Re: What is the exact value of a mole?

From: Joshua Halpern (vze23qvd_at_verizon.net)
Date: 12/31/04 

Date: Fri, 31 Dec 2004 00:42:22 GMT

Lloyd Parker wrote:
> In article <cr0hlq$7jd$1@news.iucc.ac.il>,
> schultr@mail.biu.ack.il (Richard Schultz) wrote:
>
>>In article <ckmns014riele7dcvu6otmauhgompu2rei@4ax.com>, Dr. Dickie
>
> <dr_dickie@chembench.com> wrote:
>
>>: A competent chemist would know that precision in a single measurement
>>: is impossible (to quote an *** I recently heard--sound familiar?)
>>
>>Are you saying that if I weigh something on an analytical balance, I
>>cannot cite the weight with the balance's stated precision of +/- 0.01 mg?
>
>
> Perhaps the next time you weigh it, you handle it with your fingers (or
> someone else did), or this time it had some moisture on it which
> evaporates, or someone leaves some moisture on the balance pan (some of
> which evaporates between your zeroing it and making your final weight), or
> there's an air current,...
>
> The only way you know is to measure it more than once.

these are external
>
> Suppose the balance's precision (i.e., noise) is heteroscedastic and the
> quoted value is a median?

By nature, electronic scales weigh repeatedly (they are basically
counting an oscillation over a fixed period of time). If the last place
does not move......you got it. You can hook them up to a digital
recorder/computer and read out the measurements as made.

josh halpern
>