Q: Q7. What is tincture of iodine? What is its use?

### Tincture of Iodine\nTincture of iodine is a powerful antiseptic solution. It is typically prepared by dissolving 2-3% (w/v) iodine in an alcohol-water mixture (usually ethanol and water).\n\n### Use\nTincture of iodine is used as an **antiseptic** to disinfect wounds, cuts, and abrasions on the skin. It effectively kills or inhibits the growth of microorganisms (bacteria, viruses, fungi) on living tissues, thereby preventing infection. It is not meant for internal consumption.

Q: Q8. What are food preservatives?

### Definition of Food Preservatives\nFood preservatives are chemical substances added to food materials to prevent their spoilage due to microbial growth (bacteria, yeasts, molds) and undesirable chemical reactions (like oxidation). They help in retaining the nutritive value, texture, and flavour of food for a longer period, thus increasing its shelf life.\n\n### Mechanism of Action\nFood preservatives work by:\n1. **Inhibiting microbial growth**: They either kill microorganisms or prevent their multiplication.\n2. **Slowing down enzymatic reactions**: They can interfere with enzymes that cause food degradation.\n3. **Preventing oxidation**: Some preservatives act as antioxidants, preventing rancidity in fats and oils.\n\n### Examples\nCommonly used food preservatives include:\n* **Sodium benzoate**: Used in acidic foods like fruit juices, jams, and pickles.\n* **Sodium metabisulphite**: Used in jams, squashes, and pickles.\n* **Salts of propanoic acid (propionates)**: Used in bread and baked goods.\n* **Salts of sorbic acid (sorbates)**: Used in cheese, baked goods, and fruit products.\n* **Table salt (NaCl)**: Used in curing meat and fish, and in pickles.\n* **Sugar**: Used in jams, jellies, and marmalades.\n* **Vegetable oils**: Used in pickles.

Q: Q10. What are antioxidants and why are they added to food?

### What are Antioxidants?\nAntioxidants are chemical substances that prevent or slow down the oxidation of other molecules. In the context of food, they are food additives that protect food from spoilage caused by oxidation, particularly the oxidation of fats and oils, which leads to rancidity.\n\n### Why are they added to food?\nAntioxidants are added to food primarily for the following reasons:\n1. **Preventing Rancidity**: Fats and oils in food can react with atmospheric oxygen (oxidize) over time, leading to the formation of unpleasant-smelling and tasting compounds. This process is called rancidity. Antioxidants scavenge free radicals and reactive oxygen species, thereby preventing or delaying this oxidative degradation.\n2. **Preserving Nutritional Value**: Oxidation can destroy essential vitamins (like Vitamin A, C, E) and other nutrients in food. Antioxidants help in retaining the nutritional quality of food.\n3. **Extending Shelf Life**: By preventing oxidative spoilage, antioxidants significantly increase the shelf life of food products, especially those rich in fats and oils (e.g., chips, biscuits, processed meat).\n4. **Maintaining Appearance and Flavor**: Oxidation can also lead to discoloration and off-flavors. Antioxidants help in maintaining the desired appearance and sensory qualities of food.\n\n### Examples of Food Antioxidants\nCommon examples include:\n* **Butylated Hydroxyanisole (BHA)**\n* **Butylated Hydroxytoluene (BHT)**\n* **Vitamin C (Ascorbic acid)**\n* **Vitamin E (Tocopherols)**\n* **Sulfites**

Question 1

Q1. Why is the use of aspartame limited to cold foods and drinks?

Accepted Answer

Aspartame is an artificial sweetener. Its use is limited to cold foods and drinks because it is unstable at cooking or high temperatures. At elevated temperatures, aspartame decomposes and loses its sweetness. Therefore, it cannot be used for baking or cooking.

Question 2

Q2. What are the main constituents of dettol?

Accepted Answer

Dettol is a widely used antiseptic. Its main active constituents are chloroxylenol and terpineol. These two compounds work synergistically to provide its antiseptic properties.

Question 3

Q3. What is tincture of iodine? What is its use?

Accepted Answer

Tincture of iodine is a 2-3% solution of iodine in an alcohol-water mixture.

**Use:** It is a powerful antiseptic. It is applied on wounds, cuts, and abrasions to prevent infection and promote healing. It is also used to disinfect skin before surgery.

