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Geetanjali International School, Bangalore Subject Science Acids, bases and Salt
Learning Objectives By the end of the lesson, students will be able to: Define acids, bases, and salts with examples. Identify common acids and bases used in daily life (e.g., lemon juice, soap, vinegar, baking soda). Differentiate between the physical properties of acids and bases (taste, touch, reaction with indicators). Explain the role of indicators (like litmus, turmeric, phenolphthalein) in detecting acids and bases. Demonstrate how acids and bases react with each other to form salts and water (neutralization reaction). Understand the concept of neutral substances and examples from daily life. Perform simple experiments to test substances using natural indicators (hands-on activity-based objective). List uses of acids, bases, and salts in everyday life and industries. Recall safety precautions while handling acids and bases. Develop scientific thinking by asking questions and drawing conclusions based on observations of chemical reactions.
Contents of the Chapter • Acids – Properties, examples, natural sources. • Bases – Properties, examples, uses. • Indicators – Litmus, turmeric, China rose, phenolphthalein. • Neutral Substances – Definition and examples. • Neutralization Reaction – Acid + base → salt + water. • Common Salts – Types and uses. • Uses of acids, bases, and salts in daily life. • Safety Precautions while handling acids and bases. • Simple Experiments using natural indicators.
Activity Taste the Rainbow – Guess the Nature! 🧪 Topic: Introduction to Acids, Bases, and Salts 🎯 Objective: To help students understand the basic characteristics of acids, bases, and salts using taste clues and real-life examples.
Instructions: • Get into teams of 3–4 students. • You will receive a “Taste Clue Card” or the clue will be read aloud. • Read or listen to the clue carefully. The clue will describe how something tastes or feels in daily life (e.g., sour like lemon, bitter like soap, salty like seawater). • With your team, discuss: • What everyday item is being described? • Is the item an acid, base, or salt? • Why do you think so? • Write down or share your guess when the teacher asks. • After all teams have guessed, the teacher will reveal the correct answer and explain what makes the item an acid, base, or salt. • 📌 Rules: • No tasting or touching anything — this is a guessing game! • Listen to each clue carefully. • Work as a team and respect everyone's ideas. • Have fun learning!
🧠 Think like a scientist! • Ask yourself: • Is it sour, bitter, or salty? • Do I know any common acids, bases, or salts in food or home items? • Can I guess the substance based on the clue?
Acids andBases • When we think of acids and bases we tend to think of science labs and chemicals…but did you know • Acidscause: • Lemons to besour • Acid rain to eat away at sculptures • Framed paintings to be damaged • Cavities in yourteeth • Food to digest in yourstomach • Ants and bees use it tosting
Properties of Acids andBases • Acids • turn blue litmusred tastesour • Acids corrodemetals • positively charged hydrogen ions(H+) • Bases • turn red litmusblue tastebitter • Negatively charged hydroxide ions (OH–) Feelslippery • Most hand soaps and drain cleaners arebases Strong bases arecaustic
Salt • Neutralization is a process or a chemical reaction in which an acidic and basic substance is mixed with each other in order to neutralize their acidic and alkaline nature. • The product that is formed after the neutralization process is called a Salt. • The salt can have basic, acidic or neutral nature
Neutralization • Neutralization is a process or a chemical reaction in which an acidic and basic substance is mixed with each other in order to neutralize their acidic and alkaline nature.
Neutralization in Everyday Life • Indigestion • Ant Bite • Soil Treatment • Factory Wastes
Several Types ofAcids HydrochloricAcid. Stomach acid - has the sour taste ofacid. • AceticAcid • An ingredient in vinegar. • CitricAcid • Citrus fruits such as lemons, grapefruit, oranges, and limes have citric acid in thejuice. • LacticAcid • Sour milk, sour cream, yogurt, and cottage cheese have lacticacid.
StrongAcids • Nitric acid (HNO3) • Hydrochloricacid (HCl) • Sulphuricacid (H2SO4) • StrongAcids • are acids that has many hydrogen ions (manyH+).
WeakAcids • Weak acids • Are acids that have fewer hydrogen ions (fewer H+). • Examples • aceticacid boricacid • sea-water, in plants and especially in fruits carbonic acid • Found in ourblood • citricacid
Properties ofBases Turn redlitmus tastebitter Negatively charged hydroxide ions(OH–) Feelslippery Bases neutralizeacids Poisonous and can cause severeburns Strong Bases areCaustic.
Some CommonBases • Ammonia The most widely usedbase Used in household cleaningmaterials Used asfertilizer • Calciumhydroxide Used to make mortar andplaster Used to help neutralize acidsoil • Sodiumhydroxide One of the strongestbases Used in oven cleaners and draincleaners
StrongBases • Strong bases • Are bases that produce many hydroxide ions (OH-) when it is dissolved inwater. • AreCaustic • Examples • Lithiumhydroxide (LiOH) • Sodiumhydroxide (NaOH) • Potassiumhydroxide (KOH)
WeakBases • Weak bases • Are bases that produce few hydroxide ions (OH-) when it is dissolved inwater.. • Examples • Aluminumhydroxide
Safety Precautions for Handling Acids and Bases • ️ 🧤 1. Wear Protective Gear • Always wear gloves, safety goggles, and a lab coat to protect your skin and eyes. • 🧪 2. Handle with Care • Use droppers or pipettes while transferring acids or bases. • Never touch them directly with hands. • 🚫 3. Never Taste or Smell Directly • Do not taste or directly inhale the vapors of acids or bases. • 💦 4. Add Acid to Water (Never Water to Acid) • Always add acid to water slowly, never the other way round, to avoid splashing and heat release. • 🧹 5. Clean Spills Immediately • Neutralize acid spills with baking soda. • Neutralize base spills with vinegar or lemon juice. • 🧼 6. Wash Hands After Use • Even if you wore gloves, wash your hands thoroughly after the activity. • 📦 7. Store Properly • Keep acids and bases in labeled containers and store them in a cool, dry place, away from sunlight. • 🧯 8. Know First Aid • In case of skin contact, wash immediately with plenty of water. • For eye contact, rinse eyes thoroughly and seek medical help.
