Unit 3 Chp 13 notes B and L.ppt

(1)

Physical Properties

of Solutions

Unit 3

(2)

Classification

Classification

of Matter

(3)

Solute

A solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

Solvent

Salt in salt water Sugar in soda drinks

Carbon dioxide in soda drinks

Water in salt water Water in soda

Solution:

Homogeneous mixture of two or

more substances, consists of two parts:

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Solns and Crystallization

Crystallization: Opposite process to forming

a solution (crystallization and dissolving are

opposite words)

Solute + solvent solution

*There will be an equilibrium we discuss

(5)

Preparing Solns

Solutions are identified based on their

concentrations. Most widely used measure

of concentration is:

(6)

(7)

1. A laboratory procedure requires 0.270 moles of methanol, CH₃OH to be added as a solvent. What volume of 1.50 M

CH₃OH is needed to attain this number of moles?

M = moles of solute liters of solution

3. A student needs to prepare 1 L of a 0.1 M solution of

copper (II) sulfate from solid. How many grams of copper (II) sulfate should the student measure?

Answer: 0.18 L or 180 mL

Answer: 16 g of CuSO₄, add to 1 L H₂O

2. If 80 grams of NaOH is dissolved to make 1 liter of soln, what is the molarity?

(8)

New concentration when mixing

two solutions together?

• When mixing two solutions together must calculate the moles of each solution.

• Volumes of each solution are additive. • Then divide new moles by new volume. Example:

When 70. milliliters of 3.0-molar Na₂CO₃ is added to 30. milliliters of 1.0-molar NaHCO₃ the result ing concentration of Na+ is?

(9)

AP Sample Question

A 0.20 mol sample of MgCl₂(s) and a 0.10 mol sample of KCl(s) are dissolved in water and diluted to 500 mL. What is the concentration of Cl- in the solution?

(10)

AP Sample Question

A 360. mg sample of aspirin, C₉H₈O₄, (molar mass 180. g), is dissolved in enough water to produce 200. mL of solution. What is the molarity of aspirin in a 50. mL sample of this solution?

(11)

AP Sample Question

A 40.0 mL sample of 0.25 M KOH is added to 60.0 mL of 0.15 M Ba(OH)₂. What is the molar

concentration of OH-(aq) in the resulting solution?

(Assume that the volumes are additive.) A. 0.10 M

(12)

Reminder:

Mole fraction – the ratio of moles of solute to total moles of solution

(13)

Example Problem:

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Whether or not solns form?

• Substances with similar

intermolecular

interactions

tend to be miscible or soluble

in one another.

(16)

IMFs in Soln Formation

1. Solute-solute interactions between solute particles must be overcome in order to disperse the solute particles thru the solvent.

2. Solvent-solvent interactions between solvent particles must be overcome to make room for the solute particles in the solvent. 3. Solvent-solute interactions between solvent and solute particles

occur as the particles mix.

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(18)

H₁

H₂

(19)

“

Like Dissolves Like

”

Fats BenzeneBenzene

SteroidsSteroids HexaneHexane

WaxesWaxes TolueneToluene

Polar and ionic solutes dissolve best in polar solvents Nonpolar solutes dissolve best in nonpolar solvents

Salts WaterWater

SugarsSugars Small alcoholsSmall alcohols

Acetic acidAcetic acid

(20)

Miscible or immiscible?

Miscible: Pairs of liquids that mix well (ethanol and water)

Immiscible: pairs of liquids that do not

dissolve in one another (hexane and water)

(21)

Saturation level of Solutions

 A solution that contains the maximum amount of _{A solution that contains the maximum amount of}

solute that may be dissolved under existing

solute that may be dissolved under existing

conditions is

conditions is saturatedsaturated. Solubility . Solubility is a measure is a measure of saturation.

of saturation.

 A solution that contains less solute than a _{A solution that contains less solute than a}

saturated solution under existing conditions is

unsaturated

unsaturated. .

 A solution that contains more dissolved solute _{A solution that contains more dissolved solute}

than a saturated solution under the same

than a saturated solution under the same

conditions is

(22)

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(24)

Solubility Chart (Temperature)

• What do you notice? • What is this graph

showing?

• Anything stand out?

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(26)

Think about it…

A temperature vs. solubility graph of a substance is

constructed based on data.

Why is solubility decreasing with

(27)

Temperature and Solubility

Gas solubility and temperature

solubility usually decreases with

increasing temperature, more KE more molec

(28)

Temperature and Solubility

• As temp of a solvent

increases, the solubility

of solutes increases

– As T increases, KE of molecules increases

resulting in more solute-solvent collisions

• Exception: gases lose

solubility as the

temperature of a solvent

increases.

