नोट: इस लेख का हिंदी संस्करण भी उपलब्ध है।
Introduction
- Substances are classified as acids, bases, and salts based on their chemical nature.
- Acids and bases have different physical and chemical properties, while salts are formed from the neutralization of acids and bases.
Acids
Definition
- Substances that have a sour taste and turn blue litmus paper red.
- Acids release hydrogen ions (H⁺) when dissolved in water.
Types of Acids
- Natural Acids – Found in natural sources like fruits and vegetables.
- Examples:
- Citric acid – Lemon, orange
- Acetic acid – Vinegar
- Tartaric acid – Tamarind
- Examples:
- Mineral Acids – Prepared from minerals and are stronger.
- Examples:
- Hydrochloric acid (HCl)
- Sulphuric acid (H₂SO₄)
- Nitric acid (HNO₃)
- Examples:
Strong and Weak Acids
- Strong Acids – Completely ionize in water.
- Hydrochloric acid (HCl)
- Sulphuric acid (H₂SO₄)
- Weak Acids – Partially ionize in water.
- Acetic acid (CH₃COOH)
- Citric acid (C₆H₈O₇)
Properties of Acids
- Sour taste.
- Corrosive in nature.
- Turn blue litmus paper red.
- React with metals to release hydrogen gas.
- Zn + 2HCl → ZnCl₂ + H₂
- React with carbonates and bicarbonates to release carbon dioxide.
- CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
Bases
Definition
- Substances that are bitter in taste and feel soapy to touch.
- They turn red litmus paper blue.
- Bases release hydroxide ions (OH⁻) when dissolved in water.
Types of Bases
- Strong Bases – Dissociate completely in water.
- Sodium hydroxide (NaOH)
- Potassium hydroxide (KOH)
- Weak Bases – Dissociate partially in water.
- Ammonium hydroxide (NH₄OH)
- Calcium hydroxide [Ca(OH)₂]
Natural and Synthetic Bases
- Natural Bases – Found in nature.
- Example: Lime water (Calcium hydroxide)
- Synthetic Bases – Produced chemically.
- Example: Sodium hydroxide (NaOH)
Properties of Bases
- Bitter taste.
- Slippery and soapy to touch.
- Turn red litmus paper blue.
- React with acids to form salt and water.
- NaOH + HCl → NaCl + H₂O
Indicators
Definition
- Substances that change color in the presence of acids or bases.
Types of Indicators
- Natural Indicators
- Litmus: Red in acid, blue in base.
- Turmeric: Yellow in acid, reddish-brown in base.
- Synthetic Indicators
- Phenolphthalein: Colorless in acid, pink in base.
- Methyl orange: Red in acid, yellow in base.
- Olfactory Indicators
- Onion: Loses smell in base.
- Vanilla: Loses smell in base.
Neutralization Reaction
Definition
- The reaction between an acid and a base to form salt and water.
- Acid + Base → Salt + Water
- HCl + NaOH → NaCl + H₂O
Examples
- Antacids neutralize stomach acid.
- Lime neutralizes acidic soil.
Salts
Definition
- Formed when an acid reacts with a base.
- Salts can be acidic, basic, or neutral.
Types of Salts
- Neutral Salts – Formed by strong acid and strong base.
- Sodium chloride (NaCl)
- Acidic Salts – Formed by a strong acid and weak base.
- Ammonium chloride (NH₄Cl)
- Basic Salts – Formed by a weak acid and strong base.
- Sodium carbonate (Na₂CO₃)
Properties of Salts
- Soluble in water.
- Conduct electricity when dissolved.
- Can be neutral, acidic, or basic.
Importance of Acids, Bases, and Salts in Daily Life
- Acids
- Stomach acid aids digestion.
- Used in the production of fertilizers and batteries.
- Bases
- Used in soap and detergent production.
- Lime water is used to reduce acidity in soil.
- Salts
- Used for food preservation (table salt).
- Sodium bicarbonate is used in baking.
Common Examples and Their Uses
- Acids
- Hydrochloric acid – Cleaning metal surfaces.
- Acetic acid – Food preservative.
- Bases
- Sodium hydroxide – Soap manufacturing.
- Magnesium hydroxide – Antacid.
- Salts
- Sodium chloride – Preservative.
- Potassium nitrate – Fertilizer.
Precautions While Handling Acids and Bases
- Wear protective gear.
- Handle with care to avoid burns.
- Always add acid to water, not the other way around.
Summary
- Acids and bases have distinct properties and indicators help identify them.
- Neutralization reactions produce salts and have significant applications.
- Acids, bases, and salts play a crucial role in our daily lives.
Class 7 Science :Acid Base and Salt Free Practice Quiz
1. Which of the following is a common acid found in homes?
Correct Answer: B) Vinegar
Vinegar contains acetic acid, a weak acid used in kitchens.
Vinegar contains acetic acid, a weak acid used in kitchens.
2. Which of these has a slippery feel and is a base?
Correct Answer: B) Soap solution
Bases feel slippery due to saponification on skin.
Bases feel slippery due to saponification on skin.
3. Litmus turns red in which of the following?
Correct Answer: A) Acidic solution
Red litmus indicates acid; blue litmus turns red in acid.
Red litmus indicates acid; blue litmus turns red in acid.
4. Which of the following is used to test for a base?
Correct Answer: D) Both B and C
Red litmus turns blue in bases, and phenolphthalein turns pink in bases.
Red litmus turns blue in bases, and phenolphthalein turns pink in bases.
5. Which of the following is a salt?
Correct Answer: A) Sodium chloride
Salt is formed by the reaction of an acid and a base.
Salt is formed by the reaction of an acid and a base.
6. Which of these acids is used in batteries?
Correct Answer: B) Sulphuric acid
Sulphuric acid is used in lead-acid batteries.
Sulphuric acid is used in lead-acid batteries.
7. What happens when an acid reacts with a base?
Correct Answer: A) Water and salt are formed
This reaction is called neutralization.
This reaction is called neutralization.
8. Which of the following is a weak base?
Correct Answer: B) Ammonium hydroxide
Ammonium hydroxide is less reactive and weaker than strong bases.
Ammonium hydroxide is less reactive and weaker than strong bases.
9. Which salt is obtained by the reaction of hydrochloric acid and sodium hydroxide?
Correct Answer: B) Sodium chloride
HCl + NaOH → NaCl + H₂O (neutralization reaction).
HCl + NaOH → NaCl + H₂O (neutralization reaction).
10. Which of the following salts can be used in baking?
Correct Answer: B) Sodium bicarbonate
Baking soda (sodium bicarbonate) is used as a raising agent.
Baking soda (sodium bicarbonate) is used as a raising agent.
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