In the Spectrophotometric determination of Co (II) experiment, 96T for a solutio

Question

In the Spectrophotometric determination of Co (II) experiment, 96T for a solution of Co(NOs)2.6H20 was measured at a series of different wavelengths. Use the data given below to determine the Absorbance values at these wavelengths and suggest the best wavelength that should be used for the experiment. (16 points) (A-2-log %T) Wavelength (m)| 470 | 490 | 500 | 510 | 520 540-580- 67.2 68.9662 567 57.6 682 90.7 96T Absorbance Wavelength If 6.5 g of Co(NO3)2-6H20 was dissolved in 250 mL deionized water. to prepare the stock solution, calculate the molarity of the solution. How do you prepare the following diluted solutions using the above stock solution. (i) a) 50 mL of 0.02 M solution

Explanation / Answer

5. Spectrophotometric determination of Co(II)

Absorbance = 2 - log(%T)

at 470 nm,

absorbance = 2 - log(67.2) = 0.173

at 490 nm,

absorbance = 2 - log(68.9) = 0.162

at 500 nm,

absorbance = 2 - log(66.2) = 0.179

at 510 nm,

absorbance = 2 - log(56.7) = 0.246

at 520 nm,

absorbance = 2 - log(57.6) = 0.240

at 540 nm,

absorbance = 2 - log(68.2) = 0.166

at 580 nm,

absorbance = 2 - log(90.7) = 0.042

the best wavelength would be one at which we get maximum absorbance = 510 nm

(i). moles of Co(NO3)2.6H2O = grams/molar mass

                                                = 6.5 g/291.035 g/mol = 0.0223 mol

molarity = moles/L of solution = 0.0223 mol/0.250 L = 0.09 M

(ii) to prepare dilute solution from Co(II) stock solution

a. 50 ml of 0.02 M

using,

V1 = C2V2/C1

C1 = 0.09 M

C2 = 0.02 M

V2 = 50 ml

V1 = volume of stock solution

so,

V1 = 0.02 M x 50 ml/0.09 M = 11.11 ml

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