THE VISIBLE SPECTRA OF SOFT DRINKS.docx
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OBJECTIVES
1. To identify the source of the colour of a soft drink sample based on its
absorption spectrum.
2. To investigate the wavelength of the soft drink sample at its maximum
absorbance.
3. To investigate the concentration of the unknown soft drink based on the
calibration curve.
INTRODUCTION
Spectroscopy is the study of the relationship and interaction between
electromagnetic radiation and matter. Spectroscopic techniques is one of the
technique that is mainly used nowadays. Infrared, visible light, UV and X-ray are
some of the example of electromagnetic radiation and can be used to interact with
matter. The interaction between light and matter to probe chemical structure are one
of chemical analysis that are important in instrumental method. White light is light
that is visible and consist of all colour component of rainbow. When white light hits a
coloured solution, electron in the solution will absorb some of the light, the other will
be transmitted through the solution that results in the light that can be seen by our
eye.
To measure the concentration of dilute solutions, one of the most accurate and
convenient way by using calorimetry or absorption spectrophotometry.
Absorption spectrophotometry is a widely used technique in analytical chemistry
based on the property of molecules to absorb light at specific wavelengths. Based on
the techniques, the amount of light energy a solution absorbs from a beam of light on
a particular wavelength will be measure. The colour of the aqueous solution results
from the absorption of certain wavelengths of white light falling on the solution. The
colour depends on the structure of the solute as water is transparent. The
wavelength of maximum absorption is designated as lambda max and is
characteristic of the material absorbing the light. The DR 2800 will be used in this
experiment instead of spectonic 20. The Hach Lange DR2800 is a visible light
spectrophotometer with pre-programmed Hach Lange test methods, and the ability
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for users to input their own test methods, allowing flexibility(www.edie.net). With the
visible absorption measurement, qualitative analysis to determine the wavelength of
maximum absorbance from the absorption spectrum as well as absorptivity value of
a specific molecule and quantitative analysis to determine the concentration of
unknown solution from standard calibration curve can be done.
APPARATUS
Beaker, Pipet, glass rod, Volumetric flask (25 mL), DR 2800 Hach, cuvette, kimwipe.
MATERIALS
A can of carbonated drinks, distilled water.
Procedure
A. Preparation of “standard “ solutions of soft drink of (known concentration).
1. Soft drink was pour into a beaker and strirred to remove the carbonation.
2. 2.5 mL of soft drinks then pipet and pour into 25 mL volumetric flask and was
diluted up to mark by using distilled water. The volumetric then cover and
shaken and homogeneous solution was form. The solution the poured into
small beaker.
3. Step 2 was repeated by replacing the 2.5 mL soft drinks with 5 mL, 7.5 mL, 10
mL and 12.5 mL of soft drink.
B. Operation of the DR 2800 hach and determination of λmax.
1. The DR 2800 was turned on and warmed up for about 15 minutes.
2. The wavelength was set to 600 nm.
3. The transmittance was adjusted to 0%.
4. Cuvette was obtained, cleaned and rinsed by using distilled water and then
filled until the mark or roughly about ¾ full with blank solution. Kimwipe was
then used to wipe away any impurities on its surface.
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5. 0 absorbance and 100% transmittance was adjusted with the cuvette
containing the blank in the sample holder. The cuvette the removed and set
aside without even emptying the distilled water.
6. Another cuvette were cleaned and rinsed with small amount of the standard
soft drink that the absorbance was going to be measured. Then, the cuvette
were filled with ¾ full with the solution and cleaned by using kimwipe. It then
palced on the sample holder. The absorbance were read and recorded.
7. The cuvette were removed, the top closed and the wavelength were change
to a setting which is 20 nm lower.
8. The 0% transmittance was reset.
9. The cuvette containing distilled water were inserted and was reset to 100?T.
The cuvette the removed,
10.The cuvette containing same soft drink solution in step 6 was inserted.
11.The absorbance were read and recorded in table 1.2.
12.Step 8 until 11 was repeated until 360 nm.. The absorbance were taken at
each 20 nm intervals.
13.By using the graph paper, the absorption spectrum of the soft drink were
plotted and λmax was determined.
C. Preparation of Unknown soft drink sample
The unknown soft drink sample was prepared by the lab assistant by using small
amount of soft drink that we used.
D. Quantitative analysis of the Soft drink solution.
1. The DR 2800 hach was setted to the λmax obtained from part B which is 520
nm.
2. 0 and 100%T was set.
3. The absorbance of each 5 standard soft drink solution was measured and
recorded.
4. The absorbance of the unknown soft drink solution was also measured and
recorded.
E. Cleaning Up
The waste was poured down the drain and all the apparatus used were cleaned.
