Experiment 1 Session 2 Electrons and Solution Color

 Two hours of lab 8 - 10 am or 11 am - 1 pm or 2 - 4 pm  One hour of discussion 10 - 11 am or 1 - 2 pm or 4 - 5 pm

LAB GOALS E1 Session 2  Complete E 1 (Parts 1 - 4 and 5 B).  Complete preparation for discussion.  Complete team report and give to GSI or turn in within 48 hours -- see deadlines on page 221.

Solution Color  Solution color relates to metal ion electron configuration.  The presence or absence of solution color is predictable based on the position of the metal ion’s element in the periodic table.

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Properties versus Periodic Table Position Pre-transition. Transition

Post-transition

1A 1

VIIIA 2

H

He

1 s1

IIA 4

2s1 11

2s2 12

3s1 19

3s2 20

4s1 37

4s2 38

10 1 10 2 3d1 4 s2 3d2 4 s2 3d3 4 s2 3d5 4 s1 3d5 4 s2 3d6 4 s2 3d7 4 s2 3d8 4 s2 3d 4 s 3d 4 s 4 s2 4 p14 s2 4 p2 4 s2 4 p3 4 s2 4 p4 4 s2 4 p5 4 s2 4 p6

5s1 55

5s2 56

10 1 10 2 4d1 5 s2 4d2 5 s2 4d3 5 s2 4d5 5 s1 4d5 5 s2 4d7 5 s1 4d8 5 s1 4d1 0 4d 5 s 4d 5 s 5 s2 5 p1 5 s2 5 p2 5 s2 5 p3 5 s2 5 p4 5 s2 5 p5 5 s2 5 p6

6s1 87

6s2 88

7s1

7s2

5d1 6 s2 5d2 6 s2 5d3 6 s2 5d4 6 s2 5d5 6 s2 5d6 6 s2 5d7 6 s2 5d9 6 s1 5d 6 s 5d 6 s 6 s2 6 p1 6 s2 6 p2 6 s2 6 p3 6 s2 6 p4 6 s2 6 p5 6 s2 6 p6 89 1 0 4 1 0 5 1 0 6 1 0 7 1 0 8 1 0 9 + Element synthesized, Ac# + + + + + + but no official name assigned 6d1 7 s2 6d2 7 s2 6d3 7 s2 6d4 7 s2 6d5 7 s2 6d6 7 s2 6d7 7 s2

Li

Be

Na K

Fr

B

Sr

Ba Ra

IVA 6

C

VA 7

N

VIA 8

O

F

Ne

2 s 2 2 p1 2 s 2 2 p2 2 s 2 2 p3 2 s 2 2 p4 2 s 2 2 p5 2 s 2 2 p6

13

Mg Ca

Rb Cs

IIIA 5

VIIA 1 s2 9 10

3

Al IIIB 21

Sc 39

Y

57

IVB 22

Ti 40

Zr 72

La * Hf

VB

VIB

VIIB VIIIB

⇔ VIIIB

IB

IIB

23

24

25

27

29

30

V

41

Nb 73

Ta

Cr 42

Mn Fe 43

Mo Tc 74

W

26

75

Re

44

Ru 76

Os

Co 45

Rh 77

Ir

28

Ni 46

Pd 78

Pt

Cu

10

Ga 49

Cd

79

Au

31

48

Ag

In

80 1

Hg 10

Si

15

P

16

S

17

Cl

18

Ar

3 s 2 3 p1 3 s 2 3 p2 3 s 2 3 p3 3 s 2 3 p4 3 s 2 3 p5 3 s 2 3 p6

Zn

47

14

81 2

Tl

32

Ge 50

Sn 82

Pb

33

As 51

Sb 83

Bi

34

Se 52

Te 84

Po

35

Br 53

I

85

At

36

Kr 54

Xe 86

Rn

Energy and Electrons and Color  Electrons can move to higher energy levels if available energy (heat or light) = exactly that needed for an electron energy level transition.

 If electrons move from a higher to a lower energy level, the difference in energy will be released.

DEMO

Wavelength Color  Light is a form of energy and may cause electron energy level transitions or break bonds etc.

λ 400 Violet - Blue - Green - Yellow - Orange - Red λ 800 Shorter wavelength Higher frequency Higher quantum energy

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Wavelength and Energy

Balloon containing H 2 and Cl 2

Light source →

DEMO 1. Expose the balloon to red light. 2. Expose the balloon to blue light.

Color and Light Interaction  The identity and color of a solution can be determined from its absorption (or transmission) spectrum.

 Color results from the selective absorption and transmission of visible wavelengths.

DEMO

Beer-Lambert Law Aλ=εcl Absorbance at a given λ = (abs coefficient) (concentration) (path length)

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Beer-Lambert Law 1.2

Absorbance

1 0.8 0.6 0.4 0.2 0

0

1

2

3

4

5

6

Concentration (mM)

7

8

 Absorbance is proportional to concentration at a given wavelength (λ ).

Concentration and Light Absorbance

Calibration Curve  The Beer-Lambert law becomes less and less accurate as solution concentration increase  Never extrapolate a linear line of a calibration curve beyond tested absorbance- concentration values.

