Material and Equipment:
0.00200 M KNCS,
0.00200 M Fe(NO3)3 0.200 M Fe(NO3)3, 0.10 M HNO3,
5 Cuvettes,
1 colorimeter
4 100ml beakers,
5 Test tubes
2 250ml Graduated cylinder.
The first step is to calibrate the colorimeter with0.20 M Fe(NO3)3and set the absorbance at 470 nm since it is known to keep an acidic solution throughout the entirety of the experiment. It was important to do this right at the beginning of the lab since the zeroed value of the acid was the calibration number for all of the other solutions. A total of seven solutions with different dilutions were used throughout the lab to conduct the equilibrium constant. The first step was adding 5 mL of 0.200 M Fe(NO3)3to each of the 5 test tubes. Once this was done, 0.00200 M NCS was added to the test tubes, each receiving a different amount; test tube one received 1 mL NCS-and with each test tube the amount of NCS-would increase by 1 mL, test tube 5 received 5 mL of NCS. . The next step was adding HNO3 to each test tube in different volumes; Test tube one received 10 mL of HNO3 and with each test tube the amount of HNO3 decreased by 1 mL, test tube five had no HNO3 added to it. The addition of these solutions formed five test tubes of different dilutions, but of equal volume, 10 mL each. After all of the previous trials had been completed the final step was to take each test tube and pour it into a different cuvette and measure the absorbance for each. Once the initial concentration was calculated of Fe3+, NCS and FeNCS2+ in molarity. The absorbency values were recorded and used to calculate the formation constant, K f The reference table containing volumes used in each solution is provided below