– Gases escape soln at higher T

Water Molecules

(29)

Solubility Curve

• Shows the max amount of a solute that can dissolve at a given temp.

• The curve indicates type of soln

 _{Above =}_{supersaturated}  _{On =}_saturated

 _{Below =}_unsaturated

• _{The most common curve is} that for water.

 _{What curves increase?}  _solids

(30)

On the basis of the

solubility curves shown

above, the greatest

percentage of which

compound can be

recovered by cooling a

saturated solution of

that compound from

90°C to 30°C?

A. NaCl B. KNO₃ C. K₂SO₄

(31)

How do gases stay dissolved in

solutions then?

(32)

Henry

’

s Law (Pressure)

The concentration of a dissolved gas in a

solution is directly proportional to the pressure of the gas above the solution

kP

C



Applies most accurately for dilute solutions of gases that do not dissociate or react with the

solvent _Yes__CO

2, N2, O2

(33)

Pressure and Solubility of Gases

c = kP cP is the concentration ( is the pressure of the gas over the solutionM) of the dissolved gas k is a constant (mol/L•atm) that depends only on temperature

low P

low c

high P

high c

If pressure of liquid is decreased, gas concentration will

(34)

How can you increase solubility?

• Solids? (Increase KE of particles)

o Heated o Stirred

o Ground into small particles

• Gases? (Try to decrease KE of particles)

(35)

Solubility Trends

1.

1. Temperature:Temperature:

The solubility of MOST solids increases with _{The solubility of MOST solids increases with}

temperature.

temperature.

The solubility of gases decreases with increases in _{The solubility of gases decreases with increases in}

temperature.

temperature. 2.

2. Solute-Solvent InteractionsSolute-Solvent Interactions::

The rate at which solids dissolve increases with _{The rate at which solids dissolve increases with}

increasing surface area of the solid, stirring and temp.

“_“Like Dissolves Like”_{Like Dissolves Like”}

3.

3. Pressure:Pressure:

The solubility of gases increases with the pressure above _{The solubility of gases increases with the pressure above}

the solution.

(36)

AP Sample

Question

Which of the following molecules is least

soluble in water?

(37)

Based on concepts of polarity and hydrogen bonding, which of the following sequences

correctly lists the compounds above in the order of their increasing solubility in water?

(38)

Colligative Properties

Colligative properties are those that depend on the concentration of particles in a

solution, not upon the identity of those properties.

 Vapor Pressure Lowering

 Boiling Point Elevation

 Freezing Point Depression

(39)

Vapor Pressure

Lowering

*Direct relationship with Temperature.

*Increases with decreasing IMFs.

•Defined as the pressure above the liquid at equilibrium.

•Liquids with high vapor pressures evaporate easily. They are called

(40)

Raoult

’

s Law

(41)

Raoult

’

s Law

The presence of a nonvolatile solute lowers the vapor pressure of the solvent. Why? IMFs. (interaction of particles in soln prevents

evaporation and leads to lower vapor pressure)

P

_solution = Observed Vapor pressure of the solution

P

0

solvent = Vapor pressure of the pure solvent



_solvent = Mole fraction of the solvent

P

_solution

=

X

_solvent

P

0

(42)

Examples:

Predict whether each of the following

substances is more likely to dissolve in the

nonpolar solvent carbon tetrachloride, CCl

₄

or

in water:

1.C

₇

H

₁₆

2.Na

₂

SO

₄

3.HCl

(43)

What do the results indicate about the intermolecular interactions of the substances?

A.I₂ and H₂O have similar intermolecular interactions, and I₂ and C₆H₁₄ do not.

B.I₂ and have similar intermolecular interactions, and I₂ and H₂O do not.

(44)

Example:

(45)

Liquid-liquid solutions in which both

components are volatile

both liquids contribute to the pressure

both liquids contribute to the pressure

Modified Raoult's Law:

P0 is the vapor pressure of the pure solvent

P_A and P_B are the partial pressures

P

_TOTAL

=

P

_A

+

P

_B

=

X

_A

P

0

(46)

Pure water - microscopic view. _{1.0 M NaCl solution}_{- microscopic view.}

Note that the ionic solid, NaCl, produces Na+ ions (blue) and Cl- ions (green) when dissolved in water.

Non-Volatile Solutes

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Pure liquid xenon - microscopic view. _{Krypton-xenon solution}_- microscopic view (krypton atoms are shown in blue).

