Ch 12.1 Types of Mixtures. Heterogeneous vs. Homogeneous Mixtures Heterogeneous Mixture: mixture...

Ch 12.1 Types of Mixtures

Heterogeneous vs. Homogeneous Mixtures

Heterogeneous Mixture: mixture does not have a uniform composition. Ex: Milk and soil

Homogeneous Mixture: entire mixture has the same or uniform composition. Ex: Salt water

Solutions

Soluble: capable of being dissolved. Ex. Sugar is soluble in water.

Sugar and water create a solution, or a homogeneous mixture of two or more substances in a single phase.

Solvent: the thing that does the dissolving. Solute: the thing that is being dissolved.

Solutions may exist as gases, liquids, or solids, and may also be combinations.

Solute State Solvent State Example

Gas Gas Oxygen in Nitrogen

Gas Liquid CO2 in Water

Liquid Liquid Alcohol in Water

Liquid Solid Mercury in Silver & Tin

Solid Liquid Sugar in Water

Solid Solid Copper in Nickel (alloy)

Suspensions

Suspension: When the particles in a solvent are so large that they settle out unless the mixture is constantly agitated. Ex: Muddy water

The particles in a suspension can be separated by passing the mixture through a filter.

Colloids

Particles that are intermediate in size between those in solutions and suspensions form mixtures called colloids.

These are also known as emulsions and foams and cannot be separated using a filter. Ex. Mayonnaise and Milk

Tyndall Effect: when light is scattered by the particles in a colloid.

Solutes: Electrolytes vs. Nonelectrolytes

Electrolyte: a substance that dissolves in water to give a solution that conducts an electric current.

Nonelectrolyte: a substance that dissolves in water to give a solution that doesn’t conduct an electric current.

Ch 12.2 The Solution Process

Factors Affecting Dissolution Rate

The compositions of the solvent and the solute determine whether a substance will dissolve.

Three factors that affect dissolving rate: Stirring (agitation) Temperature Surface area of the dissolving particles.

Solubility Solution Equilibrium: the physical state in

which the opposing processes of dissolution and crystallization of a solute occur at equal rates.

Solubility tells us how much solute can dissolve in a certain amount of solvent at a particular temperature and pressure to make a saturated solution. Expressed in grams of solute per 100 grams of

solvent

Saturated Solution: the solution cannot hold any more solute.

Unsaturated Solution: the solution could still dissolve more solute.

Supersaturated Solution: the solution is holding more than it should at the given temperature, and if you messed with the solution by shaking it or adding even one more crystal of solute, the whole thing would crystallize rapidly.

Solubility Values: amount of substance required to form a saturated solution with a specific amount of solvent at a specified temperature.

Solubility of sugar is 204 grams per 100 grams of water at 20°C.

Solute-Solvent Interactions

“Like dissolves Like” Polar will dissolve other polar molecules

and Nonpolar dissolves other nonpolar. Hydration: when water is used to dissolve

an ionic solution.

Liquid Solutes and Solvents Miscible: two liquids that can dissolve in

each other. Immiscible: the liquids don’t mix.

Ex. Oil and vinegar

Factors Affecting Solubility

Temperature affects the solubility of: Solid Solutes Liquid Solutes Gaseous Solutes

Temperature Gas dissolved in a Liquid: as the temperature

increases, the solubility decreases. Example: Warm soda loses its carbonation.

Solid dissolved in a Liquid: as the temperature increases, the solubility increases. Example: Sugar in hot tea versus iced tea.

Factors Affecting Solubility

Pressure affects the solubility of: Gaseous Solutes

Pressure Gas dissolved in Liquid: As pressure

increases, solubility increases. Example: Soda is carbonated under high pressure.

Solid dissolved in Liquid: As pressure increases, solubility does not change! Since you cannot compress solids and liquids,

pressure has no effect on solubility.

Henry’s Law Henry’s Law states that 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. So, as the pressure of the gas above the liquid

increases, the solubility of the gas increases.

S1 S2

P1 P2

Calculating Solubility of a Gas If the solubility of a gas in water is 0.77 g/L at 3.5

atm of pressure, what is its solubility (g/L) at 1.0 atm of pressure and a constant temperature? P1 = 3.5 atm

S1 = 0.77 g/L

P2 = 1.0 atm

S2 = ? g/L

0.77 g/L = S2 3.5 atm 1.0 atm

S2 = 0.22 g/L

Enthalpies of Solution Solvated: when a solute particle is

surrounded by solvent molecules. The formation of a solution is accompanied

by an energy change, it can be released or absorbed.

Enthalpy of solution: the net amount of energy absorbed as heat by the solution when a specific amount of solute dissolves in a solvent.

Ch 12.3 Concentrations of

Solutions

Concentrations of Solutions

Concentration of a solution: a measure of the amount of solute that is dissolved in a given quantity of solvent.

