Case Study:

Rohit, a Class 10 student from Delhi, attends a family wedding where he eats large amounts of spicy food such as chole, paneer tikka, and fried snacks. Later that night, he experiences burning pain in his stomach, commonly called acidity or indigestion. His mother gives him an antacid tablet for relief.

The human stomach normally secretes hydrochloric acid (HCl) to help digest food. The pH of gastric acid is usually around 1.5–3.5, which is strongly acidic. However, overeating or consuming very spicy or oily food may increase the amount of acid, causing irritation and heartburn. 

Antacid tablets contain basic substances such as magnesium hydroxide (Mg(OH)₂), aluminium hydroxide (Al(OH)₃), or calcium carbonate (CaCO₃). These compounds react chemically with excess hydrochloric acid in the stomach through a neutralization reaction, producing salt and water. 

For example, magnesium hydroxide neutralizes stomach acid according to the reaction:

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

This reaction reduces the concentration of acid and increases the pH of stomach contents, thereby relieving the burning sensation. 

Suppose one antacid tablet contains 400 mg of magnesium hydroxide and is capable of neutralizing 0.014 moles of HCl present in the stomach. Doctors usually advise taking antacids in controlled amounts because excessive neutralization may disturb the digestive process.

Understanding how antacids work helps students connect chemistry concepts such as acids, bases, pH, and neutralization reactions to everyday health situations

Questions

Section A – MCQs (1 mark each)

1. The main purpose of taking an antacid tablet during acidity is to:

A. Increase stomach acid
B. Neutralize excess hydrochloric acid
C. Produce more digestive enzymes
D. Stop digestion completely

2. Which of the following substances commonly acts as an antacid?

A. Sodium chloride
B. Magnesium hydroxide
C. Hydrochloric acid
D. Carbon dioxide

3. The reaction between antacid and stomach acid is best described as:

A. Oxidation reaction
B. Neutralization reaction
C. Displacement reaction
D. Decomposition reaction

4. If too many antacid tablets are consumed, the most likely effect is:

A. Increase in acidity
B. Complete digestion of food
C. Excess neutralization of stomach acid
D. No change in stomach pH

Section B – Short Answer Questions

1. Why are basic compounds used in antacid tablets instead of acidic substances?

2. Write the balanced chemical equation for the reaction between magnesium hydroxide and hydrochloric acid. Explain how this reaction helps relieve acidity.

3. A patient experiences acidity after eating oily food. Explain how the pH of the stomach changes after taking an antacid tablet.

Section C – Long Answer Question

1.A student reads that an antacid tablet contains calcium carbonate (CaCO₃) as its active ingredient.

a) Write the balanced chemical equation for the reaction between calcium carbonate and hydrochloric acid.
b) Explain how this reaction helps reduce stomach acidity.
c) If the tablet neutralizes a large amount of acid, why should antacids still be taken in limited quantities?

Answer Key

MCQ Answers

1. B
2. B
3. B
4. C

Section B Answers

1.Antacids contain basic substances because bases react with acids to form salt and water, reducing acidity through a neutralization reaction.

2.Balanced equation:

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

Explanation: Magnesium hydroxide (a base) reacts with hydrochloric acid in the stomach, forming magnesium chloride and water. This reduces the acidity and increases the pH of the stomach, relieving burning sensation.

3.Before taking an antacid, the stomach has very low pH (high acidity) due to excess HCl. After taking an antacid, the base reacts with HCl, reducing acid concentration and raising the pH toward neutral, providing relief from acidity.

Section C Answer

a) Balanced reaction:

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

b) Explanation:Calcium carbonate reacts with excess hydrochloric acid in the stomach. This neutralization reaction produces salt (calcium chloride), water, and carbon dioxide, reducing the acidity of the stomach.

c) Reason for limited consumption:
Taking too many antacids may disturb the natural acidic environment required for digestion and may lead to digestive problems or imbalance in stomach pH.