Question 4

Q4. What are food preservatives?

Accepted Answer

Food preservatives are chemical substances added to food materials to prevent their spoilage due to microbial growth (such as bacteria, yeasts, and molds) and to retain their nutritive value, freshness, and flavour for a longer period. They inhibit or kill microorganisms, thereby extending the shelf life of food.

**Examples:** Common food preservatives include sodium benzoate, sodium metabisulphite, salts of propanoic acid (e.g., sodium propanoate), and sorbic acid (e.g., potassium sorbate).

Question 5

Q5. Why are soaps not used in hard water?

Accepted Answer

Soaps are generally sodium or potassium salts of long-chain fatty acids (e.g., sodium stearate, C₁₇H₃₅COONa). Hard water contains dissolved salts of calcium (Ca²⁺) and magnesium (Mg²⁺) ions, such as chlorides, sulphates, and bicarbonates. When soaps are used in hard water, the following issues arise:

### 1. Formation of Scum
When soap comes into contact with hard water, the calcium and magnesium ions present in hard water react with the soap molecules to form insoluble precipitates. These precipitates are known as scum. For example, with sodium stearate:

2C₁₇H₃₅COONa(aq) + Ca²⁺(aq) → (C₁₇H₃₅COO)₂Ca(s) ↓ + 2Na⁺(aq)
(Sodium stearate)          (Calcium stearate - scum)

2C₁₇H₃₅COONa(aq) + Mg²⁺(aq) → (C₁₇H₃₅COO)₂Mg(s) ↓ + 2Na⁺(aq)
(Sodium stearate)          (Magnesium stearate - scum)

This scum is a sticky, white, insoluble solid that floats on the water surface or adheres to clothes, skin, and plumbing fixtures.

### 2. Reduced Cleansing Action
A significant amount of soap is wasted in precipitating the calcium and magnesium ions as scum before it can effectively perform its cleansing action. This means more soap is required to produce lather and clean effectively, leading to economic inefficiency.

### 3. Adverse Effects on Fabric and Skin
*   **On Fabrics:** The sticky scum adheres to the fabric, making clothes look dull, streaky, and feel stiff. It also makes rinsing difficult and can lead to greyish deposits on white clothes.
*   **On Skin:** When used for bathing, the scum can deposit on the skin, blocking pores and causing irritation or dryness. It also leaves a film on hair, making it dull and difficult to manage.

Due to these reasons, soaps are not suitable for use in hard water. Synthetic detergents, which do not form insoluble precipitates with calcium and magnesium ions, are preferred for washing in hard water.

Question 6

Q6. What are the main constituents of dettol?

Accepted Answer

Dettol is a widely used antiseptic. Its main constituents are:
1.  **Chloroxylenol**: This is the primary active ingredient responsible for its antiseptic properties.
2.  **Terpineol**: This compound contributes to the characteristic smell and also has antiseptic properties.
3.  **Alcohol (Ethanol or Isopropyl alcohol)**: Used as a solvent and also possesses antiseptic properties.
4.  **Castor oil soap**: Acts as an emulsifying agent, helping to mix the oil-soluble components with water.
5.  **Water**: Solvent.

Question 7

Q7. What is tincture of iodine? What is its use?

Accepted Answer

### Tincture of Iodine
Tincture of iodine is a powerful antiseptic solution. It is typically prepared by dissolving 2-3% (w/v) iodine in an alcohol-water mixture (usually ethanol and water).

### Use
Tincture of iodine is used as an **antiseptic** to disinfect wounds, cuts, and abrasions on the skin. It effectively kills or inhibits the growth of microorganisms (bacteria, viruses, fungi) on living tissues, thereby preventing infection. It is not meant for internal consumption.

Question 8

Q8. What are food preservatives?

Accepted Answer

### Definition of Food Preservatives
Food preservatives are chemical substances added to food materials to prevent their spoilage due to microbial growth (bacteria, yeasts, molds) and undesirable chemical reactions (like oxidation). They help in retaining the nutritive value, texture, and flavour of food for a longer period, thus increasing its shelf life.

