Question

A 2.93-g sample of an alkaline earth metal chloride is trated with excess silver nitrate. All of the chloride is recovered as 7.57 g of silver chloride. What is the name of the alkaline earth metal?

Answer 1

Mass of alkaline earth metal = 2.93 g

Mass of AgCl = 7.57 g

Moles of AgCl = mass/molecular weight

= (7.57 g) / (143.32 g/mol)

= 0.052819 mol

Assume any alkaline earth metal = XCl2

Silver nitrate = AgNO3

The balanced reaction

XCl2 + 2AgNO3 = X(NO3)2 + 2AgCl

Excess reactant = AgNO3

Limiting reactant = XCl2

From the stoichiometry of the reaction

2 mol AgCl produced from = 1 mol XCl2

0.052819 mol AgCl produced from = 0.052819/2

= 0.026409 mol XCl2

Molecular weight of XCl2 = mass/moles

= 2.93 g / 0.026409 mol

= 110.95 g/mol

Molecular weight of XCl2 = molecular weight of X + 2*Molecular weight of Cl

110.95 = X + 2*35.5

X = 39.95 g/mol

X = calcium (Ca)