What is a homogeneous mixture? Solutions JIGSAW Part 1.

What is a What is a homogeneous homogeneous

mixture?mixture?

Solutions

JIGSAW

Part 1

Approximately 0.0043g of Approximately 0.0043g of oxygen can be dissolved in oxygen can be dissolved in 100.0 ml of water at 20100.0 ml of water at 20°C. °C. Express this in terms of Express this in terms of

parts per million.parts per million.

Some Problems

a.) 30.0 g of sodium chloride in 100.0g of water at 90ºC

How would you describe the following solutions?

b.) 35.0 g of ammonia in 100.0g of water at 40ºC

c.) 140.0 g of sodium chloride in 200.0g of water at 10ºC

d.) What is in common with all of the compounds whose solubility curves decrease at temp. increases?

Solutions

- the substance that does the dissolving

- the substance that is dissolved

- homogeneous mixture

Solubility

Point falls right on the line on the graph

Point is below the line on the graph

Point is above the line on the graph

SATURATED

UNSATURATED

SUPERSATURATED

This graph is for 100 g of H2O

Solution vs. Suspension

Solution – homogeneous mixture

dissolving = physical change

(not a chemical change)

Dissolved particles (atoms, ions or molecules) are extremely small and solutions cannot be separated by filtering.

Suspension – heterogeneous mixture where some particles settle out upon standing ex. muddy water (clay & silt)

Tyndall EffectSmall particles (ions, molecules) in solution do not scatter the light rays. Path of the light rays in solution are not visible.

Suspension Solution                            

Light

Beam

Solutions

Polar Water Molecules with Hydrogen Bonds = surface

tension.

•One water molecule

H-bonds to another

Hydration of Ions & Orientation of Polar Water Molecule

SolubilityThe amount of solute a solvent can dissolve in a given

quantity of solvent at a specific temperature(and pressure for a gaseous solute) to make a saturated solution

The solvent dissolves the maximum amount of solute at a specific temperature

Solvent dissolved less than the maximum amount of solute. It CAN dissolve MORE!

Solvent contains more solute than it can theoretically hold at a specific temperature & pressure

Explain in terms of Explain in terms of molecular polarity, if molecular polarity, if carbon dioxide gas is carbon dioxide gas is

soluble in water. soluble in water.

Dissolution & Hydration

Water is a Polar Molecule

Solutions

Rate of Solution FormationHow much over time

• Stirring – increasesincreases contact/collisions between the solvent & solute which increasesincreases the rate of formation

• IncreaseIncrease temperature – molecules gain KE, molecules move faster, increase contact/collisions which increaseincrease the rate of solution formation

• Particle size – decrease size of particle, increasesincreases SA, increasesincreases contact which will increaseincrease the rate of solution formation

• Amount of Solute vs. Solvent – closer to saturation equals slowerslower rate of dissolving

If you want to keep soda If you want to keep soda ‘fresh’ in a plastic bottle, ‘fresh’ in a plastic bottle, how would you do it at how would you do it at

home? Explain in terms home? Explain in terms of chemistry.of chemistry.

Concentration•Compares/describes the amount of solute dissolved in the solvent

•Subjective

•Concentrated vs Dilute

•Objective

•Molarity – only in Chem

•ppm – real world uses

Formulas on Reference

Tables

SupersaturatedSupersaturatedSUPERSATURATED SUPERSATURATED

SOLUTIONSSOLUTIONS contain more contain more solute than is possible to be solute than is possible to be dissolveddissolved

Supersaturated solutions are Supersaturated solutions are unstable. unstable. The supersaturation The supersaturation is only temporary, and usually is only temporary, and usually accomplished in one of two accomplished in one of two ways:ways:1.1. Warm the solvent so that it will Warm the solvent so that it will

dissolve more, then cool the solution dissolve more, then cool the solution

2. Evaporate some of the solvent carefully so that the solute does not solidify and come out of solution.

Solutions of Ionic Compounds conduct electricity = Electrolytes

Electrolytes – charged particles (ions) in solution

Greater number (#) ions in solution…

= greater electrical conductivity

= stronger electrolyte.

Solutions3 Types of Electrolyte Compounds Salts (ionic compounds), acids(H+) & bases(OH-)

Salts = ionic = metal & non-metal K + (aq) & Cl - (aq)

Acetic = weak acid H + & CH3COO -

Covalent = no ions

bright dim dark

KCl CH3COOH C6H12O6

Solutions can be dilute (weak) or more concentrated.

Molarity (M) = expression of Concentration

M = # moles of solute

Liters of Solution

If 2.0 moles are dissolved in 4.0 Liters…

Molarity = 2.0 moles / 4.0 L = 0.50 M

Molarity ProblemsHow would you make 1.00 L of a .770M solution of NaCl?

lutio nlite rso fso

utemo le so fso lmo la rity

1 .00L

moles770.

