Introduction to Acids
and Bases
Acids: Substances
that release hydrogen ions (H⁺) in aqueous solution. Acids have a sour taste
and turn blue litmus paper red.
Examples: Hydrochloric acid (HCl), Sulfuric acid
(H₂SO₄), and Acetic acid (CH₃COOH).
Bases: Substances
that release hydroxide ions (OH⁻) in aqueous solution. Bases have a bitter
taste, feel slippery, and turn red litmus paper blue.
Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Ammonium hydroxide
(NH₄OH).
2. Indicators
Litmus: A
natural dye used as an indicator. It turns red in acidic solutions and blue in
basic solutions.
Phenolphthalein: Colorless
in acidic solutions and pink in basic solutions.
Methyl Orange: Red
in acidic solutions and yellow in basic solutions.
3. Chemical Properties of
Acids and Bases
Reaction of Acids with Metals:
Acids react with metals to
produce hydrogen gas and salt. Example: 2HCl + Zn → ZnCl2 + H2↑
The reaction of Acids with Metal Carbonates and Bicarbonates:
Acids react with metal carbonates and bicarbonates to
produce carbon dioxide, salt, and water.
Example: 2HCl + N a2CO3 → 2N aCl + H2O + CO2↑
Reaction of Acids with Bases (Neutralization Reaction): Acids
react with bases to form salt and water. Example: HCl + N aOH → N aCl + H2O
Reaction of Bases with Metals:
Bases like sodium hydroxide react with metals to
produce hydrogen gas.
Example: 2N aOH + Zn → N a2ZnO2
+ H2↑ (Sodium zincate)
4. pH Scale
The pH scale measures the strength of acids and
bases.
pH Values:
pH < 7: Acidic
pH = 7: Neutral pH > 7:
Basic
Importance of pH in Everyday Life:
pH in our Digestive System: The stomach produces HCl to aid
digestion. pH is around 1.5-
3.5.
pH and Tooth Decay:
Tooth enamel can decay when
pH drops below 5.5.
pH of Soil: Plants require specific pH ranges for
optimal growth. Fertilizers can affect soil pH.
5. Salts
Formation of Salts: Salts are formed by the neutralization
reaction of an acid and a base.
Example: HCl + N aOH → N aCl + H2O
Types of Salts:
Normal Salts: Formed by the complete neutralization of
an acid by a base (e.g., NaCl).
Acidic Salts: Formed when a dibasic acid is partially
neutralized by a base (e.g., NaHSO₄).
Basic Salts: Formed when a polyacidic base is partially
neutralized by an acid (e.g., Mg(OH)Cl).
6. Common Salts and Their Uses
Sodium Chloride (NaCl):
Common salt used in cooking and preservation.
Baking Soda (NaHCO₃): Used in baking as a leavening agent, in fire
extinguishers, and as an antacid.
Preparation: N aCl + H2O + CO2 + N H3 → N aHCO3 + N H4Cl
Washing Soda (Na₂CO₃·10H₂O): Used in cleaning agents and in softening
water.
Preparation: N a2CO3 + 10H2O → N a2CO3⋅ 10H2O
Plaster of Paris (CaSO₄·½H₂O): Used in making casts and sculptures.
Heating
Preparation:
CaSO4⋅ 2H2O
CaSO4⋅ ½H2O + 1.5H2O
7. Water of
Crystallization
Definition: The
fixed number of water molecules present in one formula unit of a salt.
Examples:
Copper sulfate pentahydrate (CuSO₄·5H₂O)
Gypsum (CaSO₄·2H₂O)
Plaster of Paris: Loses water of crystallization upon
heating and forms a dry powder.
8. Importance
of pH in Environmental and Industrial
Processes
pH in Agriculture: Maintaining soil pH is crucial for crop
yield.
pH in Industry: pH is monitored in processes like
fermentation and electroplating.
9. Hydrochloric
Acid in the Stomach
HCl helps in digesting food and killing bacteria.
Antacids like magnesium hydroxide neutralize excess
acid in the stomach.
10. Universal Indicator
A mixture of indicators that shows different colours
at different pH values, allows for the determination of the exact pH of a
solution.
11. Bleaching Powder (CaOCl₂)
Preparation:
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Uses: Disinfecting
drinking water, bleaching cotton and linen, and in the paper industry.
12. Plaster
of Paris (CaSO₄·½H₂O)
Properties: Sets
into a hard mass when mixed with water.
Uses: Making
casts for fractured bones, and in building materials.
13. Safety Measures While Handling Acids and Bases
Always add acid to water, not the other way around,
to prevent splashing.
Use protective gear such as gloves and goggles when handling
concentrated acids and bases.
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