2
5. Operation
5.1 General instructions
Rinse the lower end of the electrode
thoroughly with distilled water, shake off
any remaining water and dry with filter
paper.
Select the expected measurement range
for the test liquid by pressing the
appropriate measuring range button.
Immerse the end of the electrode with the
slot at its tip into the liquid to be tested.
Important: the graphite cell surfaces must
be completely immersed in the test liquid.
Stir the liquid gently with the electrode, and
after 5 to 10 seconds read the measured
value.
When
switching
over
to show
the
temperature of the test liquid, the chosen
measuring range button must be held
down for at least 2 seconds.
Wait for a new display to appear on the 3B
NETlog
TM
unit (“Probe Detect”) and read
off the temperature.
Press the appropriate measuring range
button again to return to conductivity
measuring mode.
Before making another measurement in a
different liquid, wash the electrode again in
distilled water and repeat the steps
described earlier.
The measurement system is suitable for a
temperature range from 15°C to 35°C. The
calibration temperature is about 25°C.
5.2 Calibration
The electrode is supplied pre-calibrated and
ready for use. Recalibration can only be
carried out at present by the manufacturer 3B
Scientific GmbH.
5.3 Cleaning and care of the electrode
If electrodes get polarised or dirty they
must be cleaned using hot water and a
mild detergent.
Organic substances should be removed
with acetone. Algae, bacteria, mould or
mildew should be removed with a solution
of sodium hypochlorite.
Do not use abrasives or objects that can
scratch the surface.
Finally, wipe the electrode with a cotton
cloth.
6. Experimental applications
Distinguishing
qualitatively
between
substances with ionic or molecular structures
in liquids, e.g. dilute solutions of acids and
alkalis.
Demonstrating the direct relationship between
conductivity and ion concentration in liquids.
Measuring ion concentrations in unknown
solutions.
Measurements
of
conductivity
for
photosynthetic processes in a basin containing
aquatic plants, and observing the simultaneous
reduction of bicarbonate ion concentration.
In-situ measurements of total quantities of
dissolved solids (TDS, in mg/l) in lakes or
streams.
Observing rates of chemical reactions involving
the uptake or release of a conducting
substance.
Conductivity changes in titrations with two
substances in stoichiometric quantities.
Measurements of the rate of diffusion of one
type of ion through a membrane (osmosis).
Measurements of conductivity and total
dissolved solids in an aquarium containing
aquatic plants and animals such as fish.
Distinguishing between photosynthesis and
respiration
7. Sample experiments
The increase in the conductivity of distilled
water when common salt is added.
Equipment required:
1 3B NET
log
TM
@ 230 V
1000540
or
1 3B NET
log
TM
@ 115 V
1000539
1 3B NET
lab
TM
1000544
1 Conductivity sensor
1000553
1 Glass beaker, 600 ml,
shallow form
1002872
1 Set of Scout Pro
electronic scales, 200 g
1009772
1 Carton of table salt (500 g approx.)
1 Petri dish
1 Teaspoon
300 ml distilled water
Pour 300 ml of distilled water into the
beaker.
Immerse the conductivity electrode (which
must first have been thoroughly cleaned) in
the water so that it reaches the bottom of
the beaker.
