Question

why do you have to rinse the pipet with the stock h2so4 solution before using the pipet to deliver 15.00 ml to each of the erlenmeyer flasks?

Answer 1

We should rinse the pipette each time before titration to ensure the accuracy of titration. For example if we had used the pippette for NaOH before, some of the acid reacts to neutralise the base. Hence, the reading of acid required for the current titration will be more than actual. If it were used for another acid, say HCl earlier, then some HCl will react with the reagent reducing the required H2SO4, throwing off the reading. So, in order to improve the accuracy of the readings, we need to rinse the pippette with the solution to be used in any titration.