Acids, Bases, and Salts

• Acids: An acid is defined as a substance whose water solution tastes sour, turns blue litmus red, and neutralizes bases.
• Bases: A substance is called base if its aqueous solution tastes bitter, turns red litmus blue, or neutralizes acids.
• Indicators: An indicator is a chemical compound that changes its colour in presence of an acid or base.

• Properties of Acids:
  
  • Acids are Sour in taste. For example: Lemon Juice, Vinegar etc.
  • Acids have a pH level lesser than 7.
  • Acids turn blue litmus paper into red.
  • They release H⁺ ions (hydrogen ions) when dissolved in water.
  • Example: HCl → H⁺ + Cl⁻
• Properties of Bases:
  
  • Bases are Bitter in taste. For example: Baking Soda, Soap etc.
  • Bases have a pH level greater than 7.
  • Bases turn red litmus paper into blue.
  • They release OH⁻ ions (hydroxide ions) when dissolved in water.
  • Example: NaOH → Na⁺ + OH⁻

• Acids: React with certain metals to produce hydrogen gas.
  Example: Zn + 2HCl → ZnCl₂ + H₂
• Bases: They generally do not react with metals to release hydrogen gas.

• When metal carbonates react with acids, they form salt, water, and carbon dioxide gas. This is a common acid-base reaction.
  Example: CaCO₃ +2HCl →CaCl₂ + H₂O + CO₂
• When metal hydrogen carbonates or metal bicarbonates react with acids, they perform a reaction to form a salt, water, and carbon dioxide gas.
  Example: Ca(HCO₃)₂ + 2HNO₃ → Ca(NO₃)₂ + 2H₂O + 2CO₂

• When there is a mutual reaction between acids and bases, it is called a neutralization reaction. In this reaction an acid reacts with a base to produce salt and water.
  Example: 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O

• Electrolytes: Both acids and bases dissociate into ions.
• Electricity conduction: Both can conduct electricity in solution.
• Proton transfer: Both involve proton transfer in chemical reactions
• Strength: Both can be strong or weak based on dissociation.
• Effect on indicators: Both change the color of indicators.
• Formation of salts: Both can form salts when neutralized.
• Corrosive properties: Both can be dangerous in concentrated forms.
• Applications: Both are widely used in various industrial and household processes.

The pH level, which measures the acidity of a solution, plays an important role in various natural processes and daily activities:

• Soil: The pH of soil directly affects the ability of plants to absorb nutrients. Most plants get better in slightly acidic to neutral soils (pH 6-7). If the soil is too acidic (pH < 6) or too alkaline (pH> 7), nutrient availability is reduced and it affects plant growth.
• Digestive System: The pH of our stomach is highly acidic. It is between 1.5-3.5, which is necessary for digesting food, especially proteins. The acidic environment also helps kill harmful bacteria and pathogens that may be ingested with food.
• Tooth Decay: The pH of the mouth plays an important role in tooth health. The enamel on teeth is damaged when exposed to an acidic environment (pH < 5.5). Saliva helps neutralize acidity and maintain a balanced pH in the mouth.

Common salt or NaCl is a source of several important chemicals that are widely used in various industries and daily life.

• Bleaching Powder
  
  • Definition: Bleaching powder is produced by reacting sodium chloride (NaCl) with calcium hydroxide (Ca(OH)₂) and chlorine gas (Cl₂).
  • Formula: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
  • Preparation: It is produced by chlorinating slaked lime (calcium hydroxide) in the presence of sodium chloride.

• Baking Soda
  
  • Definition: Baking soda is produced by reacting sodium chloride (NaCl) with ammonia (NH₃) and carbon dioxide (CO₂).
  • Formula: Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃
  • Preparation: Sodium bicarbonate is usually produced from sodium carbonate (washing soda) by adding carbon dioxide (CO₂) to it in water.

• Washing soda
  
  • Definition: Washing soda is produced in a process which involves sodium chloride (NaCl) as a starting material.
  • Formula: 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O
  • Preparation: It is produced by reacting sodium chloride (NaCl), ammonia (NH₃), carbon dioxide (CO₂), and water.

• Plaster of Paris and its Uses (CASO₄. ½ H₂O)
  
  • Definition: Plaster of Paris is a chemical compound that is commonly used in construction and medical applications.
  • Preparation: It is produced by heating gypsum (CaSO₄ 2H₂O) to remove water molecules.
  • Properties: White powder, slightly soluble in water, sets quickly with heat release.
  • Uses: In making molds, casts, plastering, orthopedic applications, fireproofing, chalk production, and art.