Acid, Bases and Salts

Acids, Bases, and Salts in Daily Life

  • Everyday substances like lemon, tamarind, common salt, sugar, and vinegar have different tastes: sour, bitter, sweet, or salty.

  • Taste Classification (Table 4.1):

    • Sour: Curd, lemon juice, orange juice, vinegar, tamarind.

    • Bitter: Baking soda.

    • Note: The term "acid" comes from the Latin word "acere" meaning sour.

    • Bases: Substances like baking soda, which are bitter and feel soapy.

Indicators

  • Indicators are substances that change color to identify if a solution is acidic or basic.

  • Common indicators include turmeric, litmus, and China rose petals.

  • Cautionary Notes:

    • Do not taste or touch unknown substances.

Natural Indicators

Litmus

  • Extracted from lichens, litmus is purple in distilled water.

  • Changes colors:

    • Red in acidic solutions.

    • Blue in basic solutions.

  • Available as strips of paper (red or blue).

Common Acids

  • Acetic Acid: Found in vinegar.

  • Formic Acid: Found in ant stings.

  • Citric Acid: Present in citrus fruits (oranges, lemons).

  • Lactic Acid: Found in curd.

  • Oxalic Acid: Found in spinach.

  • Ascorbic Acid: Vitamin C from amla and citrus fruits.

  • Tartaric Acid: Found in tamarind and unripe mangoes.

Common Bases

  • Calcium Hydroxide: Present in lime water.

  • Ammonium Hydroxide: Found in window cleaners.

  • Sodium Hydroxide: Present in soap.

  • Potassium Hydroxide and Magnesium Hydroxide: Found in various products.

Turmeric as an Indicator

Activity: Making Turmeric Indicator

  1. Mix turmeric powder with water to create a paste.

  2. Apply the paste to filter paper and dry.

  3. Test turmeric paper with soap solution; it turns red in the presence of bases.

Litmus Test Activity

Activity Instructions:

  1. Mix lemon juice with water and apply to red and blue litmus paper.

  2. Document observations on color changes (Table 4.2).

  3. Perform the same with various listed substances.

  4. Record neutral solutions that do not change litmus color.

China Rose as an Indicator

Activity: Using China Rose

  • Collect petals, add them to a beaker, and create an indicator for testing acidic (dark pink) and basic (green) solutions.

Neutralization

What is Neutralization?

  • Mixing an acid with a base results in neutralization:

    • Reaction: Acid + Base → Salt + Water + Heat

  • Example: Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water

  • Characteristics of Neutralization:

    • Neutral solutions do not affect litmus paper.

    • Heat is produced during the reaction.

Applications of Neutralization

  • Indigestion: Antacids like milk of magnesia neutralize stomach acid.

  • Ant Bite: Baking soda neutralizes formic acid from ant stings.

  • Soil Treatment: Bases are used to treat acidic soils.

  • Factory Waste: Basic substances neutralize acidic factory waste before disposal.

Summary of Key Concepts

  • Acids are sour; bases are bitter and soapy to the touch.

  • Acid turns blue litmus red; bases turn red litmus blue.

  • Neutral solutions exhibit no reaction with indicators.

  • Indicators show color changes based on pH status (acidic, basic, neutral).

  • Neutralization leads to the formation of salt and water.