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**To**:**"plants" <Aquatic-Plants at actwin_com>****Subject**:**Chemistry question****From**:**"Chuck Gadd" <cgadd at cfxc_com>**- Date: Wed, 07 Feb 2001 01:13:23 -0700

I'm attempting to understand a little more about calculating dosage and concentrations of various chemicals. I've already figured out how to determine (I think) what percentage of a compound is a certain element. For instance, while trying to come up with the right values for Potassium Sulfate, i figured: Potassium is 39 grams per mole. Since it's 'K2', I figured 2x39 = 78. Adding up the remaining parts (SO4), S=32g/mole, O=16g/mole, so 32 + (4x16) = 96. If I understand what these numbers mean, one mole of K2SO4 weighs 174 grams. And since the 'K2' is 78 g/mole, then 45% of K2SO4 is potassium. I did the same procedure for KNO3, and the values I calculated matched those listed on TheKrib (http://www.thekrib.com/Plants/Fertilizer/dosing.html) So, I think I can figure out what percentage of any given compound is comprised of a given element. Pretty simple. 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. 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. 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...) This is mostly a simple academic excersise, but I like to have an understanding of the various charts and references that I use regularly. -- Chuck Gadd

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