1) Acid- base titrations Flashcards
Describe a method you would use to make a solution.
1) weigh the sample bottle containing the required mass of the solid on a 2dp balance
2) transfer to a beaker and reweigh empty sample bottle
3) record the difference in mass
4) add 100cm^3 of distilled water t the beaker and use glass rod to stir and help dissolve the solid
5) sometimes substance may not dissolve well, so you could gently heat until solid has dissolved.
6) pour solution into a 250cm^3 volumetric flask via a funnel
7) rinse beaker and funnel and add washings form the beaker and glass rod into the volumetric flask
8) add distilled water until bottom of meniscus touched the line.
9) invert flask several times to ensure uniform concentration.
why would you not heat the volumetric flask?
flask would expand so volume would not be correct
how would you dilute a solution?
1) pipette 25.0cm^3 of original solution into a 250cm^3 volumetric flask
2) make up to the mark with distilled water using a dropping pipette for last few drops
3) invert flask several times to ensure uniform solution.
why would you use a volumetric pipette instead of a measuring cylinder?
VP has a smaller uncertainity
describe a method you would use for a titration.
1) rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)
2) pipette 25cm^3 of alkali wiht pipette
3) add acid into burette making sure th ejjet space is filled with acid
4) add few drops of indicator to alkali
5) use white tile underneath flask to help observe colour change
6) add acid whilst swirling the mixture and add acid drop wise at the end point
7) note burette reading before and sfter additon of acid
8) repeat titration until at least 2 concordant results (within 0.1 of each other)
why are titrations used?
- find out conc of a substance
- often done with neutralisation reactions but can also be done with redox
why is conical flask used instead of a beaker?
easier to swirl mixture without spilling
why is it important to fill the jet space?
will lead to larger expected titre reading
why should the burette be rinsed with substance before it is put in?
acid/alkali added may be diluted with residual water in burette or may react with substances form previous titrations
- will lead to larger than expected titre reading
when would you use indicator phenolphthalein?
with strong alkalis (NaOH)
what would you observe with phenolphthalein?
pink(alklai) to colourless (acid)
when would you use indicator methyl orange?
for neuralisation reactions where strong acids are used
what would you observe with methyl orange?
red (acid) to yellow (alkali) but orange is end point
How do you decrease apparatus uncertainties?
- using apparatus with greater scale divisions
- increase size of measurement made
How to reduce uncertainties in a titration?
-replacing measuring cylinders wit pipettes that have smaller percentage uncertainty
-make titre a larger volume
>increasing the volume and conc of substance in the conical flask
>decreasing conc of substance in burette
