# Why rinse flask with distilled water when the flask will be used for storing aliquots of HCl for titration?

In an experiment for standardisation of NaOH with titration, the lab manual instructed students to rinse conical flasks that were supposed to store 1mL aliquots of hydrochloric acid with distilled water.

Won't the excess water dilute the aliquot? Why not rinse with the HCl solution instead?

• The dilution with excess water won't affect the totat amount of HCl in the solution, which is what you will be titrating. You still know how much HCl you have from your quantitative addition of the 1 mL aliquiot. If you rinsed with HCl, you would have no idea how much HCl you really had and therefore you couldn't calculate the concentration of your NaOH. – airhuff Mar 16 '17 at 7:38
• Thanks airhuff, I think I get it now. If I used HCl for rinsing, there will be more HCl in the flask than what I put in (1mL) and will therefore impact results. Thanks alot for the help. – Bryan Mar 16 '17 at 7:50
• Technically, if you're doing very sensitive work, you would rinse with whatever you're about to use. This is assuming you can't just grab a new flask that doesn't have anything in it. – Zhe Mar 16 '17 at 13:47

The dilution with excess water won't affect the total amount of $$\ce{HCl}$$ in the solution, which is what you will be titrating. You still know how much $$\ce{HCl}$$ you have from your quantitative addition of the $$\pu{1 mL}$$ aliquiot. If you rinsed with $$\ce{HCl}$$, you would have no idea how much $$\ce{HCl}$$ you really had and therefore you couldn't calculate the concentration of your $$\ce{NaOH}$$.