Question

A sample of $Mg{CO}_3$ contains $3.01\times {10}^{23}{Mg}^{2+}$ ions and $3.01\times {10}^{23}{CO}_3^{2-}$ ions. The mass of the sample is:

• A. $42mg$
• B. $84g$
• C. $0.042kg$
• D. $42mol$

Answer 1

Answer: (C)

$0.042kg$

$6.022\times {10}^{23}M{g}^{2+}$ ions in $1$ mole of $MgC{O}_3$

$3.01\times {10}^{23}{CO}_3^{2-}$ ions in $1$ mole of $MgC{O}_3$ $=\frac{3.01\times {10}^{23}}{6.022\times {10}^{23}}=0.5mole$

So, mass of sample $\left(MgC{O}_3\right)$=$(24+12+48)\times 0.5$=$84\times \frac{0.5}{10}g=42g$$=0.042Kg$