Report Form DATA Concentration of the Fe solution (three significant figures) .o
ID: 967326 • Letter: R
Question
Report Form DATA Concentration of the Fe solution (three significant figures) .ooo Concentration of the SCN solution (three significant figures) .so Exact volumes of stock solutions used and percent transmittance values obtained Tube Number1 mL Fe mL SCN 9 0.00 5 4 3.5 32. 0.00 Date Instructor's Signature ANALYSIS Complete the following table. You will need to convert percent transmittance to absorbance and to calculate the initial concentrations of the ions (IFe and mixing but before any complex is formed. SCN 1D. These are the concentrations after Tube Number Absorbance [Fe l 0.00 ISCN l 0.00 What is the relationship between the values for [Fe 1], and [SCN 12 (HINT: Look at ([Fe3+], x ISCN-I), (IFe, I/iscN-1), (IFes. It sarb, and IFen-tscN-1). 97Explanation / Answer
If we look at table -1, row-2 and 3, mL of Fe3+ and SCN- given,
Both Fe3+ and SCN- have same concentration i.e.0.001
Milimolar concentration = Molarity(M) x volume in mL
e.g. for tube number -3
[Fe3+] = 0.0014 M x 2 mL and
[SCN-] = 0.0014 x 4 mL
Hence,
[Fe3+] + [SCN-] = 0.0014 x 2 + 0.0014 x 4
i.e. [Fe3+] + [SCN-] = (2 + 4) x 0.0014
[Fe3+] + [SCN-] = 6 x 0.0014
6 is sum of volumes in mL of Fe3+ and SCN- solutions
This number i.e. sum of volumes of Fe3+ and SCN- solutions kept constant throughout the experiment and hence their concentrations (Milimoles) varies individually but sum of concentrations (milimoles) is always 6 x 0.0014 = 0.0084 milimoles.
See those sums they are as,
Tube -1; 0 + 6 = 6 mL
Tube-2; 1 + 5 = 6 mL
Tube- 3; 2+4 = 6mL
Tube-4; 2.5+3.5 = 6 mL
Tube-5; 3+3 = 6
And hence in all tubes the sum of concentrations of Fe3+ and SCN- solutions is same,
[Fe3+]+[SCN-] = 6 mL x 0.0014 M = 0.0084 milimoles
Relation between the values of [Fe3+] and [SCN-] is, [Fe3+]+[SCN-] = constant = 0.0084 milimoles = 8.4 x 10-3 mmol.
Note: This constancy not just because the sum of volumes of Fe3+andSCN-] kept constant but also because their molarities are same.
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On the basis of above (see for tube -3) calculation table completed as,
Tube #
1
2
3
4
5
6
7
8
9
Absorbance
0
0.12
0.38
0.44
0.38
0.39
0.32
0.25
0.30
[Fe3+] x
10-3mmol
0.00
1.4
2.8
3.5
4.2
4.9
5.6
7.0
8.4
[SCN-] mmol
8.4
7.0
5.6
4.9
4.2
3.5
2.8
1.4
0.00
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Tube #
1
2
3
4
5
6
7
8
9
Absorbance
0
0.12
0.38
0.44
0.38
0.39
0.32
0.25
0.30
[Fe3+] x
10-3mmol
0.00
1.4
2.8
3.5
4.2
4.9
5.6
7.0
8.4
[SCN-] mmol
8.4
7.0
5.6
4.9
4.2
3.5
2.8
1.4
0.00