Which one of the compounds listed would we use in order to get the highest concentration of sulphate ion in a saturated solution?


> 
> Solutions are prepared by dissolving a sulphate salt in water. Which one of the compounds listed would we use in order to get the highest concentration of sulphate ion, SO42-, in a saturated solution? What would be the concentration of sulphate ion in this case?
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> 
> A. $\ce{CaSO4}$ $K\_{sp}$ = 7.1E-5
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> B. $\ce{SrSO4}$ $K\_{sp}$ = 3.4E-7
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> C. $\ce{BaSO4}$ $K\_{sp}$ = 1.1E-10
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> D. $\ce{RaSO4}$ $K\_{sp}$ = 4.0E-11
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> 


My first instinct was to simply look at the $K\_{sp}$ values.. Since $\ce{CaSO4}$ has the largest $K\_{sp}$ value, it should be the most soluble, right?


But then I looked at a data page referring to the solubility of common compounds in water (Please see image. According to the table, $\ce{SO4^2-}$ has low solubility with $Ca$, $Sr$, and $Ba$.


My question is- does the solubility depend on the $K\_{sp}$ value (was my first instinct right), or is the table correct?


Any ideas would be appreciated.
![enter image description here](https://i.stack.imgur.com/IIT34.png)




The $K\_{sp}$ values are the way to go .. the other information you mentioned are just some convenient rules of thumb for predicting relative solubilities of compounds when you don't know the $K\_{sp}$ values. Also, the 4th choice in your list .. radium .. probably also belongs on that list, since it's the next alkali earth element after barium, but it's included because it's a radioactive element, and people don't commonly use or encounter it.


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