### Mechanism of Action
Food preservatives work by:
1.  **Inhibiting microbial growth**: They either kill microorganisms or prevent their multiplication.
2.  **Slowing down enzymatic reactions**: They can interfere with enzymes that cause food degradation.
3.  **Preventing oxidation**: Some preservatives act as antioxidants, preventing rancidity in fats and oils.

### Examples
Commonly used food preservatives include:
*   **Sodium benzoate**: Used in acidic foods like fruit juices, jams, and pickles.
*   **Sodium metabisulphite**: Used in jams, squashes, and pickles.
*   **Salts of propanoic acid (propionates)**: Used in bread and baked goods.
*   **Salts of sorbic acid (sorbates)**: Used in cheese, baked goods, and fruit products.
*   **Table salt (NaCl)**: Used in curing meat and fish, and in pickles.
*   **Sugar**: Used in jams, jellies, and marmalades.
*   **Vegetable oils**: Used in pickles.

Question 9

Q9. Why is the use of aspartame limited to cold foods and drinks?

Accepted Answer

Aspartame is one of the most successful and widely used artificial sweeteners. However, its use is limited to cold foods and drinks because it is **unstable at cooking temperatures**.

### Reason for Instability
Aspartame is a methyl ester of a dipeptide formed from aspartic acid and phenylalanine. When heated to cooking temperatures, the peptide bond between aspartic acid and phenylalanine can hydrolyze, and the methyl ester can also hydrolyze to methanol. This decomposition leads to:
1.  **Loss of sweetness**: The breakdown products are not sweet, or significantly less sweet, than aspartame itself.
2.  **Formation of undesirable products**: The hydrolysis products, including methanol, are not desirable in food and can alter the taste.

Therefore, to maintain its sweetness and avoid decomposition, aspartame is added only to cold foods and drinks, or used in products that do not require heating during preparation or storage.

Question 10

Q10. What are antioxidants and why are they added to food?

Accepted Answer

### What are Antioxidants?
Antioxidants are chemical substances that prevent or slow down the oxidation of other molecules. In the context of food, they are food additives that protect food from spoilage caused by oxidation, particularly the oxidation of fats and oils, which leads to rancidity.

### Why are they added to food?
Antioxidants are added to food primarily for the following reasons:
1.  **Preventing Rancidity**: Fats and oils in food can react with atmospheric oxygen (oxidize) over time, leading to the formation of unpleasant-smelling and tasting compounds. This process is called rancidity. Antioxidants scavenge free radicals and reactive oxygen species, thereby preventing or delaying this oxidative degradation.
2.  **Preserving Nutritional Value**: Oxidation can destroy essential vitamins (like Vitamin A, C, E) and other nutrients in food. Antioxidants help in retaining the nutritional quality of food.
3.  **Extending Shelf Life**: By preventing oxidative spoilage, antioxidants significantly increase the shelf life of food products, especially those rich in fats and oils (e.g., chips, biscuits, processed meat).
4.  **Maintaining Appearance and Flavor**: Oxidation can also lead to discoloration and off-flavors. Antioxidants help in maintaining the desired appearance and sensory qualities of food.

### Examples of Food Antioxidants
Common examples include:
*   **Butylated Hydroxyanisole (BHA)**
*   **Butylated Hydroxytoluene (BHT)**
*   **Vitamin C (Ascorbic acid)**
*   **Vitamin E (Tocopherols)**
*   **Sulfites**

Question 11

Q11. Why is the use of aspartame limited to cold foods and drinks?

Accepted Answer

Aspartame is an artificial sweetener that is a dipeptide of aspartic acid and phenylalanine. Its use is limited to cold foods and drinks because it is unstable at higher temperatures. When heated, aspartame undergoes hydrolysis, breaking down into its constituent amino acids (aspartic acid and phenylalanine) and methanol. This decomposition causes it to lose its sweetness, making it ineffective as a sweetener in hot foods or during cooking processes.

Question 12

Q12. What are antiseptics? Give an example.

Accepted Answer

Antiseptics are chemical substances that either kill or prevent the growth of microorganisms. They are applied to living tissues such as wounds, cuts, ulcers, and diseased skin surfaces to prevent infection. Unlike disinfectants, they are generally not harmful to living tissues when applied in appropriate concentrations.

**Example:** Dettol (a mixture of chloroxylenol and terpineol), Bithional (added to soaps), Tincture of Iodine (2-3% solution of iodine in alcohol-water mixture).

