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Offlinezeegos
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Can anyone help me with spectroscopic analysis?
    #6382287 - 12/18/06 06:19 AM (17 years, 2 months ago)

Im doing a spectroscopic analysis of manganate (MgO4-).
Im asked to
"Record the visible spectrum of the provided solution of potassium permanganate of unknown concentration" what does that mean? pink?

and

"deduce the wavelength of radiation lambda max which is at the maximum absorbance value" (i have the maximum absorbanse value)

its just those 2 parts of this report im stuck on, the rest i can do. id really appreciate it if anyone could help me out here  :crazy:


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Offlinehobbitxkillyou
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Registered: 08/11/05
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Re: Can anyone help me with spectroscopic analysis? [Re: zeegos]
    #6382451 - 12/18/06 08:43 AM (17 years, 2 months ago)

If you're still around, here's what I have to say:

To record the visible spectrum of manganate, don't you have to look at a sample of it in a special spectrometer. Then you record down the lines that you see at various wavelengths?

Not sure about the lambda part.


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When the going gets wierd, the wierd turn pro.

-H. S. Thompson


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Offlinezeegos
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Re: Can anyone help me with spectroscopic analysis? [Re: hobbitxkillyou]
    #6382609 - 12/18/06 09:51 AM (17 years, 2 months ago)

the only practical we done was putting the solution in this square tube, placing it in the spectrometer and we got a number displayed on the machine, i think thats an absorbance value.
no worries, i'll try and find out tomorrow. cheers


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Offlinehobbitxkillyou
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Re: Can anyone help me with spectroscopic analysis? [Re: zeegos]
    #6382642 - 12/18/06 10:06 AM (17 years, 2 months ago)

Let me know how it works out. I dabbled in spectroscopic analysis in an Astro lab last year, and am curious.


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When the going gets wierd, the wierd turn pro.

-H. S. Thompson


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Invisiblegogrowgo123
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Registered: 10/18/05
Posts: 249
Re: Can anyone help me with spectroscopic analysis? [Re: hobbitxkillyou]
    #6383644 - 12/18/06 03:45 PM (17 years, 2 months ago)

Spectrophotometric Determination of Manganese
Introduction
The purpose of the conducted experiment was to utilize new equipment, such as a spectrophotometer (an instrument that measures light absorbance in a sample), to obtain data necessary to establish the relationship between the absorption of radiant energy (electromagnetic radiation; with properties of wavelength and frequency) and concentration of a solution of KMnO4 (potassium permanganate). Beer’s Law (log(P / Po) = -abc) was then used to determine the concentration of Manganese in an unknown solution, as the law bridges the relationship between concentration and absorption of a certain substance. To test the conformity of the substance to Beer’s Law, a plot of absorbance vs. concentration of various concentrations of KMnO4 was constructed, and the concentration of potassium permanganate in an unknown solution after being oxidized (2Mn2+ + 5IO4- + 3H2O → 2MnO4- + SIO3- +6H+) was determined.

Experimental
Initially, a digital spectrophotometer was turned on and allowed 15 minutes to warm up. Next, a clean 100 mL volumetric flask was filled with approximately 10 mL of 3.170 x 10-4 M KMnO4 solution using a buret suspended from an iron clamp and stand. It was labeled Standard 1. Next, three clean 50 mL volumetric flasks were filled with 20 mL, 30 mL, and 40 mL of 3.170 x 10-4 M KMnO4 solution using the same method as Standard 1. They were labeled Standard 2, Standard 3, and Standard 4, respectively. Each of the volumetric flasks was then diluted with distilled water until they were filled to their respective volume marks. In order for the spectrophotometer readings to be accurate, a blank (a solution containing everything except what is being analyzed) was created by filling a clean test tube with distilled water. The spectrophotometer was then set to a wavelength of 540 (given wavelength of maximum absorbance) and one by one, each of the four volumetric flasks had their absorbance measured by transferring some solution to a clean test tube. The spectrophotometer was blanked by placing the blank test tube in the instrument and waiting for an absorbance of 0. A test tube containing solution from Standard 1 was then placed in the spectrophotometer and its absorbance recorded. The same procedure was conducted for each of the Standard solutions, using the blank to zero the spectrophotometer in between readings. A test tube filled with undiluted 3.170 x 10-4 M KMnO4 solution (Standard 5) was then placed in the spectrophotometer and its absorbance was recorded.
To determine the concentration of potassium permanganate in an unknown solution, a glass container (unknown 113) containing an unknown concentration was emptied and rinsed with distilled water into a clean 250 mL beaker. 10 mL of nitric acid was then transferred to the beaker using a 10 mL graduated cylinder. Approximately 40 mL of distilled water was added to the solution, as well as 0.50 g potassium periodate (measured with an electronic balance). The beaker was then placed on a hot plate and constantly stirred until the solution had a pink tint. It was then stirred and heated (below boiling) for an additional 10 minutes until the solution was a dark purple color. After cooling, the contents of the beaker was transferred to a 250 mL volumetric flask, and distilled water was added until it was filled to the volume mark. The solution was then mixed before being poured into a clean test tube. After blanking the spectrophotometer, the absorbance of the unknown solution was obtained.

