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Instruction Manual
Silver/Silver Sulfide Electrode
15
The minimum silver sample concentration for this method is about 1.0X10
-4
M. For halides, it is
1.0X10
-4
M.
Data gathered by titration of less concentrated samples can be plotted using the Gran's Plot
technique. (See the chloride titration that follows.)
1.
Using Eutech Sodium Chloride Solution, 0.1M NaCl, Code No. NA0AS01, for silver
titration, or the 0.1M silver standard for halide titration, prepare a titrant about 10-20 times
the expected sample concentration by dilution. Measure out 50 ml of the sample into a 150
ml beaker, place the beaker on the magnetic stirrer, and begin stirring. Place the tips of the
electrodes in the solution.
titration, or the 0.1M silver standard for halide titration, prepare a titrant about 10-20 times
the expected sample concentration by dilution. Measure out 50 ml of the sample into a 150
ml beaker, place the beaker on the magnetic stirrer, and begin stirring. Place the tips of the
electrodes in the solution.
2.
Using a 10 ml burette, add titrant in 0.5-1.0 ml increments. Record the mV reading against
the volume of titrant added. As the mV potential change increases, add smaller increments,
down to 0.1-0.2 ml increments. Continue to add titrant and record the mV potential against
the volume until little change is noted in the mV reading even when adding 0.5-1.0 ml
increments.
the volume of titrant added. As the mV potential change increases, add smaller increments,
down to 0.1-0.2 ml increments. Continue to add titrant and record the mV potential against
the volume until little change is noted in the mV reading even when adding 0.5-1.0 ml
increments.
3.
Using linear graph paper, plot the mV readings (y-axis) against the volume (x-axis). The
endpoint is determined at the steepest slope on the titration curve as illustrated in Figure 3.
endpoint is determined at the steepest slope on the titration curve as illustrated in Figure 3.
4.
The sample concentration, Cs, is calculated as follows:
Cs = (Vt/Vs) Ct
where
Vs = sample volume (50 ml)
Vt = titrant volume at endpoint
Ct = titrant concentration (M)
Vt = titrant volume at endpoint
Ct = titrant concentration (M)
Low Level Chloride Titration
Chloride samples with a concentration below 1.0X10
-4
M or 5 ppm cannot be titrated in the usual
manner since the solubility product of silver chloride is not exceeded.
Using 10% Gran's Plot paper, data from samples down to 4.0X10
Using 10% Gran's Plot paper, data from samples down to 4.0X10
-6
M (0.04 ppm) may be plotted.
1.
Using 20 ml of standard ISA, dilute to 100 ml with distilled water. This low level ISA
(1.0M NaNO
(1.0M NaNO
3
) is added at the rate of 1 ml low level ISA to each 100 ml of sample. The
background ionic strength will be 1.0X10
-2
M.
2.
Measure out 100 ml of distilled water into a 150 ml beaker, add 1 ml of low level ISA,
place the beaker on the magnetic stirrer, and begin stirring.
place the beaker on the magnetic stirrer, and begin stirring.
3.
Prepare a 10 ml burette with the low level chloride titrant (2.82X10
-3
M AgNO
3
) mentioned
in the
GENERAL INSTRUCTIONS, Required Solutions
.
4.
Lower the tips of the electrodes into the solution.