[MATT65]

I know that I should know how to do this but I don't. lol. I work in a QC lab at a quarry. I do chemical analysis by titration method. I check for Calcium and magnesium contents. We produce a gypsum pellet in which we have a spec on sulfur (S), calcium (Ca) and calcium sulfate (CaSo4). I can determine everything but CaSo4. I know that there is a conversion factor to determine this but I don't know how to do it. We have been using an independent lab to do these tests for us. I have decided to do these tests myself. Can anyone help?

[Borek]

Please elaborate. Could be you are asking about coefficient that is a simple ratio of molar masses.

[MATT65]

I use the titration method to find the percent of calcium and magnesium content in limestone. I use barium chloride to find percent sulfur and titration to find percent calcium in gypsum but I need to find out the percent CaSo4 content in gypsum. I know that I can somehow use the total percent of calcium and percent sulfur to calculate the percent calcium sulfate ( CaSo4). I just don't know the factors or the formula to calculate this. That's what I'm looking for.

[JGK]

calcium sulphate 136.14 g/mol

Calcium mw = 40.08 = 29.4% in calcium sulphate
Sulphur mw = 32.06 = 23.5%
Oxygen mw = 15.9994 = 47.0%

If all of the calcium is derived from calcium sulphate [Ca]/0.294 = [CaSO4]
If all of the sulphur is derived from calcium sulphate [ S ]/0.235= [CaSO4]

[MATT65]

Thanks for the info. I found out how to calculate CaSO4. It's determined by multiplying %sulfur by a factor of 4.246. I done a test on a referance material and I was within .001% of the reference material.

[Borek]

So it is just ratio of CaSO₄ molar mass to S molar mass (identical to division by 0.235 suggested by JGK). Thing is, if there is not enough Ca and your gypsum contains some magnesium sulfate, your result will be off. IMHO you should calculate CaSO₄ separately from Ca (multiplying Ca by 3.397) and from S - and choose smaller number. But I can be wrong.

[MATT65]

I noticed something in JGK's post. He has a Oxygen MW at 15.9994. With 4 molecues in CaSO4 it should be factored as 63.9976 (X4) which in my calculations would give me the factor of 4.246.

[Borek]

4 atoms, not molecules.

4.246 seems to be very good value. I would go for 0.2355 when it comes to division.

[JGK]

I noticed something in JGK's post. He has a Oxygen MW at 15.9994. With 4 molecues in CaSO4 it should be factored as 63.9976 (X4) which in my calculations would give me the factor of 4.246.

True, but as your original post did not say you were quantifying Oxygen to determine [CaSO4], I didnt proceed any further than givong the MW of oxygen and stating that it formed 47% of CaSO4.

Plus if you are using the oxygen to calculate [CaSO4], the factor you use depand on how you characterise the oxygen in the analysis.

If you measure [ O ] then [ O ]/0.47 =  [CaSO4]
If you measure [ O2 ] then [ O2 ]/(0.47/2) =  [CaSO4]