# At what concentration would copper sulphate crystallise at 25 degrees Celsius?

I am doing an experiment on how increasing concentration of copper sulphate affects the voltage in a galvanic cell. The voltage increased as temperature did until 2M where it started to decrease. I know the reason it does that but I can't find any website saying for 25 degrees Celsius it would start decreasing. I hope that makes sense and thanks for ur help!

• The Handbook of Chemistry and Physics has a table giving the dehydration of metallic sulfates. Under copper sulfates, I read that the usual $\ce{CuSO4⋅5H2O}$ starts losing water at $\pu{27°C}$ giving $\ce{CuSO4⋅3H2O}$ which has the same color. Is it of any help ?`In the table of Solubility of inorganic compounds in gram per $\pu{100 mL}$, the solubility of copper sulfate (anhydrous) is reported to be $\pu{20.7}$ at $\pu{20°C}$, $25$ at $\pu{30°C}$, $28.5$ at $\pu{40°C}$. – Maurice Apr 15 at 8:34
• Be aware that for concentrated solutions, many things behave more by empirically observed rules than according suitable theories, that apply on diluted solutions. Like activity coefficients or solution permitivity. – Poutnik Apr 15 at 9:27
• I would also not entirely assume (especially if the experiment is conducted in the presence of oxygen) that one has still a pure CuSO4 aqueous mix with a change in temperature in a galvanic cell setting liberating solvated electrons interacting with H+, SO4(2-), .... – AJKOER Apr 15 at 13:09