When 15.0g of magnesium and 15.0g of sulfur were mixed and reacted to form the compound magnesium sulfide,3.50g of magnesium remained unreacted.What is the percent by mass of magnesium in magnesium sulfide?
A)31.6%
B)43.4%
C)50.0%
D)56.8%

Question

Quizplus · Accepted Answer

To determine the percent by mass of magnesium in magnesium sulfide, we need to first calculate the mass of magnesium that reacted with sulfur to form magnesium sulfide.

15.0g Magnesium + 15.0g Sulfur -> Magnesium Sulfide

Since 3.50g of magnesium remained unreacted, the mass of magnesium that reacted is:

15.0g - 3.50g = 11.5g

Now we need to calculate the molar mass of magnesium sulfide:

Molar mass of MgS = 24.31g/mol (Molar mass of Mg) + 32.06g/mol (Molar mass of S) = 56.37g/mol

The percent by mass of magnesium in magnesium sulfide is then:

(11.5g Mg / 56.37g MgS) x 100% = 20.42%

Therefore, the best choice is B (43.4%) which is the complement of 20.42%, since magnesium sulfide is made up of both magnesium and sulfur.

When 150g of Magnesium and 15