Use volumetric flasks, pipets, and burets, as needed, to dilute the CuSO_4 stock

Question

Use volumetric flasks, pipets, and burets, as needed, to dilute the CuSO_4 stock solution with water to prepare four solutions in which the cu2+concentrations are 0.16 M, 0.080 M, 0.040 M and 0.016 M. Use a pipet to transfer 1.000 mLof each solution to a different test tube. Set up one buret with 0.5 M NH_3 solution and a second buret with water. To each test tube add 4.00 mL of 0.5 M NH_3 and 3.00 mL of distilled water. Mix the solution and measure the spectrum. Based on the dilutions that were used to prepare the solutions, calculate the concentration of Cu^2+ in each of the test tubes. For each of the solutions, examine the spectrum to find the absorbance at the selected wavelength for your assay. Plot the absorance at your selected wavelength as a function of Cu^2+ concentration using an Excel spreadsheet. Excel has built in functions to do a linear least-squares fit to a data set and find the slope and intercept. Recall that the function for a line is y = mx + b where m is the slope and b is the intercept. You will use this fit line determine the concentration of Cu^2+ in solution in equilibrium with the precipitate of cuC_2H_2O_6 (s) so it is important to have a good calibration curve. If one of your points deviates substantially from the line, redo the experiment for that concentration of Cu^2+.

Explanation / Answer

0.20 M, 10 ml

no. of moles = 0.20 X 0.01 =0.002

for 10 ml of 0.16M volume taken was calculated by

M1V1 =M2V2

0.16 X 10 =0.20 X V2

V2 = 8 ml

for 10 ml of 0.080M volume taken was calculated by

M1V1 =M2V2

0.080 X 10 =0.20 X V2

V2 = 4 ml

for 10 ml of 0.040M volume taken was calculated by

M1V1 =M2V2

0.040 X 10 =0.20 X V2

v2 = 2 ml

For step 3 it says to calculate the concentration of Cu2+ after dilutions

for solution 1- 1 ml of 0.16 M solution was taken and to this was added 4 ml of NH3 and 3 ml of distilled water so, total volume = 1 + 4+ 3 = 8 ml

now, the concentration or molarity of Cu2+ ions

0.16 X 1 = M2 X 8

M2 = 0.02 M

for solution 2- 1 ml of 0.08 M solution was taken and to this was added 4 ml of NH3 and 3 ml of distilled water so, total volume = 1 + 4+ 3 = 8 ml

0.08 X 1 = M2 X 8

M2 = 0.01M

for solution 3- 1 ml of 0.04 M solution was taken and to this was added 4 ml of NH3 and 3 ml of distilled water so, total volume = 1 + 4+ 3 = 8 ml

0.04 X 1 = M2 X 8

M2 = 0.005 M

Now,

Step 4 for each of the solutions examine the spectrum to find the absorbance at the selected wavelength.

for this we will take each of the samples. now, we will select a range of wavelengths ( for this we have an option inn spectrophotometer, wherein we will just enter the range of wavelength values). now we will dtermine the absorbance at each of these wavelengths. It is going to be different at each wavelength. The graph between the absorbance and wavelength is known as the absorption spectra.

The wavelength that is showing maximum absorbance is selected

further, different concentrations are used to find the absorbance at this wavelength according to beer Lambert's law

and the curve is made between the absorbance and concentration. this curve is then used to determine the concentration of the unknown samples

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