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.
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
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
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)
- turn-on Xplorer data collection device
- insert colorimeter into Xplorer device
- open lid, then insert small glass vial (cuvette) filled with "zero" (see table 1, above) into colorimeter
- 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
- if %T not ~ 100% or ABS not ~ 0 , then press green button on colorimeter / wait till lights goes off else goto next step
- replace cuvette with samples; press "+" on Xplorer - to cycle thru various setting; record data (i.e. absorbance at different wavelengths); repeat with other samples
- DO NOT PRESS ANY OTHER BUTTON DURING YOUR MEASUREMENT
calibration curve; ICE table
Content of lab report (40 points; no lab report revision)
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:
- Kc as a function of the initial [Fe3+] & [SCN- ]; (based on table 2)
- make / label a graph of experinental data: initial [Fe3+] versus equilbrium [FeSCN2+] (based on table 3)
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
- is the value of Kc truly a constant (i.e. is the value of the Kc the same under all (different) initial conditions) ? use / refer to the appropriate statistics to support your conclusion.
- describe / rationalize the relationship between initial [Fe3+] versus equilbrium [FeSCN2+]
site1; site 2; site 3; site 4