Specific electrical conductivity and total alkalinity are tested at the same time on
unfiltered stream water samples.
These samples are collected in large wide mouth Nalgene® bottles.
In your water chemistry laboratory, check the sample bottles and arrange them in numerical
order, alongside the HI 7031L conductivity standard solution, in order to equilibrate
them to room temperature.
Before commencing any work, don a laboratory coat along with nitrile gloves
and safety glasses.
Testing involves using an electronic multi-range conductivity meter with a probe,
and an alkalinity test kit.
Before testing, the conductivity meter must be calibrated using the conductivity standard
solution, which is temperature dependent.
First, take the thermometer from the alkalinity test kit and rinse it in deionised water
or tap water.
Measure the temperature of the conductivity standard solution with the thermometer.
Record this temperature in the water chemistry data book.
Remove the thermometer from the conductivity standard solution and place to one side.
Turn on the conductivity meter and rinse the probe using deionised or tap water.
The outer case can be removed.
Shake or dry the excess away and place the rinsed probe on a clean surface.
Wait until the meter reading returns to zero before proceeding.
Press the button labelled “1999 µS/cm” to ensure that the reading unit is set to
“µS” in the top right hand corner of the display, as all measurements must be in
these units.
Begin the calibration mode on the meter.
Insert the probe into the conductivity standard solution, ensuring the whole probe is submerged.
Wait for the display to settle on a reading.
Note the temperature of the conductivity standard solution as measured by the probe, on the
meter display.
Record it in the water chemistry data book.
Referring to the temperature as measured by the analogue thermometer, read the scale on
the side of the conductivity standard solution bottle.
Note the temperature standardised conductivity value, to the nearest degree.
To calibrate the meter, remove the small yellow screwdriver from the kit.
Insert the screwdriver into the bottom of the meter.
Gently turn the screw until the display reading matches the desired temperature standardised
conductivity value.
Record this figure in the water chemistry data book.
Return the screwdriver to the kit.
Remove the probe from the solution, rinse it well with deionized or tap water and place
it on a clean surface.
Replace the cap on the conductivity standard solution and put both bottles to one side.
Thoroughly rinse the conical flask with tap water.
Also thoroughly rinse the measuring cylinder with tap water.
In the alkalinity test kit is a bottle of bromocresol green indicator solution.
Remove the small plastic pipette from its bag and open the indicator solution.
Place the opened bottle back into the kit box.
Note that the indicator solution will stain work surfaces, clothing and skin, and should
be handled with caution.
There are two titrators in each test kit, one containing a cartridge of 1.6N sulphuric
acid, and the other containing a cartridge of 0.16N sulphuric acid.
Each titrator has a delivery tube, labelled for the different acid strengths.
Always ensure you use the 1.6N acid to begin with.
Remove the cap from the cartridge, take the delivery tube out of its bag and attach it
to the end of the cartridge.
Carefully dispense a small amount of acid into the sink
or large Nalgene® laboratory beaker.
Ensure the delivery tube contains no air bubbles.
You are now ready to begin testing.
Place the titrator to one side and remove the cap from the first
stream water sample bottle.
Pour just a small amount - around 20 Ml of the stream water sample into the glass measuring
cylinder and rotate to rinse the cylinder.
Dispose in the sink or laboratory beaker.
Fill the measuring cylinder with 100 mL of the stream water sample.
Measure this precisely.
Always read from a flat surface and at eye level, from the base of the meniscus.
Meanwhile, place the conductivity probe into the remaining stream water in the sample bottle,
and leave it to stabilise.
Take the measured 100 mL water sample in the glass measuring cylinder and pour the whole
contents into the conical flask.
With the pipette, add three drops of bromocresol green indicator solution to the conical flask.
Swirl the sample well to ensure that the solution is evenly mixed.
Take the 1.6N titrator and turn the dial until the display reads ‘0000’.
You are now ready to begin dispensing the sulphuric acid.
Place the delivery tube into the water sample in the conical flask.
Rest the titrator in one hand and twist the upper wheel to deliver the 1.6N acid, slowly.
Continuously swirl the sample to ensure that the acid is evenly distributed.
Observing the water sample in natural light and against a white background will make it
easier to identify the colour change.
Do not rush the process, as adding too much acid will mean that the titration endpoint
is missed.
Some samples may require hundreds of units, or only a few, to be added before a colour
change is observed.
Continue to add sulphuric acid stepwise until you observe the first permanent colour change
from blue to green.
When you observe a permanent change in colour to green, mentally note
the reading on the dial.
To confirm the endpoint has been passed, add a few more units of acid and observe a colour
change from green to straw yellow.
Record the number of units noted at the first permanent colour change from blue to green
in the ‘Total Alkalinity’ column of the water chemistry data book.
Dispose of the flask contents in the sink or laboratory beaker.
Take note of the reading from the conductivity probe.
Record this reading in the water chemistry data book in the ‘Conductivity’ column,
adjacent to the total alkalinity reading, double checking that the site number on the
bottle matches the one in the water chemistry data book.
Rinse the probe with deionized or tap water and place it on a clean surface.
Repeat this process for all samples.
It is imperative that the conductivity and total alkalinity tests are done together and
at the same time, as this is most efficient and a sample will begin to de-gas once the
bottle is opened.
If a total alkalinity reading is 30 or less, the titration must be repeated using the cartridge
containing the weaker 0.16N acid.
When all conductivity and total alkalinity measurements have been taken, always repeat
the process for the first three samples.
Record the repeat measurements in the water chemistry data book in brackets after the
original ones.
Also take repeat measurements for any readings that you feel are atypical.
Finally, re-measure the conductivity standard solution and record the result in the water
chemistry data book.
When all the tests are complete, carefully empty the bromocresol green indicator from
the pipette into the bottle, return the pipette to its bag and replace the cap on the bottle.
Remove the delivery tube from each titrator and return each to its labelled bag.
Replace the cap on each acid cartridge and return the titrators to the kit, along with
the rest of the equipment.