titrations Flashcards
method for carrying out a titration
- rinse equipment
- pipette 25cm3 of alkali into conical flask
- touch surface of alkali with pipette
- add acid solution from burette
- make sure the jet space in the burette is filled with acid
- add a few drops of indicator and refer to colour change at end point
- phenolphthalein (pink (alkali) to colourless (acid): end point pink colour disappears) - use if NaOH used
- methyl orange (yellow (alkali) to red (acid): end point orange)
- use if HCl is use - use a white tile underneath the flask to help observe colour change
- add acid to alkali whilst swirling the mixture and add acid dropwise at end point
- note burette reading before and after addition of acid
- repeat titration until at least 2 concordant results are obtained
concordant results
two readings within 0.1 of each other
safety precautions
- acids and alkalis are corrosive (at low conc. acids are irritants)
- wear eye protection and gloves
- if spilled, immediately wash affected parts after spillage
- if substance is unknown treat it as potentially toxic and wear gloves
why is a conical flask used instead of a beaker?
easier to swirl the mixture in a conical flask without spilling the contents
why is distilled water added?
to conical flask during a titration to wash the sides of the flask so that all the acid on the side is washed into the reaction mixture to react with the alkali.
- it doesn’t affect titration reading as water doesn’t reaction with reagents or change the number of moles of acid added
working out average titre results
only make an average of the concordant titre results
recording results
- should be clearly recorded in a table
- results should be recorded in full (both initial and final readings)
- ALWAYS RECORD RESULTS TO 2 DECIMAL PLACES I BEGGGG.
testing batches
in quality control, it will be necessary to do titrations/testing on several samples as the amount/concentration of the chemical being tested may vary between samples
