chem report 問題

For a primary standard,it must be a very stable cpd, implying not to absorb any gas such as CO2 from air or moisture either . Any unstable cpds are not stable to be used as a primary standard. For NaOH, it absorbs CO2 from air and for hydrated sodium carbonate , it is already hydrated (i.e. contains water).
To remove any impurity stuck on the wall of the pipette. Don't use distilled water, water layer stuck on the pipette wall may dilute the standard solution.
cpd = compound.
I hope you may find the answers helpful.