Question

An element x forms an iodide (xi3) and a chloride (xcl3). the iodide is quantitatively converted to the chloride when it is heated in a stream of chlorine: 2xi3+3cl2â2xcl3+3i2 if 0.5500 g of xi3 is treated, 0.2596 g of xcl3 is obtained. part a calculate the atomic weight of the element x.

Answer 1

The atomic weight of the given element X = 138.9 g/mol

Step-by-step explanation:

The given chemical reaction: 2XI₃ + 3Cl₂ → 2XCl₃ + 3I₂

Given: mass of XI₃: W₁ = 0.5500 g, mass of XCl₃: W₂ = 0.2596 g

Atomic mass of: iodine (I) = 126.90 g/mol, chlorine (Cl) = 35.45 g/mol

Atomic mass of X = ? g/mol

Therefore, the molar mass of XI₃: M₁ = [X + (3 × 126.90)] = [X + 380.70]

and, the molar mass of XCl₃: M₂ = [X + (3 × 35.45)] = [X + 106.35]

As we know, Number of moles = given mass in g ÷ molar mass in g/mol

As, the number of moles of XI₃: n₁ = the number of moles of XCl₃: n₂ = 2

∴ n₁ = n₂ ⇒ W₁ ÷ M₁ = W₂ ÷ M₂

⇒ (0.55) ÷ (X + 380.70) = (0.2596) ÷ (X + 106.35)

⇒ (0.55) × (X + 106.35) = (0.2596) × (X + 380.70)

⇒ (0.55 × X + 58.49) = (0.2596 × X + 98.83)

⇒ (0.55 × X - 0.2596 × X) = (98.83 - 58.49)

⇒ 0.2904 × X = 40.34

⇒ X = 40.34 ÷ 0.2904 = 138.9 g/mol

Therefore, the atomic weight of the given element X = 138.9 g/mol .

As the chemical element Lanthanum (La) also has the atomic mass 138.9 g/mol.

Therefore, the given element X is Lanthanum (La)