Determine K

Honors Chemistry

background [prelab assignment (25 points) due at the begining of lab]

what is Beer's Law ?  calibration curve (relate to Beer's law; hint:  vitamin C lab) ? 

fill-in the below ICE table in regards to the below reaction

  [Fe3+] [SCN-] [FeSCN2+]
[inital]
5.0 mM 10.0 mM 0
[change]
     
[equilibrium]
    2.0 mM

and calculate the value of Kc based on the information in the above ICE table.

sample calculations

how to prepare 100. mL of 200. mM Fe(NO3 )3 (using solid Fe(NO3 )3 ) ?

how to prepare 10. mL of 0.5 mM SCN - & 1.0 mM Fe 3+ (using 2.0 mM SCN - & 2.0 mM Fe(NO3 )3) ?

msds on nitric acid, HNO3

view screen cast on the use of the colorimeter prior to the lab

purpose

materials (per 2 groups @ a table)

colorimeter; cuvette; 100 mL volumeric flask

100 mL, 200.0 mM iron (III) nitrate; 50 mL, 2.0 mM potassium thiocyanate

2 mM iron (III) nitrate (dilute 200 mM solution)

150 mL, 0.1 M HNO3 - use as the solvent

methods

student design; delegate your work - do calculations on how to prepare the below solutions for tables 1 - 3 prior to the lab

table 1.  calibration curve: [FeSCN 2+ vs absorbance].  Prepare separate 100. ml of 200 mM Fe(NO3 )3 and 100. mL of 2 mM KSCN (use 0.1 M HNO3 as the solvent) then label it, and share with all other groups. Each group has to make their own 10. mL solutions in the below table using the preceding solutions. 

expt std [Fe3+ ]  (mM) [SCN- ]  (µM) [FeSCN2+] absorbance
1 1
40
200
   
2 2
40
150
   
3 3
40
100
   
4 4
40
50
   
5 zero
40
0
   

table 2. to determine Kc .  One group use 2 mM Fe(NO3 )3 (dilute 200 mM solution to make 2 mM solution), 2 mM KSCN, and 0.1 M HNO3 (as the solvent) to prepare 10. mL of the solutions in the below table to use in their own measurments and to share their solution with all other groups.

expt [Fe3+ ]  (mM) [SCN- ]  (mM) absorbance
1
1.0
0.1
 
2
1.0
0.5
 
3
1.0
1.0
 

table 3. to determine the effect of [Fe3+ ] on [FeSCN2+ ].  One group prepares 10. mL of the solutions in the below table; determine how to prepare these solution then share their solution with all other groups.

expt [Fe3+ ]  (mM) [SCN- ]  (mM) absorbance
1
0.1
0.1
 
2
0.2
0.1
 
3
0.5
0.1
 
4
1.0
0.1
 
5
2.0
0.1
 

 

use of colorimeter (vodcast; assume only FeSCN2+ absorbs light)

  1. turn-on Xplorer data collection device
  2. insert colorimeter into Xplorer device
  3. open lid, then insert small glass vial (cuvette) filled with "zero" (see table 1, above) into colorimeter
  4. close lid; should display %T ~ 100 or Abs ~ 0 for all wavelengths;  press "+" on Xplorer - to cycle thru various setting (red, green, blue, & orange, where reading % T or Abs
  5. if %T not ~ 100% or ABS not ~ 0 , then press green button on colorimeter / wait till lights goes off  else goto next step
  6. replace cuvette with samples; press "+" on Xplorer - to cycle thru various setting; record data (i.e. absorbance at different wavelengths); repeat with other samples
  7. DO NOT PRESS ANY OTHER BUTTON DURING YOUR MEASUREMENT

data analysis

calibration curve;  ICE table

 

Content of lab report (40 points; no lab report revision)

data analysis

what is the rationale of choosing a specific wavelength of light for your determination of [Cu2+ ] ?  [hint:  see prelab question 1 in the below cdf based simulation]

calibration curve - based on data in table 1

determine Kcbased on the ICE table & data in table 2; show all calculations

summary tables / graph: 

statistics / conclusions: 

describe / list two NGSS science & engineering practices that correlates to an aspect of this laboratory activity; provide an example in the lab & this lab report that meets these practices

resources:

site1; site 2site 3; site 4

simulations: