Unit Eleven: Solutions

Solutions• A solution is a homogeneous mixture of two or more

substances▫Homogeneous – uniform characteristics throughout▫Heterogeneous – different compositions; various throughout

• Solutions have at least two components▫Solutes – the minority component▫Solvents – the majority component

▫75% isopropyl solution – solute is water, solvent is isopropyl▫3% H2O2 – solute is H2O2, solvent is water

Nine types of mixturesSolute Solvent Examples

**Gas Gas Air

**Gas Liquid Soda

Gas Solid Styrofoam or marshmallows

Liquid Gas Clouds

**Liquid Liquid Alcohol in water

Liquid Solid Mercury on penny (amalgam)

Solid Gas Smoke

**Solid Liquid Sugar or salt in water (Liquid is usually solvent)

**Solid Solid Coins, gemstones, alloys- ** means common type of solution- Amalgam: an alloy of mercury and another metal- Likes Dissolves Likes

Non-Solutions - Suspensions•Suspensions

▫A mixture from which particles settle out upon standing

▫Particles are larger than in a solution

▫Suspended – temporarily out of school

▫Examples: Italian Dressing, muddy water, orange juice with pulp

Non-Solutions - Colloids

•Colloids▫A permanent mixture whose particles are

smaller than in a suspension and larger than in a solution

▫Particles will reflect light, cloudy appearance

▫Do not settle out and cannot be filtered

▫Milk, starch, dusty air, fog

Name Particle Size Permanence

Examples

Solution d < 1 nm Permanent Sugar-water, acids, bases, salt water

Colloid 1 nm < d < 100nm Permanent Milk, blood, mayonnaise

Suspension d > 100 nm Settles Out Mud, clay, cement

Property Solutions Colloids Suspensions

Settling Out Do not settle Do not settle Settle on standing

Filtering Unchanged Unchanged Separates when filtered

Tyndall Effect Do not scatter light Scatters light Scatters light

Effect on Colligative Properties

Does affect Does not affect Does not affect

Tyndall Effect

Laser pointed through a solution, colloid, and suspension – what will happen?

Non-Electrolyte

•Aqueous solutions containing a solute that dissolves as molecules

•Do not conduct electricity

•CH3OH CH3OH

•C12H22O11 C12H22O11

Electrolyte• Aqueous solutions containing a solute that

dissociates into ions

• Conducts electricity

• NaCl Na1+ + Cl1- or Al2(SO4)3 2Al3+ + 3SO42-

• Strong electrolytes have large portions of solute existing as ions

• Weak electrolytes have a fraction of the solute existing as ions

Solubility

•Solubility is the amount of compound (usually in grams) that will dissolve in a certain amount of liquid

•There are three types of solutions:▫Unsaturated▫Saturated▫Supersaturated

Solubility• Saturated Solutions

▫ Hold the maximum amount of solute under the solution conditions

▫ If additional solute is added to a saturated solution, it will not dissolve

• Unsaturated Solutions▫ Hold less than the maximum amount of solute under the solution

conditions

▫ If additional solute is added to an unsaturated solution, it will dissolve

• Supersaturated Solutions▫ Hold more than the normal maximum amount of solute

▫ Any disturbance will precipitate the solute or make it come out of solution

Supersaturated Solution

Example: Rock Candy

Solubility Curves

•35 grams of NaCl per 100 grams at 25°C is a __ soln.

•25 g of KNO3 per 35 g of water at 50°C is a ___ soln.

•45 g of KNO3 per 100 g of water is cooled from 40°C to 0°C

Solubility

•Solubility depends on:▫Identity of solute and solvent

Like dissolves like -> polar dissolves polar and nonpolar dissolves nonpolar

▫Temperature For solids in liquids, solubility increases with

increasing temperature

For gases in liquids, solubility decreases with increasing temperature

Solubility▫Pressure

For solids in liquids, a change in pressure has very little effect on the solubility

For gases in liquids, higher pressure increases the solubility of the gas in the liquid

When a can of soda is opened, there is less pressure so the gas is less soluble

•Worksheet One is due Friday (Tomorrow)

•Worksheet Two is due Monday▫Skip Question 10▫Questions 3, 4, and 5 you cannot answer

until Friday’s notes

Solubility

•Rate of solution – ▫How fast a substance dissolves and how

quickly the substance goes into solution

▫Factors that increase the rate of solution for solids Decrease particle size Stirring Increase temperature

Hydration versus Solvation

•Hydration

▫A solute is dissolved by water molecules attaching to ions and moving them into solution

•Solvation

▫Process of molecules of a solvent moving molecules or ions into solution

Concentrations

•Concentrations – the amount of solute in a solution▫A dilute solution is one containing small

amounts of solute relative to solvent

▫A concentrated solution is one containing large amounts of solute relative to solvent

▫Mass percent, molarity, and molality

Mass Percents

•Mass Percents – the number of grams of solute per 100 grams of solution

Mass percent=(mass of solute)/(mass of solution)x100

Practice Problems• Calculate the mass percent of NaCl in a solution

containing 15.3 grams of NaCl and 155.0 grams H2O.

