Question

Larry has not been feeling well lately. He tells his doctor that he has discomfort and a burning feeling in his chest, and a sour taste in his throat and mouth. At times, Larry says he feels bloated after a big meal, has a dry cough, is hoarse, and sometimes has a sore throat. He has tried antacids, but they do not bring any relief.
The doctor tells Larry that he thinks he has acid reflux. At the top of the stomach there is a valve, the lower esophageal sphincter, that normally closes after food passes through it. However, if the valve does not close completely, acid produced in the stomach to digest food can move up into the esophagus, a condition called acid reflux. The acid, which is hydrochloric acid, HCl, is produced in the stomach to kill bacteria, microorganisms, and to activate the enzymes we need to break down food. (Figure 1)
If acid reflux occurs, the strong acid HCl comes in contact with the lining of the esophagus, where it causes irritation and produces a burning feeling in the chest. Sometimes the pain in the chest is called heartburn. If the HCl reflux goes high enough to reach the throat, a sour taste may be noticed in the mouth. If Larry's symptoms occur three or more times a week, he may have a chronic condition known as acid reflux disease orgastroesophageal reflux disease (GERD).
Larry's doctor orders an esophageal pH test in which the amount of acid entering the esophagus from the stomach is measured over 24 h. A probe that measures the pH is inserted into the lower esophagus above the esophageal sphincter. The pHmeasurements indicate a reflux episode each time the pH drops to 4 or less.
In the 24-h period, Larry has several reflux episodes and his doctor determines that he has chronic GERD. He and Larry discuss treatment for GERD, which includes eating smaller meals, not lying down for 3 h after eating, making dietary changes, and losing weight. Antacids may be used to neutralize the acid coming up from the stomach. Other medications known as proton pump inhibitors (PPIs), such as Prilosec and Nexium, may be used to suppress the production of HCl in the stomach (gastric parietal cells), which raises the pH in the stomach to between 4 and 5, and gives the esophagus time to heal. Nexium may be given in oral doses of 40 mg once a day for 4 weeks. In severe GERD cases, an artificial valve may be created at the top of the stomach to strength the lower esophageal sphincter.(Figure 2)

Part A

How many grams of Mg(OH)2 are required to neutralize 450. mL of stomach acid HCl with a pH of 1.7?

Express your answer to two significant figures and include the appropriate units.

Answer 1

part A)   volume of HCl = 450 mL = 0.450 L

            pH = 1.7

           [H+] = 10^-1.7 = 0.01995 M

moles of HCl = 0.01995 x 0.450

                    = 8.98 x 10^-3

Mg(OH)2 + 2 HCl ------------------>MgCl2 + 2H2O

1 mole        2 mole

moles of Mg(OH)2    = 8.98 x 10^-3 / 2 = 4.49 x 10^-3

moles = mass / molar mass

mass = 4.49 x 10^-3 58.3

          = 0.26 g

mass of Mg(OH)2 = 0.26 g