titrations Flashcards
what is a standard solution
a solution of known concentration
where does the standard solution go
250cm3 volumetric flask
what measures 25cm3 of standard solution
volumetric pipette
what is the meniscus
the curve in the surface of a liquid
how to prepare a standard solution
- weigh mass of solid using balance
- add to beaker of distilled water and stir till dissolved
- add to volumetric flask
- add rinsings from stirring rod and beaker
- make up to scratch mark with distilled water
- add stopper and invert several times to mix
why do you add rinsings to volumetric flask
to ensure that all solute particles are in the solution and not left on the rod/beaker
how to titrate
- transfer 25cm3 of standard solution to conical flask using volumetric pipette
- add few drops of indicator
- transfer acid to burette
- take initial burette reading
- add acid to conical flask and swirl until nearing end point then add dropwise
- stop when end point is reached
- take final burette reading
- repeat until you get 2 concordant results
what does concordant mean
within 0.1cm3 of each other
what does mean titre show
volume of acid used
how to calculate concentration of acid
- find moles of standard solution (concentration and volume are known)
- use balancing numbers to find moles of acid from equation
- calculate concentration using n=c x v
what to do if there is a drop left in the pipette
force it out
the pipette is calibrated to account for liquid that remains in the tip
improvements to experiment
- white tile under conical flask so colour change is more clear
suggest 2 modifications that would reduce percentage uncertainty in the mass of the residue
use a balance which weighs to more decimal places
use a larger mass
