Brass, a solid solution of Zn and Cu, is used to make musical instruments and many other objects.

Brass, a solid solution of Zn and Cu, is used to make musical instruments and many other objects.

14.1 General Properties of Solutions 14.2 Solubility 14.3 Rate of Dissolving Solids 14.4 Concentration of Solutions 14.5 Colligative Properties of Solutions 14.6 Osmosis and Osmotic Pressure

General Properties of Solutions Solution: a homogeneous mixture of one or more solutes and a solvent. Solute: substance being dissolved. Solvent: dissolving agent that is usually the most abundant substance in the mixture. Note: a solution does not always just refer to liquids. Example: Air is a solution composed of N2, O2, Ar and CO2 N2 is the solvent as it composes 78% of air.

a. sugar Soda is a mixture of sugar in water. Which substance is the solute? b. water c. soda A solution is prepared by adding 25 ml of ethyl alcohol to 75 ml of water. Which substance is the solvent? a. ethyl alcohol b. water

Common Types of Solutions

Properties of a True Solution 1. A homogeneous mixture of two or more components whose ratio can be varied. 2. The dissolved solute is molecule or ionic in size (< 1 nm). 3. Can be colored or colorless, though solutions are usually transparent. 4. The solute remains dissolved and does not settle (precipitate) out of solution over time. 5. The solute can be separated from solvent by physical means (usually evaporation).

Solubility Solubility: the amount of a substance that will dissolve in a specific amount of solvent at a given temperature. Example 27 g KBr/100g H2O at 23 ºC Miscible: when two liquids dissolve in each other. Immiscible: when two liquids do not dissolve one another. A mixture of oil and water is immiscible.

Soluble Na+, K+, NH4 + Nitrates (NO3 - ) Acetates, (C2H3O2 - ) Solubility Rules Insoluble Cl-, Br-, I- Except Ag+, Hg2 2+, Pb 2+ Sulfates (SO4 2- ), Ag+, Ca 2+ (slightly) NH4 +, Group I Except Except Ba 2+, Sr 2+, Pb 2+ Carbonates (CO3 2- ) Phosphates (PO4 3- ) OH-, Sulfides (S 2- )

Predict the solubility of barium sulfate. a. soluble b. insoluble Most sulfates are soluble, except Ba2+. Predict the solubility of NaCl. a. soluble All Na+ salts are soluble. b. insoluble

Solutions Practice Predict the solubility of silver nitrate. a. soluble b. insoluble All NO3 - salts are soluble. Predict the solubility of silver hydroxide. a. soluble b. insoluble Most hydroxides are insoluble. Predict the solubility of ammonium carbonate. a. soluble b. insoluble All NH4 + salts are soluble.

Factors Affecting Solubility Like Dissolves Like Polar compounds dissolve in polar solvents. Ethanol (CH3OH) dissolves in water (HOH). Nonpolar compounds dissolve in nonpolar solvents. Carbon tetrachloride (CCl4) dissolves in hexanes (CH3(CH2)4CH3).

Factors Affecting Solubility Ionic Compound Solubility in Polar Solvents Several ionic compounds dissolve in water, due to strong ion-dipole forces. The individual cations and anions are surrounded by H2O molecules (i.e., hydrated). The cation is attracted to the partially negative O atom. The anion is attracted to the partially positive H atoms.

Temperature and Solubility Solubility increases with temperature for most solids (red lines) Solubility decreases with temperature for all gases (blue lines). As a gas increases in temperature, the kinetic energy increases, which means it interacts less with the liquid, making it less easy to solvate.

Pressure and Solubility Pressure does not affect solubility of liquids or solids. Gas solubility in a liquid is proportional to the gas pressure over the liquid. Example: A bottle of root beer is under high pressure. As the bottle opens, the pressure decreases, and the bubbles formed indicate gas loss from the liquid.

Saturated and Unsaturated Solutions There are limits to the solubility of a compound at a given temperature. Saturated solutions: contain the maximum amount of dissolved solute in a solvent. Saturated solutions are still dynamic; dissolved solute is in equilibrium with undissolved solute. undissolved solute dissolved solute Unsaturated solutions: contain less than the maximum amount of possible dissolved solute in a solvent.

Supersaturated Solutions Supersaturated solutions: contain more solute than needed to saturate a solution at a given temperature. How is this possible? Heating a solution can allow more to dissolve. Upon cooling to ambient temperature, the solution is supersaturated. These solutions are unstable -- disturbing the solutions can cause precipitation of solute. Some hotpacks release heat by crystallization of a supersaturated solution of sodium acetate.

Solubility Practice Will a solution prepared by adding 9.0 g of KCl to 20.0 g of H2O be saturated or unsaturated at 20 ºC? Using Table 14.3, 34.0 g of KCl will dissolve in 100.0 g of H2O at 20 ºC. 6.8 g of KCl will then dissolve in 20.0 g of water at that temperature. The KCl solution should be saturated.

Rate of Dissolving Solids Effect of Particle Size: A solid can only dissolve at a surface that is in contact with the solvent. Since smaller crystals have a higher surface to volume area, smaller crystals dissolve faster than larger ones.

Rate of Dissolving Solids Effect of Temperature Increasing the temperature normally increases the rate of dissolution of most compounds. Solvent molecules strike the solid surface more often, causing the solid to dissolve more rapidly. The solute molecules are more easily separate from the solid due to a higher kinetic energy.

Rate of Dissolving Solids Effect of Solute Concentration Rate is highest at higher concentration and decreases at lower concentration. As the solution approaches the saturation point, the rate of solute dissolving decreases.