. 7 7 0m o l e s

Molarity ProblemsHow do you measure .770moles?

gfm

massmoles

58 .5g/mo l

x770. m ol

4 5 . 0g r a m s

You must convert to grams using the mole formula

So now what?

How to make a .769M Solution

Fill to

Line

Molarity ProblemsYou want a 2.0M solution of NaCl and you need 3.75L of this solution. How do you make it?

lutionlitersofso

utemolesofsolmolarity

3.75L

Xmoles2.0M

7.50moles58.5*7.50grams 439grams

How would you make How would you make 250ml of a .25M 250ml of a .25M

solution of solution of ammonium chloride?ammonium chloride?

DilutionsAdd more solvent to change the ratio of solute to solvent

(M1)(V1)= (M2)(V2)

solvent, conc. of solute

(M1)(V1) represents the original, more concentrated solution

(M2)(V2) represents the final concentration & volume after dilution

Making a Dilution1. Measure the volume of concentrated solution needed

2. Add solvent until final combined volume is reached

3. Stir to mix thoroughly

Make 500.0ml of a 3.0M solution from a 10.0M stock solution

Measure out 150.0ml of 10.0 M stock solution.

(M1)(V1)= (M2)(V2)Calculate the amount of stock solution needed:

(10.0M)(V1)= (3.0M)(500.0ml)

V1= 150.0ml

Add 350.0ml of solvent to make a final volume of 500.0ml.

Properties that depend ondepend on the number of solute particles in solution;

not the nature of the particles

Best example:

Boiling Pt. ElevationBoiling Pt. Elevation

Freezing Pt. DepressionFreezing Pt. Depression

B.P.

F.P.

100 C

0 C

Colligative PropertiesColligative Properties

A solA solnn is made by completely is made by completely dissolving 90.g of KNOdissolving 90.g of KNO3(s)3(s) in a 100.g in a 100.g

of water in a beaker. The of water in a beaker. The

temperature of the solution is 65temperature of the solution is 65ºC.ºC. 1.1. Determine the total mass Determine the total mass KNOKNO3(s)3(s) that settles to that settles to

the bottom of the beaker when the original the bottom of the beaker when the original solution is cooled to 15solution is cooled to 15ºC.ºC.

2.2. Describe what would happen if the pressure Describe what would happen if the pressure was increased.was increased.

Factors Affecting amount of Solute dissolved

Temperature of Solvent

Pressure

Solids and Liquids –

Gases -

↑ Temperature, ↑ amount dissolved

↑ Temperature, ↓ amount dissolved

Table G lines with downward slope

↑ Pressure, ↑ amount dissolved for gases

Factors Affecting amount of Solute dissolved

Nature of solute/solvent

• Polar solvents dissolve polar & ionic solutesPolar solvents dissolve polar & ionic solutes. Water (polar) dissolves ionic solids and polar covalent

solids. Salts (NaCl, KCl) are ionic & form aqueous solutions.

• Non-polar dissolves non-polar. Non-polar dissolves non-polar. Oil (non-polar) and water (polar) don’t mix = immiscible.

• AlcoholsAlcohols – dissolve polar & non-polar solutes; but not ionic solutes.

Tinctures – alcohol is solvent.

Properties that depend ondepend on the number of solute particles in solution;

not the nature of the particles

Best example:

Boiling Pt. ElevationBoiling Pt. Elevation

Freezing Pt. DepressionFreezing Pt. Depression

B.P.

F.P.

100 C

0 C

Colligative PropertiesColligative Properties

• Vapor pressure is the pressure exerted by a vapor. • Ex the H2O(g) in a sealed container.

• Yet, molecules both leave and join the surface, so vapor pressure also pushes molecules up.

Eventually the air above the water is filled with vapor pushing down. As temperature , more molecules fill the air, and vapor pressure .

Vapor Pressure DefinedVapor Pressure Defined

Solute Effect on Vapor Pressure

Vapor Pressure (V.P.) = pressure exerted by a vapor in equilibrium with its liquid (or solid)

Volatile – substance has some V.P.Non-Volatile – V.P. = zero

Another Colligative Another Colligative PropertyProperty

As solute molecules are added to As solute molecules are added to a solution, the solvent become a solution, the solvent become less volatile (=decreased vapor less volatile (=decreased vapor pressure).pressure).

Solute-solvent interactions Solute-solvent interactions contribute to this effect.contribute to this effect.

Vapor Pressure ReductionVapor Pressure Reduction

Explain why COExplain why CO2(g)2(g) is released is released

when a bottle of soda is when a bottle of soda is opened. opened.

