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Re: K+

>    And, I think I'm right in saying that
> 1 gram of an element dissolved in 1 liter of water will create a concentration
> of 1000ppm.    So, if I dissolved 1 gram of K2SO4 in 1 liter of water, I'd
> have
> a potassium concentration of 529ppm (not counting any potassium already
> present 
> in the water..).     From there, it's simple to calculate how much a given
> dosage of that solution would add to a tank.

Yep, ppm = mg/l. K2SO4 is not the most soluble stuff though.  A liquid
reference solution would not be the best idea I would think. Dry form would
be better to use therefore.
 
> 
> BUT!  Now I'd like to be able to measure out the K2SO4 in teaspoons or some
> similar volume measurement.
> 
> Looking at that page on TheKrib dealing with dosing, there is a chart that
> shows
> an approximate weight per 1/4 teaspoon of various compounds.    But, it
> doesn't
> list K2SO4.   I know I could just weigh out a known volume of K2SO4, but is
> there
> a way to calculate it based on basic chemistry information?   For some
> elements,
> I can find "Density of solid".  But for Chlorine, Oxygen, etc (gases), it
> doesn't
> list the value.    I also have a Molar Volume (cm3) which I assume means one
> mole of
> an element would take up xx cubic centimeters.   I thought I could use that
> info to
> figure it out, but my numbers would not match up to any of the grams per
> 1/4tsp
> listed
> on the page at TheKrib.

I'm going to over school today and will be by an analytical scale and will
weight some out and send the weight back to you. It will be one **level**
1/4 teaspoon, Green All Brand of K2SO4 (bout 5$ for 10 lbs) and I will do +5
runs of the weights to get a nicer average off the 1/4 teaspoon.
I am somewhat curious myself about this but since the K is not such a
"tight" parameter for me I've never been too worried about hitting a
specific amount. The test kits sure cannot do it well.

I'll let you know tonight when I get back what the averaged weight were.
Hope all 1/4 teaspoons are created equal!

I did this for KH2PO4 since a tiny level spoon had an unknown weight and
standard but I can test for PO4 much more accurately than K+. Good thing
too.   
> 
> So, first, an I missing some important concept on the first part dealing with
> percent of compound, and concentrations?    Next, what am I missing regarding
> calculating mass per given volume (or volume per given mass, I'm not picky...)

You've got it for the first part down well, The second part would be  off
due to the volume issue of a powder. Some might have more air spaces in each
sample and therefore a little less volume than another sample. This method
does work well for liquids though. A specific volume can be achieved and
weighed there. This is why I want to do an average of 5 (or 10-20 etc) so to
reduce some error in difference of each volume to mass measurement. But
suppose the Green All stuff has been ground up a little different each time?
Or there's a large variation in teaspoon weights? Moisture is another one
but since it has a high MP, we can heat the sample up to drive any water.
There's going to be some error every time to a certain degree from this. But
...it's not going to make much difference if we have 15ppm of K or 17 ppm K.
It's nice to know but a ball park amount will do. Another issue with K2SO4
is it ain't exactly the most soluble stuff around! It doesn't have the
lowest MP either like most salts.
Melting point : 1069  C
Solubility : 24% by weight at 100 0 C
Another brand had a density of about 2.662 gm/cm3. (1 cm3 = 1cc = 1
milliliter).
Hope this helps. I'll be back with the info.
Regards, 
Tom Barr