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Question

As part of the Characterization of a particular hydrated chemical salt, the percent by the weight of waters of hydration was found to be 30.52 %. Given that the molecular weight of water is 18.02 grams per mole. this is most consistent with which of the following?

Lithium Nitrate Trihydrate [MW = 122.95],

Calcium Nitrate Tetrahydrate [MW = 236.10],

or Srontium Nitrate Tetrahydrate [MW = 283.64]

Please show work.

Answer 1

Hello Mykayla

 

For each compound, divide the molar mass of H₂O by the molar mass of the compound and multiply the result by 100% to get the %-composition of water in the hydrated compound.

 

 

a) LiNO₃ • 3H₂O

 

Total mass of H₂O in hydrate = (18.02 g / mol) x 3 mol = 54.06 g H₂O

 

%-H₂O = (54.06 / 122.95) x 100% = 43.97%

 

 

b) Ca(NO₃)₂ • 4H₂O

Total mass of H₂O in hydrate = (18.02 g / mol) x 4 mol = 72.08 g H2O

%-H₂O = (72.08 / 236.10) x 100% = 30.53% (**Your answer**)

 

 

c) Sr(NO₃)₂ • 4H₂O

Total mass of H₂O in hydrate = (18.02 g / mol) x 4 mol = 72.08 g H₂O

%-H₂O = (72.08 / 283.64) x 100% = 25.41%