5 g of clacium reacts with 2 g of oxygen to form a compound. Find the molecular formula of the compound.(Atomic mass of Ca= 40 u, O=16u

Number of moles in 5g of calcium = mass /  molar mass
= (5 / 40) =  0.125

 

Number of moles in 2g of oxygen = mass / molar mass

= (2 / 16)  = 0.125

Now calculate the simplest ratio of the element. For this we will divide the number of moles of each element by the smallest value. But as the number of moles of each element is 0.125, therefore calcium and oxygen are present in a ratio of 1 : 1. Thus the empirical formula of the compound is CaO.

 

In order to calculate molecular formula we will need molecular mass of the compound which is not given. But there exist one compound with formula CaO so we can take the molecular formula as CaO.