• Calculate the mass percent of a solution containing 27.5 grams C2H6O and 175 mL of H2O

• A soft drink contains 11.5% sucrose by mass. What volume of soft drink solution, in mL, contains 85.2 grams of sucrose?

Molarity• Molarity – the number of moles of solute per liter

of solution

• A concentration of 6 M HCl contains 6 moles of HCl per 1 L of solution

• Molar solutions are prepared in a volumetricflask

• Molarity = M = moles of solute/liters of solution

Practice Problems

•Calculate the molarity of a sucrose solution made with 1.58 moles of solute diluted to a total volume of 5.0 L of solution.

•Calculate the molarity of a solution made by putting 15.5 grams of NaCl into a beaker and adding water to make 1.50 L of NaCl solution.

Practice problems• 6.7 grams of NH4Cl is dissolved in enough

water to make 803 mL of solution. What is the molarity of the solution.

• How many grams of NaOH are needed to make 500.0 mL of a 1.00 M solution?

• What volume of a 1.0 M NaNO3 solution can be prepared from 170.0 grams of NaNO3?

Solution Dilutions

•Most solutions are bought as stock solutions, however most labs need diluted solutions.

•We use M1V1=M2V2

Practice Problems

•A laboratory procedure calls for 5.00 L of a 1.50 M KCl solution. How should you prepare this solution from a 12.0 M stock solution?

•To what volume should you dilute 0.100 L of a 15 M NaOH solution to obtain a 1.0 M NaOH solution?

Practice Problems

•How much 6.0 M NaNO3 solution should be used to make 0.585 L of a 1.2 M NaNO3 solution?

Solution Stoichiometry

•Tying it all together!

How much 0.125 M NaOH solution is required to completely neutralize 0.225 L of 0.175 M H2SO4 solution?

H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + 2 H2O(l)

Solution Stoichiometry

•How much 0.115 M KI solution in liters is required to completely precipitate the lead in 0.104 L of 0.225 M Pb(NO3)2?

2 KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2 KNO3(aq)

Solution Stoichiometry

•How many milliliters of 0.112 M Na2CO3 are necessary to completely react with 27.2 mL of 0.135 M HNO3 according to the following reaction?

2HNO3(aq)+ Na2CO3(aq) → H2O(l)+ CO2(g)+ 2NaNO3(aq)

Molality• Molality – is the number of moles of solute per

kilograms of solvent

• A concentration of 6 m HCl contains 6 moles of HCl per 1 kg of solvent

• To make 1 liter of 1 m solution, one mole is added to enough water to make 1 L

• Which is more concentrated 1.0 m or 1.0 M?▫ 1.0 M

• Molality = m = moles of solute/kg of solvent

Practice Problems

•What is the molality of the solution if 5.0 grams of KI are in 500.0 grams of water?

•How many grams of calcium nitrate (Ca(NO3)2) must be added to 20.0 grams of water to make a 2.5 m solution?

Colligative Properties•A property that depends on the number of

solute particles and not the type of solute particles

•How much you have not what you have

•Two types▫Freezing point depression▫Boiling point elevation▫These depend on quantity of solute not type of

solute

Colligative Properties• Freezing point depression – difference in

temperature between the freezing point of a solution and the freezing point of the pure solvent

▫Solute disrupts the formation of the orderly pattern thus requiring more energy

Solution freezes at a lower temperature than the pure solvent

▫Magnitude is proportional to the number of solute particles dissolved

ΔTf = Kf • m • (# of particles)

•ΔTf = change in temperature

•Kf = molal freezing point depression constant

•m = molality

• (# of particles) = how many particles of solute form in solution

Colligative Properties• Boiling point elevation – difference in temperature

between the boiling point of a solution and the boiling point of the pure solvent

▫Nonvolatile solute dissolved in the solvent disrupts the vapor pressure which increases the boiling point

Solution boil at a greater temperature than the pure solvent

▫Magnitude is proportional to the number of solute particles dissolved

ΔTb = Kb • m • (# of particles)

•ΔTb = change in temperature

•Kb = molal boiling point depression constant

•m = molality

• (# of particles) = how many particles of solute form in solution

Practice Problems

•What is the freezing point depression and the boiling point elevation of a pinch of salt (0.25 grams NaCl) in a 2.00 L aqueous solution?

Kf=1.86°C/m Kb=0.512°C/m

Practice Problems

•What is the freezing point depression and boiling point elevation of a 0.40 m solution of sucrose in ethanol?

Kf=1.99°C/m Kb=1.22°C/m

F.p.=-114.6°C B.p.=78.4°C

•Unit Eleven Test Tomorrow (Friday March 8th)

•Worksheet Five due Tomorrow

•Gizmo’s due Tomorrow

•Lab Report Revisions due Tuesday▫Will have optional computer time on

Monday