Harris Quantitative Analysis, Quantitative Analysis

1. Titrations: Introduction
Volumetric Analysis
Measure volume of a reagent
needed to react with an analyte
Volumetric Titration
Add Increments of a reagent to a
solution of an analyte until the
reaction is complete
Ideal: Rxn Complete; Rxn Rapid
Common Titrations
A. Acid-Base
B. Oxidation-Reduction
C. Complex Formation
D. Precipitation Reactions

2. Definitions
Indicator - Compd whose color changes
abruptly near the equiv pt
Equivalence Point - pt in the titration where the
quantity of titrant added is stoich. equiv to amt.
of analyte present.
End Point - Typically what is measured;
marked by sudden change in prop. of soln
Titration Error - diff btwn end pt & equiv pt
Back Titration - Add excess of titrant then
determine the amount excess

3. Example
5H2C2O4 + 2 MnO4
-
+ 6H+
 10 CO2 + 2 Mn+2
+ 8H2O
analyte titrant
colorless purple
Equiv point
point when 2 mmol of MnO4
-
has been
added to 5 mmoles of H2C2O4
End point
detect by monitoring color of solution
better eyes, closer endpoint will be to equiv point
Back titration
add xs MnO4
-
, back titrate with another standard to
determine excess slow reactions, standard solutions
not stable.

4. What’s Needed
Solution of known composition
Primary standard
Standard Solution
Analytical Balance
Volumetric Flask
Accurately measure volume
Buret
Volumetric Pipet

5. Mercuric Nitrate was standardized by titrating a solution
containing 147.6 mg of NaCl. 28.06 mL of the Mercuric
Nitrate solution was required to reach the end point.
This solution was then used to titrate 2.000 mL of urine.
It took 22.83 mL to reach the endpoint.
Find the concentration of Cl- in Urine as mg/mL
Hg2+
+ 2 Cl-
= HgCl2
Titration Calculations

7. The CO in a 20.3 L sample of gas was converted to CO2 by
passage over iodine pentoxide heat to 150 C.
I2O5 + 5CO = 5 CO2 + I2
The iodine distilled at this temperature was collected
in an absorber containing 8.25 mL of 0.01101 M Na2S2O3
I2 + 2S2O3
2-
= 2I-
+ S4O6
2-
The excess Na2S2O3 was back titrated with 2.16 mL
of a 0.00947 M I2 solution.
Calculate the number of mgs of CO per liter of sample
Titration Calculations

9. Applications of Acid-Base Titrations
1. Determination of Nitrogen
Kjeldahl Analysis:
Important method to accurately
determine nitrogen in proteins and
other nitrogen containing
compounds

10. Steps
Digest the material in sulfuric acid
convert to NH4HSO4
Cool the solution and make it
alkali to convert to NH3 (gaseous)
Volatile ammonia distilled into
known volume of acid
Excess acid back titrated

11. A protein contains 16.2 wt% nitrogen. A 0.500 mL sample of
the protein solution was digested and the liberated NH3
distilled into 10.00 mL of a 0.02140 M HCl solution. The
unreacted HCl required 3.26 mL of a 0.0198 M NaOH.
Calculate the concentration (mg/mL) of protein
in the original sample.
Example