A plot is a calibration curve of absorption plotted as a function of concentrati

Question

A plot is a calibration curve of absorption plotted as a function of concentration. An absorption spectrum must be acquired first to determine the wavelength of maximum absorbance, lambda_max, for the compound being studied. All absorbances are acquired at this wavelength setting because the signal is the strongest and least likely to be obscured by instrument fluctuations. To create the plot, the absorbances of at least five solutions of known concentration are measured. A graph of absorbance versus concentration is constructed and a best fit straight line is drawn through the data points. Then the absorbance of a solution of unknown concentration is measured and its concentration is determined by comparison to the Beer's Law Plot. A = belong CI (y = mx+b) then, C= A/I belong A = absorbance (no units) belong = molar absorptivity coefficient (units = L/mol-cm) C = concentration of absorbing species (units = mol/L) I = path length (units = cm) Absorbance readings are taken for five standard ferrous (II) thiocyanate solutions and a Beer's Law Plot is created with the equation: y = 3.2975x + 0.0021. A ferrous (II) thiocyanate solution of unknown concentration is found to have an absorbance of 0.31. The cuvette was 1cm wide. What is the unknown concentration according to the above data? 0.081 0.073 0.126 0.094 0.931

Explanation / Answer

Standerd curve is plotted with Absorbance values in the Y axis and concentration values in the x axis. A linear plot will be observed. The linear equation is : y = 3.2975x + 0.0021

unknown solution has a absorbance of 0.31. Put y = 0.31 in the above equation and find the value of x.

y = 3.2975x + 0.0021

or, 0.31 = 3.2975x + 0.0021

or, x = (0.31-0.0021)/3.2975 = 0.0933

Correct answer : 0.094

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