Answer : The mass of water produced will be 32.78 grams.
Explanation : Given,
Mass of
= 21.9 g
Molar mass of
= 72.15 g/mole
Molar mass of
= 18 g/mole
First we have to calculate the moles of
.

Now we have to calculate the moles of
.
The balanced chemical reaction will be,

From the balanced reaction we conclude that
As, 1 mole of
react to give 6 moles of 
So, 0.3035 moles of
react to give
moles of 
Now we have to calculate the mass of
.


Therefore, the mass of water produced will be 32.78 grams.