Volatile Solutes

(48)

Extra Information

Suspensions and Colloids

Suspensions and colloids are NOT solutions.

Suspensions: The particles are so large that they settle out of the solvent if not

constantly stirred.

Colloids: The particles intermediate in size

(49)

Types of Colloids

Examples

Examples Dispersing Dispersing

Medium Medium Dispersed Dispersed Substance Substance Colloid Type Colloid Type

Fog, aerosol sprays

Fog, aerosol sprays GasGas LiquidLiquid AerosolAerosol Smoke, airborn germs

Smoke, airborn germs GasGas SolidSolid AerosolAerosol Whipped cream, soap suds

Whipped cream, soap suds LiquidLiquid GasGas FoamFoam Milk, mayonnaise

Milk, mayonnaise LiquidLiquid LiquidLiquid EmulsionEmulsion Butter, cheese

(50)

The Tyndall Effect

Colloids scatter light, making a beam visible.

Solutions do not scatter light.

Which glass

(51)

Separation of a Solutions: 4

main

ways to separate

1. Filtration

2. Distillation

3. Chromatography

4. Electrolysis

*For each one, we will discuss why and for what

purpose each should be used.

Question?

• How would you separate iron fillings from

sand?

(52)

The constituents of the mixture retain their

The constituents of the mixture retain their

identity and may be separated by physical

means.

(53)

1. Filtration

• When trying to

separate a solid from a liquid (solid has

(54)

(55)

Distillation

• When separating two volatile miscible liquids from

each other (Hydrocarbons are a good example) • Make use of differences in vapor pressure (and

IMFs) and boiling points to separate and re-condense back into pure liquid form

• Substance with highest vapor pressure, lowest BP, weakest IMFs condenses first

• _{Simple distillation}_{separate liquids with boiling} point gaps of at least 50 degrees whereas

(56)

Adds Fractionating Column

Fractionating column slows

(57)

A mixture containing equal numbers of moles of ethyl

acetate and butyl acetate was separated using distillation. Based on the diagrams shown above, which of the following identifies the substance that would be initially present in

higher concentration in the distillate and correctly explains why that occurs?

A.Ethyl acetate, because it has fewer C-C bonds to break B.Ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces

(58)

3. Types of Chromatography

• Paper Chromatography

• Thin-layer Chromatography (TLC)

• Column Chromatography

– separates chemical species by taking

advantage of the differential strength of intermolecular interactions between and among the components of the solution (the

(59)

Paper

Chromatography

The components of dyes such as ink may be separated by paper chromatography.

Spot a small sample of mixture on paper. Place in

(60)

Thin Layer Chromatography

(TLC)

• Works similarly to paper

chromatography, usually coated with silica (polar)

• Sometimes visualize under UV light

(61)

How to calculate Rf?

• Distance of spot from

origin divided by distance of solvent front from origin. • Example:

• Notice that:

– the bigger the Rf, the further the spot moved

(62)

Column Chromatography

• used to separate a non-volatile mixture of

chemical substances into its individual

compounds.

• Mixture moves along with mobile phase

through stationary

phase and separates depending on the

(63)

4. Electrolysis

• Use electricity to

separate a compound or molecule into

individual elements. • Only type of

(64)

(65)

Other Separation Techniques

• Separatory funnel to collect two immiscible liquids

• Less dense layer (organic layer) on top of aqueous layer

Recrystallization use temperature or chemical

(66)

A student obtains a liquid sample of green food coloring that is known to contain a mixture of two solid pigments, one blue and one yellow, dissolved in an aqueous solution of ethanol. Which of the following laboratory setups is most appropriate for the student

to use in order to separate and collect a substantial sample of each of the two pigments?

(67)

A student performed a fractional distillation of a mixture of two

straight-chain hydrocarbons, C₇H₁₆ and C₈H₁₈. Using four clean, dry flasks, the student collected the distillate over the volume ranges (A, B, C, and D) shown in the graph above. Over what volume

range should the student collect the distillate of the compound with the stronger intermolecular forces?

A

(68)

AP Practice Problem

Which of the following techniques is most appropriate for the recovery of solid KNO₃ from an aqueous solution of KNO₃?

A.Paper Chromatography B.Filtration

C.Titration

D.Electrolysis

(69)

In Lab TOMORROW

Goal: Separate 3

components out of pain relief mixture:

aspirin

acetaminophen silica gel (binder) *Each one separated by diff technique depending on IMFs

• Lab speaks to 3

separation techniques (can be considered 4)

• Filtration

• Liquid-liquid extraction • Recrystallization then

filtration

(70)

Spectroscopy

• Using light energies on EM spectrum to

analyze samples

(71)

How can light energy be used to

analyze samples?

