Unknown 0.05...

Question

    Unknown
    0.05
    0.02
    0.01


    0.620
    1.160
    0.224
    0.469
    628.0
    blue
    0.330
    0.259
    0.093
    0.045
    489.0
    Red

t
l
32
EXPERIMENT 3: UV-Visible spectroscopy
POTENTIAL HAZARDS
Salety glasses must be worn at oll times in the loboratory'
INTRODUCTTON
The Visible spectrum (about 400 nm to 800 nm) of four separate
samples of food colouring will be
ecorded along with the visible spectrum on one unknown'
Sample Preparation is the most time and
patienceconsumingpartofthisexperimentandinvolvesaccuratepipetting.
NEVERPIPETTESILUTI1NSMYM1UTH.ALWAY;L)SETHEPIPETTEFILLERPRoVIDED,
LEARNING OUTCOMES
. Experience using a UV-Visible spectrophotometer, and unclerstand how this instrument
can
eusedtodetermineconcentrationsofchemicalspecies(labexercise)'
. Learn how to make a dilution series of standards'
. construct a cali
ation curve and understand how these can be used to calculate and
determine concentrations of unknown solutions in analytical
applications (lab exercise' data
handling and calculations)'
EXPERIMENTAL
1.. Students should work in pairs in this experiment'
z.selecttwosamplesofhouseholdfoodcolouringsaresuppliedfortheknownsamples'The
concentration of the dye in the stock solutions is 1 mM'
3.Make3standardsolutionsforeachdyeyouselected.Theconcentrationsoftheseshouldbe
0.01 mM,0.02 mM and 0'05 mM'
4,Takethe0.02mMstandardandmeasurethespectrumtodeterminethewavelengththat
givesthemaximumabso
ance.settheinstrumenttothiswavelength.
5. Record the abso
ance of a blank and the 3 standards'
6.Takeasampleoftheunknownsc|utionandmeasureitsabso
ance.Youwilluseyou
cali
ation information to determine the concentration
of the dye in the 'unknown' solution'
7. Repeat the procedure for the other dye you selected'
CALCUTATIONS
Draw a cali
ation curve for each colouring and plot abso
ance
on the ordinate (y-axis)' and
concentration of dye on the abscissa (x-axis). uie lre same set of
axes for each plot' You should use
EXCEL for this task and use the regression function to find
the 'best-fit' equation for your cali
ation
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David · Accepted Answer

UV- VISIBLE SPECTROMETRIC ANALYSIS OF SOME FOOD COLOURS 
ABSTRACT: Food colours are added to increase the appearance and flavour of a 
food. It must be used only in prescribed concentration. Therefore frequent analysis 
helps to determine the concentration of the food colours such that it will be kept 
within the safe rage. UV Visible spectrometer can be used to study this 
INTRODUCTION: 
UV-VISIBLE Spectrometer can be used to find the absorbance of a particular 
wave length of light. This apparatus usually works in the range of visible Light and 
also in the UV region. It is based on the Beer- Lambert’s Law. It says that the 
absorbance of light by a solution is directly proportional to the concentration  and 
length of the container in whcih the solution is taken. 
The absorbance of two separate sample of food colours are subjected to the 
present study. Standard solutions of the compounds are prepared by dilution and 
absorbance was noted using a UV-VIS Spectrophotometer using an appropriate 
wave length filter. This helps in  the preparation of the calibration curve. Using the 
calibration curve, unknown concentration can be found out. 
EXPERIMENTAL SECTION 
1) Preparation of Standard Solutions 
Standard dye solutions were prepared  from the stock solution of the dye 
which is of  known concentration. The concentration of the stock solution is 1 mM. 
Using quantitative dilution principle, different known standard solutions were 
prepared in a standard volumetric flask. The concentration of the standard solutions 
was 0.01 mM, 0.02 mM and 0.05 mM. 
2) Measurement of absorbance 
The second step is to find which wavelength the dye absorbs maximum. The 
0.02 mM solution which is already prepared was taken in the container and 
absorbance is measured using different wavelength filters.

Unknown 0.05 0.02 0.01 0.620 1.160 0.224 0.469 628.0 blue 0.330 0.259 0.093 0.045 489.0 Red t l 32 EXPERIMENT 3: UV-Visible spectroscopy POTENTIAL HAZARDS Salety glasses must be worn at oll times in...

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