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+ Precipitation
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Omar N.

Is there any reason why CaCl2 would precipitate out of solution in...

Bill Wald  Follow

As Guido Bongi ·told, if your solution absorved CO2, you may form CaCO3, wich has a very low solubility, lower than Na2CO3. The proposed test also will give you co2 bubbles.. 

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Lance Pickup  Follow

Hi Sarah:
Calcium chloride and magnesium chloride can react with phosphate and form less soluble calcium phosphate and magnesium phosphate. Furthermore, solubility of calcium phosphate and magnesium phosphate decreases with increasing temperature. Thus, there are three solutions to your difficulty, but you will need to start over because I have never had success getting the calcium phosphate preciptitate redissolved once it has formed. One is to warm up the saline before adding the small amount of solid calcium chloride you need. Next solution, which usually works for me, is to dissolve the solid calcium chloride in water, say 0.5-1 ml, and add it slowly to the saline while mixing. Last solution is combine the first two.
Thanks for the endorsements,
Howard

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Chang Liu  Follow

Hi Sarah:
Calcium chloride and magnesium chloride can react with phosphate and form less soluble calcium phosphate and magnesium phosphate. Furthermore, solubility of calcium phosphate and magnesium phosphate decreases with increasing temperature. Thus, there are three solutions to your difficulty, but you will need to start over because I have never had success getting the calcium phosphate preciptitate redissolved once it has formed. One is to warm up the saline before adding the small amount of solid calcium chloride you need. Next solution, which usually works for me, is to dissolve the solid calcium chloride in water, say 0.5-1 ml, and add it slowly to the saline while mixing. Last solution is combine the first two.
Thanks for the endorsements,
Howard

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Debra Barnett  Follow

Thank you, everyone, for your insights. We tested the precipitate, and it did turn out to be calcium carbonate. It was likely a leftover contaminant from the original reaction using calcium carbonate to create the calcium chloride isotope.

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Daniel Silvers  Follow

Well, Guess Howard is OK, but the major problem is what sort of saline and the use of crystals. Never do so because local concentrations during crystal solution can reach  local values well above Kps of carbonate and phosphate, but use 2X solutions to make the saline. http://www.protocol-online.org/biology-forums/posts/39878.html

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Brian Yankee  Follow

I guess sone sodium carbonate is in solution; check if pH is alcaline and remove carbonates or use EDTA. Try to see if the precipitate is dissolved in HCL with gas bubbles of CO2

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Christian Altorfer  Follow

About predicting the pH of CaCl2 aq. solutions (also for for carbonated solutions) ― cf. my posts at:
https://www.researchgate.net/post/How-to-increase-pH-for-a-solution-without-making-a-chemical-reaction-with-CaCl2

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