[C_hemiscool]

Hello,

I have a burning question about weighing technique and the use of weighing boats, weighing paper, or glassware.  I somewhat new to industry (and chemistry!), so please forgive me if I'm ignorant.

I am preparing a calibration standard solution and I have to accurately weigh say 100mg of the reference standard.  Everyone I work with uses weighing paper folded into a neat envelope to which they weigh the material.  Then they take the envelope to the volumetric flask and rinse the contents into the flask before bringing it to volume.  I follow the same procedure, but I find it a very clumsy way to do this, probably because I have clumsy hands.

I don't like the weighing paper because it seems like it is very easy to lose the material.  I don't like weighing boats because there is always so much static and everything goes flying.  I do like using a small beaker, which I can tare, then weigh to.  I can then add solution to dissolve the material and then transfer to the volumetric flask.  If I rinse the beaker 3 times I get very good results.

What do you do, and why is weighing paper the preferred way for weighing materials?

[enahs]

What do you do, and why is weighing paper the preferred way for weighing materials?

Most analytical balances have a limit. If your reaction container of choice weighs say 105 g but the limit of your balance is 100 g, then you have to use weighing paper. If your reaction vessel is too big to fit on the analytical balance then you have to use weighing paper. If your reaction vessel is not movable, you have to use weighing paper.


Your situation where you use a small beaker and tare is fine (note you will never get all of it out, but that tiny difference is probably acceptable in any case you will be involved in, in a general chemistry lab).

But what if you do not want to disolve your weighed material into solution? What if you do want to disolve it in say a 25 ml volumetric flask? If your beaker is a 25 ml beaker, can you really rinse it out three times into a volumetric flask without having to worry about having too much water?

Pouring from a beaker is also not easy, especially into a volumetric flask and you risk losing some. Where with weighing paper you can roll it into a funnel.

If you are having that much trouble handling the weighing paper, then put it on a watch glass (http://en.wikipedia.org/wiki/Watch_glass) and tare the whole thing (watch glass + weighing paper). Then once your material is weighed you can easily hold the watch glass to take it back to your work station. From there the only thing you have to do with it is carefully remove the paper from the watch glass and fold it some so it directs the material to one place and pour into your container. This way you minimize your handling the weighing paper.

Of course, you could just practice and get less clumsy, as it is really the most convenient way. You can practice at home, just cut a piece of news paper to the same size of a piece of weighing paper (or take one home) and just put some sugar or salt on it and practice carrying it and transferring to a container and such.

[C_hemiscool]

Thanks enahs 

You're right, it comes down to is practice and comfort.  I never though about practicing at home -- I'll give it a shot.

I've never been comfortable with weighing on paper and with boats.  It's the static that drives me nuts, especially with the plastic boats.  If your material isn't flying around the weighing boat, then the balance isn't stable.  I prefer the weighing paper over the boat, but I try to use glassware whenever I can.