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Name: Matt
Status: educator
Grade: 4-5
Location: WI
Date: February 2008


Question:
Is water and magnesium sulfate a homogenous mixture?



Replies:
Water and magnesium sulfate form a homogeneous mixture provided the concentration is low enough that the magnesium sulfate is completely soluble.

Vince Calder


Yes, if it is completely dissolved. The solution will be crystal clear just like pure water. No, if there is excess crystals or powder or fluff swirling around in the water.

About 200gm MgSO4 can dissolve in 1 Liter of cold water. So if the amount of magnesium sulfate is less than 200gm/Liter, pretty soon it will all be dissolved and you will have a homogenous mixture.

Even a faintly milky solution is not totally homogeneous. It has very tiny bits of white solid swirling around in an otherwise clear liquid.

Suppose you really did this experiment, dissolving some magnesium sulfate in water. With calcium or magnesium sulfates, some CO2 from the air all around will go into the solution making small amounts of insoluble carbonate. so after a while the solution will get milky or cloudy. This could make it difficult to get a crystal clear solution, difficult to prove to yourself that a homogenous sulfate mixture can exist. Adding a little acid, maybe just a few drops, could help dissolve the carbonate. Keeping a lid on the container would help keep the CO2 out longer.

Jim Swenson



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