Determination of the Equilibrium Constant for Ferric Thiocyanate
Determination of the Equilibrium Constant for Ferric Thiocyanate
In this laboratory exercise, the equilibrium constant(Kc) for the reaction between the Ferric Ion (Fe3+) and the Thiocyanate Ion (SCN-) was determined. After measuring the absorbance of the Ferric Thiocyanate, and carrying out some calculations; it was determined that
Kc=130.81M
Introduction: Chemical equilibrium is established when a reaction exists in a state where the forward reaction rate is equal to its reverse reaction rate. The overall reaction of this exercise is as follows: Fe3+(aq) + SCN-(aq) Fe(SCN)2+ In this occasion, the color intensity of Ferric Thiocyanate was used to determine its absorbance using the Shimadzu UV-2550 scanning UV-VIS spectrometer. Once the concentration of Ferric Thiocyanate is determined, the concentration of the reactants can be determined; consequently, K c can be calculated.
Experimental Data:
1) Obtain the following in different beaker and label the accordingly:
Solution
Fe(NO3)3
KSCN
HNO3
Amount
40ml
25ml
20ml
2) In 5 large test tubes mix the following substances with the according amounts as shown below:
Trial
Fe(NO3)3 (2x10-3M)
KSCN (2x10-3M)
HNO3
1
5ml
1ml
4ml
2
5ml
2ml
3ml
3
5ml
3ml
2ml
4
5ml
4ml
1ml
5
5ml
5ml
0
3) Place some of each sample in the cuvettes and perform a spectroscopy.
*After adding KSCN, the solution turned pale yellow and when HNO3 was added it turned into amber looking color (brick red). This color fades from test tube 5 to 1.
Trial
1
2
3
4
5
Absorbance
0.107
0.207
0.310
0.451
0.595
Data Analysis:
1.-
Trial
[Fe3+] (M)
[SCN-] (M)
1
0.001
2.0x10-4
2
0.001
4.0x10-4
3
0.001
6.0x10-4
4
0.001
8.0x10-4
5
0.001
1.0x10-3
2.-
Trial
[Fe(SNC)2+]e (M)
[Fe3+]e (M)
[SCN-]e (M)
Kc
1
2.127x10-5
9.787 x10-4
1.787 x10-4
121.62
2
4.115 x10-5
9.588 x10-4
3.588 x10-4
119.62
3
6.163 x10-5
9.384 x10-4
5.384 x10-4
121.98
4
8.966 x10-5
In this laboratory exercise, the equilibrium constant(Kc) for the reaction between the Ferric Ion (Fe3+) and the Thiocyanate Ion (SCN-) was determined. After measuring the absorbance of the Ferric Thiocyanate, and carrying out some calculations; it was determined that
Kc=130.81M
Introduction: Chemical equilibrium is established when a reaction exists in a state where the forward reaction rate is equal to its reverse reaction rate. The overall reaction of this exercise is as follows: Fe3+(aq) + SCN-(aq) Fe(SCN)2+ In this occasion, the color intensity of Ferric Thiocyanate was used to determine its absorbance using the Shimadzu UV-2550 scanning UV-VIS spectrometer. Once the concentration of Ferric Thiocyanate is determined, the concentration of the reactants can be determined; consequently, K c can be calculated.
Experimental Data:
1) Obtain the following in different beaker and label the accordingly:
Solution
Fe(NO3)3
KSCN
HNO3
Amount
40ml
25ml
20ml
2) In 5 large test tubes mix the following substances with the according amounts as shown below:
Trial
Fe(NO3)3 (2x10-3M)
KSCN (2x10-3M)
HNO3
1
5ml
1ml
4ml
2
5ml
2ml
3ml
3
5ml
3ml
2ml
4
5ml
4ml
1ml
5
5ml
5ml
0
3) Place some of each sample in the cuvettes and perform a spectroscopy.
*After adding KSCN, the solution turned pale yellow and when HNO3 was added it turned into amber looking color (brick red). This color fades from test tube 5 to 1.
Trial
1
2
3
4
5
Absorbance
0.107
0.207
0.310
0.451
0.595
Data Analysis:
1.-
Trial
[Fe3+] (M)
[SCN-] (M)
1
0.001
2.0x10-4
2
0.001
4.0x10-4
3
0.001
6.0x10-4
4
0.001
8.0x10-4
5
0.001
1.0x10-3
2.-
Trial
[Fe(SNC)2+]e (M)
[Fe3+]e (M)
[SCN-]e (M)
Kc
1
2.127x10-5
9.787 x10-4
1.787 x10-4
121.62
2
4.115 x10-5
9.588 x10-4
3.588 x10-4
119.62
3
6.163 x10-5
9.384 x10-4
5.384 x10-4
121.98
4
8.966 x10-5