[cookalong]

I have a recipe that requires water with a calcium content between 100 and 400 ppm (or mg/L). Gellan is used in the recipe, which is why the calcium content is important. I can't find water with 100 ppm or more in my super market. Could I just buy some mineral water with a calcium content of, say, 50 ppm, and mix with 0.05 grams of calcium chloride? Will this water have the same properties as water that has a "natural" calcium level of 100ppm?

I got confused by the recipe because calcium chloride is used later on in the recipe. So I don't understand why I can't use a tiny amount of it to change the hardness of the water, since the recipe explictly mentions a calcium content between 100 and 400. Since you need Calcium Chloride anyway, I think the recipe should mention something about this.

[Arkcon]

My best guess is, if the recipe calls for 100 ppm Ca²⁺, then later wants some more CaCl₂, is that it wants more than 100 ppm Ca²⁺, but must have no more than 100 ppm Cl^- (you get 2 with each Ca in CaCl₂.)  You may find that the excess prevents Gellan form working, or the final product is inappropriate for your application in some other way.

[cookalong]

Thank you! I'm not a chemist, and haven't studied chemistry for a long time, so I apologize if I sound a bit confused.

The recipe only states "a calcium content" between 100 and 400ppm. This is the concentration of Ca right? Is the "natural" calcium content of water somehow related to Cl(chloride)-content? So water with a calcium content of 100 ppm has the same concentration of chloride?

In the recipe you first bring water, Gellan, sugar and sodium citrate to the boil. Then you whisk in some calcium chloride. My plan was to modify the water before mixing it with gellan/sugar/sodium citrate.

How would you go about "constructing" water with a calcium content of 100 pm out of mineral water with a calcium content of 80 (maximum I could find).

[fledarmus]

I believe the usual form of calcium that you would find in water is calcium carbonate, bicarbonate, or hydroxide (depending on pH) rather than calcium chloride. Arkcon could well be right about the significance of the chloride ions.

[cookalong]

Thank you! Sorry if I'm being a little slow :-)

So the problem is that I could adjust the calcium level properly with the calcium chloride, but I might throw in too many chloride ions, which are not present in "natural" water?

And even if that would be okay, then I would have to add more than 0.05g of calcium chloride? Since it's not only calcium but also (66%) chloride? So if my water has 50ppm, then I would have to add 0.15g calcium chloride, which would give me 0.05g calcium?

[fledarmus]

Yes on both counts, although your calculation isn't quite right. A calcium atom is slightly heavier than a chlorine atom - CaCl₂ is about 36% calcium by weight (only 64% chloride)

[cookalong]

Thank you!

Natural water seems to contain CaCO3, when one talks about water hardness. could I buy that and use? And not have to worry that it would be any different from mineral water that automatically comes with higher calcium content?

I can find water with 80 ppm, and I need 100. Perhaps I could add about 0.06g of calcium chloride and hope that the (roughly)40 ppm chloride won't affect the Gellan too much in the initial boiling? Later in the recipe I will add 0.25g of calcim chloride, so taste-wise I think I'll be fine. 40 ppm of chloride is still less than the chlorid content of San Pellegrino (but that's carbonated, so I can't use that).

[cookalong]

The weird thing is that the recipe says that you need "low calcium mineral water", and then it says something about 100-400ppm. Do you think they mean that the CaCO3 content should be 100-400ppm and, hence, the actual calcium content shoulder be somewhere around 40-160 ppm? In that case I understand that tap water won't be any good in a lot of countries and, hence, the request for low calcium water.

Because 400ppm of Calcium (and hence, about 1000 ppm of CaCo3) seems really really high, too high to be mentioned as low calcium mineral water, right?