Rate of Dissolving Solids Effect of Agitation/Stirring Stirring a solution briskly breaks up a solid into smaller pieces, increasing surface area, thereby increasing the rate of dissolution.

Surface Area of Two Crystals Surface area = 6(side) 2 = 6(1cm) 2 = 6 cm 2 1000 cubes have a total surface area of 1000 x 0.06 cm2 = 60 cm 2

Solutions: A Reaction Medium The purpose of dissolving reactants in a solution is often to allow them to come in close contact to react. Example: Solid-solid reactions are generally very slow at ambient temperature KCl (s) + AgNO3 (s) No Reaction By dissolving both compounds in water, the ions can collide with one another and react to form an insoluble compound. KCl (aq) + AgNO3 (aq) AgCl (s) + KNO3 (aq) K + (aq) + Cl - (aq) + Ag + (aq) + NO3 - (aq) AgCl(s) + K + (aq) + NO3 - (aq)

Concentration of Solutions Qualitative Expressions of Concentrations Dilute: a solution that contains a relatively small amount of dissolved solute. Example: A 0.1 M HCl solution is dilute acid. Concentrated: a solution that contains a relatively large amount of dissolved solute. Example: A 12 M HCl solution is concentrated acid.

Concentration of Solutions Quantitative Expressions of Concentrations: Units Symbol Definition Mass percent Part per million Mass/Volume percent Volume percent Molarity Molality % m/m ppm % m/v % v/v M m mass solute mass solution x 100 mass solute mass solution x 1,000,000 mass solute ml solution x 100 ml solute ml solution x 100 mol solute L solution mol solute kg solvent

Mass Percent Practice Calculate the mass % of NaCl in a solution prepared by dissolving 50.0 g of NaCl in 150.0 g of H2O. Knowns 50.0 g NaCl (solute mass) 150.0 g H2O (solvent mass) 200.0 g solution (solute + solvent mass) Formula Calculate mass % = mass % = mass solute mass solution x 100 50 g NaCl 200 g soln x 100 = 25% NaCl

What is the mass of Na2CO3 needed to make 350.0 g of a 12.3% aqueous solution? Knowns 12.3% solution (mass %) 350.0 g solution (solute + solvent mass) Formula mass % = Calculate mass solute mass solution x 100 mass solute = Solve for mass of solute (Na2CO3) (mass %) x (mass soln) 100 mass solute = 12.3 x 350.0 g 100 = 43.1 g Na2CO3

a. 33.0 ml soln b. 330. ml soln c. 3.00 L soln d. 165 ml soln What volume of a 3.0% H2O2 solution Formula will contain 10.0 g of H2O2? Knowns 10.0 g H2O2 (desired solute mass) 3.0 m/v% Solve for volume of solution m/v % = g solute ml solution x 100 ml solution = g solute m/v % x 100 Calculate mass solute = 10.0 g 3.0 x 100 = 330. ml sln

What volume of soda that is 6.0 % by volume alcohol contains 200.0 ml of ethanol (CH3CH2OH)?

A solution is prepared by mixing 20.0 ml of propanol with enough water to produce 400.0 ml of solution. What is the volume percent of propanol? a. 20.0 % b. 2.00 % c. 5.00 % d. 10.0 %

Molarity A common unit for solution concentration due to convenience. molarity = mol solute L solution Example: To prepare a 1.0 M KCl solution, 1.0 mol of KCl is dissolved in enough water to make 1.0 L of solution.

Calculate the molarity of a solution prepared by dissolving 9.35 g of KCl in enough water to prepare a 250.0 ml solution.

Molarity Practice How many grams of KOH are required to prepare 600.0 ml of a 0.450 M KOH solution? a. 0.270 g KOH b. 4.81 g KOH c. 1.52 x 10 4 g KOH d. 15.1 g KOH

Solution Stoichiometry Similar to previous stoichiometry problems, but we can now use molarity as an additional conversion factor. How many ml of 0.175 M Hg(NO3)2 are needed to precipitate 2.50 g of KI? Hg(NO3)2 (aq) + 2 KI (aq) 2 KNO3 (aq) + HgI2 (s) Plan g KI mol KI mol Hg(NO3)2 ml soln Calculate 2.50 g KI 1 mol KI 166.00 g KI 1 mol Hg(NO3)2 2 mol KI 1000 ml soln 0.175 mol Hg(NO3)2 = 43.0 ml Hg(NO3)2

How many grams of AgCl will form by adding enough AgNO3 to react fully with 1500. ml of 0.400 M BaCl2 solution? 2 AgNO3 (aq) + BaCl2(aq) 2 AgCl (s) + Ba(NO3)2 (aq) a. 172 g AgCl b. 86.0 g AgCl c. 8.37 x 10-3 g AgCl d. 36.0 g AgCl

Dilution Dilution: Adding a solvent to a concentrated solution to make the solution less concentrated (i.e. dilute). When a solution is diluted, only the volume changes. The number of moles of solute remains constant. moles before dilution = moles after dilution Molarity1 x Volume1 = Molarity2 x Volume2 M1 V1 = M2 V2

What volume of 12 M HCl is needed to make 500.0 ml of a 0.10 M HCl?

Dilution Practice Calculate the molarity of a NaOH solution prepared by mixing 100. ml of 0.20 M NaOH with 150 ml of H2O. a. 2.0 M NaOH b. 0.050 M NaOH c. 0.080 M NaOH d. 12.5 M NaOH