How is magnesium sulfate monohydrate $\ce{MgSO4 * H2O}$ used for in chemistry and how does it work as a valuable laboratory drying agent?

I could not find too much information in my book or the internet besides the basics (chemical formula, physical or chemical characteristics, etc.), but I did find what it can be used in. For example, fertilizer, feed additives for livestock, nutrient flavor enhancer, pharmaceuticals, leather and fur production, coloring fabrics, fermentation in beer, paper production, sewage treatment, cosmetics, but nothing about how or why chemistry labs would use it. What is its purpose?

Each time I tried to look it up other products that sounded similar but not the same appeared such as $\ce{MgSO4 * 7H2O}$ , manganese sulfate, manganous sulfate, etc.

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    $\begingroup$ I hope the additional information was sufficient enough to prove I put effort into solving this problem on my own. $\endgroup$ Feb 16, 2019 at 5:47
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    $\begingroup$ manganese sulfate and manganous sulfate are not hydrates of magnesium sulfate. There is big different between $\ce{Mg}$ and $\ce{Mn}$. $\endgroup$ Feb 16, 2019 at 6:56
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    $\begingroup$ Briefly, anhydrous magnesium sulfate ($\ce{MgSO4}$) is commonly used as a desiccant in organic synthesis due to its affinity for water (Wikipedia). Anhydrous $\ce{Na2SO4}$ and $\ce{CaCl2}$ are also used in similar manner. $\endgroup$ Feb 16, 2019 at 7:02
  • $\begingroup$ Is magnesium sulfate monohydrate MgSO4⋅H2O the same as MgSO4? What is the reason for MgSO4⋅H2O creation? What is its purpose? $\endgroup$ Feb 16, 2019 at 8:36
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    $\begingroup$ If it were the same, it would be written the same. As to the purpose: like most chemical compounds, it has none. $\endgroup$ Feb 16, 2019 at 8:59

1 Answer 1


Magnesium sulfate is frequently used in the laboratory, especially after aqueous work-up. Aqueous work-up is a common technique in the lab to get rid of residual impurities after completion of a reaction. For this the organic solution of the reaction is cooled to room temperature and mixed with water. Specific impurities will then diffuse into the aqueous phase and can be separated with a separatory funnel. Unfortunately some residual water will stay in the organic phase and this can have negative impact for following characterization of the compound. Therefore magnesium sulfate is added, which is able to catch the residual water in its crystal lattice. After filtration of the solid magnesium sulfate, the water is reduced to a non-significant amount and the compound ready for further investigation.

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    $\begingroup$ The question is specifically about magnesium sulfate monohydrate. Your answer is about the use of anhydrous magnesium sulfate. $\endgroup$
    – andselisk
    Feb 16, 2019 at 17:18
  • $\begingroup$ basically it can be used similarly. The crystal lattice bears space for up to 7 molecules of H2O/ MgSO4 $\endgroup$
    – John
    Feb 16, 2019 at 21:07
  • $\begingroup$ First, MgSO4 is not some zeolite with cavities for storing water, it's hydrates have totally different structures based on the number of crystal water! Saying there is "space to bear" is just wrong. Second, it's moderately soluble in water and sparingly in ether, so by adding MgSO4 to water–organic system you will just dissolve it. That's not how MgSO4 is used for drying at all. Third, heptahydrate is not the crystallohydrate with the highest water content, dodecahydrate arguably is, but this is not the point. $\endgroup$
    – andselisk
    Feb 16, 2019 at 21:31
  • $\begingroup$ Fourth, if you want to dry organic solvents for synthesis or GC analysis, you must use anhydrous MgSO4. $\endgroup$
    – andselisk
    Feb 16, 2019 at 21:36

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