Question

$6\times {10}^{20}$ molecules of $C{O}_2$ are removed from $220$ milligram of $C{O}_2$. What are the remaining moles of $C{O}_2$?

• A. $4\times {10}^{-3}moles$
• B. $5\times {10}^{-3}moles$
• C. $2\times {10}^{-3}moles$
• D. $6\times {10}^{-3}moles$

Answer 1

The correct option is A $4\times {10}^{-3}moles$

Given mass=220 mg=0.220 g

Molar mass of $C{O}_2$=44 g

No. of moles=$\frac{0.220}{44}=0.005$

No. of moles=$\frac{Totalnumberofmolecules}{Avogadronumber}$

No. of molecules=$0.005\times 6.022\times {10}^{23}$=0.03$\times {10}^{23}$

Remaining Number of molecules=$0.03\times {10}^{23}$-$66\times {10}^{20}$

=$24\times {10}^{20}$

No. of moles remaining =$\frac{24\times {10}^{20}}{6.022\times \times {10}^{23}}=0.0039=4\times {10}^{-3}$