What is the name of the acid in What is the name of the acid in soda water? soda water?

Dissolved particles (solute = gray)occupy/prevent solvent particles from entering vapor phase.

Electrolytes – form ions in solution

KCl (aq) 1 K+1 + 1 Cl –1

(1 mole) (2 moles particles)

CaCl2 (aq) 1 Ca+2 + 2 Cl –1

(1 mole) (3 moles of particles)

Nonelectrolytes – exist as dissolved molecules (do not form ions)

ex. Glucose C6H12O6 (aq) (1 mole)

Freezing Point ReductionFreezing Point Reduction

The solute particles interfere with the intermolecular bonds [H bonds] between the solvent molecules

The more ions/particles in solution, the lower the FP value

Greater # particles in solution = Greater effect for…

- B.P. Elevation- F.P. Depression- Lower Vapor Press.

Colligative Properties Summary

Change in Freezing Change in Freezing Point Point

Common Applications Common Applications of Freezing Point of Freezing Point DepressionDepression

Propylene glycol

Ethylene glycol – deadly to small animals

Boiling Point ElevationBoiling Point ElevationThe solute particles prevent some of the

solvent molecules from turning into the gaseous phase

The more ions/particles in solution, the higher the BP value

Which substance changes the Which substance changes the FP/BP the most?FP/BP the most?

NaClNaCl(s)(s) Na Na++(aq)(aq) + Cl + Cl--

(aq)(aq)

MgBrMgBr2(s)2(s) Mg Mg2+2+(aq)(aq) + 2Br + 2Br--

(aq)(aq)

CC66HH1212OO6(s)6(s) C C66HH1212OO6(aq)6(aq)

2 ions/particle

3 ions/particle

1 particle/particle

MgBr2 is most effective in changing the FP/BP because it produces the most ions in solution

Which has the greater # particles …

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

Hint: Write a balanced dissociation reaction

___ NaCl (s) ___ Na +1 (aq) + ___ Cl –1

(aq)

Coefficients = # moles = # particles (aq)

Hint: Write a balanced dissociation reaction

Which has the greater # particles …

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

___ NaCl (s) ___ Na +1 + ___ Cl –1

___ CaCO3 (s) ___ Ca +2 + ___ CO3 –2

___ KCl (s) ___ K +1 + ___ Cl –1

___ Fe2O3 (s) ___ Fe +2 + ___ O3 –2

Which has the greater # particles …

1) NaCl (aq) 2) CaCO3 (aq) Total # Moles of 3) KCl (aq) 4) Fe2O3 (aq) Particles; Ions

_1_ NaCl (s) 1 Na +1(aq) + 1 Cl –1

(aq) 2

_1_ CaCO3 (s) 1 Ca +2 (aq) + 1 CO3 –2

(aq) 2

_1_ KCl (s) 1 K +1(aq) + 1 Cl –1

(aq) 2

_1_ Fe2O3 (s) 2 Fe +2 (aq) + 3 O3 –2

(aq) 5

Which has the greater Boiling Point (BP), lower Freezing Point (FP) and lower Vapor Pressure?

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

Because…_________________________________

_________________________________________

Which has the greater Boiling Point (BP), lower Freezing Point (FP) and lower Vapor Pressure?

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

Because… greatest # moles of particles are formed in solution when it dissolves. Fe2O3 (aq) 2 Fe +2

(aq) + 3 O3 –2 (aq) 5 moles

Which substance would lower Which substance would lower the freezing point the most if it the freezing point the most if it

was used as a solute?was used as a solute?

CHCH33OH, Mg(OH)OH, Mg(OH)22, LiCl, or N, LiCl, or N22OO33

Boiling Point - Temperature at which the liquids vapor pressure equals atmospheric pressure.

-usually heat the liquid until its vapor pressure equals atmospheric pressure

Water

Vapor

pressure

Air

pressure

Pressure – boiling point relationship

Water

Vapor

pressure

Air

pressure

Pressure – boiling point relationship

Water

Vapor

pressure

Air

pressure

Pressure – boiling point relationship

List the above solutions in List the above solutions in order from highest boiling order from highest boiling point to the lowest boiling point to the lowest boiling

point.point.

Aqueous Solution

Molarity Solute

A 2.0 BaCl2

B 2.0 NaNO3

C 1.0 C6H12O6

D 1.0 K2SO3

EXAM

Vaporization vs. Condensation (opposing phase changes)

• Liquid to Gas (evap.)• Open Container• Liquid evaporates

completely = unlimited vaporiz.

• No significant condensation.

Evap.Evap.

Physical Equilibrium of Saturated Solution

Solid = Precipitate

Equilibrium

Rate of Precipitation = Rate of Dissolving

(equal opposing rates)Sat.

Dissolved Particles