Apparatus & Percentage Error Flashcards
The selection of the measuring instruments should be based on the __________
Level of precision/accuracy required
Relation between the design of the apparatus and the accuracy of the apparatus
The narrower the apparatus, the more accurate the apparatus is
How to read a volume from the measuring cylinder
Eye must pe parallel to the reading/cylinder
Read from the meniscus
Type of error that can appear if the eye wasn’t parallel to the reading
Parallax error
Order these apparatus from the most accurate to the least accurate
Graduated measuring cylinder
Burette
Volumetric pipette
Graduated pipette
Volumetric flask
Beaker
Erlenmyer/conical flask
- Volumetric pipette- Volumetric flask
- Burette - Graduated pipette
- Graduated measuring cylinder
- Conical flask - beaker
Maximum % of error that can happen
5%
What is an aliquot?
An aliquot is a fraction, portion, or part that is contained an exact number of times in another.
A torsion prescription balance has a sensitivity requirement of 6.5 milligrams. Explain how you would weigh 15 milligrams of atropine sulfate with an accuracy of +/- 5%, using lactose as the diluent.
5mg →100mg
6.5mg → 130mg
15×20=300mg API
2300g lactose
130×20= 2600mg Total
2600/20 = 130mg
Define percentage of error
The maximum potential error multiplied by 100 and divided by the quantity desired.
Formula for finding the percentage of error
Error × 100
———————
Quantity desired
The precision obtained in a given measurement depends
on:
• the selection of the measuring device used.
• the volume of liquid being measured.
• the skill and care of the pharmacist.
Using a graduated cylinder, a pharmacist measured 30
millilitres of a liquid. On subsequent examination, using a
narrow-gauge burette, it was determined that the pharmacist had actually measured 32 millilitres. What was the percentage of error in the original measurement?
2/30 × 100 = 6.7%
Use of sensitivity requirement
to determine the percentage of error in a given weighing.
