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## experiment 34

by: Alia Notetaker

8

1

4

# experiment 34 PSTAT 5A

Alia Notetaker

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tester
COURSE
Statistics 5A
PROF.
dr. Jim
TYPE
Class Notes
PAGES
4
WORDS
CONCEPTS
Chem, Math
KARMA
25 ?

## Popular in Math

This 4 page Class Notes was uploaded by Alia Notetaker on Friday August 19, 2016. The Class Notes belongs to PSTAT 5A at College of William and Mary taught by dr. Jim in Fall 2016. Since its upload, it has received 8 views. For similar materials see Statistics 5A in Math at College of William and Mary.

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Date Created: 08/19/16
Purpose: The purpose of this experiment was to create various solutions to be placed into a  spectrophotometer, to graph the data we retrieved and then to determine the equilibrium constant for a soluble equilibrium. Through the execution of this experiment we were hoping to  understand the role that temperature and concentration played on the equilibrium of the reaction.  Theory: In this experiment, the concepts that we are investigating are dealing with the  equilibrium of solutions. In this experiment we will be gathering data to determine the Kc, the  equilibrium constant for the solutions we create. Kc = [FeNCSN2+] / [Fe3+]*[SCN­] Procedure: In this experiment, there were two parts; one where we were creating the solution  and the other where we run the solutions in Micro Lab system.  In the first part, there were two  sub groups, A and B. In A, we prepared 5 solutions that contained various concentrations of  NaSCN that were combined with 10 ml of FE(NO3)3 and then diluted with HNO3 to 25 ml. In  the other subgroup, B, 5 solutions were prepared with various concentrations from 1­5 mL of  NaSCN and HNO3 and 5 ml of Fe(NO3)3. Once all the solutions were created, we commenced  to the second part of the experiment where we ran the solutions in the spectrophotometer. In the  system we stated the concentration of the [SCN­] and the trial and with that information the  system calculated the transmittance and the absorbance. With the solutions from part B, the  concentrations were unknown, so we had to change the spectrophotometer to an unknown  concentration so that it could give us an accurate transmittance and absorbance for each trial.   Once all the data was retrieved, it was graphed (absorbance vs. [FeNCS2+]) and from that we  performed the calculations attached.  Observations/ Raw Data: For this experiment, there were not any major changes to record. As  we continued to make the solutions for part A, we noticed that the color was getting lighter as we diluted the solution more with HCN. Again, all of our calculations of for the concentrations and  the volumes of the solutions are recorded on the attached sheet.  Calculations:  The majority of the work in this experiment was performing calculations with the raw data. We used the graph to assist us in the equilibrium from the curve, and then we  calculated the values for the concentrations to determine the Kc for each trial. All the  calculations are written on the attached sheet. Conclusion: Overall, in experiment 34, I think that we performed a good experiment when it  came to the procedure. Our solutions were prepared well and we ran the spectrophotometer as we were instructed and our values appeared correct. When we were performing our calculations is  when our numbers appeared off. We found our Kc average value to be 4344, when it is supposed to be between 100 and 200. We recalculated all the components associated with the Kc value and came up with the same average value, so I don’t know we went wrong. We could have written a  value down wrong, or used the wrong equation for calculating the concentration of one of the  ions. After we found our average Kc value we calculated the standard deviation and the relative  standard deviation and found those to be 2687.7 and 55.0 respectively.  Post Lab Questions 1. When you run the blank solution, the percent transmittance should be 100% since there is no  NASCN in the solution and the Fe(No3)3 solution remains constant across trials. If it were not  100% then we would know that it was not calibrated correctly.  2.If all the test solutions for part A are too high, then he would either see a dip in the solutions  for the solutions in part B because the curve is supposed to continually increase when performed  correctly. In part C when determining the equilibrium constant, the a) the concentration for FeNCS2+ will be too high because it is the value found from the data  from the spectrophotometer b) the concentration of Fe3+ will be lower if the concentration of FeNCS2+ is too high  c) the equilibrium constant will be lower because the Fe3+ and SCN­ concentration will be lower while the FESCN2+ concentration is higher. 3. a) too low because part B is based off of the calculations found in part A. b) the Kc value shouldn’t be too heavily effected if it was just one point, but it might be slightly  increased due to the lower FeSCN2+ concentration. 4. a) when there are smudges on the test tubes, the result is a reduced intensity, since the light  can not shine through as easily, the result is a lower transmittance and absorbance. b) the equilibrium concentration for [FeSCN2+] is subsequently less as a result of the lower  transmittance and absorbance. c) the equilibrium concentration of [SCN­] will be lower because it is based off of the  not use  the equilibrium constant of [FeSCN2+] d)Due to this error, the equilibrium concentration will be lower because the concentration of  [Fe3+] and [SCN­] are affected slightly by a decrease and the [FeSCN2+] is lower making the  Kc value decreased. 5. a) the absorbance reading for FESCN2+ will be increased because the solution has not been  diluted.  b) the Kc value will be lower because the FESCN2+ is on the numerator while the denominator  remains the same.

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