Differences in absorption or emission of photons in different spectral regions are related to the different types of molecular motion or

electronic transition:

– a. Microwave radiation is associated with transitions in molecular rotational levels, revealing the location of hydrogen in the molecule, bond distances and angles. – b. Infrared radiation is associated with transitions in

molecular vibrational states of chemical bonds, revealing the types and strengths of different bonds in the

molecules.

– c. Ultraviolet/visible radiation is associated with

(72)

(73)

How to categorize light E?

• Wavelength is the distance between 2 consecutive peaks. Units=nm or m

(74)

(75)

Units of wavelength

vary – depends on type

of radiation being

(76)

Photoelectric Effect

The diagram above represents the photoelectric effect for a

(77)

Photoelectric Effect

• When photon interacts w/ e

-

, photon’s E is

transferred to the electron, the photon

disappears and e

-

gains all the photon E.

• A high E photon is able to transfer sufficient E

for the e

-

to break away from the surface of the

metal.

• Usually a threshold value (min E needed)

*PES, solar panels, basis of spectroscopy

(78)

e-c =



C = speed of light, a constant (3.00 x 108 m/s)

 = frequency, in units of hertz (hz, sec-1)

 = wavelength, in meters

Electromagnetic radiation propagates through

space as a wave moving at the speed of light.

(79)

E = h



E

E = Energy, in units of Joules (kg·m = Energy, in units of Joules (kg·m22/s/s22))

h

h = Planck = Planck’’s constant (6.626 x 10s constant (6.626 x 10-34-34 J·s) J·s)



 = frequency, in units of hertz (hz, sec_{= frequency, in units of hertz (hz, sec}-1-1))

The energy (

The energy (E E ) of electromagnetic ) of electromagnetic radiation is directly proportional to

radiation is directly proportional to

the frequency (

the frequency (_{) of the radiation.}_{) of the radiation.}

These packets of “h” are called quanta

(80)

• Each color of light is associated with a range of wavelengths

*ranges are approximate

The Visible Spectrum

Color Wavelengths (nm)

Red 650 - 750

Orange 595 - 650 Yellow 560 - 595

Green 480 - 560

Blue 435 - 480

(81)

 x  = c

 = c/

 = 3.00 x 108 m/s / 6.0 x 104 Hz

 = 5.0 x 103 m

Radio wave

A photon has a frequency of 6.0 x 104_{Hz. What is the}

wavelength (nm). Is this visible light?

 = 5.0 x 1012 nm



(82)

Another Problem… Another Problem…

An FM radio station has a frequency of 93.3 MHz (1 MHz = 106 Hz, or cycles per second). What is the

wavelength of this radiation in meters?

3.22 m

Does this answer make sense? What range of energy does this fall under?

(83)

You Try:

1. What is the wavelength of light with a frequency 5.89 x 1014 Hz (in nm)?

What color of light is this?

Green

2.What is the wavelength of blue light with an energy of 4.55 x 10-19 J?

509 nm

(84)

Apply:

The energy required to break the O – O bond in H₂O₂(g), is 139 kJ mol-1. How much energy is

needed to break one peroxide bond (in Joules)?

2.31 x 10-19 J

Blue light has a wavelength of about 475 nm.

Does this light have enough energy to break the bond?

(85)

…produces all of the colors in a continuous spectrum

Spectroscopic analysis of the visible spectrum…

(86)

…produces a “bright line” spectrum

Atomic Spectroscopy of the hydrogen spectrum…

(87)

Atomic Spectroscopy

: Is an analytical tool used

to study electromagnetic radiation (UV and Vis)

being absorbed or emitted by atoms.

Atoms in the gaseous state can be uniquely

identified by the emission spectrum given off

when the atoms are excited with electrical

(88)

Which of the following is closest to the frequency of the light with photon energy of 3.3×10−19J?

A. 5.0×10

−53

s

−1

B. 5.0×10

−16

s

−1

C. 5.0×10

14

s

−1

(89)

When the metal surface is exposed to light with increasing frequency and energy of photons, electrons first begin to be ejected from the metal when the energy of the photons

is 3.3×10−19_J.

Using the wavelength information provided above, what is the color of the light?

A.Red

(90)

Spectrophotometry

• A spectrophotometer measures amount of light

absorbed (A) or transmitted (T) by a sample.

