umer007 Posted January 20, 2005 Share Posted January 20, 2005 Is there a mathematical way/formula to find the number of water molecules in hydrates? If someone knows the formula, could you plz also show steps to coming to that formula. Thx alot Link to comment Share on other sites More sharing options...
budullewraagh Posted January 20, 2005 Share Posted January 20, 2005 well...if you take for example, a sample of Al(NO3)3*9H2O there will be 9 water molecules per aluminum nitrate molecule Link to comment Share on other sites More sharing options...
umer007 Posted January 20, 2005 Author Share Posted January 20, 2005 no I meant like say you were given the name of the hydrate or like its mass, the anhydrous salts mass, mass of water (all grams) and percentage composition of water in the hydrate. Or molar mass of the hydrate, molar mass of the anhydrate, mass of water in the hydrate (g) and percent composition of water in the hydrate. Then how would you find out the number of water molecules? Actually Im not exactly certain about it either. I was told there is a mathematic formula to determine the number of water molecules in a hydrate. For example epson salt is magnesium sulphate MgSO4. And its hydrated formula is MgSO4*7H2O, but say you werent given the number 7 only MgSO4*nH2O, where n is a whole number. How would you find out what n is, if you were given molar mass of the hydrate and the anhydrous salt. Or what information would you need to find n? Link to comment Share on other sites More sharing options...
Tetrahedrite Posted January 20, 2005 Share Posted January 20, 2005 How would you find out what n is, if you were given molar mass of the hydrate and the anhydrous salt. Or what information would you need to find n? It is quite simple, you take the molar mass of the hydrated salt, subtract the anhydrous molar mass, and divide by 18.016 (the molar mass of water) eg Molar mass MgSO4.nH2O = 246.488g/mol Molar mass MgSO4 = 120.376g/mol 246.488-120.376 = 126.112 now divide by 18.016 = 7 waters Link to comment Share on other sites More sharing options...
budullewraagh Posted January 20, 2005 Share Posted January 20, 2005 take the molar mass of the hydrated salt if you don't have that you can't find the answer Link to comment Share on other sites More sharing options...
Gilded Posted January 20, 2005 Share Posted January 20, 2005 "if you don't have that you can't find the answer" That was quite obvious, now wasn't it. ) Of course, if you knew the individual atom masses and... Hmm... Link to comment Share on other sites More sharing options...
budullewraagh Posted January 20, 2005 Share Posted January 20, 2005 well, im just saying. you can't know the molar mass if you don't know the formula. thus, if you're just given any sample of a hydrate and you don't know the potential hydrates, you cannot quantitatively solve this problem Link to comment Share on other sites More sharing options...
Gilded Posted January 21, 2005 Share Posted January 21, 2005 Well if you're given the formula of the hydrated compound, but not the molar mass of the compound, you could calculate the approximation of the molar mass if you knew the masses of the individual atoms in it. Link to comment Share on other sites More sharing options...
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