A series of solutions, containing cobalt (II) ion were prepared and their absorb
ID: 966277 • Letter: A
Question
A series of solutions, containing cobalt (II) ion were prepared and their absorbance measured at 515 nm. The following values were obtained: Plot a calibration line Absorbance versus Concentration. From the graph determine the specific absorptivity. Using the data you obtained from the graph in the previous problem determine the concentration of cobalt (II) in 1.975 g sample of a substance, which was dissolved in water in a 100 ml volumetric flask and then diluted to the mark. For the absorbance of the cobalt solution from the flask a value of 0.405 was obtained. What is the percentage of cobalt in the unknown compound?Explanation / Answer
the plot of Concentration ( g/100ml) Vs absorbance is shown plotted below.
The equation connecting concentration (C) and absorbance (A) is given by
A= 0.927C
when A= 0.405
C= 0.405/0.927=0.436 g/100ml
The sample having mass of 1.975gm is dissolved in 100ml = mass of sample/100ml =1.975/100ml
percentage of cobalt in the sample= 100*0.436/1.975=22.08%
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