Acids: Chemistry Notes

Acids and Their Uses

• Acids are substances with a sour taste. Historically, taste was used to distinguish acids from bases.
• The word "acid" comes from the Latin word "acidus," meaning "sour."
• Acids were produced by early chemists through the distillation of substances like alum, vitriol, sal ammoniac, and common salt.

Classification of acids based on origin

• Organic Acids: are present in animal and plant material (e.g., vinegar, lemon juice).
• Mineral Acids: are obtained from minerals in rocks. They are generally corrosive and dangerous.

Properties of Acids

• Sour taste.
• Corrosive nature.
• Acidic solutions conduct electricity.

Indicators

• Indicators are substances that change color in the presence of acids or alkalis and are often plant extracts.
• Litmus: A common indicator that turns red in acidic solutions and blue in basic solutions. The color change is a chemical reaction where the molecules of the indicator are altered by the acid or base.
• Universal Indicator: A mixture of dyes that produces a range of colors to indicate the strength of an acid or alkali.
• Turmeric: A natural indicator that remains yellow in acidic solutions and turns pink in basic solutions.
• Phenolphthalein: Is colorless in acid and neutral solutions, and turns pink in alkali solutions.
• Methyl orange: Is red in acid, orange in neutral solutions and yellow in alkali solutions.

The pH Scale

• The pH scale, ranging from 1 to 14, measures the strength of an acid or base.
• A pH meter is used to accurately measure pH using an electrode.

Acids in Daily Life

• Acids are used in many products, such as dyes, construction materials, and cleaning agents.
• Sulphuric acid is called the 'king of chemicals' due to its widespread use. Over $200$ billion kg are produced annually.

Common Acids and Their Uses

• Ethanoic Acid ($CH_3COOH$): Found in vinegar (also known as acetic acid).
• Methanoic Acid ($HCOOH$): Found in ant and nettle stings; used in kettle descaler.
• Lactic Acid ($CH_3CCH(OH)COOH$): Found in sour milk and yoghurt.
• Citric Acid ($C<em>6H</em>8O_7$): Found in lemons, oranges, and other citrus fruits; a source of vitamin C.
• Carbonic Acid ($H<em>2CO</em>3$): Found in fizzy soft drinks.
• Hydrochloric Acid ($HCl$): Used in cleaning metal surfaces and found as dilute acid in the stomach.
• Nitric Acid ($HNO_3$): Used in making fertilizers and explosives.
• Sulphuric Acid ($H<em>2SO</em>4$): Used in car batteries and in making fertilizers, paints, and detergents.
• Phosphoric Acid ($H<em>3PO</em>4$): Used in anti-rust paint and in making fertilizers.

Acids and Digestion

• Acids like vitamin C (ascorbic acid) aid in the absorption of iron from food.
• Lemon juice is often added to spinach salads to enhance iron absorption.
• Vitamin C is essential for healthy blood vessels, gums, bones, and muscles, and it helps in wound healing.

Stomach Acid

• The stomach lining is protected from stomach acid by a layer of mucus.

Ulcers

• Ulcers are primarily caused by Helicobacter pylori (H. pylori) bacteria, which damages the mucus layer, exposing the stomach lining to acid.
• H. pylori creates an alkaline environment to protect itself from gastric acid and is treated with antibiotics.
• Approximately 50% of world’s population is estimated to be infected with H.pylori.

Lactic Acid

• Lactic acid bacteria convert sugar into acid through fermentation.
• Lactobacillus is a genus of lactic acid-producing bacteria that converts lactose in milk into lactic acid, causing milk proteins (casein) to solidify into curds.
• Fermentation converts sugar to acids or alcohol.

Probiotics

• Probiotics are live bacteria and yeasts beneficial for health, especially the digestive system.
• More than 260 species of microbial food culture are identified and described for their beneficial use in fermented food products globally.
• Probiotics help in digestion, nutrient absorption, and maintaining normal bowel functions.

Sporolac

• Lactic Acid Bacillus in SPORLAC tablets are in the form of spores and survive gastric acidity.
• Sporolac tablets germinate in the small intestine and make the environment acidic, which inhibits the growth of other harmful bacteria.
• These bacteria survive in acidic environments only; elsewhere, they remain in spore form.

Curd Formation

• Curd can be made by adding acidic fruits, like tamarind and ginger, to milk.
• Ginger contains the protease zingipain, which catalyses the denaturation of protein in milk, changing milk to curd.

