Seeking a salt solution
June 23, 2018 2:15 PM   Subscribe

Is it possible to dissolve more salt into water, by weight, than the weight of the water?

We are trying to grow some crystals using Epsom salts, or magnesium sulfate. We staryed with 225g of water, at 50 degrees Celsius, and added 125g of salt. Then we kept adding, and adding, and adding... At one point warming the solution back to 50 before adding some more. The solution was on a stir plate with about 5-10 minutes between additions. We didn't weigh the further additions. When we we done we weighed the container full of saturated solution at 1108g. Subtracting the combined weight of the container and stir bar (612g) left us with 496g. That should mean 271g of salt into our 225g (250ml) of water?

When I look at Wikipedia it says the solubility of Epsom salt is 50g/100mL at 100 degrees Celsius, and lower at lower temperatures. How does it seem like I've dissolved so much extra salt?
posted by Naib to Science & Nature (4 answers total) 1 user marked this as a favorite
Best answer: From Wikipedia:
Magnesium sulfate is an inorganic salt with the formula MgSO4(H2O)x where 0≤x≤7. It is often encountered as the heptahydrate sulfate mineral epsomite (MgSO4·7H2O), commonly called Epsom salt.
Then in the Properties section:
Solubility in water
26.9 g/100 mL (0 °C)
35.1 g/100 mL (20 °C)
50.2 g/100 mL (100 °C)
113 g/100 mL (20 °C)
posted by EndsOfInvention at 2:34 PM on June 23, 2018 [2 favorites]

Best answer: The solubility you see listed was for anhydrous magnesium sulfate. Epsom salt is magnesium sulfate heptahydrate. Wikipedia lists the solubility for the heptahydrate salt at 113 g / 100 mL at 20C.

If you dissolved 271 grams of salt into 250 mL of water, that is equivalent to 108.4 g / 100 mL, which seems to match up pretty closely to the listed solubility.
posted by Iron Carbide at 2:38 PM on June 23, 2018 [1 favorite]

Response by poster: This got answered really fast, thank you! As a bonus follow up question, does anyone have a good resource for troubleshooting crystals?
posted by Naib at 3:13 PM on June 23, 2018

225g (250ml) of water

Are you sure about those measurements? The density of water at atmospheric pressure should be above 0.95kg/l at any temperature, but your measurements would put it at 0.90.
posted by flabdablet at 10:21 PM on June 23, 2018

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