Solutions Unit 8

Vapor Pressure Video 8.1

Vapor Pressure When a partially filled container of a liquid is sealed, some particles vaporize while some condense. The gas particles exert a pressure on it’s own liquid, called the vapor pressure. If temperature increases, more gas evolves and Vapor Pressure increases.

Vapor Pressure The boiling point is the temperature at which the vapor pressure equals the external pressure and the liquid becomes a gas. Normal Boiling Point is the temperature at which a substance boils at 1 atm pressure.

Vapor Pressure At higher altitudes, such as Denver Colorado, air pressure is much lower due to decreases in amount of air molecules. Therefore, water boils at a lower temperature and food takes longer to cook. At lower altitudes the opposite is true.

Vapor Pressure Using Table H answer the following questions: At which temperature will water have the highest vapor pressure: 25, 75, 90 or 120? If the VP of propanone is 90kPa, what is the boiling point? When the temperature of ethanoic acid is changed from 55C to 110C the change in the VP is _______? What are the normal boiling points of all gases listed in table H? 120 52C 80-10 = 70 kPa 55, 79, 100, 118 respectively

Solubility Rules Video 8.2

Properties of Liquids Surface Tension: elastic force on the liquid surface. The stronger the intermolecular force, the higher the surface tension.

Properties of Liquids Viscocity: measure of a liquid’s resistance to flow. The greater its intermolecular forces of attraction, the greater the viscosity, the slower it flows. If you increase the temperature, viscosity decreases.

Solutions Solutions are homogeneous physical mixtures of two or more pure substances. They should be transparent and pass through a filter. In a solution, the solute is dispersed uniformly throughout the solvent. Solute: The minor part, get dissolved. Solvent: The major part, does the dissolving. Water is a universal solvent.

Solutions Aqueous solutions have a water solvent. The solute can change phase in order to dissolve. Solids and gases can be solutions too like air and alloys (steel, brass, jewelry).

Solubility If a solute dissolves in the solvent, it is soluble. If the solute does not dissolve in the solvent it is not soluble and forms a solid (precipitate). Solubility refers to the amount of solute that can dissolve in 100 grams of water.

Factors that affect solubility: Chemical Nature: Remember the rule: like dissolves like. Polar solvents dissolve polar solutes only. Temperature: Increasing the temperature will increase the rate of solubility. (Think of iced tea dissolving sugar versus hot tea; hot tea dissolves faster). However, for gases, the relationship is reversed. If you increase the temperature of a gas, the gases will escape (their solubility will decrease).

Factors that affect solubility: Pressure: For gases only: if the pressure is increased, the solubility increases. This is why soda companies package soda under high pressures.

Soluble or insoluble? Use Table F Potassium fluoride Ammonium hydroxide Calcium carbonate Lithium phosphate S Lead acetate Strontium sulfate Magnesium chromate Barium hydroxide Silver chloride S I S I S S S I

Saturation Curves Video 8.3

Types of Solutions Saturated: solvent holds as much solute as is possible at that temperature. In Table G, saturated solutions are on the line. Dissolved solute is in equilibrium with solid solute particles (some may dissolve and some may precipitate out at the same time).

Types of Solutions Unsaturated: solvent holds less than the maximum amount of solute for that temperature is dissolved in the solvent. In table G, unsaturated solutions fall under the line.

Types of Solutions Supersaturated: solvent holds more solute than is normally possible at that temperature. In table G, supersaturated solutions are found above the line. These solutions are unstable; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask.

Temperature Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

Temperature The opposite is true of gases: Carbonated soft drinks are more “bubbly” if stored in the refrigerator. Warm lakes have less O2 dissolved in them than cool lakes.

Gases in Solution The solubility of liquids and solids does not change a lot with pressure. The solubility of a gas in a liquid is directly proportional to its pressure (increase the pressure on a gas, increase the solubility.)

Table G Questions Which solute is the most soluble at 10C? KI Which solute is the most soluble at 10C? What is the solubility of NaNO3 at 80C? How many grams of NaCl dissolve at 30C? At what temperature can 30g of NH4Cl dissolve in 100 grams of water? If 10 grams of KI are dissolved in 100 grams of water at 20C, what type of solution is formed? If 38 grams of NH4Cl is dissolved in 100 grams of water at 20C what type of solution is formed? If 10 grams of SO2 are dissolved in 100 grams of water at 50C what type of solution is formed? 147g 38g 4C US S SS

Concentration Video 8.4

Concentration Concentrated solutions contain large amounts of solutes dissolved in the solvent. Dilute solutions contain small amounts of solutes dissolved in solvent. Which is concentrated?

Concentration On Table G, concentrated solutions are near the top and dilute solutions are near the bottom. You can add more solvent to a solution in order to dilute the solution. There are many ways to calculate the concentration of a solution.

Molarity (M) mol of solute M = L of solution Because volume is temperature dependent, molarity can change with temperature. The equation can be found on table T.

Examples If 3 moles of NaCl are dissolved in 6L of water, what is the molarity? If 29 grams of NaCl are dissolved in one liter of water, what is the molarity? 3moles/6L = 0.5M 29g/58g = 0.5moles 0.5moles/1L = 0.5M

Examples If 100 grams of KF are dissolved in 300ml of water, what is the molarity? Calculate the volume needed to create a 2M solution with 3.5 moles of Li2O. 100g/58.1g =1.72mol 1.72mol/.3L = 5.7M 2M=3.5mol/x X = 1.75L

Percent and Parts Per Million Video 8.5

Mass Percentage mass of solute Mass % of A = total mass of solution  100

Calculate the % by mass: 25 grams of solute in 250 grams of solution. 75.5 grams of NaCl in 255 grams of water. 2 moles of NaOH in 250 grams of solution. 25/250 x 100 = 10% 75.5/(255+75.5) x 100 = 22% 2x40g = 80g/250 x 100 = 32%

Parts per Million CO concentration over 70 ppm can cause illness. Over 150ppm can cause death. Ocean water contains over 35000 ppm of salt. 350ppm of CO2 is considered safe. We are at 380ppm in our atmosphere. Global warming?

Parts per Million mass of A in solution  106 total mass of solution ppm =  106

Find the concentration in ppm: 125 grams of solution with 12 grams of solute. 32.5 grams of NH3 in 200 grams of water. A solution with 25% solute. A solution with 60% solvent. 12/125 x 106 = 1.0 x 105ppm 32.5/232.5 x 106 = 1.4 x 105ppm 25/100 x 106 = 2.5 x 105ppm 40/100 x 106 = 4.0 x 105ppm

Colligative Properties Video 8.6

Colligative Properties Changes in colligative properties depend only on the number of solute particles present, not on the identity of the solute particles.

Colligative Properties of Electrolytes Since these properties depend on the number of particles dissolved, solutions of electrolytes (which break down into ions in solution) should show greater changes than those of nonelectrolytes. But it also depends on the Molarity.

Boiling Point Elevation and Freezing Point Depression Nonvolatile solute-solvent interactions also cause solutions to have higher boiling points and lower freezing points than the pure solvent.

Examples Which compound when dissolved in water, will have the highest boiling point? CaCl2 NaI C6H12 Which compound when dissolved in water, will have the lowest freezing point? 1M NaOH 2M NH3 0.5M Mg3N2