Question

Analysing the data from natural water sample. Diff students used the same method to perform an experiment the result is high RSD %. Describe 3 possible reasons for the relatively high RSDs not including any form of the “human error”

Answer 1

RSD means relative standard deviation. It is also called as Coefficient of variation.

RSD = 100s/

where, s = Standard deviation, x= Sample mean

high perecentage of RSD may be due to

A. Systematic error

1. There is a fault in the measuring instrument.

2. change of environment in the time of experiment.

3. Sometime the measuring instrument has limiltation in analysis.e.g if someone wants to collect 20mL of solution, he or she could use beaker, a graduated cylinder or a burret. Here, the most accurate result can be found in burret because beaker is accurate within 5 mL, graduated cylinder is accurate within 1 mL and burret has accuracy limit of 0.05 mL.

B. Random error

Caused by uncontrollable variables, which can not be defined.