• Used to determine unknown concentrations of

colored, liquid solutions, absorbance is related to concentration.

• Used widely in pharmaceutical companies.

(91)

Absorbance vs. Transmittance?

• Absorbance: How much

light energy is absorbed by a sample (high

concentration, high

amount of light absorbed) • _{Transmittance:}_How

much light energy passes through the sample (high concentration, low

(92)

How does this process work?

• Sample to be studied? What color is the sample?

• Sometimes, a calibration plot of absorbance vs. wavelength is constructed to pick the correct wavelength setting on machine where absorbance is highest.

• Measure solns of your substance of known concentrations to make a plot (Beer’s Law plot)

(93)

Br₂ (l) + HCOOH (aq) 2Br- _(aq) + 2H+ _(aq) + CO

2 (g)

time

393 nm

light _ Detector

[Br₂]  _Absorption

13.1 • Color calibration plot. What color or wavelength

(94)

How do you determine color?

• Remember that absorption of color is opposite of

reflection of color.

• When choosing a color for absorption on spec, must consider this and always pick the opposite color.

This is where absorption is at its maximum.

• If a solution is purple, what color will it absorb the

most?

Use the Color Wheel

(95)

Color of light and associated wavelengths:

(in case you forgot)

*ranges are approximate

The Visible Spectrum

Color

Wavelengths (nm)

Red

650 - 750

Orange

595 - 650

Yellow

560 - 595

Green

480 - 560

Blue

435 - 480

(96)

Once wavelength (color) is set,

measure known samples:

• Create various known conc of samples

• Measure the absorbance value of each

• Make a plot of Absorbance vs.

(97)

Determine Conc of Unknown

• Once Graph of absorbance vs.

concentration constructed, measure

unknown sample

• Use graph to figure out unknown

concentration of solution or another

method!

Unknown has

absorbance value of 0.8. What is the

concentration?

(98)

Beer-Lambert Law

Often times, just “Beer’s Law”

Plot of absorbance vs. concentration

Allows for determination of unknown concentration

to be found in colored

solutions

A = abc

A = absorbance

a = molar absorptivity (slope) b = path length (cm)

(99)

Understanding Beer’s Law

A = abc

y = mx + b

ab = m = slope

c = x = concentration

(100)

Beers Law Example:

A soln of KMnO₄ has an absorbance of 0.539

when measured at 540 nm in a 1.0 cm cell. What is the concentration of the KMnO₄? Prior to

determining the absorbance for the unknown soln, the following calibration data were collected for the spectrophotometer:

Concentration of KMnO4 Absorbance

(101)

Several ways to solve:

A soln of KMnO₄ has an absorbance of 0.539

when measured at 540 nm in a 1.0 cm cell. What is the concentration of the KMnO₄?

*Use proportions: C / A and set equal *Use graphing calculator

*Use the equation, solve for a first

Concentration of KMnO4 Absorbance

(102)

To determine the number of moles of Cu in the sample of the mixture, the students measured the absorbance of known concentrations of Cu(NO₃)₂(aq) using a

spectrophotometer. A cuvette filled with some of the solution produced from the sample of the mixture was also tested. The data recorded by one student are

shown in the table above. On the basis of the data provided, which of the following is a possible error that the student made?

A.The Cu(NO₃)₂(aq) from the sample of the mixture was not diluted properly.

B.The spectrophotometer was calibrated with tap water instead of distilled water. C.The student labeled the cuvettes incorrectly, reversing the labels on two of the solutions of known concentration.

(103)

Absorbance vs. Transmittance

• A and T are related

• Should be determined by plotting data on

graphs in your lab tomorrow.

• Relationship: TBD by you:

1/T versus [dye] 1 × 10T versus [dye]

logT versus [dye] –logT versus [dye]

(104)

Goals of Lab tomorrow:

• Determine the correct relationship

between A and T (by constructing graphs)

• Determine the unknown concentration of

blue dye in Gatorade.

• Only 1 spec machine, each group given a

time slot to use the machine.

(105)

From Lab Yesterday:

• Fill out data table (pre-lab)

• Include entry for unknown sample

• Convert %T to decimal T

• Construct 4 graphs using Excel and print x2

• 1/T versus [dye]

• 1 × 10T versus [dye] • logT versus [dye] • –logT versus [dye]

• Determine correct relationship between A and T

• Use this equation to convert T to A

•

Construct a new Absorbance. vs Conc graph

https://www.youtube.com/watch?v=VqAa_cmZ7OY