Tuesday, March 17, 2009

Practical P31/32 (Part 2)

Maximum error

Maximum error is usually marked on the glassware.

• A pipette has a maximum error of 0.05 cm3 in each measurement.

Calculation of percentage error

Percentage error = (maximum error ÷ quantity measured ) x 100%

Reading burettes
A burette is graduated in divisions every 0.1 cm3.
Using the half-division rule, the estimation is 0.05 cm3.
Burette is recorded to two decimal places with the last figure either ‘0’ or ‘5’.
The maximum error in each measurement = 0.05 cm3.
The overall maximum error in any volume measured always comes from two measurements, so
the overall maximum error = 2 x 0.05 cm3 = 0.1 cm3.
In a titration, a burette will typically deliver about 25 cm3 so the percentage error is small.

Percentage error = (2 × 0.05 ÷25.00) x 100% = 0.4%

The percentage error becomes more significant when burette is used to deliver small volume
For delivery of 2.50 cm3,

Percentage error = (2 × 0.05 ÷ 2.50)× 100% = 4%


Melvin Goh Leong Seek said...

I'm in group PAPER 32...
dunno will be harder or not..
are u handling section 32? or 31? or not handle both?
tq...but from the past yrs....paper 32 is far way harder. true?


chauky said...

I don't think that P32 is always harder than P31. In the last May practical exam, P32 is easier. That's my opinion.