spectrophotometric analysis prelaboratory assignment 2. In the laboratory exerci

Question

spectrophotometric analysis prelaboratory assignment 2. In the laboratory exercise you will prepare a series of solutions of Cu(NH:)2 from a standard solution of copper (II) nitrate. In one experiment a standard solution was prepared by adding 8.00 mL of 0.09864 M copper (II) nitrate to a 50.00 mL volumetric flask. After the addition of 5.00 mL of 6 MNHs(aq), the solution was diluted to the 50.00 mL mark with deionized water. The ammonia added to the flask is in excess of that required to prepare the copper-ammonia complex. a. Use the molarity and volume of the added copper (ID) nitrate solution to calculate the number of moles of Cu* added to the volumetric flask. This is accomplished, as you recall, by multiplying the molarity of the solution (mol/L) by the volume of the solution (L). b. Use the number of moles of copper (I) in the volumetric flask and the final volume of the flask to calculate the concentration (M) of copper (II) in the filled volumetric flask. (In the presence of excess ammonia all of the copper (II) will be in the form of the copper-ammonia complex ion, Cu(NH2, so the concentration calculated in part b is the concentration of Cu(NH:)) 3. What will you plot on the y-axis and on the x-axis when graphing your data from the spectrophotometric lab? y-axis x-axis -116

Explanation / Answer

Ans. #2a. Number of moles of Cu(NO3)2 = Molarity x Volume of solution in liters

                                                            = 0.09864 M x 0.008 L

                                                            = 0.00078912 mol

#2b. 1 mol Cu(NO3)2 dissociates into 1 mol Cu2+ and 2 moles NO3-.

So, moles of Cu2+ taken = 0.00078912 mol

Now,

            [Cu2+] = Moles of Cu2+ / Volume of solution made upto in liters

                        = 0.00078912 mol / 0.050 L

                        = 0.0157824 mol/ L

                        = 0.0157824 M

Therefore, [Cu2+] in 50.0 mL solution = 0.0157824 M

#3. Y-axis Absorbance          , x-axis concertation

The graph is prepared by plotting absorbance on y-axis and concertation on X-axis.

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