Question 13

Q13. Why are cimetidine and ranitidine better antacids than sodium hydrogencarbonate or magnesium or aluminium hydroxide?

Accepted Answer

Cimetidine and ranitidine are considered superior antacids compared to traditional ones like sodium hydrogencarbonate, magnesium hydroxide, or aluminium hydroxide due to their different mechanisms of action and fewer side effects.

**1. Mechanism of Traditional Antacids:**
Traditional antacids work by directly neutralizing the excess hydrochloric acid (HCl) present in the stomach. They are basic compounds that react with the acid to form salt and water.
*   **Sodium hydrogencarbonate (NaHCO₃):** This is a systemic antacid. While it effectively neutralizes acid, it can increase the alkalinity of the stomach, which in turn can trigger the secretion of even more acid (a 'rebound effect'). It also produces carbon dioxide, causing flatulence, and can be absorbed into the bloodstream, leading to systemic alkalosis.
*   **Magnesium hydroxide (Mg(OH)₂) and Aluminium hydroxide (Al(OH)₃):** These are non-systemic antacids. They are insoluble and do not cause systemic alkalosis. However, they only provide symptomatic relief by neutralizing existing acid and do not address the root cause of excessive acid production. Magnesium hydroxide can cause diarrhea, while aluminium hydroxide can cause constipation. High doses of aluminium hydroxide can also lead to phosphate deficiency.

**2. Mechanism of Newer Antacids (Cimetidine and Ranitidine):**
Cimetidine (Tagamet) and Ranitidine (Zantac) are much more effective because they prevent the secretion of excess acid in the first place, rather than just neutralizing it after it has been produced.
*   **Histamine and H₂-receptors:** The stomach produces acid in response to various stimuli, one of which is histamine. Histamine interacts with specific receptors (H₂-receptors) present in the stomach wall, stimulating the secretion of acid.
*   **Receptor Blocking:** Cimetidine and ranitidine are antihistamines. They work by blocking the interaction of histamine with the H₂-receptors in the stomach. By doing so, they prevent the cells in the stomach lining from being stimulated to produce and secrete excessive amounts of hydrochloric acid.

**3. Advantages of Cimetidine and Ranitidine:**
*   **Targeted Action:** They address the underlying cause of acidity by inhibiting acid secretion, leading to more sustained relief.
*   **Fewer Side Effects:** They avoid the drawbacks associated with traditional antacids such as rebound acidity, systemic alkalosis, flatulence, constipation, or diarrhea.
*   **Healing of Ulcers:** By reducing acid secretion, they create a more favorable environment for the healing of stomach and duodenal ulcers.

In conclusion, while traditional antacids offer temporary relief by neutralizing stomach acid, cimetidine and ranitidine provide a more effective and long-lasting solution by preventing the excessive secretion of acid, making them superior choices for managing acidity and peptic ulcers.

Question 14

Q14. Explain the term, broad spectrum antibiotics.

Accepted Answer

Antibiotics are chemical substances produced by microorganisms (or synthesized) that, in low concentrations, can inhibit the growth of or kill other microorganisms (pathogens) without causing significant harm to the host. They are classified based on their spectrum of activity, which refers to the range of microorganisms they are effective against.

**Broad-spectrum antibiotics** are those antibiotics that are effective against a wide range of pathogenic microorganisms. This includes both Gram-positive and Gram-negative bacteria. They are particularly useful in situations where the exact identity of the infecting microorganism is not known, or when the infection is caused by multiple types of bacteria. Using a broad-spectrum antibiotic ensures that a wide variety of potential pathogens are targeted.

**Examples:** Chloramphenicol, Ampicillin, Amoxicillin, Tetracycline.

Question 15

Q15. How do antiseptics differ from disinfectants? Give one example of each.

Accepted Answer

Both antiseptics and disinfectants are chemical agents that kill or prevent the growth of microorganisms. However, they differ significantly in their application, toxicity, and the concentration at which they are used.

