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Prelab Questions

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Subject
Chemistry
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Homework
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1.
When we mix the solutions of KSCN and Fe(NO3)3, the first thing that will happen before the
reaction starts is that they will dilute by the increase in volume. Taking this into account, we can
estimate the concentration of each ion in the solution as:


Where [A]o and Vo are the concentration and volume before the dilution and Vf is the final
volume after the dilution has been done.
According to our data we know:
Solution 1: [SCN-]o = 2.0*10
-4
M; Vo = 5.0 mL
Solution 2: [Fe3+]o = 2.0*10
-4
M; Vo = 2.0 mL
Mixture: Vf = 5.0 + 2.0 = 7.0 mL
Taking this into account we find:

 



 


 



 

2.
Since according to the Beer-Lambert law the absorbance of the solution is directly proportional to
the concentration of the absorbing compound (Fe(SCN)
2+
) we can use this data to estimate the
concentration of a solution by comparing the absorbances of this solution and that of a solution of
known concentration (standard) since:



According to our data, we know:
[Standard] = 1.0 * 10
-4
M
Abs (Standard) = 0.40
Abs (Solution) = 0.15
Substituting these data into the equation, we find that the concentration of FeSCN
2+
formed in the
complexation reaction is:

 



 


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1. When we mix the solutions of KSCN and Fe(NO3)3, the first thing that will happen before the reaction starts is that they will dilute by the increase in volume. Taking this into account, we can estimate the concentration of each ion in the solution as: [𝐴] = [𝐴]𝑜 ∗ 𝑉𝑜 𝑉𝑓 Where [A]o and Vo are the concentration and volume before the dilution and Vf is the final volume after the dilution has been done. According to our data we know:    Solution 1: [SCN-]o = 2.0*10-4 M; Vo = 5.0 mL Solution 2: [Fe3+]o = 2.0*10-4 M; Vo = 2.0 mL Mixture: Vf = 5.0 + 2.0 = 7.0 mL ...
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