Why does Na2CO3H2O break down into Na2CO3+H2O?

Question

The rule in our notes says that a hydrated salt will always decompose into the salt and water, but we also have another rule in those notes that says a metallic carbonate always has to break down into a metallic oxide and carbon dioxide.

So, wouldn't the products be NaO+CO2+H2O instead? (it's not balanced obviously)

I don't understand, am I not supposed to use all the decomposition rules for the reaction?

Answer 1

Because divorce causes many to break down!

Answer 2

Li,

 

The final products of the decomposition also depend on the conditions. Since water of hydration is only weakly held (as part of the crystal structure), relatively mild heating will drive off these water molecules, leaving the anhydrous compound behind. To get decomposition of the carbonate salt into the metal oxide and CO₂, you need rather extreme amounts of energy. Consider the decomposition of CaCO₃ (limestone) to form CaO (quicklime, a key component of cement) and CO₂ requires temperatures over 1000°C, and you will realize why dehydration happens without the further decomposition.

 

Jim S.

Answer 3

Your first rule is correct.  There is no such thing as NaO. Na2O does exist, but not in water solution, it immediately hydrates to NaOH.  Sodium is a very strong metal and it will ionize in water leaving the carbonate ion instead.  There probably is a little reaction of:

 

Na2CO3 +2 H2O <=>2 NaOH + H2CO3