titrations triple Flashcards
(2 cards)
method for acid alkali titration
Use a pipette and pipette filler to accurately measure 25.0 cm³ of sodium hydroxide solution and transfer it into a clean conical flask.
Place the conical flask on a white tile.
The white tile helps you see the colour change more clearly.
Add a few drops of a suitable indicator (e.g. phenolphthalein, which is pink in alkali and colourless in acid) to the sodium hydroxide in the flask.
Rinse the burette with hydrochloric acid to ensure accurate results, then fill it with the acid using a funnel.
Remove the funnel after filling to avoid extra drops entering the burette.
Place a beaker underneath the burette tap in case it’s accidentally open.
Run a small amount of acid through the burette to remove air bubbles, especially from the jet space (the area between the tap and the burette tip).
Record the initial burette reading to the nearest 0.05 cm³.
You can adjust the acid level so it starts at 0.00 cm³, but this is not essential.
Make sure the tip of the burette is inside the conical flask to avoid splashing.
Perform a rough titration first:
Run the acid into the flask in 1–3 cm³ portions, swirling the flask vigorously each time.
Watch for a sudden colour change (end-point).
Quickly close the tap when this happens and record the final burette reading.
This gives an estimate of the volume needed.
Repeat the titration using fresh sodium hydroxide:
As you approach the rough end-point volume, add the acid one drop at a time, swirling constantly.
Stop adding acid as soon as the indicator changes colour sharply (e.g. pink to colourless).
Record the final burette reading and calculate the volume used.
Read the bottom of the meniscus at eye level to avoid parallax error.
Repeat the titration until you get two concordant results — that means within 0.10 cm³ of each other.
purpose of titrations
determine exactly how much alkali is needed to neutralise a quantity of acid or vice versa
