Question

directions: show all work for full credit and circle final answers.
use:

\\(\\%\text{ element} = \dfrac{\text{mass of element in formula}}{\text{molar mass of compound}} \times 100\\)

1. calculate the percent composition of each element in mgo.

1. determine the percent composition of each element in alcl₃.

Explanation:

Step1: Find molar masses of elements

Atomic masses: Mg=24.31 g/mol, O=16.00 g/mol, Al=26.98 g/mol, Cl=35.45 g/mol
(Note: Assume AlCl₃ for valid formula, as AlCl is unstable)

Step2: Calculate MgO molar mass

Molar mass of MgO = 24.31 + 16.00 = 40.31 g/mol

Step3: Compute % Mg and O in MgO

% Mg = $\frac{24.31}{40.31}×100 ≈ 60.3\%$
% O = $\frac{16.00}{40.31}×100 ≈ 39.7\%$

Step4: Calculate AlCl₃ molar mass

Molar mass of AlCl₃ = 26.98 + (3×35.45) = 26.98 + 106.35 = 133.33 g/mol

Step5: Compute % Al and Cl in AlCl₃

% Al = $\frac{26.98}{133.33}×100 ≈ 20.3\%$
% Cl = $\frac{106.35}{133.33}×100 ≈ 79.7\%$

Answer:

1. % Mg ≈ 60.3%, % O ≈ 39.7%
2. % Al ≈ 20.3%, % Cl ≈ 79.7%