Chapter 15: Solutions Parts of a solution: 1.Solute: substance being dissolved (NaCl) 2.Solvent: dissolving medium (H 2 O)

Solvation: the process of solvent particles surrounding solute particles to form a solution

“Like dissolves Like” This is the general rule to determine whether solvation occurs. “Like” refers to the solvent and solute being either polar or nonpolar. Polarity of a molecule is a result of how the electrons are shared and arranged. Water is a polar molecule. “Universal solvent”

When Substances Combine: 1.Soluble: a substance that dissolves in a solvent 2.Insoluble: a substance that does not dissolve in a solvent 3.Immiscible: two liquids that are immiscible, they separate after mixing (water & oil) 4.Miscible: two liquids that are soluble in each other.

Rate of Solvation Factors affecting the rate of solvation: 1. Agitation: stirring, shaking; allows particles to dissolve faster 2. Temperature: heat adds energy which allows particles to move faster and disassociate from each other faster. 3. Particle size: smaller particles increase surface area for the solvent to act on.

Affect of Temperature on Solubility

Solubility : maximum amount of solute that will dissolve in a given amount of solvent, 100g usually

Solubility Terminology: 1.Saturated solution: contains the maximum amount (g) of dissolved solute LESS 2.Unsaturated solution: contains LESS than the maximum amount (g) of dissolved solute MORE 3.Supersaturated solution: contains MORE that the maximum amount of dissolved solute.

What type of a solution is a solution that contains 70g PbNO 3 at 40ºC in 100g H 2 O? SATURATED

What type of a solution is a solution that contains 35g NaCl at 80ºC in 100g H 2 O? UNSATURATED

What type of a solution is a solution that contains 120g K 2 NO 3 at 60ºC in 100g H 2 O? SUPER- SATURATED

Factors Affecting Solubility: 1.Temperature: many substances are more soluble at high temperature. But gases will dissolve better at colder temperatures.

Factors Affecting Solubility: 2. Pressure: Gases will dissolve best under pressure. Henry’s Law: solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid.

“The BENDS” Deep sea divers may experience a condition called the "bends" if they do not readjust slowly to the lower pressure at the surface. As a result of breathing compressed air and being subjected to high pressures caused by water depth, the amount of nitrogen dissolved in blood and other tissues increases. If the diver returns to the surface too rapidly, the nitrogen forms bubbles in the blood as it becomes less soluble due to a decrease in pressure. The nitrogen bubbles can cause great pain and possibly death. To alleviate this problem somewhat, artificial breathing mixtures of oxygen and helium are used. Helium is only one-fifth as soluble in blood as nitrogen. As a result, there is less dissolved gas to form bubbles.

Solution Concentrations Concentration: the amount (g) of solute dissolved in a specific amount of solvent 1.Concentrated: large amount of solute for the amount of solute. 2.Dilute: small amount of solute for the amount of solution.

Calculating Molarity Molarity (M) is the number of moles of solute dissolved per liter of solution. Also known as molar concentration. A liter of solution containing one mole of solute is a 1M solution. Formula: Molarity(M) = moles of solute liters of solution

Calculating Molarity Example: A mL intravenous (IV) solution contains 5.10g of glucose (C 6 H 12 O 6 ). What is the molarity of this solution? [molar mass of glucose is g/mol] 1.Use molar mass to calculate the number of moles of C 6 H 12 O g C 6 H 12 O 6 1 mol C 6 H 12 O g C 6 H 12 O 6 =.0283 mol C 6 H 12 O 6

Calculating Molarity 2. Convert mL to L mL x 1L = L solution 1000mL 3. Substitue the known values into the equation. Molarity = moles solute liters of solution M = mol C 6 H 12 O 6 = mol L soln. L soln. = 0.282M

Diluting Solutions Often stock solutions must be diluted from one concentration to another. How is the volume of the stock solution to be diluted determined? Rearrange the molarity equation and the number of moles solute does not change and we get the equation: M 1 V 1 = M 2 V 2

Diluting does Not add solute, Only solvent.

Diluting Stock Solutions What volume, in milliliters of 2.00M calcium chloride solution would you use to make 0.50 L of 0.30M calcium chloride solution? 1.Analyze the problem: what do you have and what are you looking for. GivenUnknown M 1 = 2.00M CaCl 2 V 1 = ? L M 2 = 0.300M V 2 = 0.50L

Diluting Stock Solutions What volume, in milliliters of 2.00M calcium chloride solution would you use to make 0.50 L if 0.30M calcium chloride solution? 2. Solve for the Unknown: rearrange the equation to solve for the unknown M 1 V 1 = M 2 V 2 V 1 = M 2 V 2 M 1

Diluting Stock Solutions What volume, in milliliters of 2.00M calcium chloride solution would you use to make 0.50 L if 0.30M calcium chloride solution? 3.Substitute known values and solve. V 1 = 0.50L x 0.300M 2.00M V 1 = 0.075L x 1000mL ( the question asked for mL!!!) 1L V 1 = 75mL

Colligative Properties Physical properties of a solution that are affected by the number of particles in the solution. Lowers vapor pressure: less gas escapes from the liquid because of the solute

Colligative Properties Raises boiling point: it takes more energy to overcome the attraction between the solute and solvent Lowers freezing point: solute disrupts the solvent particles from forming a solid example: Antifreeze (ethylene glycol)