Solutions Chemistry

Solution = homogeneous mixtures made up of individual particles (molecules, atoms or ions). 1.May include combinations of phases –gas in liquid (CO 2 in water = club soda) –gas in gas (oxygen and nitrogen = air) –liquid in liquid (alcohol in water) –solid in solid (metal alloy such as steel) –solid in liquid (salt in water)

Properties : 1. Homogeneous, particles spread evenly throughout. 2. The dissolved particles will not come out of solution, no matter how long it stands. 3. The solution is clear and transparent. The dissolved particles are too small to be seen. 4. Particles are too small to be filtered (cannot be separated this way)

–Solute: the substance that dissolves Substance that changes phases substance in lesser quantity (mass) - Solvent: the substance in which the solute dissolves water for all substances = aqueous (aq) –if ionic – attraction for water molecules to salt ions –if molecular – then molecule-molecule attractive forces other solvents include alcohols, acetone (for organic substances)

Degree of Solubility “Solubility” of a solute is the MAXIMUM quantity of solute that will dissolve in a given quantity of solvent at a specific temperature.

Factors that Affect Solubility a. Nature of Solute and Solvent –“like dissolves like” –polar and ionic molecules (asymmetrical) dissolve in polar substances like water –nonpolar molecules dissolve in nonpolar solvents such as cyclohexane

Insoluble mixtures form “precipitates”

Practice Problems: 1.Based on Table F indicate which of the following compounds is water soluble and which is insoluble? a. Li 2 CO 3 b. CaCrO 4 c. Al(ClO 3 ) 3 d. AgCl e. Ba(HCO 3 ) 2

b. Temperature –most solids increase in solubility with increasing temperature –all gases decrease in solubility with increasing temperature c. All gases in liquids increase in solubility with pressure increases

Factors that Affect Rate of Dissolving 1. Size of particles - Solid solutes ( an increase in surface area) 2. Stirring- brings fresh portions of solute to be dissolved. 3. Temperature- Solids increased rate with increase temp. 4. Gases – decrease rate with increase temp. 5. Amount already dissolved – with no solute dissolved, faster than with some solute dissolved.

8. Solubility Curves All solutions are in 100g (mL) of water Saturated = on line Unsaturated = below the curve of line Supersaturated = above the curve of line

Unsaturated – when a solution is not holding as much Solute as it possibly can at that temperature. Saturated – when a solution is holding as much solute as it possibly can at that temperature. “Dynamic Equilibrium” between dissolved and undissolved solute. Supersaturated – unusual situation where a solution can hold more solute than it should be able to hold at a specific temperature. Unstable (cool). Only a few solutes will form a supersaturated solution NaC 2 H 3 O 2, and Sodium thiosulfate “hypo” used in developing pictures. (rock candy is due to the crystallization of a super saturated solution of sugar)

1.As the temperature increases from 0 o C to 25 o C the amount of NH 3 that can be dissolved in 100 grams of water is? a. Decreases by 10 grams b. Decreases by 40 grams c. Increases by 10 grams d. Increases by 40 grams 2.A solution containing 55g of NH 4 Cl in 100grams of water is saturated at a temperature of: Answer: 60 o C

Solution Concentration Dilute = little solute in a given amount of solvent Concentrated = a lot of solute in a given amount of solvent - insoluble substances cannot form concentrated solutions

Molarity – is the number of moles of solute in 1L of solution Ex. What is the molarity of a solution that contains 4.0mol of NaOH on 0.5L of solution? Answer: 8.0M Ex2: What is the molarity of a solution containing 82.0g of Ca(NO 3 ) 2 in 2.0L of solution? Answer: 0.250M

Titration When mixing acids and bases or other substances together it is important to know how their concentrations will neutralize or balance each other out. This is called “titration.” Formula: M 1 V 1 = M 2 V 2 Ex: If 100mL of a 1.0M solution is evaporated to a volume of 25mL, what will the concentration of the resulting solution be? Answer: 4.0M

Molality (m) Where temperature is a factor (since volume is temperature dependant) Molality = Mols of Solute Kg of Solvent Ex1: What is the Molality of a solution, when.300 mols of dextrose C 6 H 12 O 6 is dissolved in 800 g of water?

Percent Composition by Mass % mass = mass of partx 100% mass of the whole Ex: What is the percent by mass of sodium hydroxide if 2.5g of NaOH are added to 50g of H 2 O? Answer: 4.76%

Percent Composition by Volume % Volume = volume of solute x 100% Volume of solution Ex: What is the percent by volume of alcohol if 50.0mL of ethanol is diluted with water to form a total volume of 300mL Answer: 16.7%

Parts per million P.P.M. (ppm) = grams of solute x 1,000,000 grams of solution Ex: Barium sulfate is listed as insoluble on the solubility table, however, it dissolves to a small extent. Its solubility at 50 o C is g in 100g of water. Express this solubility in parts per million. Answer: 3.4ppm

Colligative Properties = these are properties of solution that depend on the number of solute particles in the solution A.Vapor Pressure Reduction when a solute is added to a solution, the vapor pressure will decrease

A.Vapor Pressure Reduction Vapor pressure is the amt of pressure exerted outwards by a solution When vapor pressure = atm pressure, a substance will boil!!!! when a solute (ionic or covalent) is added to a solution, the vapor pressure will decrease Ionic solutes have a greater effect b/c they break into ions, thus increasing the # of nonvolatile substances in the water. Ex. MgCl 2  Mg +2 + Cl - + Cl -

Atmospheric pressure! The b.p.’s for the above substances are where their v.p. crosses the atm pressure line!!!!!!!

B.Boiling Point Elevation When a solute is added to a solution, the b.p. will increase Due to the reduced vapor pressure Ex. Adding salt to water before you boil it, increases b.p. so that when you put your pasta in, it will cook faster

Calculating Boiling Point Elevation: ∆T b = i × K b × m T = temperature ( o C) K = molal b.p. elevation constant (0.512 for H 2 O) m = molal [conc] i = # of particles Ex. What is the boiling point of a solution that contains 1.25mol CaCl 2 in 1400g of water? Answer: o C

C.Freezing Point Depression when a solute is added to a solution, the f.p. will decrease Adding salt to snow is an example  when salt is added to ice, it will lower the f.p. so that the ice will melt even if the outside temp is lower than water’s freezing point. Not related to vapor pressure reduction

Calculating Freezing Point Depression: ∆T f = i × K f × m T = temperature ( o C) K = molal f.p. elevation constant (1.86 for H 2 O) m = molal [conc] i = # of particles Ex. What is the f.p. depression of a 0.20m K 2 SO 4 solution? Answer: -1.1 o C

Distillation and Water Purification Distillation is the process in which liquid is evaporated into a gas, and then condensed back into a liquid Liq.  Gas  Liq. Process: 1. Boil liquid at boiling point 2. Carry gas away 3. Cool gas to reform liquid in “condenser” 4. Many solutes boil at much higher temperatures and remain behind – “ purification”