The daily output of stomach acid (gastric juice) is 1000 to 2000 mL. Prior to a

Question

The daily output of stomach acid (gastric juice) is 1000 to 2000 mL. Prior to a meal, stomach acid (HCl) typically has a pH of 1.42. (8.5, 8.6) What is the [H_3O^+] of stomach acid? One chewable tablet of the antacid Maalox contains 600. mg of CaCO_3. Write the neutralization equation, and calculate the milliliters of stomach acid neutralized by two tablets of Maalox. The antacid milk of magnesia contains 400. mg of Mg(OH)_2 per teaspoon. Write the neutralization equation, and calculate the number of milliliters of stomach acid neutralized by one tablespoon of milk of magnesia (one tablespoon = three teaspoons).

Explanation / Answer

a. pH = -log[H3O+] = 1.42

[H3O+] = 0.038 M

b. Neutralization reaction,

CaCO3 + 2HCl ---> CaCl2 + H2O + CO2

moles of CaCO3 = 0.6 g/100.09 = 0.006 mol

with 1000 ml HCl, moles HCl = 0.038 x 1 L = 0.038 mol

Two tablets of antacid = 2 x 0.006 = 0.012 mol

HCl neutralized = 0.012 mol x 2/0.038 M = 0.6316 L = 631.6 ml

c. moles Mg(OH)2 = 3 x 0.4/58.32 = 0.0206 mol

moles HCl needed = 0.0206 x 2 = 0.0412mol

Volume of HCl neutralized = 0.0412 mol/0.038 M = 1.084 L = 1084 ml

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