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Experiment Eight: Spectrophotometric Analysis

Name: Mark Aw

gtID: 902510497 must be submitted via the T-Square report submi

Section: a1

Email: m/lUnknown No: 47 co 0.19

cr 0.05

wavelength 1= 399.3

wavelength 2= 503.9

A1 A2 A1-A2 A1/A2

Blank 0 0 0 0 concentration

Co g/L

1) 0.047 0.184 -0.137 0.255 2.216

2) 0.008 0.366 -0.358 0.022 4.432

3) 0.052 0.567 -0.515 0.092 6.6474) 0.115 0.750 -0.635 0.153 8.863

11.079

Cr g/L

1) 0.170 0.076 0.094 2.237 0.520

2) 0.310 0.127 0.183 2.441 1.040

3) 0.430 0.183 0.247 2.350 1.560

4) 0.665 0.254 0.411 2.618 2.080

2.600

unknown mixture: %Co

1) 0.3620 0.2720 0.090 1.3309 43.65

2) 0.3700 0.2810 0.089 1.3167 45.563) 0.3660 0.2710 0.095 1.3506 42.87

1) 0.3750 0.2800 0.095 1.3393 44.66

2) 0.3770 0.2820 0.095 1.3369 45.06

3) 0.3620 0.2750 0.087 1.3164 44.59

Mean 0.3687 0.2768 0.0918 1.3318 44.40

Standard Dev. 0.0064 0.0048 0.0036 0.0134 0.98

Points

Final Grade

NOTE: This experimental report, including an ab

markaw91@gatech.edu

mailto:markaw91@gatech.edumailto:markaw91@gatech.edu

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Plot Absorbance vs Concentration graphs for both Co and Cr on ONE graph!

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

f(x) = 0.01x + 0.01

f(x) = 0.04x - 0.01f(x) = 0.02x + 0.01

f(x) = 0x + 0

Absorbance vs. Concentration

Column E

LinearRegression forColumn E

Column F

LinearRegression for

Column F

Column E

LinearRegression forColumn E

Column F

LinearRegression for

Column F

Concentration (M)

Ab

sor

banc

e

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f A Complex Mixture

questions

sion link within 72 hours of completion.

g/mol 58.93

52

5ml

10ml

15ml20ml

5ml

10ml

15ml

20ml

%Cr mass (g) Co concen Cr concent

42.64 13.71 0.5 g 8.73 8.53

43.54 10.90 0.5 g 9.11 8.7143.17 13.95 0.5 g 8.57 8.63

44.20 11.14 0.5 g 8.93 8.84

44.43 10.51 0.5 g 9.01 8.89

42.60 12.81 0.5 g 8.92 8.52

43.43 12.17 0.5008

0.77 1.51 0.0005

absorptivity in units of L/g-cm

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TABLE OF RESULTS:

Co= 8.88 g/L

Cr= 8.69 g/L

44.40 % Co in sample

43.43 % Cr in sample

12.17 % of sample that was neither Co or Cr

Note: This spreadsheet is only meant to be a guide to the

calculations required for the experiment. If you noticethat the experimental procedure calls for other

calculations, you are still required to perform those.

Note: All calculations not inherent to this spreadsheet

must have their formula and calculations shown.

A1

aCo 1

bcCo

aCr 1

b=c

Cr

0=aCr 2

b

A

1

aCo 1

bcCo

aCr 1 b

a

Co 2

bcCo

A2

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Abstract

TA Comments:

Points:

NOTE: Your abstract should be clear, concise and well thought out.It should never contain first person, and should always be in a past,passive voice. An abstract should briefly describe what the goal(s) ofthe experiment were, how you attained those goals, numericalresult(s) of the experiment, and concluding statement.

The objective of the lab is to obtain a representative sample of a dispersible solid and determine thof two metals were obtained and pipetted into 25 ml volumetric flasks with varying molarities andto begin finding the absorbance of the different concentrations for each of the two metals to createabsorbance was greatest. The absorbtivity was then found from the slope, giving a value for eachinto a formula to solve for the percent composition. The percent composition of unknown 47 was43.43% +/- 0.77%. The experiment was successful and fairly accurate due to a homogenous mixtur

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e composition of the sample by visible spectrophotometry. Stock solutionsdiluted with DI water. Logger Pro was then used along with a spectrometern absorbance vs concentration graph using the two wavelengths where theetal at each absorbance wavelength. The observed data can then be pluggedetermined to be 44.4% +/- 0.8% Co and the %Cr was determined to bee and low standard deviation.

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Questions: (Include these in the spreadsheet in the spac1

TA Comments:

Points:

2

TA Comments:

Points:

3

TA Comments:

Points:

4

The instrument was double beam because the solution contains more than one chromophore that enthe sum of the absorbances of each component. The two beams are used to calibrate the blank and tthe absorbancies of the metal complexes

The precision of the result was precise, with a 0.98% standard deviation for %Co and a 0.77% standa

devaition for %Cr. Sources of inaccuracies include not making the mixture homogenous enough to enmetal ratios throughout and losing some mass while quantitatively transfering and making the homogmixture. A machine can be used to make the homogenization process efficient and perfect. The transsamples using DI can then be used to quantitatively transfer the crystals.

The weight percent of each three samples vary a bit due to the fact that the homogenous mixture wasperfectly homogenous and the fact that samples were lost while quantitatively transfering the crystals.problem was the fact that the wavelengths seemed to vary when trying to see if the absorbance meawas repeatable. It was repeatable, but the wavelengths would vary by 50-60 nm.

Different cuvettes would bring in more room for systematic and random errors. Each cuvette may resudifferent blank calibration and each cuvette may not be perfectly the same length b. Each cuvette maskew their respective data in a certain way and to minimize the error one cuvette should be used. Thewere washed with DI then prewashed a few times with the sample before measuring the absorbancy.

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TA Comments:

Points:

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s up beingo measure

rd

sure equalnouser of

notAnotherurement

lt in athencuvettes

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Concentration Absorbance at 399.3 nm Absorbance at 503.9 nm

Conc Abs-399.3 Abs-503.9mol/L

10.94 0.05 0.18

21.89 0.01 0.37

32.83 0.05 0.57

43.77 0.12 0.75

54.71 0.1 0.9

Concentration Absorbance at 399.3 nm Absorbance at 503.9 nm

Conc Abs-399.3 Abs-503.9

mol/L

4 0.17 0.08

8 0.31 0.13

12 0.43 0.18

16.01 0.66 0.25

20.01 0.8 0.31

0 10 20 30 40 500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.80.9

1

f(x) = 0.01x + 0.01

f(x) = 0.04x - 0.01f(x) = 0.02x + 0.01

f(x) = 0x + 0

Absorbance vs. Concentration

Column E

LinearRegression forColumn E

Column F

LinearRegression forColumn F

Column E

LinearRegression fColumn E

Column F

LinearRegression fColumn F

Concentration (M)

Ab

sor

banc

e

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comcem

10.94

21.89

32.83

43.77

54.71

4

8

12

16.01

20.01

0

or

or