Drying the conical flask during titration (1 Viewer)

[starshine02]

My textbook says that the conical flask used to hold the standard solution only has to be washed with distilled water and doesn't have to be dried. I've also checked up on some notes and most of them say that drying the flask is unnecessary too.

I don't really understand why? Doesn't the leftover water there dilute the standard solution so it changes the concentration slightly? When I performed the experiment, I remember drying it because my teacher told me to.

Thanks in advance.

 

[golgo13]

Umm doesn't need to be dried so long as you've washed it well with distilled water, the water doesn't change much tbh cause u still use a wash bottle to wash down the sides of the concial flash during the titration

 

[deswa1]

Because the concentration of the stuff in the conical flask is irrelevant. You are trying to find the concentration of say the acid in the burette. The way you do this is you pour it into the conical flask and when you see a change in colour blah blah, you know when equal numbers of H+ and OH- have reacted. So in the conical flask you have a fixed number of MOLES of say a base in this case. So when the colour changes, you can work out the number of moles of acid that were poured in the volume measured by the burette and hence the concentration of the acid in the burette.

The concentration of the base doesn't matter- no matter how much water you add, the number of moles of base will remain UNCHANGED. Does that make sense?

 

[starshine02]

Oh ok thanks deswa. I didn't think of the moles reacting! Yes it makes sense now I just compared it to the burette cleaning to prevent impurities and dilution and it seemed a bit odd that it wasn't being cleaned as much.

 

[someth1ng]

What deswa1 is correct. I would like to reiterate.

Once you add say 20mL of a standard solution (this is measured and matters), you can determine the amount of moles of the standard solution present - once you add this to the conical flask, the number of moles that react is what matters - if you add more water to the flask, it won't matter (and it is not measured either) as the number of moles still present is the same.

However, in the burette, you don't know the concentration and so, you don't know the amount of moles reacting. If you add more water, it will dilute and more water is needed - this will affect your calculation.