How does Dalton’s atomic theory account for the fact that when 1.000 g of water is decomposed into its elements, 0.111 g of hydrogen and 0.889 g of oxygen are obtained regardless of the source of water?

Question

anonymous · Answer

The second part of Dalton's 4 part theory states all atoms of a given element are identical in mass and properties. The atomic mass of hydrogen is close to 1the atomic mass of oxygen is close to 16. Since water(H20) is 2 parts Hydrogen(1*2) and 1 part Oxygen(16) 
we can divide 2/18 for Hydrogen and 16/18 for Oxygen to get the atomic mass percentage.