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23 Nov 2019

A STUDENT STUDYING THE FE+3- HSCN equilibrium put into a test tube 10.00ml of 2.00 x 10-3 M Fe(NO3)3 with 10.0 mL of 2.00 x 10-3 M HSCN.THE H+ in the resulting solution was manteined at 0.500.By spectrophotometric analysis of the equilibrium solution, the equilibrium concentration of FESCN+2 was found to be 1.00x10-4M. 1.-CALCULATE THE INITIAL MOLARITY OF THE FE+3 AFTER DILUTION BUT BEFORE REACTION OCCURRED. 2.- CALCULTE THE INITIAL MOLARITY OF HSCN AFTER DILUTION. 3.- CALCULATE THE FE+3 WHICH REMAINED UNREACTED IN SOLUTION. 4.- CALCULATE THE HSCN MOLARITY WHICH REMAINED UNREACTED IN SOLUTION. 5.- CALCULATE THE VALUE FOR KC FOR THE REACTION

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DATA AND CALCULATIONS

Absorbance

Trial 1

0.039

Trial 2

0.045

Trial 3

0.063

Trial 4

0.086

Absorbance of standard (Trial 5)

0.792

Temperature

25Â°C

K_c expression K_c =

[Fe³⁺]i

Trial 1

Trial 2

Trial 3

Trial 4

[SCN^â]_i

[FeSCN²⁺]_eq

[Fe³⁺]_eq

[SCN^â]_eq

K_c value

Average of K_c values

Kc = ________________________ at ___25_____Â°C

beaker	Fe(NO₃)₃ (mL)	KSCN (mL)	H₂O (mL)
1	5	2	93
2	5	3	92
3	5	4	91
4	5	5	90

PROCESSING THE DATA
1. Write the Kc expression for the reaction in the Data and Calculation table.
2. Calculate the initial concentration of Fe3+, based on the dilution that results from addingKSCN solution and water to the original 0.0020 M Fe(NO3)3 solution. See Step 2 of theprocedure for the volume of each substance used in Trials 1-4. Calculate [Fe3+]i using theequation:

[Fe3+]i =

Fe(NO3)3 mLtotal mL X (0.0020 M)

This should be the same for all four test tubes.
3. Calculate the initial concentration of SCNâ, based on its dilution by Fe(NO3)3 and water:

[SCNâ]i =

KSCN mLtotal mL X (0.0020 M)

In beaker 1, [SCNâ]i = (2 mL / 100 mL)(.0020 M) = .000040 M. Calculate this for the otherthree beakers.
4. [FeSCN2+]eq is calculated using the formula:

[FeSCN2+]eq =

AeqAstd

X [FeSCN2+]std

where Aeq and Astd are the absorbance values for the equilibrium and standard solutions,
respectively, and [FeSCN2+]std = (1/100)(0.0020) = 0.000020 M. Calculate [FeSCN2+]eq foreach of the four trials.
5. [Fe3+]eq: Calculate the concentration of Fe3+ at equilibrium for Trials 1-4 using the equation:

[Fe3+]eq = [Fe3+]i â [FeSCN2+]eq

6. [SCNâ]eq: Calculate the concentration of SCN- at equilibrium for Trials 1-4 using theequation:

[SCNâ]eq = [SCNâ]i â [FeSCN2+]eq

7. Calculate Kc for Trials 1-4. Be sure to show the Kc expression and the values substituted infor each of these calculations.
8. Using your four calculated Kc values, determine an average value for Kc.

1) A solution is 1.00x10^-4 M in SCN^- an0.36 M in Fe³⁺ are mixed and react according to equationâ¨â¨

Fe³⁺_(aq)+SCN^-_(aq)<--> (Fe(SCN))²⁺_(aq)

Under these conditions, the equilibrium is driven all of the way tothe right. The absorbance of the solution at 447 nm is 0.500, andthe path length of the test tube is 1.00 cm. What is the value ofthe molar absorptivity, Îµ, for the complex FeSCN²⁺?

2) In a test tube, you combine the following:

2.00 mL of 0.00200 M Fe(NO₃)₃solution
2.00 mL of 0.00100 M KSCN solution
1.00 mL of 2.0 M HNO₃ solution
3.00 mL of distilled water

a) What are the initial concentration of the reactants (i.e.,assuming no reaction occurs)?
(Fe³⁺)_init = M
(SCN^-)_init= M

b) The absorbance of the resulting solution is 0.101 at 447 nm.What is the equilibrium concentration of the FeSCN²⁺product, based on the molar absorptivity determined above?

(FeSCN²⁺)_equil= M

c) Set up an ICE table for the reaction, and determine the value ofKc from the data

Kc=