Question

calculate the percent composition by mass of magnesium in the fictional compound shown below. include the units, but do not write the chemical formula. round the answer to 3 significant figures. la₆mg₄p₄ magnesium =

Explanation:

Step1: Find molar masses

Molar mass of La: \(138.9055\space g/mol\), Mg: \(24.305\space g/mol\), P: \(30.9738\space g/mol\).
For \(La_6Mg_4P_4\):
Mass of La: \(6\times138.9055 = 833.433\space g/mol\)
Mass of Mg: \(4\times24.305 = 97.22\space g/mol\)
Mass of P: \(4\times30.9738 = 123.8952\space g/mol\)

Step2: Total molar mass

Total = \(833.433 + 97.22 + 123.8952 = 1054.5482\space g/mol\)

Step3: Percent composition of Mg

Percent = \(\frac{97.22}{1054.5482}\times100 \approx 9.219\%\) (rounded to 3 sig figs)

Answer:

\(9.22\%\) (or \(9.21\%\) - slight rounding differences, but typically \(9.22\%\) with 3 sig figs)