A sample of magnesium is partially oxidised to magnesia. 3 grams of such sample is treated with excess dilute sulphuric acid and the hydrogen collected measures 1.12 L at STP. What is the weight ratio of metal and metal oxide in the sample? 

Explanation

Reaction of sulphuric acid with components is given as
`Mg+H_(2)SO_(4)rarrMgSO_(4)+H_(2)`
`MgO+H_(2)SO_(4)rarr MgSO_(4)+H_(2)O`
1 mole of `H_(2) = 1` mole of Mg
22.4 L of `H_(2)` at STP = 24 g of Mg
1.12 L of `H_(2)` at STP `= ?`
Weight of magnesium in given sample `=(1.12)/(22.4)xx24=1.2` grams
Weight of MgO in given sample `= 3 - 1.2 = 1.8` grams
Weight ratio of Mg and `MgO = 1.2:1.8 = 2: 3`