Ch 12.1 Types of Mixtures. Heterogeneous vs. Homogeneous Mixtures Heterogeneous Mixture: mixture...
-
Upload
katherine-ramsey -
Category
Documents
-
view
220 -
download
3
Transcript of 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
Example 3 Look at the solubility chart to determine if the
following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Cadmium Nitrate Ammonium Sulfide
Example 3 Look at the solubility chart to determine if the
following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Insoluble Cadmium Nitrate Ammonium Sulfide
Example 3 Look at the solubility chart to determine if the
following are Soluble or Insoluble? Sodium Carbonate Soluble Calcium Phosphate Insoluble Cadmium Nitrate Soluble Ammonium Sulfide
Example 3 Look at the solubility chart to determine if the
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.
Example 4 Will a precipitate form when solutions of cadmium
nitrate and ammonium sulfide are combined? Step 2: Write double-displacement reaction
between the two compounds. (NH4)2S + Cd(NO3)2 CdS + 2NH4NO3
Example 4 Will a precipitate form when solutions of cadmium
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.