In this acid-base titration, a standard solution of sodium carbonate will be used
to determine the exact concentration of a
dilute solution of hydrochloric acid.
An indicator solution will be used to help find the endpoint
of the titration, in this case methyl orange will be used,
which will turn from a red to yellow.
Here is the equation for our reaction.
Pour approximately 50 cm3 of your stock sodium carbonate solution
into a dry, clean beaker.
Rinse the burette several times with distilled water.
Using the funnel, add a little of the sodium carbonate solution to rinse
through the burette above and below the tap.
Discard the rinsings and repeat this
step two more times.
This makes sure that you do not dilute the solution when you fill the burette.
Fill the burette with sodium carbonate solution above the zero mark,
and remove the funnel.
Using the tap at the base of the burette,
allow the sodium carbonate solution to flow into the beaker
until the level of liquid is at, or a little below the zero mark.
Ensure there are no air bubbles in the nozzle.
These can be removed by just running a little more solution through the tap.
Next you'll need to be record the level of the solution in the burette.
It can be tricky to see the meniscus clearly,
it helps to hold a piece of white card behind the burette
so that it lights up the bottom of the meniscus.
Take the first burette reading
with the meniscus at eye level.
Take a reading from the
bottom of the meniscus to the nearest 0.05 cm3.
Make a note of the reading.
Rinse the pipette with some distilled water.
and then, two or three times with some of the dilute hydrochloric acid solution.
Rinse the conical flask with distilled water only.
Using the pipette and the pipette filler, transfer exactly 25 cm3 of
the hydrochloric acid solution into the clean conical flask.
Allow the pipette to drain for several seconds after it's been emptied,
then touch the tip against the side of the flask.
Do not force the last drop of liquid from the tip of the pipette
Add two to three drops of methyl orange indicator to the flask.
Take note of the colour of the solution,
placing a white tile underneath the conical flask to make the colour more obvious.
Before proceeding with the main experiment, carry out a rough titration
this is to determine roughly how much of the alkaline solution is needed to
neutralise the acid, and will give us an approximate value of the endpoint.
Start by running the sodium carbonate solution quickly from the burette into the
conical flask, while swirling the contents.
When the colour change of the indicator
starts to be more persistent, slow down the flow, then start by adding
0.5 cm3 at a time until the endpoint is reached.
Swirl the flask continuously until this is achieved.
Note the burette reading.
Then take your conical flask empty and wash it
and using your pipette add a second
25 cm3 sample of hydrochloric acid solution, along with
those two to three drops of methyl orange indicator.
Now you're ready for
your first accurate titration.
As the amount of sodium carbonate required to reach the
endpoint is now roughly known, you can stop by rapidly adding the solution
until the amount added is approximately 2 cm3
from the endpoint.
As the endpoint is approached, gently swirl the conical flask,
then while continuing to swirl, add the sodium carbonate solution
drop by drop from the burette.
After the addition of each drop, rinse the tip of the burette
with distilled water.
Swirl the flask. Then rinse the side of the conical flask
with further distilled water.
When a permanent colour change occurs note the reading.
Repeat the titration until two titers agree within 0.1 cm3.
Once you've recorded your data, you should have all you need to
calculate the concentration of the hydrochloric acid.