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Topic 7 SolutionsTopic 7 Solutions

SolutionsSolutions

A solution is a homogeneous mixture of substances in the same physical state

Homogeneous means the particles are evenly distributed and spread uniformly throughout the mixture

Types of SolutionsTypes of SolutionsSolutions can exist in all three states (s, l, g)

gas - both solvent/solute are gases ex. Air

liquid - gas, liquid, or solid dissolved in a liquid ex. salt water, antifreeze

• Miscible – ex. Sugar and water• Immiscible – ex. Oil and water

Solids - 2 or more solids are uniformly spread out

•alloy- ex. brass = Cu/Znbrass = Cu/Zn; steel = iron + carbonsteel = iron + carbon

aqueous –water is the solvent, (aq) ex. NaCl(aq)

SOLUTIONSSOLUTIONS Are homogeneous mixtures are made up of two parts:

2. Solvent 2. Solvent - present in greater amount

1. Solute 1. Solute - substance being dissolved

Water in salt water

Salt in salt water

Water in soda

Carbon dioxide or sugar in soda drinks

Water is a common solventSolutions made with water are called aqueous solutions (aq)

Charateristics of liquid solutions

Charateristics of liquid solutions

1. Homogeneous mixtures2. Are clear and don’t disperse

light3. Can have color4. Will not settle upon standing5. Will pass through a filter

HydrationHydration

the process of dissolving a solid in water

solute particles are separated and pulled into solution

solute particles are surrounded by solvent particles

Dissolution of sodium Dissolution of sodium ChlorideChloride

Dissolution of sodium Dissolution of sodium ChlorideChloride

Hydration

Hydration processHydration processDissociation: separation of an ionic solid into aqueous ions

Molecular solvation: molecules stay intact; covalent

NaCl(s) Na+(aq) + Cl–(aq) C6H12O6(s) C6H12O6(aq)

Electrolyte –conducts

Why? Ions present

Non Electrolyte –doesn’t conductWhy? Ions are NOT present

Solvation and ConductivitySolvation and Conductivity

StrongElectrolyte

Non-Electrolyte

solute exists asions only

- +

salt

- +

sugar

solute exists asmolecules

only

- +

acetic acid

WeakElectrolyte

solute exists asions and

molecules DISSOCIATION

SolubilitySolubility

How much of a solute that will dissolve in a certain amount of solvent at a given temperature

Substances with a high solubility are soluble (aq)

Substances with a low solubility are insoluble (s) – they are precipitates

Use Reference Table F to determine

““Like Dissolves Like”Like Dissolves Like”““Like Dissolves Like”Like Dissolves Like”

used to describe what solutes will dissolve in what solvent depends on the forces of attraction

used to describe what solutes will dissolve in what solvent depends on the forces of attraction

Solute type nonpolar solvent (soap) polar solvent(water)

Nonpolar(grease) soluble insoluble

Polar (sugar) insoluble soluble

Ionic (salt) insoluble soluble

Solubility: Temperature

Solubility: Temperature

•As temp increases, most solids become more soluble in water

•As temp increases, most gases become less soluble in water

temp

temp

Sol (s & l)

Sol (g)

Solubility: PressureSolubility: Pressure

• Pressure has little or no effect on the solubility of solid or liquid solutes. Pressure does effect the solubility of gases in liquids

• As press increases, the solubility of gases in a liquid increases

• See Reference Table Gpressure

Sol (g)

Factors Affecting SolubilityFactors Affecting Solubility

•Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes.

Rate of Solution FormationRate of Solution Formation

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

• The factors that determine how fast (rate) a The factors that determine how fast (rate) a substance dissolves aresubstance dissolves are

• temperaturetemperature• stirring (agitation)stirring (agitation)• the surface area of the dissolving particlesthe surface area of the dissolving particles

Rate of Solution FormationRate of Solution Formation

Temperature and Solution Formation •At higher temperatures, the kinetic

energy of water molecules is greater than at lower temperatures, so they move faster. As a result, the solvent molecules collide with the surface of the sugar crystals more frequently and with more force.

Temperature and Solution Formation Temperature and Solution Formation

A cube of sugar in cold tea dissolves slowly.

Granulated sugar dissolves in cold

water more quickly than a sugar cube,

especially with stirring.

Granulated sugar dissolves very

quickly in hot tea.

• At higher temperatures, the At higher temperatures, the kinetic energy kinetic energy of water of water molecules is greater than at lower temperatures, so molecules is greater than at lower temperatures, so they move faster. they move faster.

