Question
Calculate number of electrons in 3.0 gm ethane.

Answer

$\begin{array}{l}\text { Mole }=\frac{\text { mass }( g )}{\text { molar mass }} \\ \text { Molar mass of ethane }=24+6=30 \\ \text { Moles of ethane }=\frac{3.0}{30}=0.1 \\ \text { Hence number of molecules of ethane }=\text { number } \\ \text { of moles } \times 0.1 \times 6.022 \times 10^{23} \\ \text { As in } 1 \text { molecule of ethane }=12+6=18 \\ \text { Hence number of electrons in ethane }=\text { number of } \\ \text { molecules } \times \text { number of electrons in } 1 \text { molecule } \\ =0.1 \times 6.022 \times 10^{23} \times 18 \\ =1.083 \times 10^{24}\end{array}$

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