Here's a comparison:

| Feature           | Antiseptics                                      | Disinfectants                                      |
| :---------------- | :----------------------------------------------- | :------------------------------------------------- |
| **Application**   | Applied to living tissues (e.g., skin, wounds, cuts, mucous membranes). | Applied to inanimate objects (e.g., floors, surgical instruments, sanitaryware, water pipes). |
| **Toxicity**      | Less toxic and generally safe for application on living tissues. | Highly toxic and harmful to living tissues. They can cause severe damage if applied to skin or ingested. |
| **Concentration** | Used in lower concentrations.                    | Used in higher concentrations.                     |
| **Purpose**       | To prevent infection in living beings by reducing microbial load. | To sterilize surfaces and kill microorganisms on non-living things, making them free from infection. |
| **Examples**      | Dettol (chloroxylenol + terpineol), Savlon, Bithional, Tincture of Iodine (2-3% iodine in alcohol-water). | Chlorine (0.2-0.4 ppm in water), Sulphur dioxide, 1% solution of Phenol, Formaldehyde. |

**Example of an Antiseptic:**
*   **Dettol:** A common antiseptic used for cleaning wounds and cuts. It is a mixture of chloroxylenol and terpineol.

**Example of a Disinfectant:**
*   **1% solution of Phenol:** Used to disinfect floors, drains, and sanitaryware. (Note: A 0.2% solution of phenol acts as an antiseptic, illustrating that the same chemical can act as an antiseptic or disinfectant depending on its concentration).

Question 16

Q16. What is the difference between a narrow spectrum antibiotic and a broad spectrum antibiotic?

Accepted Answer

Antibiotics are chemical substances produced wholly or partly by microorganisms that, in low concentrations, inhibit the growth or even destroy other microorganisms by interfering with their metabolic processes. They are used to treat infections.

**Narrow Spectrum Antibiotics:**
These are antibiotics that are effective mainly against a limited range of microorganisms. They are specific in their action, targeting either primarily Gram-positive or Gram-negative bacteria, but not both. Their use is preferred when the causative pathogen is known, as it minimizes the disruption of the body's normal microbial flora.
*   **Example:** Penicillin G is a narrow spectrum antibiotic, primarily effective against Gram-positive bacteria.

**Broad Spectrum Antibiotics:**
These are antibiotics that are effective against a wide range of microorganisms, including both Gram-positive and Gram-negative bacteria, and sometimes even other types of microbes like fungi or protozoa. They are useful when the identity of the infecting microorganism is not known or when there is a mixed infection.
*   **Examples:** Chloramphenicol, Tetracycline, Ampicillin, Amoxicillin, Ofloxacin, Vancomycin. Chloramphenicol is effective against a wide range of Gram-positive and Gram-negative bacteria, rickettsiae, and certain viruses.

**Key Difference:** The primary difference lies in the range of microorganisms they can effectively target. Narrow spectrum antibiotics target a limited range, while broad spectrum antibiotics target a wide range.

Question 17

Q17. How do antiseptics differ from disinfectants? Give one example of each.

Accepted Answer

Antiseptics and disinfectants are both antimicrobial agents that kill or prevent the growth of microorganisms, but they differ significantly in their application and toxicity.

**Antiseptics:**
*   **Definition:** These are chemical substances that are applied to living tissues (like skin, wounds, mucous membranes) to kill or inhibit the growth of microorganisms. They are generally less harmful to living tissues than disinfectants.
*   **Application:** Used on living surfaces to prevent infection.
*   **Toxicity:** Mild enough to be safely applied to living tissues.
*   **Examples:**
    *   **Dettol:** A mixture of chloroxylenol and terpineol.
    *   **Savlon:** Contains chlorhexidine and cetrimide.
    *   **Boric acid:** A mild antiseptic for eyes.
    *   **Iodine tincture:** 2-3% solution of iodine in alcohol-water mixture.
    *   **Furasin (nitrofuranazone)** and **Soframycin** are also used as antiseptics.

**Disinfectants:**
*   **Definition:** These are chemical substances that are applied to inanimate objects (like floors, instruments, sanitaryware) to kill microorganisms. They are generally too strong and toxic to be applied to living tissues.
*   **Application:** Used on non-living surfaces to sterilize or sanitize.
*   **Toxicity:** Harmful and toxic to living tissues.
*   **Examples:**
    *   **Chlorine (0.2-0.4 ppm solution in water):** Used for sterilization of water.
    *   **Sulphur dioxide:** Used for fumigation.
    *   **Phenol:** A 1% solution of phenol is a disinfectant, while a 0.2% solution is an antiseptic.
    *   **Formaldehyde solution (Formalin):** Used to preserve biological specimens and sterilize surgical instruments.

