Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Katarina Ong
Connor Wilson
Michael Oliver
February 4 & 11, 2014

Investigation 37: What is the Formation Constant
Experiment Background
Fe​3+​(aq)​+ NCS​-​(aq)​ ↔ FeNCS​2+​(aq)
A theater company has recently discovered this reaction and wants to use it to
prepare solutions that look like blood
...
This will help the
company understand the conditions under which to control the reaction
...
This was accomplished by preparing various
solutions of Fe​3+​ and NCS​-​, allowing the solutions to reach equilibrium, then
determining the concentrations of the reactants
...
With this relationship
established, the concentration of FeNCS​2+​ in the solutions of Fe​3+​ and NCS​allowed to equilibrate could be determined
...
With the equilibrium concentrations of all
three reactants determined, it was now possible to calculate the equilibrium
constant, following the formula

1

Materials and Equipment
Materials

Equipment

Prepared FeNCS​2+​ Solutions

3 - 50mL Pipette

2
...
00 × 10​-5​M FeNCS​2+

Lint-free tissue paper

6
...
00 × 10​-5​M FeNCS​2+

6 15mL Test Tubes

1
...
20 × 10​-4​M FeNCS​2+
1
...
00 × 10​-3​M Fe​3+
2
...
00 × 10​-1​M HNO​3
Deionized Water
Method
The first step in determining the formation constant for the reaction
Fe​3+​(aq)​+ NCS​-​(aq)​ ↔ FeNCS​2+​(aq)
was to establish a relationship between concentration and absorbance for
solutions of FeSCN​2+​
...
First, a 3mL cuvette was filled with 1
...
This wavelength was determined to be 470nm, as can be seen in
Table 1
...
The absorbance values
noted in Table 2 were collected in this manner
...
It is this value that allows concentration data to
be determined from absorbance data, following the Beer-Lambert law
A = ε bC
Where A is absorbance, ε is the proportionality constant, b is the length of the
light path in the colorimeter, and C is the concentration of the solution being
tested
...

The quantities noted in Table 2 were added to 6 15mL test tubes, one for each
solution, and the reaction was allowed to come to equilibrium for several minutes
...
With this
data, in conjunction with the Beer-Lambert curve, the equilibrium concentration of
FeSCN​2+​ for each solution could be determined, and the concentrations of Fe​3+
and SCN​-​ could also be determined using stoichiometric ratios

---