Chem 218 Assignment 1 numbers 1, 2e, 2f, 2g, 3a, 3b

1.                  An analytical lab needed to determine the content of phosphorus in a commercial sample of plant food. The phosphorus in a 4.258 g sample of this plant food was converted to PO₄^3- and precipitated by adding 50.00 mL of 0.0820 M AgNO₃. The excess AgNO₃ was then titrated using 4.06 mL of 0.0625 M KSCN. What was % P₂O₅ in the original plant food sample?

P₂O₅ + 9 H₂O → 2PO₄^3- + 6H₃O⁺

2PO₄^3- + 6 Ag⁺ → 2Ag₃PO_4(s)

Ag⁺ + SCN^- → AgSCN_(s)

2.                  2. A solution of volume 25.00 mL containing 0.0311 M Na₂C₂O₄ was titrated with 0.0257 M La(ClO₄)₃ to precipitate lanthanum oxalate:

2 La³⁺  + 3 C₂O₄^2-  La₂(C₂O₄)_3(s)

(e)               Plot the titration curve for this titration using Excel or other spreadsheet software

(f)                 Plot the titration curve for the same titration if the concentration of the titrant is increased to 0.0500 M. What effect does this have on the shape of the titration curve?

(g)               Another analytical chemist performed the titration of the same oxalate sample using calcium to precipitate calcium oxalate. Is this a better approach to this analysis? Why or why not?

3.      3. (a)  Calculate pCu⁺ for the titration of 10.00 mL of 0.05000 M of I^- with 0.02500 M Cu⁺ standard solution when 4.500 mL, 20.00 mL and 21.40 mL of titrant have been added. Plot the titration curve for this titration using Excel or other spreadsheet software.

(b) Calculate pCu⁺ for the titration of 10.00 mL of 0.05000 M of Cl^- with 0.02500 M Cu⁺ standard solution when 4.500 mL, 20.00 mL and 21.40 mL of titrant have been added. Plot the titration curve for this titration using Excel or other spreadsheet software on the same graph as (a). How does K_sp value influence the shape of the observed titration curves?