Question 18

Q18. Why are cimetidine and ranitidine better antihistamines than brompheniramine and terfenadine?

Accepted Answer

The statement implies a comparison of their effectiveness in a specific context, which is the treatment of acidity and heartburn. Cimetidine and ranitidine are indeed considered 'better' in this context because they target a specific type of histamine receptor responsible for stomach acid secretion, while brompheniramine and terfenadine target different histamine receptors involved in allergic reactions.

Here's a detailed explanation:

1.  **Histamine and its Receptors:** Histamine is a potent vasodilator and has various functions in the body. It interacts with different types of receptors, primarily H1, H2, H3, and H4 receptors, each mediating different physiological responses.

2.  **Role of H1 Receptors:**
    *   H1 receptors are primarily involved in allergic reactions, causing symptoms like sneezing, watery eyes, runny nose, and skin rashes.
    *   **Brompheniramine and Terfenadine** are **antihistamines** that selectively block H1 receptors. They are used to treat symptoms of allergies and cold. Terfenadine was later withdrawn due to cardiac toxicity when taken with certain other drugs.

3.  **Role of H2 Receptors:**
    *   H2 receptors are primarily located in the parietal cells of the stomach lining. When histamine binds to these receptors, it stimulates the secretion of hydrochloric acid (HCl) in the stomach.
    *   Excessive histamine binding to H2 receptors can lead to increased acid production, causing hyperacidity, heartburn, and peptic ulcers.

4.  **Cimetidine and Ranitidine as H2-Antagonists:**
    *   **Cimetidine (Tagamet)** and **Ranitidine (Zantac)** are specific drugs that act as **H2-receptor antagonists**. They prevent the binding of histamine to the H2 receptors in the stomach wall.
    *   By blocking these receptors, cimetidine and ranitidine effectively reduce the secretion of hydrochloric acid, thereby treating hyperacidity, heartburn, and preventing the formation of ulcers.

**Conclusion:**
Cimetidine and ranitidine are considered 'better' antihistamines for treating conditions related to stomach acidity (like heartburn and ulcers) because they specifically target the H2 receptors responsible for acid secretion. Brompheniramine and terfenadine, on the other hand, target H1 receptors and are effective for allergic symptoms but have no significant effect on stomach acid production. Therefore, their 'betterness' depends on the specific therapeutic goal.

Question 19

Q19. Explain the following terms with suitable examples:
(a) Cationic detergents
(b) Anionic detergents
(c) Non-ionic detergents

Accepted Answer

Detergents are cleansing agents that have surface-active properties. They are broadly classified based on the nature of the charge on the hydrophilic (water-loving) part of their molecule.

### (a) Cationic Detergents

**Definition:** Cationic detergents are quaternary ammonium salts of amines with acetates, chlorides, or bromides as anions. The long hydrocarbon chain is attached to the nitrogen atom, which carries a positive charge. Thus, the cationic part of the molecule is the active part in cleansing action.

**Structure:** They consist of a long hydrocarbon chain (hydrophobic part) and a positively charged head group (hydrophilic part), typically a quaternary ammonium ion.

**Properties and Uses:**
*   They are generally more expensive than anionic detergents.
*   They possess germicidal properties and are therefore widely used as germicides and in hair conditioners.
*   Their cleansing action is not as strong as anionic detergents.

**Example:**
*   **Cetyltrimethylammonium bromide (CTAB):** CH₃(CH₂)₁₅—N⁺(CH₃)₃ Br⁻
    *   This is a common example used in hair conditioners due to its germicidal properties and ability to make hair soft.

### (b) Anionic Detergents

**Definition:** Anionic detergents are sodium salts of sulphonated long-chain alcohols or hydrocarbons. In these detergents, the anionic part of the molecule is involved in the cleansing action.

**Structure:** They consist of a long hydrocarbon chain (hydrophobic part) and a negatively charged head group (hydrophilic part), typically a sulphonate (-SO₃⁻) or sulphate (-OSO₃⁻) group.