Results
Table I: Standard Solutions 1-4
Standard Solutions Initial buret reading, (mL) Final buret reading, (mL) Volume added, (mL)
Standard 1 1.24 11.29 10.05
Standard 2 11.29 31.32 20.03
Standard 3 2.28 32.38 30.10
Standard 4 4.99 45.08 40.09

Table II: Spectrophotometer Data
Standard Solutions Conc. of KMnO4 (M) Absorbance
Standard 1 3.19 x 10-5 .065
Standard 2 1.27 x 10-4 .318
Standard 3 1.91 x 10-4 .421
Standard 4 2.54 x 10-4 .670
Standard 5 (undiluted) 3.170 x 10-4 .799
Unknown Solution (113) 1.50 x 10-4 .366



Figure 1: Concentration vs. Absorbance



Calculations
To determine the desired properties of the experiment, certain calculations were made using the compiled data to obtain further information. The first calculation made was to determine the exact volume of potassium permanganate released from the buret into the volumetric flasks. It was calculated:
Final buret reading – Initial buret reading = Volume added
Example 1: The precise volume of potassium permanganate in the four standard solutions was calculated:
Standard 1
Final buret reading – Initial buret reading = Volume added
11.29 mL – 1.24 mL = Volume added
Volume added = 10.05 mL
Standard 2
Final buret reading – Initial buret reading = Volume added
31.32 mL – 11.29 mL = Volume added
Volume added = 20.03 mL
Standard 3
Final buret reading – Initial buret reading = Volume added
32.38 mL – 2.28 mL = Volume added
Volume added = 30.10 mL
Standard 4
Final buret reading – Initial buret reading = Volume added
45.08 mL – 4.99 mL = Volume added
Volume added = 40.09 mL
Before absorbance readings were obtained, the exact concentration of potassium permanganate in each of the 4 standard solutions was calculated:
Concentration = M KMnO4 x Vol. Added / Size of container
Example 2: The exact concentration of potassium permanganate in each of the 4 standard solutions was calculated:
Standard 1
Concentration = M KMnO4 x Vol. Added / Size of container
Concentration = (3.170 x 10-4 M)(10.05 mL) / (100 mL)
Concentration = 3.19 x 10-5 M
Standard 2
Concentration = M KMnO4 x Vol. Added / Size of container
Concentration = (3.170 x 10-4 M)(20.03 mL) / (50 mL)
Concentration = 1.27 x 10-4 M
Standard 3
Concentration = M KMnO4 x Vol. Added / Size of container
Concentration = (3.170 x 10-4 M)(30.10 mL) / (50 mL)
Concentration = 1.91 x 10-4 M
Standard 4
Concentration = M KMnO4 x Vol. Added / Size of container
Concentration = (3.170 x 10-4 M)(40.09 mL) / (50 mL)
Concentration =2.54 x 10-4 M
The exact concentration of potassium permanganate in the unknown solution (113) was then calculated using the equation of the line generated by the data obtained of absorbance (y) and concentration (x), y = 2604.8x – 0.0252. Because the absorbance of the unknown solution was obtained with the spectrophotometer, it can be plugged in as the variable y and the equation can be solved:
y = 2604.8x – 0.0252, where y = .366
.366 = 2604.8x – 0.0252
.3912 = 2604.8x
x (concentration) = 1.50 x 10-4 M

Discussion/Conclusions
Data obtained in the experiment proved to be both precise and accurate, as all of the calculations made yielded reasonable data. The standard solutions used yielded sufficient data to create a graphical representation of the absorbance vs. concentration, which in turn was used to determine whether or not the unknown solution conformed to Beer’s Law. After calculating the concentration, the set of x and y coordinates for the unknown concentration were traced on the graph, positioned almost exactly on the generated line (Beer’s Law was successful at showing the relationship between absorbance and concentration).
New equipment and procedures, such as the proper utilization of spectrophotometers and blanks to obtain an accurate absorbance of a solution, was learned. Also, properties such as radiation, energy, wavelength, and frequency were introduced and a foundation in such terms and relations was developed. The ability to calculate concentrations was strengthened, as well as proof of the relationship between such different properties as concentration and absorbance was justified (Beer’s Law).
Although the experiment yielded accurate data, there is always the possibility of error in the procedure, in the form of human and experimental error. Incorrect usage of equipment such as electronic balances, spectrophotometers, and measuring equipment could increase the amount of error in the data. Also, human errors involved with measurements, preparation of necessary solutions, and boiling of certain solutions could render some of the data erroneous.


--------------------
"For everything to be consummated, for me to feel less alone, I had only to wish that there be a large crowd of spectators the day of my execution and that they greet me with cries of hate."


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