Question

An element, X, can form a chloride (XCl3) and an iodide (XI3). The chloride can be converted quantitatively into the iodide when heated and exposed to excess iodine. If 0.760 grams of XCl3 are heated with iodine, 1.610 g of XI3 are produced. What is the chemical symbol for this element? Use stoichiometry to create an equation that allows you to solve for the molecular weight of X.2 XCl3 + 3 I2 ---------> 2 XI3 + 3 Cl2

Answer 1

Answer : The chemical symbol for this element is, (La)

Explanation : Given,

Mass of $XCl_3$ = 0.760 g

Mass of $XI_3$ = 1.610 g

The given chemical reaction is:

$2XCl_3+3I_2\rightarrow 2XI_3+3Cl_2$

First we have to calculate the moles of $XCl_3$ and $XI_3$.

$\text{Moles of }XCl_3=\frac{\text{Mass of }XCl_3}{\text{Molar mass of }XCl_3}$

Molar mass of Cl = 35.5 g/mole

Let the molar mass of element 'X' be, M

$\text{Moles of }XCl_3=\frac{0.760}{[M+3(35.5)]}$

and,

$\text{Moles of }XI_3=\frac{\text{Mass of }XI_3}{\text{Molar mass of }XI_3}$

Molar mass of I = 126.9 g/mole

Let the molar mass of element 'X' be, M

$\text{Moles of }XI_3=\frac{1.610}{[M+3(126.9)]}$

From the balanced chemical reaction we conclude that,

The moles of ratio of $XCl_3$ and $XI_3$ is, 1 : 1

That means,

$\frac{0.760}{[M+3(35.5)]}=\frac{1.610}{[M+3(126.9)]}$

$\frac{0.760}{[M+106.5]}=\frac{1.610}{[M+380.7]}$

$M=138.667g/mol$

From this we conclude that the element (X) is lanthanum (La) that has molecular weight, 138.667 g/mol.

Hence, the chemical symbol for this element is, (La)