CHEMISTRY 231

Spring, 2013 Homework Set 1 Solutions

 

Statistics Calculations

1. Download the file on the Chem 133 website labeled filterHW.txt. (this gives the time in minutes and the signal in fluorescence units) and transfer to an Excel File. Print a table from Excel showing two columns collected over the first 30 s period.

 

2. Make a plot of the raw data from above and also data processed with a 2 s moving average over both the first 30 s and over the first 4 min. This can be done by either using Excel's Plotting routines or by creating a 2 s moving average using a new column in Excel.

 

Statistical Problem Solutions This link goes to the Excel File.

 

Here are 4 plots (A, B, C, and D corresponding to 30 s data with 2 s moving average trend line, 30 s data with 2 s moving average using Excel average function, 4 min data with 2 s moving average trend line, and 4 min. data with 2 s moving average using Excel average function, respectively) .

Plot A

 

PlotC

 

Plot D

 

3. Given the following data, determine the concentration of levoglucosan in an unknown and the standard deviation in its concentration.

Standards   Unknown Data Levoglucosan Area
Levoglucosan conc Levoglucosan Area Levoglucosan conc  
 (ug/mL)   (ug/mL)  
0.5 469.11 Unknown 2276.40
1 826.57    
2 1578.66    
5 3973.85    
10 8043.47    

  Excel Results

Levoglucosan conc Levoglucosan Area        
 (ug/mL)          
0.5 469.11   LINEST Results    
1 826.57 m 799.7293 19.33312 b
2 1578.66 Sm 6.067866 30.9699 Sb
5 3973.85 R^2 0.999827 47.7013 Sy
10 8043.47        
           
Levoglucosan conc Levoglucosan Area        
(ug/mL)          
Unknown 2276.40        
           
    equation      
Number Stds 5 =COUNT(B4:B8)      
Mean Area 2978.33 =AVERAGE(C4:C8)      
Sum of (xi - mean x)^2 61.8 =DEVSQ(B4:B8)      
      equation    
Conc. 2.82 (ug/mL) =(C14-F9)/E9    
Std Deviation 0.07  

=(F11/E9)*

(1 + 1/C17+((C14-C18)^2/(E9^2*C19)))^0.5

   
Uncertainty 0.21   =TINV(0.05,3)*C22    
Uncertainty_2* 0.09   =C23/(C17)^0.5    
*calculated based on HPLC instructions          

updated 2/8/13