rp1 - solution + titration

describe the method for 1a - making up a standard solution (250 cm³ of NaHSO₄ w/ a conc of approx 0.100 mol dm^-3):

1. calculate mass of NaHSO₄ solid needed using mol = conc x vol and mol = mass/Mr

2. weigh a clean, dry weighing boat w/ mass balance

3. place weighing boat and use a spatula to transfer approximately the calculated mass of NaHSO₄

4. use mass balance to weigh weighing boat and contents and record precise mass

5. pour contents into beaker and reweigh weighing boat

6. calculate mass of NaHSO₄ transferred

7. add approx 100 cm³ of deionised/distilled water to beaker containing solid and stir until dissolved w/ glass road

8. using a funnel, pour contents of beaker into a 250 cm³ volumetric flask and using the wash bottle, rinse beaker, funnel and glass rod into same volumetric flask

9. make volumetric flask up to graduated mark w/ deionised/distilled water from wash bottle

10. stopper and shake volumetric flask thoroughly to mix contents

11. calculate exact conc of solution in mol dm^-3 and use this to label flask

describe the method for 1b - titration:

1. pour approx 100 cm³ of NaHSO₄ solution into clean, dry, labelled beaker and use a small vol of this solution to rinse the burette

2. pour approx 100 cm³ of NaOH into a second clean, dry, labelled beaker

3. rinse a 25 cm³ pipette w/ NaOH and use a pipette filler to pipette exactly 25 cm³ NaOH into a 250 cm³ conical flask (rinsed w/ distilled water)

4. add 2-3 drops of phenolphthalein in solution in conical flask

5. record initial burette reading

6. titrate contents of conical flask by adding NaHSO₄ solution from burette slowly, then dropwise near end point, swirling flask gently

7. when titration has been completed and solution has turned colourless from pink, record final reading on burette and use this to calculate vol of NaSO₄ needed to neutralise NaOH

8. this is your rough titre - repeat until concordant results are obtained and calculate mean vol of NaSO₄ used

why do we rinse the burette w/ NaHSO₄ instead of water?

prevents dilution of NaHSO₄ solution by any residual water left in burette, which would decrease precision of titration

why do we rinse the pipette w/ NaOH instead of water?

prevents dilution of NaOH solution by any residual water left in pipette, which would decrease precision of titration

what are concordant results?

results that are w/in 0.1 cm³ of each other

what is a standard solution?

a solution for which the concentration is accurately known

what is the purpose of ‘washing’ the beaker/glass rod into the solution in the volumetric flask?

ensures there is no solute left behind in the beaker or on glass rod

why must the tip of the burette be filled w/ liquid before the titration begins?

to prevent any air bubbles being present, which would produce an inaccurate volume

give a suitable table for the titration results to be recorded in:

how can we calculate the uncertainty and % error of the equipment used?

uncertainty = no. of readings taken x smallest increment/2

% error = uncertainty/reading x 100