**Properties and Uses:**
*   They are the most widely used type of detergents.
*   They are effective cleansing agents, especially in hard water, as the calcium and magnesium salts of sulphonates are also soluble in water.
*   They are primarily used in household laundry products, dishwashing liquids, and toothpastes.

**Examples:**
*   **Sodium alkylbenzenesulphonates (e.g., Sodium dodecylbenzenesulphonate):** CH₃(CH₂)₁₁—C₆H₄—SO₃⁻ Na⁺
    *   These are commonly found in laundry detergents.
*   **Sodium lauryl sulphate:** CH₃(CH₂)₁₁—OSO₃⁻ Na⁺
    *   Derived from lauryl alcohol, it is used in toothpastes and shampoos.

### (c) Non-ionic Detergents

**Definition:** Non-ionic detergents do not contain any ionic groups in their molecules. The hydrophilic part is typically a polyether chain (like polyethylene glycol) formed by the condensation of long-chain alcohols with a large number of ethylene oxide molecules.

**Structure:** They consist of a long hydrocarbon chain (hydrophobic part) and a neutral, highly polar head group (hydrophilic part) containing multiple ether linkages and hydroxyl groups.

**Properties and Uses:**
*   They are effective in removing greasy stains from crockery.
*   They do not produce much foam, which makes them suitable for automatic dishwashers.
*   They are also used in liquid dishwashing detergents.

**Example:**
*   **Polyethylene glycol stearate:** This is formed by the reaction of stearic acid with polyethylene glycol.
    *   CH₃(CH₂)₁₆COOH + HO(CH₂CH₂O)nCH₂CH₂OH → CH₃(CH₂)₁₆COO(CH₂CH₂O)nCH₂CH₂OH
    *   The stearate part is hydrophobic, and the polyethylene glycol part is hydrophilic but non-ionic.

Question 20

Q20. What are the main constituents of dettol?

Accepted Answer

Dettol is a widely used antiseptic. Its main constituents are chloroxylenol and terpineol. It also contains a small amount of alcohol and castor soap.

Question 21

Q21. What is tincture of iodine? What is its use?

Accepted Answer

Tincture of iodine is an antiseptic solution. It is a 2-3% solution of iodine in an alcohol-water mixture.

**Use:** It is applied to wounds and cuts as an antiseptic to prevent infection. It kills or inhibits the growth of microorganisms on living tissues.

Question 22

Q22. What are food preservatives?

Accepted Answer

Food preservatives are chemical substances that are added to food materials to prevent their spoilage due to microbial growth (bacteria, yeasts, molds) and to retain their nutritive value for a longer period. They inhibit or kill microorganisms, thus extending the shelf life of food.

**Examples:** Common food preservatives include sodium benzoate, sodium metabisulphite, salts of sorbic acid, and propanoic acid. Sugar and salt are also used as traditional food preservatives.

Question 23

Q23. Why is the use of aspartame limited to cold foods and drinks?

Accepted Answer

Aspartame is an artificial sweetener that is approximately 100 times sweeter than cane sugar. However, its use is limited to cold foods and drinks because it is unstable at cooking temperatures.

At higher temperatures, aspartame undergoes hydrolysis, breaking down into its constituent amino acids (phenylalanine and aspartic acid) and methanol. This decomposition causes it to lose its sweetness, making it ineffective as a sweetener in hot foods or during cooking processes.

Question 24

Q24. What are the main constituents of dettol? What is the use of dettol?

Accepted Answer

Dettol is a popular antiseptic. Its main constituents are:

1.  **Chloroxylenol**: This is the primary active ingredient and provides the antiseptic properties.
2.  **Terpineol**: This acts as a synergist, enhancing the antimicrobial activity of chloroxylenol, and also contributes to the characteristic smell.

Other minor constituents include alcohol (as a solvent), castor oil soap (as an emulsifying agent), and water.

**Use of Dettol:**
Dettol is widely used as an antiseptic for:
*   Cleaning and disinfecting wounds, cuts, and abrasions to prevent infection.
*   Disinfecting surgical instruments (though more advanced sterilisation methods are used for critical instruments).
*   Pre-operative skin preparation before injections or minor surgical procedures.
*   General household disinfection of surfaces and floors.

Chapter 16: Chemistry in Everyday Life