The chemical formula for washing soda is - Na2CO3.10H2O
It is prepared by heating baking soda and then recrystallizing the product so obtained.
The equations related to the above reaction are:-

Na2CO3 + 10H2O → Na2CO3.10H2O
Two applications of washing soda are:-
1. It is used in glass, soap and paper industries
2. It is used for removing permanent hardness of water.