Question

48g of magnesium and 32g of oxygen react to form 80g of magnesium oxide.
2Mg + O2 --> 2MgO

What mass of oxygen is needed to make 20g of MgO?

Answer 1

Mass of Oxygen : 8 g

Further explanation

Given

48g of Magnesium

32g of Oxygen

Required

Mass of Oxygen

Solution

The ratio of Mg and O in MgO :

48 g : 32 g = 3 : 2

Total ratio = 3+2 = 5

So for 20 g MgO, mass of Oxygen :

=2/5 x 20 g

=8 g

Or

%mass O = 32/80 x 100%=40%

mass O in 20 g MgO =

40% x 20 g =8 g