Answer to Question #157329 in Chemistry for Marc

Question

A teaspoon of milk of magnesia contains 25.0 mg of magnesium hydroxide, Mg(OH)2.  What volume of 0.010 M HCl in a person’s stomach would be neutralized by this teaspoon of antacid?

Answer 1

Solution:

The balanced chemical equation:

Mg(OH)₂ + 2HCl = MgCl₂ + 2H₂O

According to the equation: n(Mg(OH)₂) = n(HCl)/2

Mass of Mg(OH)₂ = 25.0 mg = 0.025 g

Moles of Mg(OH)₂ = Mass of Mg(OH)₂ / Molar mass of Mg(OH)₂

The molar mass of Mg(OH)₂ is 58.32 g mol^-1.

Hence,

n(Mg(OH)₂) = 0.025 g / 58.32 g mol^-1 = 0.0004287 mol

n(HCl) = 2 × n(Mg(OH)₂) = 2 × 0.0004287 mol = 0.0008574 mol

Molarity of HCl = Moles of HCl / Volume of HCl

Hence,

Volume of HCl = Moles of HCl / Molarity of HCl

V(HCl) = 0.0008574 mol / 0.010 M = 0.08574 L = 85.74 mL

V(HCl) = 85.74 mL

Answer: 85.74 mL of HCl would be neutralized.