.split() Qeustion

[Gene Heskett]

I remember it as 6.022e23

In my high school chemistry class, there was a wooden cube, about 1/2
meter on a side, sitting on the lecture desk in the front of the room.
The only writing on it was "6.022 x 10^23". It sat there all year.

The volume of the cube was that of 1 mole of an ideal gas at STP.


Hold your hands out in front of you, palms facing towards each other,
one shoulder-width apart. That distance is about one light-nanosecond.

Or a quite noticeable color shift when you are cutting coax cables for
color phase matching, which we often had to do in an analog NTSC broadcast
facility. Where a 1 degree shift, may or may not have been noticeable, was
the cable equivalent of 7.7601420788892939683e-10 seconds, which was for
the small foam cored cables used for such, with a Propagation Velocity of
0.78*C, only a very short length of cable. I'd have figured how much but I
got lost pushing buttons in kcalc just now and came up with something I'd
have to use a micrometer to measure. Its been close to 30 years since I had
to do such calcs on a near daily basis. Your trivia factoid for the day,
and I now return you to the regularly scheduled discussion going no where
specifically.

Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene> is up!
My views
<http://www.armchairpatriot.com/What Has America Become.shtml>
I suppose that in a few hours I will sober up. That's such a sad
thought. I think I'll have a few more drinks to prepare myself.
A pen in the hand of this president is far more
dangerous than 200 million guns in the hands of
law-abiding citizens.

 

[Gene Heskett]

Narrow shoulders.

I figure it just under a foot. I once attended a lecture by Grace
Hopper where she handed out "nanoseconds," pieces of wire about a foot
long. She said that the beaurocrats were always asking how much is a
nanosecond, and couldn't imagine what a billionth was like. So she gave
them something physical.

Chuckle. I always figured Grace Hopper had to have been a stand up comic
in some previous life. She sure could translate the problem into something
the paper pushers could grok.

Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene> is up!
My views
<http://www.armchairpatriot.com/What Has America Become.shtml>
Nachman's Rule:
When it comes to foreign food, the less authentic the better.
-- Gerald Nachman
A pen in the hand of this president is far more
dangerous than 200 million guns in the hands of
law-abiding citizens.

 

[Gregory Ewing]

Where a 1 degree shift, may or may not have been noticeable, was
the cable equivalent of 7.7601420788892939683e-10 seconds, which was for
the small foam cored cables used for such, with a Propagation Velocity of
0.78*C, only a very short length of cable. I'd have figured how much but I
got lost pushing buttons in kcalc

Python says about 180mm.

 

[Steven D'Aprano]

I figure it just under a foot. I once attended a lecture by Grace
Hopper where she handed out "nanoseconds," pieces of wire about a foot
long.

Is that based on the speed of light in a vacuum, speed of light in
copper, speed of electron drift in copper, speed of sound in copper? Or
perhaps it was aluminium wire?

She said that the beaurocrats were always asking how much is a
nanosecond, and couldn't imagine what a billionth was like. So she gave
them something physical.

Hmmm, given when Grace Hopper was active in the navy, I would have
thought that the simplest way to imagine a billionth would be "one dollar
is a billionth of the US National Debt" or "one person is a billionth of
the world's population". None of which really helps the typical person
visualise a billionth, since the typical person can't really visualise a
billion people or a billion dollars.

I think a simple analogy that works is: the width of a single human hair
is a billionth of 100 metres (or yards, for Americans). People can
visualise 100 metres, and they can visualise a hair. No need to relate
things to the speed of light, which most people cannot visualise, or the
circumference of the earth, or the distance from New York to Tokyo, or
from Venus to Mars at aphelion

 

[Chris Angelico]

Is that based on the speed of light in a vacuum, speed of light in
copper, speed of electron drift in copper, speed of sound in copper? Or
perhaps it was aluminium wire?


I think a simple analogy that works is: the width of a single human hair
is a billionth of 100 metres (or yards, for Americans). People can
visualise 100 metres, and they can visualise a hair.

Further information here:

http://en.wikipedia.org/wiki/Grace_Hopper#Anecdotes

It was specifically looking at satellite comms, and it's the speed of
light through a vacuum (the ideal maximum speed of satellite
communication signals). Check the Wiki page's footnotes for reliable
references.

ChrisA

 

[Alfonso Andalon Jr.]

 

[wxjmfauth]

Le vendredi 16 août 2013 15:23:37 UTC+2, Roy Smith a écrit :

(e-mail address removed) wrote:








That's because chemists are lazy.



The recipe says, "Add one mole of carbon atoms". So, does the chemist

follow the recipe and count out 6.022 x 10^23 atoms like he's supposed

to? No. He says, "I don't have time for that. I'll just weigh out 12

grams. Good enough for government work." Sheesh.

--------

You don't understand the concept of "mole".

In this formal reaction

Na + Cl --> NaCl

the chemist combines *one mole* of sodium and *one
mole* of chlorine to get *one mole* of sodium chloride
(cooking salt).

It's independent of the number of "particles" in a mole.

It's not a question of laziness, the chemist can only weight
22.98 g of sodium to work with one mole of sodium, because the
nature is like this.


The work with relative quantities has a name: stoichiometry.


jmf

 

[Roy Smith]

You don't understand the concept of "mole".

You don't understand the concept of "joke"

 

[Gregory Ewing]

Na + Cl --> NaCl

the chemist combines *one mole* of sodium and *one
mole* of chlorine to get *one mole* of sodium chloride

It's independent of the number of "particles" in a mole.

The actual number chosen for the unit is arbitrary, but
number of particles is still the central issue. The
important thing is to have the *same* number of particles
of Na and Cl.

Weight only comes into it because it's totally impractical
to count particles. And the particular number 6.02e23 is
chosen because it happens to give a convenient relationship
between number of particles and grams. If chemists had
decided to use ounces instead, the number would be different.

 

[wxjmfauth]

Le dimanche 18 août 2013 01:30:14 UTC+2, Gregory Ewing a écrit :

The actual number chosen for the unit is arbitrary, but

number of particles is still the central issue. The

important thing is to have the *same* number of particles

of Na and Cl.



Weight only comes into it because it's totally impractical

to count particles. And the particular number 6.02e23 is

chosen because it happens to give a convenient relationship

between number of particles and grams. If chemists had

decided to use ounces instead, the number would be different.

--------


"The actual number chosen for the unit is arbitrary, but
number of particles is still the central issue."

No.


"The important thing is to have the *same* number of particles
of Na and Cl."

Yes.
And it is precisely for that reason, a chemist works in "mole
arithetic".

Same reaction as above

Na + Cl --> NaCl

in pseudo math, with n = number of elements in a mole.


n * Na + n * Cl --> n * NaCl <==>
n * (Na + Cl) --> n * NaCl <==> division by n
Na + Cl --> NaCl


for any n.

----

The determination of n, the number of elements in
a mole, is an indipendent and separate problem.
(BTW, a very complicate task).


jmf