Definitions and Properties of Acids, Bases and Salts

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Definitions and Properties of Acids: Learn about acids, bases, and salts, their properties, pH scale, and neutralization reactions. Explore definitions, examples, and revision questions for better understanding.

READ ALSO – Gas Laws: Boyle’s Law, Charles’s Law and Ideal Gas Equation

Table of Contents

  1. Acids, Bases, and Salts
  2. Definitions and Properties of Acids, Bases, and Salts
  3. pH Scale and Indicators (Litmus, Phenolphthalein, Methyl Orange)
  4. Neutralization Reactions and Salts Formation.

Acids, Bases, and Salts: Definitions, Properties, and Reactions

Acids, bases, and salts are fundamental chemical substances that play vital roles in our daily lives and industrial processes. From the sour taste of vinegar to the alkaline nature of soap, these compounds are everywhere. Let’s study their definitions, properties, pH scale, indicators, and how they form salts through neutralization reactions.

1. Definitions and Properties of Acids, Bases, and Salts

Acids

  • Definition: Acids are substances that release hydrogen ions (H⁺) when dissolved in water. They have a sour taste and turn blue litmus paper red.
  • Examples: Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄), Acetic acid (CH₃COOH).
  • Properties:
    • Sour taste.
    • Corrosive in nature.
    • Conduct electricity in aqueous solutions.
    • React with metals to produce hydrogen gas.

Bases

  • Definition: Bases are substances that release hydroxide ions (OH⁻) when dissolved in water. They have a bitter taste and turn red litmus paper blue.
  • Examples: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)₂), Ammonium hydroxide (NH₄OH).
  • Properties:
    • Bitter taste and slippery feel.
    • Can be corrosive.
    • Conduct electricity in aqueous solutions.
    • React with acids to form water and salts.

Salts

  • Definition: Salts are ionic compounds formed by the neutralization reaction between an acid and a base.
  • Examples: Sodium chloride (NaCl), Potassium nitrate (KNO₃), Calcium sulfate (CaSO₄).
  • Properties:
    • Usually solid and crystalline.
    • High melting and boiling points.
    • Conduct electricity when dissolved in water or molten.

2. pH Scale and Indicators

The pH scale is a measure of the acidity or alkalinity of a solution. It ranges from 0 to 14.

  • Acidic Solutions: pH less than 7.
  • Neutral Solutions: pH equal to 7 (e.g., pure water).
  • Basic (Alkaline) Solutions: pH greater than 7.

Indicators

Indicators are substances that change color in the presence of an acid or base.

  • Litmus Paper:
    • Red litmus turns blue in a base.
    • Blue litmus turns red in an acid.
  • Phenolphthalein:
    • Colorless in acidic solutions.
    • Pink in basic solutions.
  • Methyl Orange:
    • Red in acidic solutions.
    • Yellow in basic solutions.

3. Neutralization Reactions and Salts Formation

Neutralization is a chemical reaction between an acid and a base to produce salt and water.

General Equation:

Acid+Base→Salt+WaterAcid + Base → Salt + Water

Examples:

  • Hydrochloric Acid and Sodium Hydroxide:
    HCl+NaOH→NaCl+H2OHCl + NaOH → NaCl + H₂O
    Sodium chloride (table salt) and water are produced.
  • Sulfuric Acid and Calcium Hydroxide:
    H2SO4+Ca(OH)2→CaSO4+2H2OH₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O
    Calcium sulfate and water are produced.

Applications of Neutralization Reactions:

  • Antacids neutralize stomach acid.
  • Treating acidic soil using lime (calcium hydroxide).
  • Wastewater treatment to neutralize acidic or basic effluents.

Conclusion

Understanding acids, bases, and salts is crucial for various applications in daily life, industry, and environmental management. From cooking and cleaning to manufacturing fertilizers and medicines, these chemical compounds are indispensable.

Revision Questions and Answers on Acids, Bases, and Salts

Question 1:

What is an acid, and what are its common properties?

Answer:
An acid is a substance that releases hydrogen ions (H⁺) when dissolved in water. Common properties of acids include:

  • Sour taste.
  • Corrosive nature.
  • Turning blue litmus paper red.
  • Conducting electricity in aqueous solutions.
  • Reacting with metals to produce hydrogen gas.

Question 2:

Define a base and list its key properties.

Answer:
A base is a substance that releases hydroxide ions (OH⁻) when dissolved in water. Key properties of bases include:

  • Bitter taste and slippery feel.
  • Turning red litmus paper blue.
  • Conducting electricity in aqueous solutions.
  • Reacting with acids to form water and salts.

Question 3:

What is a salt, and how is it formed?

Answer:
A salt is an ionic compound formed by the neutralization reaction between an acid and a base. It consists of the cation from the base and the anion from the acid. Salts are typically crystalline solids with high melting and boiling points.

Question 4:

Explain the pH scale and its significance.

Answer:
The pH scale is a measure of the acidity or alkalinity of a solution, ranging from 0 to 14.

  • pH < 7: Acidic solutions.
  • pH = 7: Neutral solutions (e.g., pure water).
  • pH > 7: Basic (alkaline) solutions.
    The pH scale helps to determine the concentration of hydrogen ions in a solution, which is important in chemical reactions, biology, and environmental science.

Question 5:

What is neutralization, and give an example of a neutralization reaction.

Answer:
Neutralization is a chemical reaction between an acid and a base to produce salt and water.

Example:
Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water:
HCl+NaOH→NaCl+H2OHCl + NaOH → NaCl + H₂O

This reaction is used in everyday applications like antacids neutralizing stomach acid and in wastewater treatment.

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