Concentration and Light Absorbance

 A change in sample concentration will alter the absorbance readings proportionately across all wavelengths of an absorption spectrum; the pattern will not alter.

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Beer-Lambert Law  Path length and light absorbance are directly proportional at a fixed wavelength and concentration.

DEMO

Error caution: Spectrophotometers/sample holders have different path lengths! Don’t change spectrophotometers in the middle of an analysis!

Absorbance and Path Length  The path length (and λ) must be fixed when plotting a calibration curve or absorbance readings will be in error. DEMO

Absorbance

2.5 2.0 1.5

= 1/2path length

1.0 0.5 0.0 0.0 0.1 0.2 0.3 0.4 0.5 [Plastocyanin], mM

Beer-Lambert Law Aλ=εcl Absorbance at a given λ = (abs coefficient) (concentration) (path length)

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Beer-Lambert Law Spectrum of 0.10 M _________

Red

Yellow

Orange

Green

Blue

Violet

Absorbance

Absorbance differences across wavelengths are due to? 1. Differences in the absorptivity coefficient ( ε ) 2. Differences in the concentration of the sample. 3. Differences in the path length of the sample holder. 4. All the above.

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 400 450 500 550 600 650 700 Wavelength λ (nm)

Which statement below is correct? 1. Color of Abs λ max = blue-purple. 2. The sample is green. 3. E is greater at λ 500 than at λ 400.

Part 4. Concentration and Light Absorbance  Prepare a calibration curve graph (Abs vs. concentration plot) at a team chosen and fixed λ.  Use known concentrations of the assigned sample of unknown concentration 1.2

Absorbance

1 0.8 0.6 0.4 0.2 0

0

1

2

3

4

5

6

Concentration (mM)

7

8

6

Preparation of Calibration Curve

1. Prepare a set of solutions of known concentration (e.g., 0.08 M, 0.06 M, 0.04 M, 0.02M) from your assigned 0.10 M solution. 2. Choose an appropriate wavelength for your calibration curve graph. 3. Plot a calibration curve graph. 4. Determine the slope (εl) of the calibration line.

Preparation of Solutions #M = Molarity of Solution

# = mmoles per mL of solution or moles per 1000 mL of solution

1. Preparation of calibration curve solutions. Reminder:

M1V1 = M2V2 If V= milliliters: MxV=

mmol x mL = mmol mL

Example: 20.0 mL of a 0.07 M solution contains 1.4 mmol.

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Q. What volume of 0.10 M Ni(NO3)2 and water do you use to prepare 20.0 mL of 0.07 M Ni(NO3)2?

M1V1

=

M2V2

___ mL 0.10 M Ni(NO3)2 + ___ mL H2O ?

2. Wavelength Choice for Calibration Curve?

 The wavelength of maximum absorbance is typically chosen so that changes in absorbance with changes in concentration are maximum and the calibration graph line has a maximum slope.

Wavelength Choice for Calibration Curve? 2.5 Absorbance

Absorbance

1.20 0.80 0.40

2.0 1.5 1.0 0.5

0.00 250 350 450 550 650 Wavelength (nm)

Absorption Spectrum: 0.16 mM Plastocyanin

750

0.0 0.0 0.1 0.2 0.3 0.4 0.5 [Plastocyanin], mM

Calibration curve at: 600nm • • 550nm?



8

Red

Yellow

Orange

Blue

0.8 0.7

1

0.6

0.8

Absorption

Absorption

1.2

Green

Purple

Wavelength of Calibration Graph?(F 05 exam)

0.6 0.4

0.5 0.4 0.3 0.2

0.2

0.1

0 400

0 450

500

550

600

650

700

0

0.1

λ (nm)

0.2 +

0.3

0.4

0.5

[M ] (Molar)

M+

Q. A 0.4M solution of has the absorption spectrum on the left. Circle the wavelength of its calibration graph: 425 500 550 600 650

3. Determine the slope of the calibration curve

Slope in Abs/ M?

Part 5B. What is the sample concentration?

Absorbance

2.5 2.0 1.5 1.0 0.5

Calibration Curve λ 600

0.0 0.0 0.1 0.2 0.3 0.4 0.5 [Plastocyanin], mM

Q. A sample of plastocyanin has Abs = 0.65 at λ 600 . What is its concentration (mM)?

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Part 5B. What is the sample concentration?

Absorbance

2.5 2.0 1.5 1.0 0.5

Calibration Curve λ 600

0.0 0.0 0.1 0.2 0.3 0.4 0.5 [Plastocyanin], mM

“Eyeball” the graph only to determine an approximate concentration  Use the Beer-Lambert law to determine an exact concentration.

Absorbance

2.5 2.0 1.5 1.0 0.5 0.0 0.0 0.1 0.2 0.3 0.4 0.5 [Plastocyanin], mM

 The slope of the calibration graph line is = εl in the Beer-

Lambert equation A λ = εlc  Substitute the slope value in the Beer-Lambert equation to solve for the unknown concentration.

Absorbance

2.5 2.0 1.5 1.0

Calibration Curve λ 600

0.5 0.0 0.0 0.1 0.2 0.3 0.4 0.5 [Plastocyanin], mM

Q. A sample of plastocyanin has Abs = 0.65 at λ 600. What is its concentration (mM)?

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Questions? Contact [email protected]

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