Question

Calculate the number of calcium ions in 8.2 g of calcium oxide.

[Atomic weight $Ca=40$]

• A. $3.44\times {10}^{20}$ ions
  
• B. $3.44\times {10}^{12}$ ions
  
• C. $3.44\times {10}^{23}$ ions
  
• D. $8.810\times {10}^{22}$ ions
  

Answer 1

The correct option is D $8.810\times {10}^{22}$ ions

molar mass of calcium oxide $=40+16=56g$

Number of moles of $CaO=\frac{\text{Given Weight}}{\text{Molar mass}}=\frac{8.2g}{56g}=0.1464g$

In 1 mole $CaO$, there are $6.023\times {10}^{23}$ atoms of $Ca$ ions.

So, in 0.14644 moles, there are $=0.1464\times 6.023\times {10}^{23}$ atoms

$=8.810\times {10}^{22}$ atoms.

Each atom having one $C{a}^{+}$ ions $=8.810\times {10}^{22}$ ions.

Hence, the correct option is $\text{D}$