[Per]

Hi everybody, I wrote a exam in physical chemistry today and it was a question I really couldn't answer. If anyone has any ideas I would really appreciate it!
This is freely translated please ask if something isn't cleary explained.

Sodium hydrogen carbonate was heated to 100 degres celcius i a 500 cm3, airfree, container. I the container carbon dioxide, sodium carbonate and water in gas phase ( whats that in english btw?) was formed. The total pressure was 97.6 kPa, how much sodium carbonate was formed.

I thought that with the ideal gas law one could calculate the moles of the gas, CO2 and H2O, and after that maybe calculate mole fraction. But I had no partial pressure and that was a dead end.

I really should know how to do this, it's embarrasing...

[Borek]

Start with the reaction equation. What is the stoichiometrical ratio of gases (carbon dioxide and water vapor) produced? And remember that container was initially air free.

[Per]

If I calculate the total amount of moles I get amount of moles of the gas mixture. Which should be 50/50 mixture of CO2 and H2O. Can I calculate mass of sodium carbonate
(n(gas)/2)*M(sodium carbonate)

That was my train of thought but I was so uncertain of it.

[ARGOS++]

Dear Per;

Your assumptions are completely wrong, because you did not a balanced reaction equation.
That’s why your gas ratio is also wrong.

But your basic idea is correct.

So please do first a balanced reaction equation before any calculation!

Good Luck!
                    ARGOS⁺⁺

[Borek]

So please do first a balanced reaction equation before any calculation!

2NaHCO₃ -> Na₂CO₃ + H₂O + CO₂

1:1

[ARGOS++]

Dear Per;

Sorry!  - did a mistake in my equation.

Good Luck!
                    ARGOS⁺⁺

[Per]

So please do first a balanced reaction equation before any calculation!

2NaHCO₃ -> Na₂CO₃ + H₂O + CO₂

1:1

So my idea is correct?

[Borek]

Yes.

[Per]

Yes.

Thanks, I appreciate the help