Accidently rinse pipette or burette (1 Viewer)

[fatassmcfat]

OK this is confusing me
Say in your burette you have your KNOWN solution and you accidently rinse with water. What effect does it have on calculated concentration of your UNKNOWN?
And same for other way around- if unknown was in burette?

 

[aimpacc]

rinse water means u dilute ur sht. so the volume needed by unknown to reach the whatever point (i forgot) is less.
now c=n/v. if v decrease, so the perceived c increase.

burettes are fat, so its easier to continually run liquids from top to bottom, u essentially can just wash out ur water with the whatever solution. u shouldnt have a problem with burette....unless u dont know wat ur doing....

goodluck..

 

[golgo13]

Generally tho it shouldn't matter as much, but if you do it means u need more solution in the burette to dilute for the unknown meaning, he concentration of unknown would be more

 

[Kurosaki]

If you accidently rinse with water, then the solution will become diluted when you add it in.
Therefore, you will require a greater volume of solution to reach equivalence point.
However, we don't know this, so we assume it is still the initial concentration, which is HIGHER than the actual concentration.
Therefore, we overestimate the moles used, using n=cv.
More moles- greater concentration obtained.
I hope that that helps!

 

[hit patel]

If you accidently rinse with water, then the solution will become diluted when you add it in.
Therefore, you will require a greater volume of solution to reach equivalence point.
However, we don't know this, so we assume it is still the initial concentration, which is HIGHER than the actual concentration.
Therefore, we overestimate the moles used, using n=cv.
More moles- greater concentration obtained.
I hope that that helps!

+1

 

[someth1ng]

Generally tho it shouldn't matter as much, but if you do it means u need more solution in the burette to dilute for the unknown meaning, he concentration of unknown would be more

No, it matters A LOT.

 

[enigma_1]

No, it matters A LOT.

lol yeah I learnt that the hard way by screwing up my titration in my prac exam :rage: ck

 

[golgo13]

Maybe i haven't done it in a while but last i checked you rinse down your concical flask with purified water progressively during the prac?

 

[2xL]

Yeah but OP is talking about diluting the solution of known concentration (standard) in the burette. Not the conical flask.

 

[golgo13]

But you can apply the same principle, you're rinsing the burette you aren't exactly leaving huge amounts of water, yes your result will change but the change is small is what i'm saying, which alters your results slightly not a huge amount.

 

[Kurosaki]

But you can apply the same principle, you're rinsing the burette you aren't exactly leaving huge amounts of water, yes your result will change but the change is small is what i'm saying, which alters your results slightly not a huge amount.

In titration we require an extremely high degree of accuracy so it does matter a lot...?

 

[2xL]

In titration we require an extremely high degree of accuracy so it does matter a lot...?

Yes. I'd say it would matter significantly even if we had a few drops. Saying that "it wouldn't change much" is very poor justification imo.

 

[golgo13]

Ok, then i think it's fair to say if you guys want it acurate, then you should be rising with your use of solution, and drying with alcohol, because then the argument goes, if it was rinsed it may contain contamanent left in the droplets left within the burette even though it should be ok but your results wouldn't be accurate.
Principally i agree yes it requires a high degree of accuracy, but put into perspective and be practical for someone doing this in High School chem...

 

[someth1ng]

Maybe i haven't done it in a while but last i checked you rinse down your concical flask with purified water progressively during the prac?

No, don't do that. This would result in diluting too much - effectively resulting in pushing the pH closer to 7. If anything, you want the least amount of water possible to prevent this from happening.

 

[someth1ng]

Ok, then i think it's fair to say if you guys want it acurate, then you should be rising with your use of solution, and drying with alcohol, because then the argument goes, if it was rinsed it may contain contamanent left in the droplets left within the burette even though it should be ok but your results wouldn't be accurate.
Principally i agree yes it requires a high degree of accuracy, but put into perspective and be practical for someone doing this in High School chem...

This is very poor advice, it's not even funny.

There are a couple of times you should/need to wash with alcohol or ether or acetone. You do it when you want DRY glassware or when you need to get rid of organic residue. Ideally, what you really want to do is wash with water, then acetone, then water (deionised), then the solution it will hold but acetone is usually not needed because burettes should rarely have organics in them anyway. In any case, the results should be accurate just by washing with water and the solution it will hold. What's wrong with your argument is that there shouldn't be any significant amount of contaminants in the water you washed with if you used deionised anyway, and especially so if you washed properly. So no, your argument is not valid and even for a high school experiment, to propagate an idea that it's okay to be inaccurate in analytical chemistry is ridiculous.