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Re: Sodium Hydroxide in local drinking water.

Roger Miller wrote:
. . .  in ppm of *nitrogen*, not nitrate;
10 ppm of nitrogen is equivalent to 44 ppm of nitrate,
and that's how we usually measure nitrate in aquariums.    (. . .)

I am now confused.
I thought that one PART per million means
by the EACH, rather than by mass.

So a nitrogen atom happily going about its existence as one atom in a 
nitrate ion,
surrounded by a million other "parts,"
would count exactly the same as the whole nitrate ion.
Whether you're counting the nitrogen as one atom, or as the whole ion, 
it's still one ppm.

If on the other hand ppm is by mass, well, of course a whole nitrate ion
weighs 4.4 times what a lone naked nitrogen atom does,
and Roger is right.

(But I think then you'd have to account for the mass
of whatever counter-ion the nitrate came in with.)

And if you mean to measure by grams per liter but call it ppm, again,
a nitrate weighs more than a nitrogen, and Roger is right.

Can someone straighten out for us all,
when to count by molecule and when to reckon by weight?
Steff Zimsen