Chapter 2 · Question 8
How is pH relevant to our digestive system and dental health? Explain the role of antacids and the chemical basis of tooth decay.
Q8
How is pH relevant to our digestive system and dental health? Explain the role of antacids and the chemical basis of tooth decay.
Answer Revealed
Direct Answer:
The stomach produces hydrochloric acid (HCl) for digestion. During indigestion, excess acid is produced, causing pain and irritation. Antacids — mild bases like milk of magnesia () — are taken to neutralise this excess acid. Tooth decay starts when the pH inside the mouth falls below 5.5. Tooth enamel, made of calcium hydroxyapatite (a crystalline form of calcium phosphate), is the hardest substance in the body but corrodes when the mouth pH drops below 5.5. Bacteria in the mouth break down sugars and food particles, producing acids that lower the pH. Toothpastes, which are generally basic, help neutralise the excess acid and prevent decay.
Simple Explanation
Your stomach is full of hydrochloric acid — it helps digest food. But when there is too much, you feel the burning pain of acidity. That is when you take an antacid like milk of magnesia — it is a base that neutralises the extra acid. For teeth: bacteria in your mouth feed on sugars and produce acid. If the mouth pH drops below 5.5, the acid starts eating away at your tooth enamel. Brushing with toothpaste (which is basic) neutralises that acid. This is also why eating sweets and not brushing causes cavities — the sugar-fed bacteria keep pumping acid onto your teeth.
Exam-Ready Structure
The importance of pH in everyday life is established in NCERT Class 10 Chapter 2 through two significant examples within the human body — digestion and dental health. 1. pH in the digestive system: (a) The stomach produces hydrochloric acid (HCl), which helps in the digestion of food without harming the stomach lining under normal conditions. (b) During indigestion, the stomach produces an excess of acid, leading to pain, irritation, and a burning sensation. (c) Treatment: Antacids are medicines that contain mild bases. Common examples include milk of magnesia (magnesium hydroxide, ). These bases neutralise the excess stomach acid to provide relief. The neutralisation reaction is the basis of antacid action. 2. pH and tooth decay: (a) Tooth decay begins when the pH of the mouth falls below 5.5. (b) Tooth enamel is composed of calcium hydroxyapatite, a crystalline form of calcium phosphate, and is the hardest substance in the human body. (c) It is insoluble in water, but it begins to corrode (dissolve) when the pH in the mouth drops below 5.5 — the acid chemically attacks the enamel. (d) How acid forms in the mouth: Bacteria present in the mouth break down sugars and food particles that remain after eating, producing acids as metabolic by-products. These acids lower the mouth pH. (e) Prevention: Using toothpastes, which are generally basic in nature, helps neutralise the excess acid produced by bacterial action and prevents the mouth pH from falling below the critical 5.5 threshold. Regular brushing cleans away food particles before bacteria can convert them to acid. 3. Both examples illustrate a common principle: the human body functions optimally within a narrow pH range, and deviations — whether excess stomach acid or mouth acidity — can be corrected by applying neutralisation using mild bases.
Key Points
- Stomach produces HCl for digestion; excess acid during indigestion causes irritation
- Antacids (mild bases like , milk of magnesia) neutralise excess stomach acid
- Tooth decay begins when mouth pH drops below 5.5
- Tooth enamel (calcium hydroxyapatite) corrodes in acidic conditions
- Bacteria break down sugars → produce acids → lower mouth pH
- Toothpastes are basic and help neutralise mouth acid, preventing decay
Related Questions
Q7
What is the pH scale? How does it help classify solutions? Distinguish between strong acids and weak acids, giving one example of each. Does a basic solution contain ions?
Q9