• As a result, the solvent molecules collide with the As a result, the solvent molecules collide with the surface of the sugar crystals more frequently and with surface of the sugar crystals more frequently and with more force.more force.

Stirring and Solution FormationStirring and Solution Formation

• Stirring speeds up the dissolving process because fresh solvent (the water in tea) is continually brought into contact with the surface of the solute (sugar).

Particle Size and Solution Formation

• A spoonful of granulated sugar dissolves A spoonful of granulated sugar dissolves more quickly than a sugar cube because more quickly than a sugar cube because the smaller particles in granulated sugar the smaller particles in granulated sugar expose a much greater surface area to expose a much greater surface area to the colliding water molecules.the colliding water molecules.

Therefore…Therefore…Therefore…Therefore…

Solids tend to dissolve best when:

o Heatedo Stirredo Ground into small particles

Gases tend to dissolve best when:

o The solution is coldo Pressure is high

Rate of SolutionRate of SolutionFactor Factor   

Affect on Solid Solute Affect on Solid Solute   

Affect on GaseousAffect on GaseousSoluteSolute

CrushingCrushing  

increases the rate by increasing surface area = collisions

not applicable

StirringStirring  

increases the rate by exposing fresh solvent to solute and increasing KE = collisions

decreases the rate by increasing KE, thereby reducing solubility (gas particles escape); gases should be in a closed space

Amount ofAmount ofdissolved dissolved solutesolute  

as the amount of dissolved solute increases, the rate decreases 

as the amount of dissolved solute increases, the rate decreases

TemperatureTemperature  

as the temperature increases, the rate increases ( KE = collisions)

as the temperature increases, the rate decreases

Definitions:

Potential Energy (PE) – energy stored within the chemical bonds of a substanceKinetic Energy (KE) – molecules in motionTemperature – measurement of the average KE• direct relationship between the two temp = KE

Saturation and Solubility Saturation and Solubility CurvesCurves

Saturation and Solubility Saturation and Solubility CurvesCurves1. Saturated solution – solution that cannot dissolve

any more solute at a given temperature• added solute will NOT dissolve • At equilibrium:

• Ratedissolving = Ratecrystallization

• NaCl (aq) NaCl (s)

2. Unsaturated solution – solution that can dissolve more solute at a given temperature

• added solute will dissolve – NOT at equilibrium

3. Supersaturated solution – solution that holds more solute than it can dissolve at a given temperature

• produced by dissolving solute at a high temperature and allowing it to cool slowly

• addition of solute causes precipitation of the excess

Concentration – the amount of solute compared to solventConcentration – the amount of solute compared to solvent Qualitative descriptions concentrated – large amount of solute compared to the

amount of solvent• example: frozen concentrated OJ

dilute – small amount of solute compared to the amount of solvent• example: weak coffee

Concentrated vs. DiluteConcentrated vs. DiluteConcentrated vs. DiluteConcentrated vs. Dilute

Solubility – the ability to dissolve in water

Solubility – the ability to dissolve in water

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

concentration

• shows the dependence of solubility on temperature

Solubility CurvesSolubility CurvesSolubility CurvesSolubility Curves

• shows the dependence of solubility on temperature

• maximum grams of solute that will dissolve in 100 g of solvent at a given temperature

• varies with temp• based on a saturated

solution

Solubility CurvesSolubility CurvesSolubility CurvesSolubility Curves

Saturation –vs- UnsaturatedSaturation –vs- Unsaturated Saturation –vs- UnsaturatedSaturation –vs- UnsaturatedA solution that A solution that contains the contains the maximum amount of maximum amount of solute in a given solute in a given amount of solvent.amount of solvent.

A solution that contains A solution that contains less solute than a less solute than a saturated solution saturated solution under existing under existing conditions is conditions is unsaturated.unsaturated.

SupersaturatedSupersaturatedSupersaturatedSupersaturated• A solution that

contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

• The crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added.

SupersaturatedSupersaturated

• A supersaturated solution is clear before a seed crystal is added.

SupersaturatedSupersaturated

• Crystals begin to form in the solution

immediately after the addition of a seed crystal.

• Excess solute crystallizes rapidly.

Practice Question #1Practice Question #1

1) According to Reference Table G, which compound solubility decreases most rapidly as the temperature changes from 10°C to 70°C?

a) NH4Cl

b) NH3 c) HCl d) KCl

Answer to problem #1Answer to problem #1

Correct Answer Number: 2Explanation: See Ref. Table G.

