59 Problems of solutions, containing cobalt (II) chloride were prepared and thei

Question

59 Problems of solutions, containing cobalt (II) chloride were prepared and their corresponding to each solution. Molar mass of Co is 58.933 g/mol. 1. A seri absorbance measured at 515 n m. Using PhET Simulation find the absorbance Absorbance Concentration (g/L) 0005 7.18 5.71 6 3.53 1.41 0.884 O.ou 0.03 Ooo Plot a calibration line Absorbance versus Concentration. From the graph the specific absorptivity determin 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 For the absorbance of the cobalt solution from the flask a value of 0.55 was 2. mL volumetric flask and then diluted to the mark. obtained. What is the percentage of cobalt in the unknown compound?

Explanation / Answer

Q1. The plot of absorbance vs concentration gave the equation of best fit line as y = 0.0066x + 0.0035

where y = absorbance, x = concentration (g/L), slope = 0.0066 = specific absorbtivity

Q2. given : absorbance = 0.55

From the equation of best fit line, x = (y - 0.0035) / 0.0066

or x = (0.55 - 0.0035) / 0.0066

or x = 82.8 g/L

mass of cobalt in 100 mL solution = concentration x volume (L)

mass of cobalt in 100 mL solution = (82.8 g/L) x (100 mL) x (1 L / 1000 mL)

mass of cobalt in 100 mL solution = 8.28 g

this value is very high than mass of sample (1.975 g) which is not possible as all cobalt comes from this sample. This means the data is incorrect

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