do you think that washing soda, Na2CO3, could be used for the same purpose a baking soda, NaHCO3? would Na2CO

Answer 1

No, it cannot. The reaction that makes NaHCO3 suitable for baking is :

2*NaHCO3 ----tº---> Na2CO3(s) + CO2(g) + H2O(g)

The resulting gases, CO2 and H2O(vapors) make the cake grow, since they will go UP :)
At first, (NH4)2CO3 was used, with even better results(because more gases evolve), but NaHCO3 is much cheaper, much easier to store(non toxic), more stable in time - (NH4)2CO3 slowly discomposes by itself while NaHCO3 will only discompose when heating

Answer 2

http://fins.actwin.com/live-foods/month.9810/msg00016.html

Na2CO3 is Soda Ash
NaHCO3 is Bicarbonate of Soda that is used for upset stomach.
You definitely not want to swallow Soda Ash