SOLUTIONS

Chapter 15

What are solutions?

Homogeneous mixtures containing two or more substances called the solute and the solvent

Solute- is the substance that dissolves Solvent- is the dissolving medium May exist as a solid, liquid or gas (usually are

liquids)

Soluble- A substance that dissolves in a solvent

Insoluble- A substance that does not dissolve in a solvent (ex. Sand is insoluble in water)

Immiscible- Two liquids that are insoluble in each other (ex. Oil and water)

Miscible- Two liquids that are soluble in each other (ex. Vinegar (water + acetic acid) )

Examples of Solutions

Solvation in Aqueous Solutions Why are some substances soluble in

one another whereas others are not? Solvation- the process of surrounding

solute particles with solvent particles to form a solution Solvation in water is called hydration“Likes dissolve likes”

This phrase means that polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.

Oil- Non PolarWater- Polar

Factors that affect the rate of solvation Solvation occurs only when and where

the solute and solvent particles come in contact with each other

Commons ways to increase the collisions Agitating the mixture (stirring and shaking) Increasing the surface area of the solute

(breaking the solute into smaller pieces) Increasing the temperature of the solvent

(increases the kinetic energy)

Solubility

Solubility refers to the maximum amount of solute that will dissolve in a given amount of solvent at a specified temperature and pressure Saturated solution- contains the maximum

amount of dissolved solute for a given amount of solvent at a specific temperature and pressure

Unsaturated solution- contains less dissolved solute for a given temperature and pressure than a saturated solution

Supersaturated Solution- contains more dissolved solute than a saturated solution at the same temperature (and if you messed with the solution by shaking it or throwing in one more crystal, the whole thing would crystallize rapidly!)

Supersaturated Sodium Acetate Solution

Factors that Affect Solubility

Temperature Many substances are

more soluble at high temperatures than at low temperatures

Pressure Solubility of a gas in a

solvent increases as its external pressure (the pressure above the solution) increases

Henry’s Law

At a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid.

Formula:

2

2

1

1

P

S

P

S

Practice Problem

A gas has a solubility of 0.66 g/L at 10.0 atm of pressure. What is the pressure on a 1.0-L sample that contains 1.5 g of gas?

2

2

1

1

P

S

P

S

Solution Concentration

The concentration of a solution is a measure of how much is dissolved in a specific amount of solvent or solution

Qualitative Vocabulary Dilute- contains a small

amount of solute Concentrated- contains a

large amount of soluteconcentrated dilute

Expressing Concentration

Concentration description Ratio

Percent by mass

Percent by volume

Molarity

Molality

Mole Fraction

100x solution of mass

solute of mass

100x solution of volume

solute of volume

solution ofliter

solute of moles

solvent of kilogram

solute of moles

solvent of moles solute of moles

solute of moles

Calculating Percent my Mass What is the percent my mass of NaHCO3

in a solution containing 20 g NaHCO3 dissolved in 600mL H2O?

Calculating Percent by Volume What is the percent by volume of

ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL of water?

Calculating Molarity

What is the molarity of an aqueous solution containing 40.0g of glucose (C6H12O6) in 1.5 L of solution?

Preparing Molar Solutions

How many grams of NaOH are in 250mL of a 3.0M NaOH solution?

Diluting Solutions

M1xV1=M2xV2

• M1 -- the initial concentration of the solution.

• V1 -- the initial volume of the original solution that is going to be diluted with water.

• M2 -- the final concentration of the solution after it’s diluted with water.

• V2 -- the total volume of the final solution after it has been diluted with water.

Practice Problem

What volume of a 3.00M KI stock solution would you use to make 0.300 L of a 1.25M KI solution?

If you dilute 20.0 mL of a 3.5M solution to make 100.0 mL of solution, what is the molarity of the dilute solution?

Calculating Molality

What is the molality of a solution containing 30.0g of napthalene dissolved in 500.0g of toluene?

Calculating Mole Fraction

An aqueous solution of NaCl has a mole fraction of 0.21. What is the mass of NaCl dissolved in 100.0mL of solution?

Colligative Properties of Solutions Physical properties of solution that are

affected the number of particles but not the identity of dissolved solute particles

Colligative Properties include: Vapor Pressure Lowering Boiling Point Elevation Freezing Point Depression Osmotic Pressure

Vapor Pressure Lowering

The greater the number of solute particles in a solvent, the lower the resulting vapor pressure

Boiling Point Elevation

The temperature difference between a solution’s boiling point and a pure solvent’s boiling point

Formula: ∆Tb= Kbm Kb is the molal boiling point elevation constant m is the molality

The value of the boiling point elevation is directly proportional to the solution’s solute molality- the greater the number of solute particles in the solution, the greater the boiling point elevation

Freezing Point Depression

The temperature difference between a solution’s freezing point and a pure solvent’s freezing point

Formula: ∆Tf= Kfm Kf is the molal boiling point elevation

constant m is the molality

Increasing Temperature

Practice Problem

What are the boiling point and freezing point of a 0.40m solution of sucrose in ethanol?

Osmosis and Osmotic Pressure Osmosis is the diffusion of solvent

particles across a semipermeable membrane from an area of higher solvent concentration to an area of lower solvent concentration

Osmotic Pressure- the amount of additional pressure caused by the water molecules that moved into solution Depends upon the number of solute

particles in a given volume of solution