Natural Indicators Natural indicators are substances obtained from nature (plants, fruits, flowers) that change color in acidic or basic conditions.
Natural Indicators Examples • 🧪 1. Red Cabbage • Contains a pigment called vanthocyanin • In Acid: Turns red or pink • In Base: Turns green, blue, or yellowish-green • 🌼 2. Turmeric • A yellow spice used in cooking • In Acid: Remains yellow • In Base: Turns reddish-brown • 🌺 3. Hibiscus Petals • Can be used to make a natural indicator solution • In Acid: Turns pink or reddish • In Base: Turns green or yellowish • 🍒 4. Beetroot Juice • Rich in natural pigments • In Acid: Slight change, remains reddish • In Base: May turn purple or bluish • 🌻 5. Rose Petals (dark pink/red) • Works similarly to hibiscus • In Acid: Pinkish • In Base: Greenish or bluish • 🍇 6. Grape Juice / Blueberries • Natural color changes due to pH • In Acid: Purple or red • In Base: Greenish-blue
Activity: Testing Acids and Bases with Natural Indicators • 🔍 Objective: • To observe color changes when natural indicators react with acids and bases, and to identify the nature of different substances. • 🌿 Materials (per group): • Natural indicators (choose at least one): • Red cabbage juice • Turmeric solution • Hibiscus water • Transparent cups/test tubes • Droppers or spoons • Substances to test (label them A, B, C, etc.): • Lemon juice (acid) • Vinegar (acid) • Baking soda solution (base) • Soap water (base) • Salt water (neutral) • Plain water (neutral) • Observation sheet or notebook
Instructions for Students: Wash your hands and keep your workspace tidy. Carefully pour or spoon a small amount of each test liquid into a separate labeled cup. Add a few drops of the natural indicator to each sample. Observe the color change carefully. Record your observations in the table below: 6. Based on the color change, decide whether the sample is an: 7. Acid (usually turns pink/red with red cabbage) 8. Base (usually turns green/blue with red cabbage, reddish-brown with turmeric) 9. Neutral (no color change) 10. Compare your guesses with the actual answers revealed by the teacher.
Think & Discuss: • Which indicator showed the most noticeable color change? • Were you surprised by any result? • Why do we use indicators instead of tasting chemicals? • 🚫 Safety Rules: • Do NOT taste or touch any substances. • Use droppers carefully and don’t mix samples. • Clean your workspace after the experiment.
Blue Litmus and Red Litmus • 🔹 Litmus Paper • Litmus is a natural indicator extracted from lichens. It comes in two colors: • Blue litmus paper • Red litmus paper • These papers change color when they come in contact with acidic or basic substances. • 🔴 Red Litmus Paper: • Stays red in acids • Turns blue in bases • ✅ Use it to test for bases • 🔵 Blue Litmus Paper: • Stays blue in bases • Turns red in acids • ✅ Use it to test for acids • ⚪ No Color Change = Neutral • If neither red nor blue litmus changes color, the substance is likely neutral (like pure water or salt solution).
Summary • Acids • Taste: Sour • Litmus Test: Turns blue litmus red • Examples: Lemon juice, vinegar, curd • 🧼 Bases • Taste: Bitter, feel soapy • Litmus Test: Turns red litmus blue • Examples: Soap water, baking soda • ⚖️ Salts • Formed by: Reaction of acid and base (Neutralization) • Taste: Salty • Example: Table salt (NaCl) • Neutralization Reaction: Acid + Base → Salt + Water • Indicators • Used to test if a substance is acidic or basic. • Common Indicators: • Litmus paper: • Blue → Red = Acid • Red → Blue = Base • Turmeric: • Yellow in acid • Reddish-brown in base • Red cabbage: • Red in acid • Green/blue in base
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UNIT END ASSESSMENT • Short Answer Questions: • Define acids and bases with examples. • What is neutralization? Give one example. • List two uses of salts in daily life. • What are indicators? Name two natural indicators. • Higher-Order Thinking Questions (HOTs) • Ria was testing two solutions using litmus papers. In one solution, blue litmus turned red, and in another, red litmus turned blue. What type of solutions did she test? Explain. • Why should we not taste or touch unknown laboratory substances even if they look like common salt or lemon juice? • A student added lemon juice to soap solution. What type of reaction will occur? Write the expected result. • Application-Based Question • A farmer added lime (calcium hydroxide) to his field after checking the soil. Why do you think he did this? What does it tell you about the nature of the soil?