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RESULTS AND DATA
Wavelength (nm) Absorbance
600 0.166
580 0.270
560 0.507
540 0.662
520 0.747
500 0.691
480 0.572
460 0.391
440 0.307
420 0.285
400 0.275
380 0.247
360 0.275
Table 1.2: The wavelength and absorbance of soft drink.
Λmax = 520 nm
Solutions Concentration ( Volume
%)
Absorbance
1 2.5 0.189
2 5 0.751
3 7.5 1.247
4 10 1.424
5 12.5 1.838
Unknown sample ? 0.153
Table 1.3 : Table of soft drink concentration (volume %) and absorbance.
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CALCULATIONS:
Sample calculation for the concentration of solution 2:
Concentration of unknown:
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QUESTION:
1) Based on Beer’s Law, when the concentration of any analyte increases, how will
the following be affected (increase, decrease, no change)?
a) Absorbance
As A=abc thus, it will also increase
b) Transmittance
As A= - log T, thus it will decrease
2) Why is it important to first obtain the absorption spectrum of the soft drink before
making calibration curve?
The importance of obtaining the absorption spectrum before making the calibration
curve is generally we will select the wavelength of maximum absorbance for a given
sample and use it in our absorbance measurements.
3) What is the purpose of using blank solution?
A blank solution is a solution containing little to no analyte of interest, it is usually
used to calibrate instruments in this case the DR 2800.
4) What colour is being absorb in your soft drink?
Based on the lambda max, the colour absorb by our soft drink is blue-green.
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DISCUSSION
For this experiment, initially for our group we supposly to be determining the
absorbance for blue soft drinks. However, the solution gave an unrealistic results
that turn out to be ununiformly increase and decrease drastically for the reading of
the data. Then we changed the soft drink with another canned carbonated drinks.
Based on the results, the reading of the absorbance were relatively increasing from
360 nm with 0.275 until it reach the peak which is at 520 nm with 0.747. After 520
nm, the absorbance reading relatively decreasing. Based on the data obtained, the
lambda max or the wavelength of the maximum absorbance turn out to be 520 nm.
Based on the table on the introduction of the lab manual, the absorbed colour is at
blue green range. Thus, based on the graph, the origin of the soft drink that we gain
turn out to be blue and green.
For the reading of the soft drink concentration versus absorbance, the reading of the
absorbance keep increase propotionally woth the concentration. As the
concentration of the soft drink increase, so does the absorbance. As the plotted
graph, the concentration os directly propotional to the absorbance.
For the concentration of solution 2, to get the formula of A=£bc is used and to get
the c or the concentration the £ is gain by using the gradient of the graph that turn
out to be 0.1452. Based on the absorbance gain in the data sheet, at 520 nm which
is the maximum absorbance, the absorbance turn out to be 0.747. By substituting all
data inside the formula, then we gain the concentration of solution 2 to be 2.0853 M.
Meanwhile for the concentration of the unknown solution can be detrermine by
drawing line on the absorbance reading which is at 0.153 and thus based on the
plotted graph the concentration of it turn out to be 0.8 M.
During the experiment, a few precaution were taken to minimized any error that
might present on collecting the data. First, before using the pipet we rinse it by using
some of the soft drink to remove any other impurities that might present on the
glassware. when pipet the carbonated drinks, the eye were ensure to be parallel with
the reading needed. Then, when diluting the soft drink, the distilled water were
ensure to be not more or less than the calibration mark of the volumetric flask. Then,
before pouring the solution into a small beaker, the beaker were rinsed first with a
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small amount of the solution. When using the cuvette, the surface of it were wiped
using kimwipe each time before inserting it on the DR 2800.
CONCLUSION
The source of the colour of the souft drink is from blue and green spectrum. The
wavelength of soft drink at maximum absorbance is at 520 nm and the concentarion
of th unknown soft drink turn out to be 0.8 M.
REFERENCES
1. Chemistry 111 LAB: intro to spectrophotomeetrey, june 2005..
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MARA UNIVERSITY OF TECHNOLOGY
FACULTY OF APPLIED SCIENCE
DIPLOMA IN SCIENCE
CHM 260
EXPERIMENT 1
THE VISIBLE SPECTRA OF SOFT DRINKS
NAME : AHMAD ISMI ZULFADLI BIN ISHAK
STUDENT ID : 2010852022
LAB GROUP 1
DATE OF SUBMISSION : 31ST DECEMBER 2012
LAB PARTNER NAME:
A.ZUL RAFIQ SAPILIH
ALEXANDER TAGANDAP
ATIQAH ARIMI
AUDRINA SHIRLEY NORBERT
ABDUL HADI BIN MOHD YUSSOF
LECTURER’S NAME: MISS NOOR EZAWANIEE HJ MOULTON