Question

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calculate the percent composition by mass of magnesium in mg(no3)2:
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Explanation:

Step1: Calculate molar mass of Mg(NO₃)₂

Molar mass of Mg = \(24.305\space g/mol\)
Molar mass of N = \(14.007\space g/mol\), and there are 2 N atoms in \(Mg(NO_3)_2\), so mass from N: \(2\times14.007 = 28.014\space g/mol\)
Molar mass of O=\(15.999\space g/mol\), and there are \(6\) O atoms (\(2\times3\)) in \(Mg(NO_3)_2\), so mass from O: \(6\times15.999=95.994\space g/mol\)
Molar mass of \(Mg(NO_3)_2=24.305 + 28.014+95.994 = 148.313\space g/mol\)

Step2: Calculate mass percent of Mg

Mass percent of \(Mg=\frac{\text{Mass of Mg in one mole of }Mg(NO_3)_2}{\text{Molar mass of }Mg(NO_3)_2}\times100\)
\(=\frac{24.305}{148.313}\times 100\)
\(\approx16.4\)

Answer:

\(16.4\)