(a) Why are metal hydroxides better alternatives than sodium hydrogen carbonate in antacids ? (b) Why is aspirin used in the prevention of heart-attacks ? (c) Why antihistamines do not affect the secretion of acid in stomach ? OR Define the following terms with a suitable example of each : (a) Tranquilizers (b) Antibiotics (c) Non-ionic detergents

(a) Why are metal hydroxides better alternatives than sodium hydrogen carbonate in antacids ? (b) Why is aspir

Question

Q. (a) Why are metal hydroxides better alternatives than sodium hydrogen carbonate in antacids ?

(b) Why is aspirin used in the prevention of heart-attacks ?

(OR)

Define the following terms with a suitable example of each :

(a) Tranquilizers

(b) Antibiotics

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Concept understanding — Antacids

Antacids: What They Are and How They Work

Imagine you've just eaten a heavy, spicy meal. Your stomach works by releasing hydrochloric acid (HCl) to digest food. That acid is strong — strong enough to break down proteins. Normally, your stomach lining is protected. But sometimes, the acid gets too much: you feel a burning sensation in your chest or stomach. That's hyperacidity.

What do you want? Something that will neutralise that extra acid — turn it into harmless substances like water and salt. That's exactly what an antacid does.

Note

The word "antacid" literally means "against acid." An antacid is a base that reacts with stomach acid to raise the pH of the stomach contents, relieving the burning sensation.

The Chemistry in Simple Terms

Stomach acid is mostly hydrochloric acid, HCl. An antacid is typically a weak base — often a metal hydroxide or carbonate. The reaction is a simple acid-base neutralisation:

\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}

For example, magnesium hydroxide, $\ce{Mg(OH)2}$ , reacts with HCl:

\ce{Mg(OH)2 + 2HCl -> MgCl2 + 2H2O}

The acid is gone; the burning stops.

Common Antacids and Their Chemistry

Antacid	Chemical Formula	How It Works
Magnesium hydroxide	$\ce{Mg(OH)2}$	Neutralises acid, but can cause a laxative effect
Aluminium hydroxide	$\ce{Al(OH)3}$	Neutralises acid, but can cause constipation
Sodium bicarbonate	$\ce{NaHCO3}$	Neutralises quickly, but produces $\ce{CO2}$ gas (burping)
Calcium carbonate	$\ce{CaCO3}$	Also neutralises, produces $\ce{CO2}$

Many commercial antacids combine magnesium and aluminium hydroxides to balance the side effects.

Watch out

Sodium bicarbonate reacts violently with acid, producing carbon dioxide gas. This can cause belching and, in rare cases, stomach rupture if taken in excess. It also adds a lot of sodium to your system — not ideal for people with high blood pressure.

A Common Confusion: Ranitidine

You mentioned ranitidine. Here's the critical distinction: …

Part (a): (i) metal hydroxides give no $\text{CO}_2$ and no rebound acidity, unlike $\text{NaHCO}_3$ ; (ii) aspirin prevents heart attacks by its antiplatelet (anti-clotting) action; (iii) antihistamines block $\text{H}_1$ -receptors, not the $\text{H}_2$ -receptors controlling acid secretion.

Part (b): Tranquilizers reduce anxiety (Equanil/diazepam); antibiotics kill/inhibit microbes (penicillin); non-ionic detergents carry no charge (PEG ester).

(i) Why metal hydroxides are better than $\text{NaHCO}_3$ in antacids

$\text{NaHCO}_3$ neutralises HCl but has two drawbacks:

\text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2\uparrow

the $\text{CO}_2$ causes belching, and because $\text{NaHCO}_3$ is soluble it can make the stomach alkaline, which is sensed and triggers even more acid (rebound). Metal hydroxides such as $\text{Mg(OH)}_2$ and $\text{Al(OH)}_3$ are insoluble, release no gas, and can never make the medium alkaline (they only neutralise excess acid):

\text{Mg(OH)}_2 + 2\text{HCl} \rightarrow \text{MgCl}_2 + 2\text{H}_2\text{O}

Hence they are gentler, longer-acting and safer.

