Milk of magnesia is often taken to reduce the discomfort associated with heartburn. The recommended dose is one teaspoon, which contains 175 mg of Mg(OH)2. If t

Question

Milk of magnesia is often taken to reduce the discomfort associated with heartburn. The recommended dose is one teaspoon, which contains 175 mg of Mg(OH)2. If the stomach contains 352 mL of pH 1.3 solution, what percent of the acid will be neutralized?

Answer 1

From pH = 1.3, you can calculate the [H+] as follows:

pH = -log [H⁺] and thus [H⁺]= 1x10^-1.3 = 5.01x10^-2 M

Now, convert this to moles of H⁺ present in 352 mls (0.352 L)

5.01x10^-2 moles/L x 0.352 L = 1.76x10^-2 moles H⁺

How much Mg(OH)₂ is present?

175 mg Mg(OH)₂ x 1 mmole/58.3 mg = 3.00 mmoles

Since 1 mole Mg(OH)₂ produces 2 moles OH^-, 3.00 mmoles Mg(OH)₂ will neutralize 6.00 mmoles H⁺

1.76x10^-2 moles H⁺ x 1000 mmoles/mole = 17.6 mmoles H⁺ present

6.00 moles/17.6 mmoles (x100%) = 34.1% neutralized