysis, uptake of nutrients by plants. Osmotic Pressure is the amount of additional pressure caused by the water molecules that moved into the solution. Dependent upon the number of solute particles in a given volume of solution.

Homework Effect of a Solute on Freezing and Boiling Points Worksheet

14.4 heterogeneous mixtures

14.4 Heterogeneous Aqueous Mixtures Solutions are homogenous mixtures (the same throughout, extremely small particles). Colloids have intermediate sized particles that do not settle out but are too big to be a solution (can be seen under a microscope). Ex. Paint, gelatin, milk (emulsions are liquid-liquid colloids) Suspensions are mixtures from which particles settle out upon standing (large particles). Can clearly identify two or more substances (muddy water)

Properties of Colloids The random movement of colloidal sized particles which keeps them from settling is called Brownian Motion. The scattering of light by colloid or suspension sized particles is called the Tyndall effect. You can see a beam of light passed through a colloid, like a sunbeam in a dusty room or headlights through a fog.