rp 01 making volumetric solution and acid-base titration Flashcards
volumetric solution method
1) read mass of weighing boat + solid
3) empty solid in beaker
2) read mass of empty weighing boat
4) record difference in mass
5) add distilled water to dissolve solid with glass rod. transfer to volumetric flask with washings
6) make up to 250cm3 with distilled water w pipette in volumetric flask
7) shake flask
volumetric solution common errors
1) fill so the bottom of the meniscus is at the line on the neck of the flask - place white paper behind so its easier to see
2) flask should be stoppered to prevent evaporation of any of the solution therefore altering concentration
3) incomplete dissolution of solute - results in less concentrated solution
reducing uncertainties in measuring mass
using a more accurate balance or larger mass will reduce uncertainty. weighing by difference will ensure a more accurate measurement of the mass of the solid added
titration method
1) 100cm3 of standard solution in a beaker
2) fill burette with standard solution of known concentration
3) using a graduated pipette transfer 25cm3 of solution with unknown concentration into a conical flask w 3 drops of indicator
4) record initial burette reading, titrate, record final burette reading, calculate average titre with concordant results
how to improve accuracy of the titration
1) use a clean, dry beaker
2) rinse the beaker w a small vol of solution
3) rinse the 25cm3 pipette with solution of unknown conc
4) rinse conical flask with deionised water
5) make sure burette readings are to the appropriate precision and are read from bottom of meniscus
6) add solution slowly and swirl flask, then add solution dropwise
7) use a white tile underneath to help observe colour change
what happens if the jet space below the tap is not filled
it fills during the titration then leads to a larger than expected titre vol
why is a conical flask used rather than beaker
better suited to swirling the flask, less likely for contents to splash/spill from the flask
why only add a few drops of indicator
too much will affect the pH and therefore the titration result
why is distilled water used to wash the flask
the sides of the flask are washed down, ensures all reactants are washed down to the bottom of the flask into the mixture
why does the distilled water not affect the accuracy of the titre
it does not change the number of moles of each reactant so the same titre volume would be obtained
reducing uncertainties in titration
1) replace measuring cylinder etc with pipettes which have lower apparatus uncertainty
2) make titre vol larger by inc conc/vol of conical flask or dec conc of burette
what is a standard solution
solution of known conc
