Chapter 14 Solutions Types of Mixtures Solution Concentration Factors Affecting Solvation Colligative Properties of Solutions

New Vocabularies 2 Suspension, colloid, Brownian motion, Tyndall effect Soluble, miscible, insoluble, immiscible A heterogeneous mixture is a mixture that does not have a uniform composition and in which the individual substances remain distinct. Suspensions are mixtures containing particles that settle out if left undisturbed. Suspensions can also be separated by filtering. – Ex. Muddy water, some clays

3 Colloids are heterogeneous mixtures of intermediate sized particles (between 1 nm and 1000 nm) and do not settle out, nor can they be filtered apart. Ex. Milk The most abundant substance in a mixture is the dispersion medium. Colloids are categorized according to the phases of their particles:

4 Brownian motion is the random movements of particles in a liquid colloid, from the results of particle collisions. The Tyndall effect is the scattering of light by dispersed colloid particles. Soluble: A substance that dissolves in a solvent Miscible: Two liquids that are soluble in each other in any proportion. Insoluble A substance that does not dissolve in a solvent Immiscible: Two liquids that can be mixed but separate shortly after Solutions are homogeneous mixtures that contain two or more substances called the solute and solvent. Most solutions are liquids, but gaseous and solid solutions exist.

5 e.g. saltwater Solution: Homogeneous mixture e.g. saltwater salt Solute: Dissolved particles in a solution salt water Solvent: The dissolving medium in a solution water The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent or solution. dilute solution concentrated solution Saturated solution + Supersaturated (later)

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7 %(m/m) %(V/V) What is the percent by volume of ethanol, when 85 mL of ethanol is diluted to a final volume of 250 ml with water? volume of solute x 100% = 85 mL ethanol x 100% volume of solution 250 mL solution = 34% ethanol (v/v) 1. If 25 mL of acetone is diluted with water to a total solution volume of 180 mL, what is the percent by volume of acetone in the solution? 2. A bottle of rubbing alcohol (isopropanol) is labeled 70.0 % (v/v). How many mL isopropanol are in a mL bottle of this solution?

8 Molarity is the number of moles of solute dissolved per liter of total solution. Dilution equation: M 1 V 1 = M 2 V 2 Molality is the ratio of moles of solute dissolved in 1 kg of solvent. Molarity (M) = moles of solute liters of solution example 2 mol glucose = 0.4 mol/L = 0.4 M 5 L solution

9 To make a 0.5-molar (0.5 M) solution, (a) add 0.5 mol of solute to a 1-L volumetric flask half filled with distilled water. (b) Swirl the flask carefully to dissolve the solute. (C) Then fill the flask with water exactly to the 1-L mark. The most important unit in chemistry to express concentration quantitatively is molarity

10 Mole fraction is the ratio of the number of moles of solute in solution to the total number of moles of solute and solvent. Percentagebymoles

11 1. A 5.0 L solution contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution? 2. A solution has a volume of 4500 mL and contains 9.0 mol NaCl. What is its molarity? 3. How many grams of Na 2 SO 4 are in 1.5 L of 0.24 M? (molar mass = g/mol) 4.How many moles of sodium hydroxide are in 550 mL of 0.75 M NaOH?

12 Making Dilutions You can make a specific less concentrated solution by diluting it with solvent… but how much?? with M 1 = initial molarity V 1 = initial total volume M 2 = final solution’s molarity V 2 = final total volume Solve equation for unknown M 1 x V 1 = M 2 x V 2 5) Example: How many mL of a stock solution of 2.00M MgSO 4 would you need to prepare mL of 0.4M MgSO 4 ? Answer: 20.0 mL of the initial solution must be diluted with enough water to a total volume of mL.

13 7) What are the mole fractions for HCl and H 2 O in a 22% HCl solution? 6) Determine the molality of a solution prepared from 150g water and 5.0g NaOH?

14 New vocab’s: Solvation, heat of solution, unsaturated solution, saturated solution, supersaturated solution, Henry’s law Section 14.3 Factors affecting Solvation Factors such as temperature, pressure, and polarity affect the formation of solutions. Solvation is the process of surrounding solute particles with solvent particles to form a solution. Solvation in water is called hydration. The attraction between dipoles of a water molecule and the ions of a crystal are greater than the attraction among ions of a crystal.

