Does it matter? (1 Viewer)

[kimmeh]

Does it matter what you're putting into the burette for titrations? i remember my teacher saying it doesnt matter. I've asked two people and theyve given me two different opinions. So, does the standard solution (solution on known concentration) got into the burette or the pipette?

 

[Xayma]

In theory it shouldn't matter, ie you will get the same answer but the calculations become easier when you use a simple volume like 25mL to calculate moles of known instead of something like 18.6mL

 

[kimmeh]

so when writing up procedures for conducting titrations, it doesnt matter what solution you put in what ?

 

[Xayma]

I think standard convention is to put the unknown in the burette but aslong as you rinse it with the solution you are using you will be fine.

 

[xiao1985]

yea, agree wif xayma... the if u do the reverse, the calculation would be alot more confusing (esp to markers)... and that's the last thing u want to happen durin an exam...

altho the procedure would prolly won't be much different, aprt from u need to rinse the conical flash with the soln of unknown conc and burette with soln of known conc... (because u want you know the exact amount of known soln is needed to reach end pt...

 

[CM_Tutor]

Standard Convention in an acid / base titration is to put the acid into the burette, and the base into the conical flask. The reason is historical - bases can damage glass, and could weld together the burette and its tap when they were both glass (as opposed to the plastic taps of today). The only exception was if a strong base was being used and phenolphthalein was the indicator, as phenolphthalein decomposes at high pH, so with it as indicator you usually titrate the base into the acid.

Given current equipment, it doesn't much matter for an acid / base titration, and so the convention is often violated, but it is still (theoretically, at least) the convention. Note that this is NOT true for other types of (Uni) titrations - in which case there can be requirements that a particular solution go into the burette.

As for the calculations, I really don't see how the complexity is changed whichever way you are titrating.

NOTE: The above discussion of acid / base titrations hinges on the indicator choice being appropriate - if it isn't, then the rules would change...

 

[beta-omega]

Thats totally true CM_Tutor. IT mostly depends on the indicator used, and whether it is a strong/strong, weak/strong, or strong/weak titration. Generally speaking, it is simplier to add the soln of known concentration in to the burette, but as for bases like NaOH, they may crystalize and thus clog up the appartus.