Question
In: Chemistry
Write out Beer’s Law and define the variables Sketch an example calibration curve using Beer’s Law....
Write out Beer’s Law and define the variables
Sketch an example calibration curve using Beer’s Law. Be sure to label the axes and identify the variables contained in the slope.
Show/state how you will determine an unknown concentration from a measured absorbance using a calibration curve.
Add the highlighted terms/phrases to your glossary
Solutions
Expert Solution
Beer's Law is an equation that relates the diminishing of light intensity to properties of a material. The law states the concentration of a chemical is directly proportional to the absorbance of a solution. The relation may be used to determine the concentration of an unknown chemical species in a solution using a colorimeter or spectrophotometer. The Beer's Law is very useful in the low solution concentrations which is very difficult to coumpute otherwise.Thus a small amount of sample is only required for the analysis.
It is based on the property that the intensity of a light decreases whie passing through any substance which is absorbed at a particular wavelength and thus inherently dependent on the properties of the substance.
Beer's Law may be written simply as:
A = εcl
where A is absorbance (no units)
ε is the molar absorbtivity with units of L mol-1
cm-1 (also called the extinction coefficient)
l 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
It is easy to prepare a graph using standard solutions to determine the concentration of an unknown specimen. The graphing method assumes a straight-line relationship between absorbance and concentration, which is valid for dilute solutions. For example if we take wish to know the concentration of the unknown solution we can easilty derive so from the absorbance v/s the concentration curve. The slope of the curve is ε multiplied by the path length (l).
The following is the Absorbance v/s the concentration curve drawn for the four standard solutions along with the unknown solution. The concentration can be recorded by the value at the x-axis at that particular value of absorbance.
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