15 Sucrose molecules have several O–H bonds, which become sites for hydrogen bonding with water molecules. Oil does not form a solution with water because there is little attraction between polar water molecules and nonpolar oil molecules. During solvation, the solute must separate into particles and move apart, which requires energy. The overall energy change that occurs during solution formation is called the heat of solution.

16 “Like dissolves like” Remember???? Polar or nonpolar…

17 Factors That Affect Rate of Solvation Stirring or shaking moves dissolved particles away from the contact surfaces more quickly and allows new collisions to occur thereby increasing the rate of solvation. Breaking the solute into small pieces increases surface area and allows more collisions to occur thereby increasing the rate of solvation. As temperature increases, rate of solvation increases.

18 Solubility depends on the nature of the solute and solvent. Solubility (the maximum amount of solute that can dissolve in a given amount of solvent at specific temperature and pressure) depends on the nature of the solute and solvent. Unsaturated solutions are solutions that contain less dissolved solute for a given temperature and pressure than a saturated solution. Saturated solutions contain the maximum amount of dissolved solute for a given amount of solvent at a specific temperature and pressure. Solubility is affected by increasing the temperature of the solvent because the kinetic energy of the particles increases.

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20 A supersaturated solution contains more dissolved solute than a saturated solution at the same temperature. To form a supersaturated solution, a saturated solution is formed at high temperature and then slowly cooled. Supersaturated solutions are unstable.

21 Gases are less soluble in liquid solvents at high temperatures. Solubility of gases increases as its external pressure is increased. Henry’s law states that at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P). Solubility of Gases in liquid solvents Example problem: If 0.85g of a gas at 4.0 atm. dissolves per 1.0L of water at 25  C, how much will dissolve at 1.0 atm. at the same temperature?

New Vocab’s: colligative property, vapor pressure lowering, boiling point elevation, freezing point depression, osmosis, osmotic pressure 22 Section 14.4 Colligative Properties Main idea: Colligative properties depend on the number of solute particles in a solution Colligative properties are physical properties of solutions that are affected by the number of particles but not by the identity of dissolved solute particles. – Colligative means depending on the collection – Colligative properties include: * vapor pressure lowering, * boiling point elevation, * freezing point depression and * osmotic pressure.

23 Ionic compounds are electrolytes, because they dissociate in water to form a solution that conducts electricity. – Strong Electrolytes produce many ions – Weak Electrolytes produce only a few ions Most molecular compounds are nonelectrolytes (don’t dissociate nor conduct electricity), but exceptions exist, most importantly acids. Electrolytes

24 Electrolytes compound that conducts electricity when melted or dissolved in water. In order to conduct electricity, ions must be free to move because they must migrate to the oppositely charged electrode to take on or give up electrons.

25 Vapor Pressure Lowering Adding a nonvolatile solute (= little tendency to become a gas) to a solvent lowers the solvent’s vapor pressure. It occupies the surface area, and fewer particles enter the gaseous state. The greater the number of solute particles, the lower the vapor pressure. Vapor pressure lowering is due to the number of solute particles in solution and is a colligative property of solutions.

26 Boiling Point Elevation When a nonvolatile solute lowers the vapor pressure of a solvent, the boiling point is also affected. More heat is needed to supply additional kinetic energy to raise the vapor pressure to atmospheric pressure. The temperature difference between a solution’s boiling point and a pure solvent's boiling point is called the boiling point elevation. i K b m i represents the # of dissolved particles per formula of solute For Water: K b = 0.512

27 Freezing Point Depression At a freezing point temperature, particles no longer have sufficient kinetic energy to overcome interparticle attractive forces. The freezing point of a solution is always lower than that of the pure solvent compound. Solute particles interfere with the attractive forces among solvent particles A solution's freezing point depression is the difference in temperature between its freezing point and the freezing point of the pure solvent

28 i K f m i represents the # of dissolved particles per formula of solute

29 1) What is the new boiling point if 25 g of NaCl is dissolved in 1.0 Kg of water? 2) What is the new freezing point of the solution in the previous problem? For Water: K b = K f = ) What are the new freezing and boiling points of water if 50. g of ethylene glycol (molecular mass = 62 g/mol) is added to 50. g of water? 4) When 5.0 g of a nonelectrolyte is added to 25 g of water, the new freezing point is -2.5° C. What is the molecular mass of the unknown compound?

30 Osmotic Pressure Osmosis is the diffusion of a solvent through a semipermeable membrane. Osmotic pressure is the amount of additional pressure caused by water molecules that moved into the concentrated solution.