A student performs a serial dilution, but is not careful about the correct proce
ID: 532901 • Letter: A
Question
A student performs a serial dilution, but is not careful about the correct procedures for using the pipet and volumetric flask. Explain how the following errors would affect the concentrations of the diluted solution.
a) The pipet is rinsed with water, but not with the solution that is measured.
b) The student uses a rubber bulb to force out the liquid remaining in the tip of the pipet into the volumetric flask
c) After carefully mixing the diluted solution in the volumetric flask, the student pours the solution into a beaker that was not carefully rinsed with solution.
Explanation / Answer
For a and c, the beaker and the pippete are not rinsed with the solution that is used in the experimentation, instead he used water. In this case, there is a chance that water adds to the dilution and the concentration of the solution decreases. If the beaker is not rinsed well with the solution, there is a chance that impurities or other chemicals are included.
b) The pippete is so designed that the last drop needs to be left in case of TD marked which means to deliver and to overcome the surface tension, it is so designed that it can be left there itself.if a tc which means to contain and last drop in the pippete should be blown off. So pippetes which are calibrated td, the liquid shouldn't be forced out. The change in concentration because of forcing may be little.but still may it is more pronounced when high precision or accuracy are considered
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