Hcl (1 Viewer)

[SBHS4EVER]

Why is it HCL cannot be used as a primary standard... it isnt hygroscopic or delisquecent right?
SBHS4EVER

 

[+:: $i[Q]u3 ::+]

a primary standard is a solution made by dissolving an accurately measured mass of solute in solvent - so you know the exact molarity. =)

um.. i don't know what hygroscopic or delisquecent (??? means) but the thing wiv HCl is that it's really difficult to get it in pure form, (the concentration of HCl varies from batch to batch) so HCl has to be a secondary standard~...

 

[kini mini]

I seemto remember that there are quality control issues with HCl, also concentrated HCl fumes quite spectacularly .

 

[timmii]

hygroscopic/deliquescent means it absorbs water ----> why NaOH isn't a primary standard.

I understood HCl to be an inadequate standard to be because it was volatile - its molarity changed and thus could not be relied upon to always be exactly the same as when you may have calculated previously. Also, since HCl is a gas, it is far more difficult to measure and dissolve than a solid such as Na2CO3.

edit - uh, nothing...no problems here....

 

[kini mini]

Deliquescent!

The spelling is deliquescent

 

[inasero]

good to see a fellow high boy posting here...btw who are you exactly?

anyways to help you out...HCl cannot be used as a primary standard because it is too volatile and absorbs heaps of water from the air...so at any given time you wouldn't be able to determine it's molarity which is the whole point of volumetric analysis....

so therefore we use some primary standard whose solution we can ascertain the concentration of to an accurate extent and which doesn;'t react with gases from the atmosphere (such as CO2, H2O etc)....

Also if the primary standard is in a powder form originally and you're making up a solution you must ensure that all the water has been removed and the remaining solid is completely dehydrated...with some compunds they have "waters of crystallinity" and so even then they cannot be used accurately...

Hope this helps

 

[bluebubble]

We have a sciencist in the house "inasero". I also have a question, where would we need to know all this?

 

[bluebubble]

....besides the HSC. i mean what sorta experiment was this technique used in. and damn that download was supposed to appear there not to be redownloaded.

 

[kini mini]

Originally posted by bluebubble
....besides the HSC. i mean what sorta experiment was this technique used in. and damn that download was supposed to appear there not to be redownloaded.

It could come up an experiments such as titrations where primary standards are necessary. We used to standardise our reagents before most titrations if the lab assistants hadn't already done it.

Your gif won't necessarily appear to everyone, it depends on the board settings. Some boards allow people to choose how attached pics are rendered.

 

[SBHS4EVER]

Inasero- its a me- Paul
Who u?
Anyway- that HCL thing- if u get a question about reliability and validity (i.e. accuracy and the repitition of such results)- u gotta say that the titration may be affected by the loss of subsatnces to the atmosphere such as NaOH or here- HCL.
Hope that helped Bluebubble!

SBHS4EVER