Question

How many molecules of oxygen are produced from the simple decomposition of 25 g of water?

Answer 1

Try to see the decomposition equation first;
2H2O --> 2H2 + O2

Then notice that 2mol of H20 decompose into 1 mole of O2
So the ratio is 2:1

Then find the mol of water:

mol of water is: 25/(2(1.001)+15.99)=_______mol

* where (2(1.001)+15.99) is the molar mass of water.

Then divide the mol of water by 2 to get no. of mol of O2 as you remember that the ratio is 2:1.
Then;
no. of mol of O2 x (6.022x10^23)

where: 6.022x10^23 is the Avogadro Constant.