The relationship between calcium sulfate, barium chloride, and sodium carbonate

I have no idea whether barium sulfate can be formed or not, but I know for sure that calcium carbonate can definitely be formed! The solubility of calcium carbonate is very low; it falls into the category of insoluble substances. Barium sulfate, on the other hand, should be slightly soluble! Calcium carbonate can definitely be formed!

This post was last edited by qugd on 2011-4-16 at 09:08. The original poster’s question is very simple; however, to answer such questions, it is necessary to define certain conditions—namely, that there are no complexing agents for alkaline earth metals in these two solutions, nor any significant amounts of other soluble salts. 1. When barium chloride solution (assumed to be 1 M) is added to the solution, barium sulfate precipitate will definitely form, because the solubility product of barium sulfate is much smaller than that of calcium sulfate ； 2. When a sodium carbonate solution (assumed to be 1 M) is added to the solution, calcium carbonate precipitate will definitely form, as the solubility product of calcium carbonate is also much smaller than that of calcium sulfate. There is another very special property: in a precipitate solution containing barium sulfate, adding a relatively concentrated sodium carbonate solution causes the barium sulfate precipitate to be converted into barium carbonate precipitate. This process transforms barium salts that are insoluble in acids into barium salts that are soluble in acids.

First, I’d like to thank the two friends for their enthusiastic participation and guidance. We conducted experiments to verify this issue: In Case 1, after adding barium chloride, barium sulfate was formed; however, the calcium ion concentration did not increase； For Case 2: After adding sodium carbonate, calcium carbonate indeed forms; moreover, the sulfate concentration in the solution increases upon analysis. Situation 2 can be theoretically explained. But how should Situation 1 be explained? Why does the reaction Ca2+ + SO42- = CaSO4 proceed to the right, yet the concentration of calcium ions does not increase? Why is this so?

This post was last edited by qugd on 2011-4-16 at 09:14. Reply to 4# YiNuoZhang: Since you used a calcium sulfate solution, the concentration of calcium ions in the system is already in a dissolved state and remains constant; it will not change due to the addition of barium ions and chloride ions. However, if you conduct the aforementioned experiment again using a calcium sulfate concentration system containing a small amount of calcium sulfate precipitate, the amount of calcium ions will definitely increase. This increase is related to the quantity and concentration of barium chloride added. The experiment you conducted is essentially a process of precipitation or transformation of a slightly soluble compound; its reaction mechanism involves the formation of a substance with even lower solubility.

Let me reiterate: I’d like to mention the concentrations of each component in the solution I’m using for my experiments. Among the analyzed indicators, the sulfate concentration is 2 g/L, and the calcium ion concentration is 1.2 g/L. The concentration of calcium sulfate remains unknown at present. My goal is to alter the concentrations of sulfate and calcium ions in the solution by adding barium chloride and sodium carbonate separately. Based on the changes in the concentrations of these ions under both conditions, I hope to calculate the amount of calcium sulfate present in the solution. I wonder if this method is feasible; any advice would be greatly appreciated.

I don’t quite understand this. Similarly, I’d like to ask: since SO42- is consumed and the equilibrium shifts to the left, if we assume that the amount of Ca2+ increases, will this increase in Ca2+ ions cause the equilibrium to shift to the right?

I remember there was a similar post; I had done detailed calculations for it. That original post might be the one you posted—please do a search for it. The calculations at the time did not take into account the salt effect during precipitate formation (the salt effect generally increases the solubility of poorly soluble substances). If no results are found, please send me your detailed requirements; sometimes I’ll recalculate them.

Firstly, an increase in calcium sulfate is inevitable, because according to the equilibrium constant relationship, the equilibrium Ca2+ + SO42- ⇌ CaSO4 shifts to the right； Secondly, not necessarily. If the solution is acidic, then calcium sulfate remains largely unchanged. Otherwise, calcium sulfate decreases while calcium carbonate increases, as calcium carbonate is less soluble. If you don’t understand, feel free to contact me again.