Question

if hydrogen and oxygen combine in a ratio 1:8 by mass respectively to form water molecule.explain how many moles of water will be formed using 10 moles of hydrogen gas and 5 moles of oxygen gas

Answer 1

First we have to find the mass of the following,
10 mole of hydrogen will weigh 10 x 2 g = 20 g
And 5 moles of oxygen wil weigh 5 x 16 g = 80 g

Now we know hydrogen and oxygen in 1:8 ratio
So we get that if we take 20 g of H2 as 1 x then it needs 160 g of O2
So we take 80 g of O2 as 8x and thus it needs 10 g of H2, which is available
So they would combine to form
80 + 10 = 90 g of water

Now we know molecular mass of water is 18 g

So its forms 90/18 = 5 moles of water

Answer 2

weight of hydrogen=2g x 10 moles= 20 g
weight of oxygen= 16g x 5 moles = 80 g
we know, 20 g hydrogen requires 160g of oxygen
so, 80g of oxygen reacts with 10 g of hydrogen.
so  we get 10 + 80=90g of water
to find ratio we need to divide it with molecular mass of water giving = 90 /18=5:1 ratio.