This is the apparatus and materials that we will be using for the titration. The
burette pipette pipette bulb and burette clamp can be found along the side bench.
The indicators will be provided by the TA. Everything else can be found in your
drawer. First start off with the clean workbench and place a retort stand on
top of it. Obtain a burette clamp and attach it about half the height of the
retort stand. Place a white tile on top of the working bench just in front of
the retort stand. This can be found in the drawer under your fume hood. Now
obtain a 50 mil burette and attach it to the burette clamp. Check if the stock
is open.
You don't want to spill your chemicals on your workbench.
When horizontal the burette stock is closed
otherwise it is open. After that place a short stem funnel on top of the burette.
Obtain a large beaker and label it waste. Place this beaker on top of the
white tile just under the burette.
Obtain another beaker and fill it up with distilled
water to rinse the burette. Fill the burette with distilled water to about a
quarter of its height then remove the burette from its clamp and swirl it to
ensure thorough rinsing. Make sure to coat
all the sides of the burette. Drain the water into the waste beaker to the
burette tip as well as a top of the burette to rinse completely.
Repeat this process twice with distilled water and then three times with about
five mils of your titrant. The titrant is the reagent of known concentration which
is dispensed from the burette during titration. At this point before filling
up the burette with your titrant make sure that the stopcock is closed.
Once the burette has been rinsed with the titrant clamp the burette and ensure
that it is vertical.
You are now ready to fill the burette with the same titrant. Using the short
stem funnel.
Fill the burette from the top with the solution close to the top of the burette.
You may need to lift up the funnel slightly to allow the solution to flow
in freely. If any solution gets on the outside of the burette be sure to wipe
it off. Once the burette has been filled.
remove the funnel. It is important that you remove the funnel at this step
before taking any readings or else you may drip
additional solution into your burette which may lead to inaccurate readings.
Make sure that there are no air bubbles in either the barrel or the tip of the burette.
This is an indication of a dirty burette. It is important that the tip is filled with
solution or otherwise inaccurate volumes may be dispensed. If the burette is leaky
tighten the knob on the stopcock. Now allow the solution to drain until it is within
the graduated portion of the barrel just under the 0.00 mil mark. Also ensure
that the burette is flowing freely.
There is no reason to attempt to start each titration with the solution exactly
at 0.00 mill. This practice wastes time and chemicals. Touch the beaker to the
tip of the burette to remove any hanging drops. Remove any drops adhering to the
sides of the tip with a clean tissue.
Once you're set up take the initial volume reading to the nearest 0.02 mill.
You will have to estimate the last digit. This digit is important and significant.
Be sure your eye is at the level of the meniscus. Reading from an angle rather
than straight on results in parallax error.
You may want to use a burette reading card to help you take a more accurate
reading. Record the level of the meniscus in the burette carefully before and
after every titration. Record this reading in your lab notebook. Now obtain
three Erlenmeyer flasks and label them appropriately. Obtain a pipette bulb and
squeeze out all the air then place it on top of the appropriate grade A pipette.
Ensure that there is good contact between the pipette and the pipette bulb.
Do not force the pipette bulb on to the pipette. Any size pipette would fit in
these blue bulbs. As you release the bulb lift the tip of the pipette from the
bottom of the beaker to allow proper flow. Suck up enough distilled water so
that it fills about half the pipette. Release the bulb slowly to ensure slow
and controlled up flow of the liquid. Remove the pipette bulb and scroll the
pipette horizontally to rinse it thoroughly. Drain the solution into the
waste beaker through the tip as well as the top of the pipette to rinse completely.
Repeat this process two more times with distilled water and then repeat three
times with your titrant.
Dry the top of the pipette before each rinsing to avoid sucking up liquid into the pipette bulb.
After this fill your pipette with titrant using your pipette bulb past the
graduation near the top of the pipette.
You do not need to fill the pipette in one go.
Place your index finger on top of the pipette to re-evacuate the bulb and
continue on from that point. Do not hold the body of the pipe at as your hand
will supply heat to the instrument and affect the calibration.
Now raise the pipette to eye level over the waste beaker and slowly twirl the
pipette on your hand so that the level of the solution or the bottom of the
meniscus is directly on the line.
Hold the pipette vertically and place into the Erlenmeyer flask and let it drain.
Touch the tip of the pipe at to the side of the flask to break the surface tension.
Do not blow out the pipette or shake it after the liquid has drained out.
The pipette is calibrated to include the small amount of liquid left in the tip.
The flask does not have to be dry for the solution to be transferred
however it must be clean. Add three drops of the appropriate indicator to the
flask. Place the flask under the burette and adjust the height of the burette so
that the tip of the burette is
slightly below the rim off the flask. This is to ensure that the liquid falls
directly into the flask. Position the burette so that the stopcock is on the same
side as your dominant hand. Hold a flask with your dominant hand and the stopcock
with the other. Position your fingers as shown.
They remain in this position throughout the titration. To start the titration
open the stopcock and allow the titrant to flow slowly and swirl the flask at
the same time.
Periodically close the stopcock and use the wash bottle to wash down the sides
of the flask. Rrotate the flask to avoid washing the tip of the burette. Do not
wash the tip of the burette as this will create a vacuum and pull out more
titrant from the burette. Note that adding water to the solution in the Erlenmeyer
flask changes the concentration of the reaction mixture
however it does not affect the number of moles of chemicals in the flask and
therefore the reading is not affected.
Continue adding titrant until the end color of your indicator becomes more
prevalent. When this happens
start dispensing partial drops. Open the stopcock slightly and let a drop grow
on the tip of the burette. Touch the tip to the side of the flask to add the
partial drop. Wash down the side of the flask with distilled water to ensure
that the partial drop of titrant added drains into the solution.
Ty to add progressively smaller partial drops as you approach the end point. When the
end point is reached the palest color of the appropriate indicator will be
visible for 30 seconds or more with constant swirling. If you are unsure take
the reading and add another partial drop to see if it is closer to the end point or
if it is over the end point. Record the correct final volume into your notebook.
Repeat this titration two more times as titrations are done in triplicates.
Each day and with each
change of solution the burette should be thoroughly washed with soap and water
rinsed with distilled water rinsed with the new titrant. Once you finish your
titration rinse the burette with distilled water at the burette tap
which can be found along the side bench. Burettes are stored upside down but then
open the stopcox so that the material does not collect in their tip.