Question

DATA:

Calibration Solution	0.2M Fe(NO3)3 in 0.5M HNO3	0.002M KSCN in 0.5 HNO3	0.5M HNO3	Absorbance
#1	5mL	.50	4.5	.339
#2	5mL	1	4	.758
#3	5mL	1.5	3.5	1.150
#4	5mL	2	3	1.518

Equilibrium Solution	0.002M in Fe(NO3)3 in 0.5M HNO3	0.002 KSCN in 0.5M HNO3	0.5M in HNO3	Absorbance
#1	5mL	1	4	.124
#2	5	2	3	.212
#3	5	3	2	.308
#4	5	4	1	.406
#5	5	5	0	.672

1. Concentration of Fe(SCN)2+ in calibration solutions- recall that the concentration of Fe(SCN)2+ in the calibratic solutions is essentially the concentration of the SCN initially in the solution. So, determine the concentration of SCN- initially in each of the 10.0mL calibration solutions. This is a simple dilution!

Answer:

#1 - 0.0001

#2 - 0.0002

#3 - 0.0003

#4 - 0.0004

y = 3929x - 0.041

slope = 3929

r2 = 0.9992

2. What is the value of eb?

3. For each sample, account for the dilution effect and determine the intial concentration of the reactants in the 10mL samples:

Equilibrium Solution	(Fe(NO3)3)0 / M	[KSCN]0 /M
#1
#2
#3
#4
#5

4. For each sample, calculate the equilibrium concentration of Fe(SCN)2+ using the value of eb that you found.

Equilibrium Solution	Absorbance	Fe(SCN)2+ eq
#1
#2
#3
#4
#5

5. For each example set up an ICE chart with the information from analysis 4 and 5. Fill in all the blanks and calculate values of Kc for each solution.

Answer 1

(1)

M1V1=M2V2

V1=10 ml

V2=5 ml

M2=0.2 M

1. Concentration of Fe(SCN)2+ in 10 ml=0.002*0.5/10=0.0001

2. Concentration of Fe(SCN)2+ in 10 ml=0.002*0.1/10=0.0002

Same way for othe two data

Absorbance	Concen
0.339	0.0001
0.758	0.0002
1.15	0.0003
1.518	0.0004

(b)

eb=3929

(c)

Fe(NO3)3=0.002*5/10=0.001

KSCN = 0.002*1/10=0.0002

Fe(NO3)3	KSCN
0.001	0.0002
0.001	0.0004
0.001	0.0006
0.001	0.0008
0.001	0.001

(4)

Using this equation find eqm concentration.

y=3929x-0.041

y=Absorbance

x= Fe(SCN)2+ concentration

Absorbance	Fe(SCN)2 eq
0.124	4.19954E-05
0.212	6.4393E-05
0.308	8.88267E-05
0.406	0.000113769
0.672	0.000181471

(5)

Kc= [Fe(SCN)2+]/([Fe3+][SCN-])

Now ICT table

Data 1:

	Fe 3+	SCN-	Fe(SCN)2+
Initial	0.001	0.0002
Change	-4.19954E-05	-4.19954E-05	4.19954E-05
Eqm	0.000958005	0.000158005	4.19954E-05
		Kc	277.4371727

Data 2:

	Fe 3+	SCN-	Fe(SCN)2+
Initial	0.001	0.0004
Change	-6.4393E-05	-6.4393E-05	6.4393E-05
Eqm	0.000935607	0.000335607	6.4393E-05
		Kc	205.0755929

Data 3:

	Fe 3+	SCN-	Fe(SCN)2+
Initial	0.001	0.0006
Change	-8.88267E-05	-8.88267E-05	8.88267E-05
Eqm	0.000911173	0.000511173	8.88267E-05
		Kc	190.7103295

Data 4:

	Fe 3+	SCN-	Fe(SCN)2+
Initial	0.001	0.0008
Change	-0.000113769	-0.000113769	0.000113769
Eqm	0.000886231	0.000686231	0.000113769
		Kc	187.0719532

Data 5:

	Fe 3+	SCN-	Fe(SCN)2+
Initial	0.001	0.001
Change	-0.000181471	-0.000181471	0.000181471
Eqm	0.000818529	0.000818529	0.000181471
		Kc	270.8566349