Question

If we have a pure $MgC{O}_3$ sample that contains a total of 1.26 millimoles of electrons, the number of moles of $MgC{O}_3$ present in the sample is $x\times {10}^{-5}$, x is.

Answer 1

One molecule of $MgC{O}_3$ contains $=12+6+(8\times 3)=42$ electrons.
So, number of electrons in 1 mole of $MgC{O}_3=42\times 6.022\times {10}^{23}$
Therefore, 1.26 millimoles of electrons will present in
$=\frac{1.26\times {10}^{-3}\times 6.022\times {10}^{23}}{42\times 6.022\times {10}^{23}}\text{moles}=3\times {10}^{-5}$ moles of $MgC{O}_3$