Hach AutoCAT 9000, Instruction Manual

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Amperometric Titration Theory
Amperometric Titration Theory
Page 146
50081_Titration.fm
Figure 1 Total Chlorine Forward Titration
1.1.3 Determining Concentration
Experimentally the concentration of the titrant is known very accurately, as is the volume
of titrant that must be added to reach the titration end point. Use the following formula to
calculate the concentration of the analyte in an unknown sample:
Where:
V
Sample
is the sample volume
V
Titrant
is the volume of titrant solution that must be added to reach the end point
N
Titrant
is the concentration (normality) of the titrant solution
N
Sample
is the concentration (normality) of the analyte in the sample solution
1.1.3.1 Conversion Factor
Use a conversion factor to convert normality to more tangible units such as mg/L or ppm.
The precise conversion factor depends on the particular analyte and concentration units
involved. For example, one equivalent weight of chlorine (Cl
2
) is 35.453 g.
Consequently, a 0.100 N chlorine solution contains 3.5453 grams of Chlorine per liter of
solution. The following conversion factors can be used to convert from normality to the
more common concentration units.
Inserting the conversion factor into the equation permits the chlorine concentration to be
expressed in (mg/L), as shown below:
The above equation applies to forward titrations only. A slightly different calculation,
shown below, is used for back titrations.
Titrant Volume (mL)
Current (µAmp)
NSample
VTitrantNTitrant
VSample
------------------------------------------- =
Chlorine Concentration: (mg/L) (ppm) N
chlorine
35453 mg/eq wt.
×
= =
C
sample
N
Reductant Spike
V
Reductant Spike
V
Sample
----------------------------------------------------------------------------- 35453 mg/equ wt.
×
=