Question

A student is instructed to determine the concentration of a solution of CoCl2 based on absorption of light (spectrometric/colorimetric method). The student is provided with a 0.10 M solution of CoCl2 with which to prepare standard solutions with concentrations of 0.020 M, 0.040 M, 0.060 Mand 0.080 M

(a) Describe the procedure for diluting the 0.10 Msolutions to aconcentration of 0.020 M using distilled water, a 100 mL volumetric flask, and a pipet or buret. Include specific amounts where appropriate.
The student takes the 0.10 M solution and determines the percent transmittance and the absorbance at various wavelengths. The two graphs below represent the data.

Answer 1

To dilute a 0.10 M solution of CoCl2 to 0.020 M, measure 20 mL of the stock solution and add to a 100 mL volumetric flask, then fill to the mark with distilled water.

Step-by-step explanation:

To dilute a 0.10 M solution of CoCl2 to 0.020 M, one must use the formula C1V1 = C2V2, where C and V represent concentration and volume respectively. First, calculate the volume of the original solution that contains the total moles of CoCl2 needed for the new concentration:

V1 = (C2 \( \times \) V2) / C1

Next, use the concentration of 0.020 M (C2) and a final volume (V2) of 100 mL to find V1:

V1 = (0.020 M \( \times \) 100 mL) / 0.10 M = 20 mL

Withdraw 20 mL of the 0.10 M CoCl2 stock solution using a pipet or buret, add it to a 100 mL volumetric flask, and then add distilled water to the mark to achieve a final volume of 100 mL, thus diluting the solution to the desired concentration of 0.020 M.