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 * 9 H2O) ?

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

review below content prior to lab

purpose

materials (per 2 groups @ a table)

colorimeter; cuvette; 100 mL volumeric flask, 5 mL pipets, 1 mL micropipet; 10 mL beakers; 250 mL beaker

200.0 mM iron (III) nitrate; 2.0 mM potassium thiocyanate

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

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

organize into multiple of three groups, where there's separate groups making solutions for table 1,2, & 3 ,then sharing it with the other groups. table 1 group shares 200 mM Fe(NO3 )3 and 2 mM KSCN; use 0.1 M HNO3 as the solvent. each group collects experimental data for all tables and makes their own zero (see table 1) and use the zero to calibrate / blank the colorimeter and collect absorbances from each color / wavelength of light in the colorimeter.

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, then make 10 mL of the solutions in the below table.

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

table 2. to determine Kc .  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.

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+ ].  use 4 mM Fe(NO3 )3 (dilute 200 mM solution to make 4 mM solution), 2 mM KSCN, and 0.1 M HNO3 (as the solvent) to prepare 10. mL of the solutions in the below table.

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