Core Practical 3 Flashcards
What happens to a solution during a dilution?
The volume increases, so the concentration decreases. Moles stays the same.
Why is a conical flask used in preference to a beaker?
Easier to swirl without spilling the contents
Why would you wash the sides of the conical flask with distilled water during a titration?
So that all acid reacts with alkali (adding distilled water doesn’t change the titration reading as it doesn’t react with the reagents)
What happens if you don’t fill the jet space (run some acid/base through the tap) ?
You’ll have a larger than expected titre reading
If titres are concordant what does this mean for the experiment?
Results are reproducible
The uncertainty of a reading (a single judgement) is at least….
+ or - 0.5 from smallest scale reading
The uncertainty of a measurement (two readings e.g. burette) is at least…
+ or - 1 from smallest scale reading
How can you decrease the uncertainty of apparatus?
Increase size of measurement made.
How can you decrease the uncertainty of a burette reading?
Make the titre a larger volume by increasing the volume and concentration of the substance in conical flask or decreasing concentration of substance in the burette.
How can you reduce uncertainty in measuring mass?
Weighing sample before and after addition and then calculating difference will ensure a more accurate measurement of the mass added.
Why should you rinse the pipette/burette with solution opposed to water?
The pipette and burette should be rinsed with the solution being used so that any water or other solution in the pipette / burette does not dilute the solution we are measuring.
What should we rinse the conical flask? Why?
The conical flask should be washed with water and not the solution going into it. If we used the solution, we
would have more moles of that substance in the flask than we think we have.
Why may phenolphthalein become colourless again after end point?
reacts with CO2 in air
