Experiment 34-An Equilibrium Constant.docx - Experiment 34:...

Experiment 34: An Equilibrium Constant
Varun Andrews
Pooja Patel
General Chemistry (DAI)
Professor Arthur Sikora
Krina Patel
3/28/2019

Hypothesis:
The equilibrium constant for the equation, Fe
3+
( aq ) + SCN

( aq ) FeNCS
2+
( aq )
,
can be
determined through the collection of the absorbance values of five different solutions with
various concentrations of Fe (NO
3
)
3,
NaSCN, and HNO
3
.
Materials and Methods:
Please refer to Experiment 34 on pages 387-398 of Laboratory Manual for Principles of General
Chemistry by J.A. Beran (10
th
Ed.). Deviations from the published procedure are:
1. We did not graph the Absorbance versus FeNCS 2+ on linear graph paper. We
graphed on Excel after the procedure was completed.
Results:
In this table the molar concentration of Fe (NO
3
)
3
and NaSCN are shown.
A
A Set of Standard Solutions to Establish
a Standardization Curve
Molar Concentration of Fe (NO
3
)
3
( mol/L ) 0.2 (~0.2 M )
Molar Concentration of NaSCN (mol/L ) 0.001
(~0.001
M)
Data Plot appears below and on
Sheet 2
Standard
Solutions
Blank 1 2 3 4 5
1 Volume of NaSCN ( mL ) 0.00 1.00 2.00 3.00 4.00 5.00
2 Moles of SCN
-
( mol ) 0.00E+00
1.00E-
06 2.00E-06
3.00E-
06
4.00E-
06
5.00E-
06
3 [SCN
-
] (25 mL) ( mol/L ) 0.00E+00
4.00E-
05 8.00E-05
1.20E-
04
1.60E-
04
2.00E-
04
4 [FeNCS
2+
] ( mol/L ) 0.00E+00
4.00E-
05 8.00E-05
1.20E-
04
1.60E-
04
2.00E-
04
5 Percent Transmittance, % T 100 94.6 82 70.3 58.3 51.9
6 Absorbance, A 0 0.024 0.086 0.153 0.234 0.285
In this table the absorbance values of the first 5 standard solutions that were made were tested
and recorded.
B. Absorbance for the Set of Test Solutions

Test
Solution
s
6 7 8 9 10
1 Volume of Fe (NO
3
)
3
( mL ) 5.00 5.00 5.00 5.00 5.00
2 Moles of Fe 3+ , initial ( mol )
1.00E-
05
1.00E-
05 1.00E-05
1.00E-
05
1.00E-
05
3 Volume of NaSCN ( mL ) 1.00 2.00 3.00 4.00 5.00
4 Moles of SCN - , initial ( mol )
2.00E-
06
4.00E-
06 6.00E-06
8.00E-
06
1.00E-
05
5 Percent Transmittance, % T 97.1 87.5 83 74.8 69.5
6 Absorbance, A 0.013 0.058 0.081 0.126 0.158
Molar Concentration of Fe (NO
3
)
3
( mol/L ) 0.002 (~0.002 M)
Molar Concentration of NaSCN ( mol/L ) 0.002 (~0.002 M)
This table shows the molar concentration of Fe (NO
3
)
3
and NaSCN.
This table shows the absorbance values of the 5 test solutions that were produced as well as the
moles of Fe 3+ and SCN -. .