Experimental details -- Heating hydrated barium nitrate

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Homework Statement


[/B]
Q- Hydrated barium nitrate, Ba(NO3)2.4H2O, is strongly heated in a boiling tube and the following changes occur.
Stage 1: The white solid forms a clear colourless solution.
Stage 2: Condensation forms around the mouth of the boiling tube and a white solid starts to form at the bottom of the tube.
Stage 3: As the heating continues, the colourless solution disappears leaving another white solid.
Stage 4: This white solid melts.
Stage 5: Nitrogen dioxide and oxygen gases are given off, and barium oxide is left in the test tube.

(a) Give the formula for the white solid formed in Stage 3.
Ans- Barium nitrate

The Attempt at a Solution



I dont understand the experimental procedure here. Can someone please outline what is happening in each stage and what solid is forming in Stage 2 and what condenses and how the thermal decomposition takes place? Shouldnt Barium oxide be formed at Stage 3?
 

Answers and Replies

  • #2
Charles Link
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In stage 2, water=## H_2 O ## is eliminated from the test tube. The decomposition of the ## NO_3 ## part of the compound has yet to occur, and apparently is a process that will only take place well above the temperature at which water boils. Does this make sense?
 
  • #3
Borek
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In other words: on heating the salt dissolves in its hydration water, then the solution dries out leaving the same salt, but in the anhydrous form.
 
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In other words: on heating the salt dissolves in its hydration water, then the solution dries out leaving the same salt, but in the anhydrous form.

So the solid in stage 2 and 3 are both barium nitrate?
 
  • #5
Borek
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So the solid in stage 2 and 3 are both barium nitrate?

Yes, just a different form than the one you started with.

Actually things can be a bit more complicated, many salts have several different hydrates that can be stable if the conditions (temperature and vapor pressure) are correct - but it doesn't matter much here.
 

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