LAB REPORT Pre-Lab Questions 1. A0.250 L sample of a 0.80 M NaOH stock solution

ID: 712053 • Letter: L

Question

LAB REPORT Pre-Lab Questions 1. A0.250 L sample of a 0.80 M NaOH stock solution is diluted to a volume of 1.20 L. What is the new concentration of the NaOH? 2. Given a reaction with a measured equilibrium constant, Ke, of 1 x 1010, what can be said about the equilibrium position? 3. Write the equilibrium constant expressions for each of the following reactions: The reaction in this experimentLAER DATA Stock solution concentrations 1. Concentration of SCN in stock solution 2. Concentration of Fes in stock solution #1 3, Concentration of Fe3. in stock solution #2 4. Concentration of Fe, in stock solution #3 20Y 10- 32 X 10-3 Calibration Curve [FeSCN"] Solution %Tat450 nm A at 400 nm Di Heo To calculate the [FeSCN"2) assume all the SCN has been reacted to produce FeSCN

Explanation / Answer

10.

S No.

Value of Kc

Average Kc

Overall Average Kc

31.4

22.14

26.77

43.84

85.43

65.22

30.6

25.4

24.57

27.78

26.18

42.88

86.55

64.72

41.92

62.39

52.16

FeSCN2+ <--> Fe3+ + SCN-

Theoretical equilibrium constant, Kc for the above reaction is ~138.

The obtained values of Kc above are different from that of theoretical value.

The possible sources of error are:

1) Inaccurate preparation of solutions

2) Faulty usage of instruments

3) Improper cleansing and rinsing

4) Minor solution temperature variations

Fe(SCN)2+ formation is an equilibrium reaction, where the equilibrium constant is obtained experimentally by various trials. To determine equilibrium concentrations, a standard curve is prepared to help determine the concentration of Fe(SCN)2+ at equilibrium