Question

In an experiment, someone is preparing 50.00 mL of a 0.200M CoCl₂ stock solution. They calculates that they needs 10.00 mL from the concentrated reagent bottle. Why can’t they simply pour 10.00 mL of concentrated CoCl₂ into a beaker and then add 40.00 mL of water, using graduated pipettes to keep the same level of precision?

Answer 1

Every time we do a measurement , there is some error associated with it .

More times we will use the apparatus for measurements , more will be the errors associated with it as error of every time is added up .

As per the stated method , he has to use that graduated pipet 5times (1time for stock + 4 times for water) , thus associated error will be high by this method.

Better method is take a 50mL volumetric flask and add 10mL of stock solution with graduated pipet into it. Then raise the volume of flask upto 50mL mark with distilled water , in this method apparatus are used twice only and thus errors associated will be minimum.