A student performs an experiment to determine the volume of hydrogen gas produced when a given mass of magnesium reacts with excess HCl (aq), as represented by the net ionic equation above. The student begins with a 0.0360 g sample of pure magnesium and a solution of 2.0 M HCl (aq).

(a) Calculate the number of moles of magnesium in the 0.0360 g sample

1.48x10⁻³ mol

Explanation:

The balanced equation is

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

The aqueous solution will disociate, so:

Mg (s) + 2H⁺ (aq) + 2Cl⁻ (aq) → Mg²⁺ (aq) + 2Cl⁻ (aq) + H₂ (g)

Simplifying by eliminating the bolded substances that have the same amount in both sides, we have the net ionic equation:

Mg (s) + 2H⁺ (aq) → Mg²⁺ (aq) + H₂ (g).

a) The number of moles of Magnesium is the mass divided by the molar mass (24.305 g/mol):

n = 0.0360/24.305

n = 1.48x10⁻³ mol