Notice the curves for choices 1 and 4 increase. Choice 2 and 3 both decrease but choice 2 (NH3) decreases more than 50 degrees, while HCl decreases only about 16 degrees.

Concentrations of SolutionsConcentrations of Solutions

• Water must be tested continually to ensure that the concentrations of contaminants do not exceed established limits. These contaminants include metals, pesticides, bacteria, and even the by-products of water treatment. You will learn how solution concentrations are calculated.

Quantities in SolutionsQuantities in SolutionsQuantities in SolutionsQuantities in Solutions

The amount of solute in a solution.

Describing Concentration

• % by mass - medicated creams

• % by volume - rubbing alcohol

• ppm, ppb - water contaminants

• molarity - used by chemists

• molality - used by chemists

MolarityMolarity

• Molarity (M) is the number of moles of solute dissolved in one liter of solution.

• To calculate the molarity of a solution, divide the moles of solute by the volume of the solution.

MolarityMolarity

• To make a 0.25 molar (0.25M) solution, first add ? mol of solute to a 0.50-L (500mL) volumetric flask half filled with distilled water.

Solve for MolesSolve for Moles

Solute used is NaClWe want to prepare 500 mL of a 0.25

Molar solutionUsing the Molarity formula solve for

moles of solute

M = Moles of Solute

Liters of Soln

Plug in NumbersPlug in Numbers

0.250 mol/Liter = x moles

0.500L

# of Moles = 0.250mol/liter x 0.500 L

x = 0.125 moles

Convert Moles to GramsConvert Moles to Grams

0.125 moles NaCl ? GramsUse Mole Conversion Formula

Moles = given mass

gfm

Plug in NumbersPlug in Numbers

0.125 moles = x grams

58 g/mol (gfm of NaCl)

X= 7.25 grams NaCl

MolarityMolarity

• Add 7.25 grams of NaCl to water in flask• Swirl the flask carefully to dissolve the solute.

MolarityMolarity

• Fill the flask with water exactly to the 500-mL mark.

16.2

#1: How many moles of NaOH are contained in 200 ml of 0.1M solution of NaOH?

Answer: moles = (M)(L) = (0.1 M)(.2L) =.02 mol

Answer:M = (moles)/(L) = 1.50 moles .5000L = 3.00 M

Ex #2: What is the molarity of a 500.0 mL solution of NaOH (GFM = 40.0g) with 60.0 g of NaOH (aq)?

Different style problemDifferent style problem1) Which solution is the most concentrated?

a) 1 mole of solute dissolved in 1 liter of solution? b) 2 moles of solute dissolved in 3 liters of solution? c) 6 moles of solute dissolved in 4 liters of solution? d) 4 moles of solute dissolved in 8 liters of solution?

Answer to different style problemAnswer to different style problem

Correct Answer Number: 3 Explanation: #3 (1.5 M. ) is the most concentrated. Find the molarity ( moles of solute/liter of solution) for

each answer.

#1) 1 mole / 1 liter or 1 M.       #2) 2 moles / 3 liters or 0.67 M. #3) 6 moles / 4 liters or 1.5 M.      #4) 4 moles / 8 liters or 0.5 M.

1) Which solution is the most concentrated?

a) 1 mole of solute dissolved in 1 liter of solution? b) 2 moles of solute dissolved in 3 liters of solution? c) 6 moles of solute dissolved in 4 liters of solution?

d) 4 moles of solute dissolved in 8 liters of solution?

Percent SolutionsPercent Solutions

• Concentration in Percent (Mass/Mass)

16.2

• Substitute “volume” for “mass” in the above equation and vice versa.

• Ex.#1 What is the percent by volume of hexane if 20.0 mL of hexane are dissolved in benzene to a total volume of 80.0 mL?

% volume = volume of solute x 100 volume of solution

= 20.0 mL x 100 80.0 mL= 25.0%

Concentration = Mass of solute (g)

Volume of Solvent or Solution (mL)

A 50.0 gram sample of a solution is evaporated and found to contain 0.100 grams of sodium chloride. What is the percent by mass of sodium chloride in the solution?

