No Brain Too Small CHEMISTRY AS 91161 v2 Carry out quantitative analysis (Internal assessment)
Burette
– use to accurately measure the volume of
liquid needed in a reaction
Burette Scales
– read to the bottom of
the meniscus – you can read to 0.05 mL
(half way between the 0.1 mL divisions. Eye
is level with the bottom of the curve. Some
say you can read to 0.02 mL with care and
practice!
Example results table
– the volume delivered
(the titre) is the difference between the last scale
reading and the first (initial) scale reading. Answers
must not be negative!
Example
Rough
1st
2nd
3rd
Final volume
(mL)
15.30
30.10
Initial Volume
(mL)
0.00 15.30
Volume used
(mL)
15.30
Record volumes to 2 decimal places. Your initial reading
does not have to start at 0.00 mL
You are aiming for 3 results within 0.20 mL of each
other. It should be possible to get them within 0.10
mL. These will then be classed as concordant results.
You use concordant results to calculate the average
titre.
Pipette -
used to accurately measure a volume of
solution and deliver into a conical flask.
- Volumes measured are usually 20.0 or 25.0
mL. At our school we use Diji pipettes.
Make sure you are familiar with the type of pipette
that you will use in your assessment.
You rinse a pipette before use with a little of the
solution you will be using it with.
Diji example
– deliver a 20.0 mL sample
into a conical flask
Pipette Techniques – may vary according
to the type of pipette you use at
your school
Rinse the burette with
some of the solution that
you are going to use in your
titration. Don’t use water!
Don’t forget to check that
there are no air gaps below
the tap – drain some of the
liquid through until all air
has gone!
Eye is too low in the first picture and
too high on the third. The middle gives
correct reading of 25.65 (mL)
Keep pipette vertical
Use a slow smooth action
Have your eye level with the bottom of the
meniscus.
Touch tip of pipette on side of conical flask at
end of delivery.
Avoid having unexpected air bubbles when
drawing up the liquid.
