Question

Milk of magnesia has the chemical formula Mg(OH)2. What is the mass of 3.2 moles of milk of magnesia? The molar mass of magnesium is 24.3 grams per mole. The molar mas of hydrogen is 1.0 grams per mole. The molar mass of oxegyn is 16.0 grams per mole.

Answer 1

The answer is C. 186. 6 g

The molar mass (Mr) of Mg(OH)₂ is the sum of atomic masses (Ar) of the elements.
Ar(Mg) = 24.3 g/mol
Ar(H) = 1
Ar(O) = 16

Mr(Mg(OH)₂) = Ar(Mg) + 2Ar(O) + 2Ar(H) = 24.3 + 2· 1 + 2 · *16 = 24.3 + 2 + 32 = 58.3 g/mol

Now, make a proportion. If 58.3 g are in 1 mol, how much will be in 3.2 mol:
58.3 g : 1 mol = x : 3.2 mol
x = 58.3 g · 3.2 mol ÷ 1 mol = 186.56 ≈ 186.6 g