Mixtures & Solutions

Mixtures & SolutionsChapter 14

What is a Solution?Which of the following are solutions?

BronzeCoffee

GasolineAir

HeliumConcrete

What is a Solution?A solution is a homogeneous, single phase

mixture.It can be a gas, liquid, or solid.

Solvent, Solute – There is a Difference

The solute dissolves in the solvent.Sugar Water

The water is the solventThe sugar is the solute

Salt WaterThe water is the solvent.The salt is the solute.

Solvent, Solute – There is a Difference

Your textbook says that the substance present in the largest amount is the solvent and this is true most of the time.

If a solid is added to a liquid and the resulting solution is liquid, the liquid is considered to be the solvent even is there is more of the solid.

Example, you can dissolve 109 grams of NaOH in 100 grams of water. The result is a liquid solution and water would be the solvent.

SIX TYPES OF SOLUTIONSOLUTE SOLVENT EXAMPLEsolid liquidliquid liquidgas liquidgas gassolid solidliquid solid Note: the solution is in the same phase as the

solvent.

Heterogeneous Mixtures

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.

Colloids are heterogeneous mixtures of intermediate sized particles (between 1 nm and 1000 nm) and do not settle out.

The most abundant substance in a mixture is the dispersion medium.

Colloids are categorized according to the phases of their particles.

Solution Concentrations

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

Concentration can be described as concentrated or dilute.

In order to maintain a sodium chloride concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per 100.0 g of water. What is the percent by mass of NaCl in the solution?

What is the percent by Mass of NaHCO3 in a solution containing 20.0 g of NaHCO3 dissolved in 600 mL of water?

The percent by mass of calcium chloride in a solution is found to be 2.65 %. If 50.0 g of calcium chloride is used, what is the mass of the solution?

Molarity is the number of moles of solute dissolved per liter of solution.

Preparation of a standard aqueous solution.

TYPE ONE PROBLEMSGiven Moles Desired Unit

1. What is the volume, in ml, of 2M Na2SO4 containing 20.0g of the solute?

2. What mass of ammonia, NH3, is contained in 300.ml of 2.75M NH3.

3. 40.0 g of Sodium Hydroxide, NaOH, are dissolved into 200.ml of solution. What is the resultant molarity?

PROBLEM SET1.What volume of 2.25 M

H2SO4 contains 9.81g?2.What is the mass of CaCl2 in

100.0 ml of 1.75M CaCl2?3.19.6 g of H3PO4 are

dissolved in 500.0 ml of solution. What is the resultant molarity?

TYPE TWO PROBLEMSDiluting solutions with water. Dilution equation: M1V1 = M2V2

1. 15.0ml of water are added to 30.0ml of 2.00M KCl. What is the new molarity?

2. How much water must be added to 40.0ml of 2.75M Na2S to reduce it to 2.50M?

1.What volume of water must be added to reduce 20.0ml of 1.5M HCl to 1.0M HCl?

2.What must 30.0 cm3 of 2.75 M KBr be diluted to reduce it to 2.50M?

3.15.0ml of water are added to 30.0ml of 3.00M HBr. What is the new molarity?

TYPE THREE PROBLEMS

Mixing solutions of different concentrations

MV = MFVF

1. 10.0ml of 2.00M KCl, 35.0ml of 1.25M KCl, and 50.0ml of 3.75M KCl are mixed. What is the new molarity?

2. What volume of 2.00M HCl must be mixed with 20.0ml of 3.25M HCl to reduce it to 3.00M HCl?

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

where XA and XB represent mole fractions of each substance

Suppose a hydrochloric acid solution contains 36 g of HCl and 64 g of water. What is the mole fraction present of each?

What will dissolve, what won’t?

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.

Polar water molecules interacting with positive and negative ions of

a salt.

The ethanol molecule contains a polar O—H bond.

The polar water molecule interacts strongly with the polar O—H bond in ethanol.

Structure of common table sugar.

A molecule typical of those found in petroleum.

SIMILA SIMILIBUS SOLVUNTUR

This statement simply translates into “like dissolves like”

a. Polar solvents dissolve polar and ionic solutes.

An oil layer floating on water.

How much? How fast?SolubilitySaturated, unsaturated, supersaturated.What affects the RATE at which a solid dissolves

in a solvent?

Solubility - the amount of solute in g that saturates 100ml of water.

Factors affecting solubility a. Temperature b. Surface Area c. Agitation-stirring or shaking

Unsaturated solution - less than the maximum amount of solute is dissolved.

Saturated solution - the maximum amount of solute is dissolved.

Supersaturated solution - more than the maximum amount of solute is dissolved.

a. This is unstable. b. This can be brought back to the saturated

state by either scratching the surface of the container with a file or adding a crystal of the solute.

SATURATED SOLUTIONSThese are solutions that have the maximum

amount of solute dissolved in the solvent.A saturated solution is an equilibrium state. a. How is it recognized? b. What are the conditions? c. How is it defined on the molecular level?

Factors that affect the rate of dissolving for a solid solute in aqueous solution.

a. Stirring b. Temperature c. Surface Area

GASES DISSOLVED IN AQUEOUS SOLUTION

Factors affecting solubility of a gas in a liquid

a. Temperature

b. Pressure

HENRY’S LAW - the solubility, S, of a gas is directly proportional to the pressure exerted by the gas above or on the liquid.

Henry’s Law

PROBLEM SET1.A gas has a solubility of

0.0123 mol/liter at 1.18 atm of pressure. What is the solubility at 355 atm of pressure?

2.A gas has a solubility of 1.235 g/liter at 4550 mm Hg. What is the solubility at 760 mm Hg?

Colligative properties are physical properties of solutions that are affected by the number of particles but not by the identity of dissolved solute particles.

Ionic compounds are electrolytes because they dissociate in water to form a solution that conducts electricity.

Some molecular compounds are also electrolytes.

Vapor Pressure Lowering

Adding a nonvolatile solute to a solvent lowers the solvent’s vapor pressure.

When a solute is present, a mixture of solvent and solute 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.

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.

ΔTb = Kbm where ΔTb is the boiling point elevation, Kb is the molal boiling point elevation constant, and m represents molality.

Freezing Point DepressionAt a solvent's 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.

A solution's freezing point depression is the difference in temperature between its freezing point and the freezing point of the pure solvent.

ΔTf = Kfm where ΔTf is the freezing point depression, Kf is the freezing point depression constant, and m is molality.

What are the boiling and freezing points of a 0.29 m aqueous solution of sodium chloride?

1.What is the freezing point of a 8.07 molal aqueous methanol solution? Kf = 1.86 *C/m

2. What is the boiling point of a 1.17 molal aqueous sucrose solution? Kb = 0.512 *C/m

1. A solution freezes at -1.050C when 20.0 grams of an unknown are dissolved into 200.g of water. What is its molecular mass?

2. A solution boils at 100.220C when 25.0 grams of an unknown are dissolved in 100.g of water. What is the molecular mass?