(ii) Why aspirin prevents heart attacks

Aspirin (acetylsalicylic acid) is an analgesic/antipyretic with an important side effect — it prevents platelet aggregation. It inhibits the synthesis of thromboxane $\text{A}_2$ , the mediator that makes platelets clump. With fewer clumps, clots are less likely to form and block a coronary artery, so a low daily dose is used to prevent heart attacks.

(iii) Why antihistamines do not affect stomach acid

Histamine acts on more than one receptor. $\text{H}_1$ -receptors mediate allergic responses; $\text{H}_2$ -receptors in the stomach lining stimulate HCl secretion. Ordinary antihistamines (e.g. brompheniramine, terfenadine) are $\text{H}_1$ -antagonists — they cannot bind the $\text{H}_2$ -receptor, so they leave acid secretion unchanged. (Acid secretion is reduced instead by $\text{H}_2$ -blockers such as ranitidine/cimetidine.)

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Concept understanding — Tranquilizers and Antidepressants

Tranquilizers and Antidepressants

Imagine your brain as a busy city with messengers (neurotransmitters) constantly running between buildings (neurons). Some messengers calm traffic down; others speed it up. When the city gets too chaotic — too much anxiety, too much stress — you need a traffic controller. That’s what tranquilizers do. When the city feels empty and sluggish — no energy, no joy — you need a construction crew to rebuild the roads. That’s what antidepressants do.

Both are psychoactive drugs: they cross the blood-brain barrier and change how your brain’s chemical messengers work.

Tranquilizers (Anxiolytics)

Intuition: You’re about to give a speech. Your heart races, palms sweat, mind goes blank. A tranquilizer brings that panic down to a manageable level — not by making you unconscious, but by calming the overactive alarm system.

Precise statement: Tranquilizers are drugs that reduce anxiety, tension, and agitation without causing excessive drowsiness (at low doses). They work primarily by enhancing the activity of GABA — the brain’s main inhibitory neurotransmitter. More GABA means less neuronal firing, which means less anxiety.

\text{Tranquilizer} \rightarrow \uparrow \text{GABA activity} \rightarrow \downarrow \text{neuronal excitability} \rightarrow \downarrow \text{anxiety}

Common examples:

Benzodiazepines (diazepam, alprazolam) — bind to GABA receptors and make GABA more effective
Barbiturates (phenobarbital) — older, more dangerous, now rarely used for anxiety

Watch out

Tranquilizers are not sedatives (sleeping pills) at therapeutic doses. A sedative puts you to sleep; a tranquilizer just takes the edge off. But at high doses, tranquilizers become sedatives — and can be fatal if mixed with alcohol.

Antidepressants

Intuition: Imagine you’ve lost interest in everything. Food tastes bland, friends feel distant, getting out of bed is a mountain. Antidepressants don’t give you happiness — they restore the brain’s ability to feel happiness again. They fix the plumbing so joy can flow.

Precise statement: Antidepressants are drugs that relieve symptoms of major depressive disorder by increasing the levels of monoamine neurotransmitters — especially serotonin, norepinephrine, and dopamine — in the synaptic cleft. The most common theory is the monoamine hypothesis: depression is linked to low levels of these chemicals.

\text{Antidepressant} \rightarrow \uparrow \text{serotonin/norepinephrine/dopamine} \rightarrow \uparrow \text{mood, energy, interest}

Major classes:

Class	How it works	Example
SSRIs (Selective Serotonin Reuptake Inhibitors)	Block serotonin reuptake, so serotonin stays longer in the synapse	Fluoxetine (Prozac)
SNRIs	Block reuptake of both serotonin and norepinephrine	Venlafaxine
Tricyclic antidepressants	Block reuptake of serotonin and norepinephrine (but also hit other receptors, causing side effects)	Amitriptyline
MAOIs (Monoamine Oxidase Inhibitors)	Block the enzyme that breaks down monoamines	Phenelzine (rarely used now due to food interactions)

Part (b): Tranquilizers reduce anxiety (Equanil/diazepam); antibiotics kill/inhibit microbes (penicillin); non-ionic detergents carry no charge (PEG ester).

Definitions with examples

(i) Tranquilizers

Chemical compounds (neurologically active drugs) used to relieve stress, anxiety, mild and severe mental diseases and to induce a sense of well-being; part of "sleeping pills".

Example: Equanil (meprobamate) or Diazepam (Valium). …