spectrophotometric determination of fd&c red dye #40 in kool-aid POST-EXPERIMENT
ID: 1025410 • Letter: S
Question
spectrophotometric determination of fd&c red dye #40 in kool-aid POST-EXPERIMENT DISCUSSION QUESTIONS The class will discuss these questions during the last hour of lab class. Be prepared to participate in the class discussion. A list of these discussion questions will be provided in lab, so you don't need to write them down at this time. I. We had blue dye, red dye and yellow dye in the samples. How could we focus on just the red dye's concentration? b. a. Was significant error introduced by using the method we used to analyze the red dye? 2. What is the wavelength setting on the spectrophotometer for this experiment? Why does the instrument need to be set at this wavelength? 3. Why did we need to prepare and analyze all those standards? What is Beer's Law? Was Beer's Law used in this experiment? If so, how? If so, why could we use it? 5. Of what exactly are we measuring the absorbance?Explanation / Answer
1. Prepare known concentration of given dye and prepare blank with water.
Scan the absorbance with blank and calibrate the instrument. Record the absorbance using red dye solution from 400-700nm.
Note down lambda maximum for red dye.
Prepapre several dilution of red dye and measure absorbance at maximax wavelength what you have noted in the above step.
2. Setting of maximum wavelength in the instrument means at that particular wavelength absorbance for given sample will be maximum.
3. Standard solutions will help you to calculate unknown concentration
5. Absorbance will give you the amount of dye present in the solution. See below for details
4. Beer law states that concentration of a samplsais directly proportional to the absorbance. A = bc.
Yes here we will use above law.
Beer's Law may be written simply as:
A = bc
where A is absorbance (no units)
is the molar absorbtivity with units of L mol-1 cm-1 (formerly called the extinction coefficient)
b is the path length of the sample, usually expressed in cm
c is the concentration of the compound in solution, expressed in mol L-1
Calculating the absorbance of a sample using the equation depends on two assumptions:
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