RP titrations Flashcards
method
- use a pipette and pipette filler to put exactly 25cm³ NaOH solution into the conical flask
- clamp the burette vertically in the clamp stand, and place the conical flask and white tile underneath
- fill burette with sulfuric acid to the 0cm³ line using a funnel
- add a 5 drops of phenolphthalein to the solution and swirl
- carefully open tap so sulfuric acid flows into flask, continually swirl and look for colour change from pink to colourless
- slow the drops down when there are signs of a permanent colour change
- read burette scale and record the volume of acid added to neutralise NaOH
- repeat and calculate mean, excluding rough titrations and anomalies
why is a white tile used?
to make the colour change easier to see
equipment list
-burette
-conical flask
-white tile
-indicator
-pipette and pipette filler
-clamp stand
-0.1 mol/dm³ NaOH solution
-sulfuric acid
-funnel
-clamp stand
safety
wear goggles when working with acids
tie hair back
report broken glassware
why might a volumetric pipette and pipette filler be used rather than a measuring cylinder?
a volumetric pipette will measure 25cm³ more accurately
what is the purpose of repeating a titration?
to allow a mean titre to be calculated, reducing the effect of random error
why is the first titration often called a rough trial?
it gives an approximate idea of where the end point is so for further titres you can be more precise as you know the approximate volume required
why are burettes used?
they allow the solution to be added drop by drop, in small quantities
what indicators could be used and what colour change would you see?
methyl orange-yellow (alkalis) to red (acids)
litmus indicator-blue (alkalis) to red (acids)
phenolphthalein-pink (alkalis) to colourless (acids)
variables
independent-volume of titrant
dependent-pH solution, colour change
control-volume of NaOH
what is a titration used for?
to find the exact volume of acid needed to neutralise a set volume of alkali or vice versa
