Question

How many grams of water can be produced by the combination of 8 grams of oxygen and 8 grams of hydrogen?

Answer 1

Hint: Law of conservation of mass is used that states that “mass can neither be created nor can be destroyed, but can be changed from one form to another”, through this it is observed that mass of reactants is equal to the mass of products in any chemical reaction.

Formula used:
Number of moles=$\dfrac{given\,mass}{molecular\,mass}$

Complete answer:
We have been given to find the mass of water produced from a reaction of 8 grams of hydrogen and oxygen. So, the reaction for this will be-
\[2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O\]
This reaction clearly tells that 2 moles of hydrogen and 1 mole of oxygen produce 2 moles of water. The molar mass of hydrogen is 2, oxygen is 32 and water is 18.
Now, when 8 grams of hydrogen and oxygen is used, then number of moles will be:
Number of moles of hydrogen=$\dfrac{8}{2}$ = 4 moles
Number of moles of oxygen= $\dfrac{8}{32}$ = 0.25 moles
Number of moles of water= $\dfrac{16}{36}$ = 0.5 moles
So, the mass of water will be:
Number of moles=$\dfrac{\,mass}{molecular\,mass}$
Mass of water= number of moles $\times $ molecular mass
Mass of water= 0.5 moles $\times $18 g/mol
Mass of water= 9 gram
Hence, with 8 grams of both hydrogen and oxygen, the mass of water produced is 9 gram.

Note:
When 8 gram of both hydrogen and oxygen are taken, then the mass of water that has to be taken will be $8+8=16$. This is in accordance with the law of conservation of mass that the total mass of reactants is the same as that of total mass of products in a reaction.