% mass = 0.100 g X 100 50.0 g

= 0.200%

100.0 grams of water is evaporated and analyzed for lead. 0.00010 grams of lead ions are found. What is the concentration of the lead, in parts per million?

ppm = grams of solute x 1,000,000 grams of solution

= (0.00010 g) x 1,000,000 100.00010 g = .9 ppm

•If the legal limit for lead in the water is 3.0 ppm, then the water sample is within the legal limits (it’s safe and ok)

CHEM DOCHEM DOCHEM DOCHEM DOTurn in your hw & write Turn in your hw & write

down the weekend down the weekend assignmentassignment

QuietlyQuietly read the intro read the intro and purpose of today’s and purpose of today’s activity.activity.

Kool-Aid Activity Kool-Aid Activity

Make 3 different solutions of Make 3 different solutions of Kool-Aid with the following Kool-Aid with the following concentrations: concentrations:

•0.1 M, 0.1 M, 0.4 M, 0.4 M, & & 0.7M0.7M

Conduct a taste test.Conduct a taste test.

OVERVIEWOVERVIEW

As a group: Complete the Pre-lab questions 1-4As a group: Complete the Pre-lab questions 1-4

Check answers with the teacherCheck answers with the teacher

Conduct experiment – Conduct experiment – read directions FIRST!!!!! read directions FIRST!!!!! • Record data into tableRecord data into table

Clean up work area – throw out tasting cups, Clean up work area – throw out tasting cups, clean measuring cups and spoon, return kool-aid clean measuring cups and spoon, return kool-aid powderpowder to tableto table

Work on remaining questions with your group – Work on remaining questions with your group – on loose leaf paperon loose leaf paper• Omit 2b and 3 b in the disc section.Omit 2b and 3 b in the disc section.

Mole CalculationsMole CalculationsMole CalculationsMole Calculations

Molarity (M) = Molarity (M) = moles of moles of solutesolute liters of liters of solutionsolution

# moles = # moles = given mass (g)given mass (g)

gram molecular massgram molecular mass

Clean up work area – throw out tasting Clean up work area – throw out tasting cups, clean measuring cups and cups, clean measuring cups and spoon, return kool-aid powderspoon, return kool-aid powder to tableto table

Work on remaining questions with Work on remaining questions with your group – on loose leaf paperyour group – on loose leaf paper

Help yourself to some kool-aidHelp yourself to some kool-aid

Colligative Properties of Solutions

Colligative Properties of Solutions

The wood frog is a remarkable creature because it can survive being frozen. Scientists believe that a substance in the cells of this frog acts as a natural antifreeze, which prevents the cells from freezing. You will discover how a solute can change the freezing point of a solution.

16.3

ApplicationsApplications

•salting icy roads•making ice cream•antifreeze

•cars (-64°C to 136°C)•fish & insects

Colligative PropertiesColligative Properties

depend on the number of particles (molality) rather than the nature of the particles in the solution.

Boiling point, freezing point, vapor pressure and osmotic pressure are some of the properties affected.

Freezing Point Depression Freezing Point Depression

• f.p. of a solution is lower than f.p. of the pure solvent

Boiling Point ElevationBoiling Point Elevation

Solute particles weaken IMF in the solvent.

b.p. of a solution is higher than b.p. of the pure solvent

Colligative Properties Colligative Properties con’t.con’t.

Colligative Properties Colligative Properties con’t.con’t.

• # of Particles# of Particles

•Nonelectrolytes (covalent)– remain intact when dissolved –1 particle

•Electrolytes (ionic)–dissociate into ions when dissolved–2 or more particles

Vapor-Pressure LoweringVapor-Pressure Lowering

• Three moles of glucose dissolved in water produce 3 mol of particles because glucose

does not dissociate.

16.3

Vapor-Pressure LoweringVapor-Pressure Lowering

• In a solution, solute particles reduce the number of free solvent particles able to escape the liquid. Equilibrium is established at a lower vapor pressure.

16.3

Vapor-Pressure LoweringVapor-Pressure Lowering

• Three moles of calcium chloride dissolved in water produce 9 mol of particles because each formula unit of CaCl2 dissociates into three ions.

16.3

Boiling point elevationBoiling point elevation

called molal boiling point elevation (Kb). It is proportional to the concentration of

dissolved particles 1 mole of particles in solution raises the BP of

water by 0.52 C

Which 1 molal solution will have the highest boiling point?

KNO3 Mg(NO3)2 Al(NO3)3

Freezing Point Depression

Freezing Point Depression

called molal freezing point depression (Kf).

1 mole of particles in solution depresses the FP of water by 1.86 C

What will depress the FP of water the most….AlCl3or MgCl2? Why? What would the new FP be?