Answer
Mass percentage of Al in the sample of alloy is 72.3 % .
Mass percentage of Mg in the sample of alloy is 27.7 %
Work Step by Step
Strategy: Convert moles to mass by using conversion factor Molar mass/ 1 mol. Then find the total mass of the alloy by adding the masses of Al and Mg. Lastly find the mass percentage of Al and Mg in the alloy.
1- Mass of 0.0898 mol Al
Molar mass of Al= 26.981 g/mol
0.0898 mol Al x $\frac{26.981g}{1 mol}$ =2.4229 g
Mass of 0.0898 mol Al is 2.4229 g.
Mass of 0.0381 mol Mg
Molar mass of Mg= 24.305 g/mol
0.0381 mol Mg x $\frac{24.305g}{1 mol}$ =0.9260 g
Mass of 0.0381 mol Mg is 0.9260 g.
2- The total mass of alloy is: mass Al + mass Mg.
So the total mass is 2.4229 g + 0.9260 g = 3.3489 g.
3- Mass percentage of Al in the sample of alloy = $\frac{2.4229 g (Al )}{3.3489(sample of alloy)}$ $\times$ 100%
Mass percentage of Al in the sample of alloy = 0.72348 $\times$ 100%
Mass percentage of Al in the sample of alloy is 72.3 % ( to three significant figures).
Mass percentage of Mg in the sample of alloy = $\frac{0.926 g (Mg)}{3.3489(sample of alloy)}$ $\times$ 100%
Mass percentage of Mg in the sample of alloy = 0. 2765 $\times$ 100%
Mass percentage of Mg in the sample of alloy is 27.7 % ( to three significant figures).
