Question

The weight of calcium oxide formed by burning $20$g of calcium in excess oxygen is$:$

• A. $36$g
• B. $56$g
• C. $28$g
• D. $72$g

Answer 1

The correct option is C $28$g

The atomic mass of $Ca=40$ g/mol.
20 g of $Ca=\frac{20g}{40g/mol}=0.5mol$
0.5 moles of $Ca$ will give 0.5 moles of $CaO$.
The molecular weight of $Ca=40+16=56$ g/mol.
0.5 moles of $CaO=0.5mol\times 56g/mol=28$ g.
The weight of calcium oxide formed by burning 20 g of calcium in excess oxygen is 36 g
Hence, the option (C) is the correct answer.