Which of the following substances has a molar mass of 208g

Missing question: P₂O₅, BaCl₂, AlCl₃, MgCl₂.

Answer is: barium chloride (BaCl₂).

a) M (P₂O₅) = 2 · Ar (P) + 5 · Ar (O) · g/mol.

M (P₂O₅) = 2 · 31 + 5 · 16 · g/mol = 142 g/mol.

b) M (BaCl₂) = Ar (Ba) + 2 · Ar (Cl) · g/mol.

M (BaCl₂) = 137,3 + 2 · 35,45 · g/mol = 208,2 g/mol.

c) M (AlCl₃) = Ar (Al) + 3 · Ar (Cl).

M (AlCl₃) = 27 + 3 · 35,45 · g/mol = 133,35 g/mol.

d) M (MgCl₂) = Ar (Mg) + 2 · Ar (Cl) · g/mol.

M (MgCl₂) = 24,3 + 2 · 35,45 · g/mol = 95,2 g/mol.

The list of substances is:

a) P2O5

b) BaCl2

c) AlCl3

d) MgCl2

Answer:BaCl2

Explanation:

I will find the molar mass of each substance

The molar mass is the sum of the masses of each atom in the unit formula.

1) P2O5

Molar mass = 2 * atomic mass of P + 5 * atomic mass of O = 2 * 31 g/mol + 5 * 16 g/mol = 62g/mol + 80g/mol = 140 g/mol.

∴ This is not the answer.

2) BaCl2

Molar mass = atomic mass of Ba + 2 * atomic mass of Cl = 137.3 g/mol + 2 * 35.5 g/mol = 208.3 g/mol ≈ 208 g/mol

∴ This is the answer

3) AlCl3

Molar mas = atomic mass of Al + 3 * atomic mass of Cl = 27 g/mol + 3 * 35.5 g/mol = 133.5 g/mol

∴ This is not the answer

4) MgCl2

molar mass = atomic mass of Mg + 2*atomic mass of Cl = 24.3 g/mol + 2*35.5 g/mol = 95.3 g/mol

∴ this is not the answer