Grade 9

Grade 9Acids, Bases and Salts


Introduction to Acids and Bases


Welcome to the fascinating world of acids and bases! These substances are all around us. They are present in the food we eat, the drinks we drink, the cleaning products we use, and even in our bodies. It is important to understand acids and bases because they play a vital role in chemistry and have practical applications in many areas of life.

What are acids?

Acids are substances that can donate protons (H +) to another substance. They taste sour, like the taste of lemon juice or vinegar. Acids turn blue litmus paper red and have a pH value less than 7.

Here's a simple acid, hydrochloric acid, often found in stomach acid:

HCl
H Chlorine

In this structure, hydrogen (H) is bonded to chlorine (Cl), forming hydrochloric acid.

Common examples of acids

  • Lemon juice (C 6 H 8 O 7) - citric acid
  • Vinegar (CH 3 COOH) - acetic acid
  • Battery acid (H 2 SO 4) - sulfuric acid

What are the bases?

Bases are substances that can accept protons or donate electron pairs. They taste bitter and feel slippery like soap when touched. Bases turn red litmus paper blue and have a pH greater than 7.

Here's an example of an alkali called sodium hydroxide, which is commonly used in soap making:

NaOH
Na OH

In this structure, sodium (Na) bonds with the hydroxide ion (OH) to form sodium hydroxide.

Common examples of bases

  • Baking soda (NaHCO 3) - sodium bicarbonate
  • Ammonia (NH 3)
  • Milk of magnesia (Mg(OH) 2) - magnesium hydroxide

Understanding pH

The pH scale measures how acidic or alkaline a solution is. It ranges from 0 to 14. A pH of 7 is neutral, indicating a balance between acids and bases. This is the pH of pure water.

When the pH value is less than 7 it indicates an acidic solution, whereas when the pH value is more than 7 it indicates an alkaline solution.

0 7 14

Examples include:

  • pH 3 (acidic): orange juice
  • pH 7 (neutral): pure water
  • pH 10 (basic): milk of magnesia

Neutralization reactions

When acids and bases react with each other, they undergo a neutralization reaction. This reaction usually results in the formation of water and salt.

The general equation for the neutralization reaction is:

Acid + Base → Salt + Water

The reaction between hydrochloric acid and sodium hydroxide is a common example:

HCl + NaOH → NaCl + H 2 O

In this reaction, sodium chloride (NaCl), which is a table salt, is formed along with water.

Applications of Acids and Bases

Acids and bases have many applications in everyday life and industry. Here are some examples:

Domestic use

  • Vinegar: Used in cooking and cleaning. Its acidic nature helps remove stains and odors.
  • Baking soda: Used as a leavening agent in baking. It reacts with acidic ingredients to form carbon dioxide gas which makes baked goods rise.

Industrial uses

  • Sulphuric acid: Used in the manufacture of fertilisers, detergents, and car batteries.
  • Ammonia: Used in cleaning products and as a refrigerant.

Biological uses

  • Hydrochloric acid in the stomach: This acid aids digestion and helps kill bacteria.
  • Bicarbonate ions: These ions present in the blood help maintain the pH balance of the body.

Conclusion

Acids and bases are fundamental concepts in chemistry that affect many aspects of the natural and industrial world. Understanding their properties, behaviors, and reactions helps us better understand the chemical processes that occur around us every day. From the food we eat to the products we use, acids and bases play an integral role in our lives.


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