Solutions can be referred to as dilute or concentrated, but these are not very definite terms.

Molarity Molarity (M): the number of moles of solute

dissolved in one liter of solution.

Note: it is the total volume in liters of solution, not the liters of solvent.

solution of liters

solute of moles(M)Molarity

Calculating Molarity of a Solution IV Saline Solutions are 0.90 g NaCl in exactly

100 mL of solution. What is the molarity of the solution?

Step 1: convert mL to L (divide by 1000) Step 2: convert the grams of NaCl to moles

of NaCl using molar mass. Step 3: put moles of NaCl and L of solution

into the molarity equation and divide.

Finding Moles of Solute Household bleach is a solution of sodium

hypochlorite (NaClO). How many moles of solute are present in 1.5L of 0.70M NaClO?

Moles Solute = M x L = mol/L x L Multiply the given volume in L by the molarity

expressed in mol/L.

MolalityMolality

Another way to express solution concentration Another way to express solution concentration is is Molality (Molality (mm)) NOT THE SAME AS MOLARITY!NOT THE SAME AS MOLARITY!

MolalityMolality ( (mm) is the concentration of a solution ) is the concentration of a solution expressed in moles of solute per kilogram expressed in moles of solute per kilogram solvent.solvent.

solvent kg 1

solute of moles )(molality m

• Calculate the molality of a solution Calculate the molality of a solution prepared by dissolving 10.0g of NaCl prepared by dissolving 10.0g of NaCl in 600.g of water.in 600.g of water.

Calculating Molality of a Solution

m m == mol of solutemol of solute

kg of solventkg of solvent

10.0g NaCl 10.0g NaCl 0.171 mol NaCl 0.171 mol NaCl

== 0.171 mol of NaCl0.171 mol of NaCl

0.600 kg of water0.600 kg of water

600.0 g 600.0 g 0.600 kg 0.600 kg

== 0.285 0.285 mm NaCl NaCl

Finding Moles of Solute using molality.

How many moles of sodium fluoride are How many moles of sodium fluoride are needed to prepare a 0.40needed to prepare a 0.40mm NaF solution that NaF solution that contains 750.0g of water?contains 750.0g of water?

mol NaF= 0.40 mol NaF= 0.40 molmol x 0.75 kg = 0.30 mol x 0.75 kg = 0.30 mol kgkg

mol solute = mol solute = m m x kg of solventx kg of solvent

m m == mol of solutemol of solute

kg of solventkg of solvent

Making Dilutions Diluting a solution reduces the number of

moles of solute per unit volume, but the total number of moles of solute in solution does not change.

M1 x V1 = M2 x V2

Preparing a Dilute Solution How many mL of 2.00M MgSO4 solution must

be diluted with water to prepare 100.0mL of 0.400M MgSO4?

Use the dilution formula and plug in the known values and then solve for the unknown.

Volume can be in any unit, as long as they are both the same. (Just like gas laws).

0.400 M MgSO4 x 100.0 mL = 2.00 M MgSO4 x V2

V2 = 20.0 mL

Chapter 13: Ions in Aqueous Solutions and

Colligative Properties

Section 1: Compounds in

Aqueous Solutions

Dissociation When an ionic compound dissolves in water, the

ions separate. To find how many moles of ions are produced,

we write a balanced dissociation equation and look at the coefficients in front of the ions.

NaCl Na+ + Cl-

1 mol of Sodium Ion and 1 mol of Chloride Ion These are like decomposition reactions.

Example 1 Write the equation for the dissolution of

aluminum sulfate, Al2(SO4)3, in water. How many moles of Al ions and SO4 ions are produced by dissolving 1 mol of Al2(SO4)3? What is the total number of moles of ions produced?

Al2(SO4)3 2Al3+ + 3SO42-

2 mol Al3+ and 3 mol SO42-

Total moles = 2 + 3 = 5 moles

Example 2

Do the same thing as the last example, except now you are dissolving 2 mols of Al2(SO4)3.

2Al2(SO4)3 4Al3+ + 6SO42-

4 mol Al3+ and 6 mol SO42-

Total moles = 4 + 6 = 10 moles

Precipitation Reactions

GENERAL SOLUBILITY GUIDELINES

1. Sodium, potassium, and ammonium compounds are soluble in water.

2. Nitrates, acetates, and chlorates are soluble.

3. Most chlorides are soluble, except those of silver, mercury (I) and lead. Lead (II) chloride is soluble in hot water.

Precipitation Reactions

GENERAL SOLUBILITY GUIDELINES CONT…

4. Most sulfates are soluble, except those of barium, strontium, lead, calcium, and mercury.

5. Most carbonates, phosphates, and silicates are insoluble, except those of sodium, potassium, and ammonium.

6. Most sulfides are insoluble, except those of calcium, strontium, sodium, potassium, and ammonium.

Example 3 Look at the solubility chart to determine if the

following are Soluble or Insoluble? Sodium Carbonate Calcium Phosphate Cadmium Nitrate Ammonium Sulfide


following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Cadmium Nitrate Ammonium Sulfide


following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Insoluble Cadmium Nitrate Ammonium Sulfide


following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Insoluble Cadmium Nitrate Soluble Ammonium Sulfide


following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Insoluble Cadmium Nitrate Soluble Ammonium Sulfide Soluble

Example 4 Will a precipitate form when solutions of cadmium

nitrate and ammonium sulfide are combined? Step 1: Determine if the compounds are

soluble, if soluble, continue to step 2.

