Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: gloinddark on August 17, 2011, 01:11:09 PM
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This is related to a biology issue. I am preparing media for cell culturing, and I need to measure out a lot of salts in very exact amounts. Sometimes, the recipe requires a salt with a certain water of hydration, and the salt which I have in my disposition has a different water of hydration.
So I tried to devise a formula to enable me to quickly convert the grams of salt.xH2O into grams of salt.yH2O
Since sometimes I struggle with numbers, I would really appreciate if someone checks it out.
Grams of salt.yH2O = [Grams of salt.xH2O X (Molar mass of salt y)2] / (Molar mass of salt x)2
Thanks
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why molar mass squared?
you need a fixed amount of moles I gather, which is in recipes given in grams of a certain hydrated salt, which you want to convert to grams of a differently hydrated salt
moles of salt = mass of salt / molar mass
so if you have mass of Salt.xH2O {let's call this mass (X)} given, you have: moles of salt = mass (x) / molar mass (x)
these moles need to be the same in y:
moles of salt = mass (y) / molar mass (y)
so this gives:
mass (x) / molar mass (x) = mass (y) / molar mass (y)
and solving:
mass (y) = mass (x) * molar mass (y) / molar mass (x)
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Check out concentration calculator (http://www.chembuddy.com/?left=CASC&right=solution_preparation) - for any salt you can select which hydrate you have, calculations of mass needed to prepare solution of given concentration are carried out automatically (doesn't matter how many salts you need in your solution). This is not visible on the page I linked to, as it describes the most general and simple case, but you can download the program and use it freely for 30 days without obligations. Feel free to ask for support here ;)
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That equation makes a lot more sense than mine, DevaDevil - thank you for enlightening me!
Borek, that program will certainly come in handy!
Thanks to both :)