Acids, Bases and Salts

Detailed Notes on Acids, Bases, and Salts

1. Introduction to Acids and Bases

• Acids are substances that generally have a sour taste, and they typically change blue litmus paper to red. Common examples include substances like lemon juice (citric acid) and vinegar (acetic acid).
• Bases are bitter in taste and slippery to touch; they change red litmus paper to blue. Common bases are substances such as soap (sodium hydroxide) and baking soda (sodium bicarbonate).
• Indicators are substances that change color in response to acidic or basic environments. Litmus, turmeric, methyl orange, and phenolphthalein are commonly used indicators in the laboratory.

2. Properties of Acids and Bases

• Litmus Test: This is a simple way to test for acids and bases. The litmus paper changes color based on the pH of the solution:
  • Blue litmus turns red in acidic solutions.
  • Red litmus turns blue in basic solutions.
• Natural Indicators: Other than litmus, natural indicators include red cabbage juice and turmeric, which can also be used to identify acids and bases by their color change.

3. Reactions of Acids and Bases

3.1 Reactions with Metals

• Acids react with metals to produce hydrogen gas and a salt. For example:

  • Metal + Acid → Salt + Hydrogen gas

  • Example: Zinc + Hydrochloric Acid → Zinc Chloride + Hydrogen gas.

• The reaction can be demonstrated using zinc granules in dilute sulfuric acid. Hydrogen gas is evolved, and this can be tested (it will pop when ignited).

3.2 Reactions with Carbonates

• Acids react with metal carbonates and hydrogen carbonates to produce a salt, water, and carbon dioxide:

  • Metal Carbonate + Acid → Salt + Water + Carbon Dioxide

• An example is sodium carbonate reacting with hydrochloric acid producing sodium chloride, water, and carbon dioxide.

3.3 Neutralization Reactions

• When acids and bases react, they often form a salt and water in a neutralization reaction:

  • Acid + Base → Salt + Water

• Example: Hydrochloric acid + Sodium hydroxide → Sodium Chloride + Water (neutralization results in a solution at a pH of 7).

4. The pH Scale

• The pH scale is a crucial way of expressing how acidic or basic a solution is. The scale ranges from 0 (very acidic) to 14 (very basic), with 7 being neutral.
• Acids have a pH less than 7, and bases have a pH greater than 7.
• The pH can significantly impact biological systems; for example, our stomach operates at an acidic pH, which assists in digestion.

5. Salts and Their Properties

• Salts are formed during the reaction of acids and bases. Salts can come from the neutralization of:
  • Strong Acid + Strong Base = Neutral Salt (e.g., NaCl)
  • Strong Acid + Weak Base = Acidic Salt (e.g., NH4Cl)
  • Weak Acid + Strong Base = Basic Salt (e.g., Na2CO3)
• Some common types of salts include sodium chloride (table salt), potassium sulfate, and copper sulfate.

6. Common Household Applications

• Baking Soda (sodium bicarbonate) is a mild base used in cooking and for alleviating acidity in the stomach.
• Washing Soda (sodium carbonate) is commonly used in cleaning and household chemistry.
• Bleaching Powder (calcium oxychloride) is used for bleaching and disinfecting.
• Antacids, which are basic, are used to neutralize excess stomach acids (like magnesium hydroxide).

7. Importance of pH in Daily Life

• pH affects digestion and health. When the stomach produces excess acid, it can cause discomfort, prompting the use of antacids for relief.
• The pH of environmental water systems affects aquatic life; acid rain (pH < 5.6) can harm ecosystems.
• Plants also thrive in specific pH ranges, and farmers must monitor soil pH for optimal crop growth.

8. Water of Crystallization

• Many salts contain water molecules as part of their structure, known as water of crystallization. For example, copper sulfate (CuSO4·5H2O) has five water molecules per formula unit.
• Heating these salts can remove water, turning them to an anhydrous form, which can then revert to its hydrated state upon adding water.

9. Conclusion

• Understanding the behavior and reactions of acids, bases, and salts is crucial for various applications in daily life, including cooking, cleaning, and health management.

1. Acids taste sour, turn blue litmus red, and produce H+ ions in solution.
2. Bases taste bitter, turn red litmus blue, and give OH- ions in solution.
3. Indicators help identify acids and bases; common examples include litmus, phenolphthalein, and turmeric.
4. Neutralization results in the formation of a salt and water when an acid and a base react together.
5. The pH scale measures acidity and basicity of solutions, ranging from 0 (acidic) to 14 (basic).
6. Salts are produced from the reaction of acids and bases, with varied properties based on parent reactants.
7. Baking soda and washing soda are common household alkaline substances useful in cooking and cleaning.
8. Water of crystallization refers to water integrated within the crystal structure of certain salts.
9. pH influences biological processes and environmental health, affecting both plants and animals.
10. Care is needed when mixing concentrated acids or bases with water due to the exothermic reaction that occurs.