1. Determination of Mn in Steel (Standard Addition)
Sample Calculations of
Determination of Mn in Steel (Standard Addition)
Vikram Sharma

2. Initial Values
Find the mass of your steel for each trial, in this calculation it will be .5091g, in a mL flask
Mn Standard concentration (Cs) = mg/mL
Absorbance data 
Absorbance
Blank
0.031
Sample
0.198
Sample+5mL
0.631
Sample+10mL
1.082

3. Why are we using the standard addition calculation?
We have to use the standard addition calculation because we have to take into account the matrix effect
Matrix effect- the change in the analytical signal (absorbance in this case) because of all the stuff other than the analyte (Mn) in the solution.

4. Part I, 2 equation 2 unknowns
Use aliquots 2 and 3
1.082
Sample+10mL
0.631
Sample+5mL
0.198
Sample
0.031
Blank
Absorbance
Remember to subtract your blank!!!

5. Defining Variables Ax,T=Corrected Absorbance of aliquot 2 = .167
Ax+s,T=Corrected Absorbance of aliquot 3 = .600
Vs=Volume Standard mg/mL Mn= L
Vx=Volume Unknown with conc. Cx = L
Cx= Concentration Mn in sample

6. The Numbers… Cx = [.167/(.600-.167)]* [(.00500L*.1025mg/mL)/.02000L]
Cx= mg/mL
Cx*100mL=.988mg
.988mg/1000mg/g= g Mn
gMn/.5091gSample*100%= .194%

7. Part II, Graphical Procedure
The X axis equation
Xn=[S]i*(Vs/Vo)
Where
[S]i= Original Conc. Std Mn (.1025 mg/mL)
Vs = Volume standard (0, 5, 10 mL)
Vo = Volume unknown (20 mL)

8. Graphical Procedure The Y axis equation Yn=IS+X*(V/Vo) Where:
IS+X= Absorbance value
V = Total volume (50 mL)
Vo = Volume unknown (20 mL)

9. Graphical analysis X values Y Values Sample 0.4175 Sample+5mL 0.025625
0.4175
Sample+5mL
1.5
Sample+10mL
2.6275

10. Find the conc. of unknown, [X]f
[X]f is the magnitude of the X-intercept value
Therefore Y=0, so find X in the calculated equation from the least squares line:
y=43.1[X]f+.410
0=43.1[X]f+.410
-.410/43.1= [X]f
[X]f =| |=.00951mg/mL

11. Finding %(wt/wt) [X]f *100mL=.951mg .951mg/1000mg/g=.000951g Mn
gMn/.5091gSample*100%= .187%
Compare .194% to .187%

12. Question
In the graphing procedure, is the x intercept supposed to be positive or negative?
Negative. If it’s positive, you screwed up.