Compounds are both soluble…so we continue to step 2.


nitrate and ammonium sulfide are combined? Step 2: Write double-displacement reaction

between the two compounds. (NH4)2S + Cd(NO3)2 CdS + 2NH4NO3


nitrate and ammonium sulfide are combined? (NH4)2S + Cd(NO3)2 CdS + 2NH4NO3

Step 3: Determine if the newly formed compounds are soluble. If one is insoluble, then it is a precipitate.

CdS or Cadmium Sulfide is insoluble,

so it is the precipitate.

Net Ionic Equations Includes only those compounds and ions that

undergo a chemical change in a reaction in an aqueous solution.

Basically, if the ions are part of a soluble product, they don’t end up in the final equation, only the ions for the precipitate that is formed, remain in the equation.

The ions that do not take part in the chemical reaction are called spectator ions.

Example 5 Write the net ionic equation for the production of

ammonium nitrate and cadmium sulfide.

2NH4+ + 2NO3

- + Cd2+ + S2-

CdS + 2NO3- + 2NH4

+

If ions show up on both sides of the equation, cross them out and rewrite the equation without them.

Cd2+ + S2- CdS

Ionization

Ions are formed from solute molecules by the action of the solvent.

Different from dissociation because it involves molecular compounds rather than ionic compounds.

In order for ions to form, the strength of the bond within the solute molecule must be weaker than the attractive forces of the solvent molecules.

The Hydronium Ion H3O+

When a compound ionizes in a solution and releases a H+ ion, it binds to the H2O and forms H3O+.

H2O + HCl H3O+ + Cl-

Electrolytes and Nonelectrolytes Electrolyte: a compound that conducts an

electric current when it is in an aqueous solution or in the molten (liquid) state.

All ionic compounds are electrolytes because they dissociate into ions.

Nonelectrolyte: a compound that does not conduct an electric current in either aqueous solution or the molten state.

Strong Electrolyte: nearly all the ionic compound exists as separate ions.

Weak Electrolyte: only a fraction of the ionic compound exists as separate ions.

Section 2: Colligative Properties of

Solutions

Vapor-Pressure Lowering

The addition of a nonvolatile substance will raise the boiling point and lower the freezing point.

This has to do with vapor pressure of the solvent.

As the number of solute particles increase, the proportion of solvent molecules decreases.

Freezing-Point Depression. When 1 mol of a nonelectrolyte solution is

dissolved in 1 kg of water, the freezing point is -1.86°C instead of 0.0°C.

If 2 mols are dissolved, it is 2 x -1.86°C. This is called the molal freezing-point constant (Kf)

and changes for different solvents. Freezing-point depression Δtf is the difference

between the two freezing points. Changes according to concentration.

Example 6

What is the freezing-point depression of water in a solution of 20.54 g of sucrose, C12H22O11, in 200 g of water? What is the actual freezing point of the solution?

Find molality of the sugar solution. Multiply the Kf (of water) by the molality.

Take normal freezing point 0°C + Δtf.

Boiling-Point Elevation When 1 mol of a nonelectrolyte solution is

dissolved in 1 kg of water, the boiling point is 100.51°C instead of 100.0°C. An increase of 0.51°C

This is called the molal boiling-point constant (Kb) and changes for different solvents.

Boiling-point elevation Δtb is the difference between the two boiling points. Changes according to concentration.

Example 7

What is the boiling-point elevation of a solution made from 20.1 g of a nonelectrolyte solute and 400.0 grams of water? The molar mass of the solute is 62.0 g/mol.

Osmotic Pressure

A semipermeable membrane allows only water molecules to pass through during osmosis. This can cause an increase in volume on one side of the membrane.

Osmotic pressure is the external pressure that must be applied to stop osmosis.

The higher the concentration of a solution, the greater the osmotic pressure.

Electrolytes & Colligative Properties

When electrolytes are dissolved in a solvent, the effects are greater than that of nonelectrolytes. This is because more moles of solute particles are formed when the compounds dissolve.

Homework

Ch 13.2 pg 456 #1-4 and 458 #14, 19, 25

For #2, look at the chart on page 448 once you solve for the Kf value.

Ch 12.1 Types of Mixtures. Heterogeneous vs. Homogeneous Mixtures Heterogeneous Mixture: mixture...

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