Hanna Instruments HI 4115 - Manual (Page 9)

16 17
C
S2-
= C
Pb2 +
V
Pb2 +
V
S2 -
*
Plot generated on Hanna HI 901 Titrator during Plot generated on Hanna HI 901 Titrator during Plot generated on Hanna HI 901 Titrator during Plot generated on Hanna HI 901 Titrator during Plot generated on Hanna HI 901 Titrator during
automated chloride titration using HI 4115
automated chloride titration using HI 4115 automated chloride titration using HI 4115 automated chloride titration using HI 4115 automated chloride titration using HI 4115
electrode.
electrode. electrode. electrode. electrode.
determined slopes at the temperature of measurement
should be used if known.
Example: Sulfide ion determination by sample subtrac-
tion.
1) A volume of standard solution of silver reagent
(V
std
) (C
std
) plus ISA (V
ISA
) is placed in a beaker
with the sensor pair. The mV1 is recorded.
2) A known volume (V
sam
) of the unknown sulfide
sample is added (mV should change at least 10 –
30 mV). The new mV is recorded (mV2) and the
difference is calibrated using the equation below
∆
mV = mV2-mV1 . S is the slope of the silver
electrode.
3) The unknown sulfide concentration in the sample
(C
sam
) can then be determined by the following
equation. For an example a sensor is placed into
100 mL of a 0.001 M Ag
+ standard. 1.0 mL of
unknown was added. The mV changed 12.5 mV.
The unknown sulfide value is found to be 1 X 10
-2
M. n= ½ because ½ mole of sulfide reactions
with 1 mole of silver ion .
n = Mole ratio of ions in sample that
react with 1 mole of standard
C
sample
= n
*
10 ∆E/S
-
V
Std
*C
Std
V
std
+
V
ISA
V
std
+V
ISA
+V
sam
V
Sam
*
V
Std
*C
Std
V
std
+ V
ISA
Titration of Chloride
A silver electrode may be used as an indicator to follow
the progress of a chloride (or other halide) titration with
silver nitrate. The electrode can be used in colored
samples where other indicators suffer from interferences.
During the titration the sensor follows the decrease in the
halide concentration while small additions of silver
nitrate titrant are added. The silver reacts with the
chloride ions forming a precipitate of silver chloride. At
the stoichiometric end point, a large change in mV occurs
as the silver is in excess. Measurements may be
automated by use of the Hanna Titrator HI 901 or titrated
manually.