Methane and oxygen react to form carbon dioxide and water. What mass of water is formed if 0.80g of methane reacts with 3.2 g of oxygen to produce 2.2 g of carbon dioxide?

Question

rushwr · Answer

$$CH _{4} + 2O _{2}\rightarrow CO _{2} + 2H _{2}O$$
This is easy now . 
Number of moles = mass divided by molar mass right?
We are given with the mass of carbon dioxide formed right? So don't think about any other masses. Just go on with CO2.
Look at the molar ratio of carbon dioxide and water. that is 1:2 . so if x no. of moles of carbon dioxide is formed then 2x moles of water will be formed.  

We will now find the no. of moles of carbon dioxide. 
moles = mass divided by molar mass. 
Mass - 2.2g 
Molar mass = 44g
$$Moles= \frac{ 2.2g }{44  } = 0.05 moles $$
This is the moles of carbon dioxide , to find the moles water formed we have to multiply this by 2 
no. of moles of water - 0.1 moles 

The stuff we know about water now-- > Moles = 0.1mol
molar mass = 18gmol^-1
if moles = mass/ molar mass
mass = moles * molar mass right?
so mass of water formed = 0.1 moles * 18gmol^-1 = 1.8g