Lactic Acid and Exercise

• Lactic acid forms in muscles during vigorous exercise, causing muscle pain. It serves as a source of energy for the muscles.
• Otto Meyerhof's experiments showed that anaerobic conditions lead to lactic acid formation during work and its removal during rest.

pH and Food Spoilage

• A high pH favors the growth of yeasts and fungus. In neutral or alkaline pH foods, such as meats, bacteria are more dominant and food spoils faster.

Curdled Milk

• Milk curdles due to a chemical reaction where lactic acid bacteria digest lactose, producing lactic acid.
• As lactic acid increases, the pH drops, causing protein (casein) molecules to clump.

Spoiled vs. Fermented Milk

• Spoiled milk has a yellowish color and foul smell due to cold-loving bacteria, while fermented milk (curd) has a different flavor and smell, as well as health benefits.
• Spoiled milk can harm health due to the presence of harmful microbes.

Sour Food

• Sour food can be fermented food like curd, pickles, buttermilk, and yoghurt, which are good for the body and have specific health benefits.
• Spoiled food is rotten food and is full of dangerous bacteria and pathogens.

Vinegar

• Vinegar consists mainly of acetic acid and has been used since 3rd century BC.
• It is commonly used as a flavoring agent and has several medicinal benefits.

Benefits of Vinegar

• Vinegar lowers blood sugar level.
• Vinegar has antibacterial properties.
• Vinegar has antioxidant properties.

Vinegar and Blood Sugar

• Vinegar prolongs satiety by maintaining a constant blood sugar level in the body.
• It helps in absorption of other minerals in the diet. The acetic acid in vinegar increases the body’s absorption of important minerals from the foods we eat.
• Vinegar increases calcium absorption from green vegetables.

Glycaemic Index (GI)

• The glycaemic index, or GI, measures how a carbohydrate-containing food raises blood glucose.
• Glycaemic index uses a scale of $0$ to $100$, with higher values given to foods that cause the most rapid rise in blood sugar.
• Carbohydrates like table sugar and bread are easier for the body to change into glucose.
• Low GI foods take longer to digest and help you feel satisfied for longer.

Medicinal uses for vinegar mentioned in ʽThe Canon of Medicineʼ

• It is a powerful clotting agent.
• Heals burns and skin inflammations
• Relieves headaches caused by heat.
• Considered vinegar a good digestive supplement.

Vinegar as Antibacterial

• Vinegar strengthens the mouth and kills germs in the stomach and Acetic acid is a potent antimicrobial agent and can kill many types of bacteria.
• Hippocrates used vinegar for cleaning wounds over two thousand years ago.
• Vinegar is used in the food industry to lower the pH of products, preventing the growth of harmful bacteria.

Vinegar and Tuberculosis

• Acetic acid, the active ingredient in vinegar, can effectively kill mycobacteria.
• Exposure to a $6\%$ solution of acetic acid for $30$ minutes effectively kills tuberculosis, even strains resistant to almost all antibiotics.

Free Radicals and Antioxidants

• Free radicals are atoms with unpaired electrons that are highly reactive and can cause chain reactions.
• Antioxidants neutralize free radicals by donating electrons, preventing cell and tissue damage.
• Vitamin C and vitamin E are examples of antioxidants found naturally in many fruits and vegetables.

Vinegar and Gallbladder

• Vinegar contains chlorogenic acid, a natural compound that functions as an antioxidant. It helps the gallbladder by facilitating the flow of bile and dissolving gallstones.

Vinegar and Heart

• Vinegar refreshes the heart. Cardiovascular diseases (heart disease, high blood pressure and stroke) are currently the world’s biggest cause of death.
• Vinegar is a good dietary source that contains antioxidants. It prevents the oxidation of low-density lipoprotein (LDL), thus preventing the buildup of plaque and heart attacks.
• Moreover, the acetic acid in vinegar also reduces blood pressure.

Equations

• $acid + base \rightarrow salt + water$

Summary Points

• An acid is a compound that tastes sour and causes litmus paper to turn red.
• Natural indicators are substances that change color in acidic and alkaline solution.
• Lactic acid is the reason for the curdling of milk
• Strains of lactic acid bacteria are known as friendly bacteria and are used widely in probiotics
• Vinegar is an excellent idaam because of the various health benefits it possesses:
  • Glucose lowering property - a remedy for diabetic and insulin resistant patients
  • Anti-microbial property - because of acetic acid
  • Antioxidant property - because of chlorogenic acid.