Untitled Quiz

• Indicators are substances to test the acidic or basic nature of a substance.

Synthetic Indicators

• Synthetic indicators are created in the laboratory.
• Examples include phenolphthalein and methyl orange.
• Phenolphthalein is colorless in acidic solutions and pink in basic solutions.
• Methyl orange is red in acidic solutions and yellow in basic solutions.

Natural Indicators

• Natural indicators are obtained from naturally occurring substances.
• Examples include litmus, turmeric, and China rose.

Litmus

• Litmus is a common natural indicator.
• It is extracted from lichens, a composite organism of fungi and algae in a symbiotic relationship.
• Litmus is available as a solution or paper strips (red and blue).
• Litmus paper and solution versions detect acidity/basicity.
• Litmus is purple in distilled water.
• Blue litmus turns red in an acidic solution, red remains red.
• Red litmus turns blue in a basic solution, blue remains blue.

Activity-1

• Testing the effect of acidic and basic solutions on litmus paper.
• Materials: Blue and red litmus paper, dropper, dilute lemon juice, detergent, shampoo, vinegar, salt/sugar solution, milk of magnesia
• Procedure:
  • Place a drop of lemon juice on red litmus paper and then blue litmus paper.
  • Observe the color change.
  • Repeat with other solutions and record observations.
• Results:
  • Lemon juice turns blue litmus red, indicating an acidic solution.
  • Detergent turns red litmus blue, indicating a basic solution.
  • Shampoo turns red litmus blue, indicating a basic solution.
  • Vinegar turns blue litmus red, indicating an acidic solution.
  • Salt and sugar had no color change, indicating a neutral solution.
  • Milk of magnesia turns red litmus blue, indicating a basic solution.
• Conclusion: Lemon juice and vinegar are acidic; detergent, shampoo and milk of magnesia are basic.

Turmeric

• Turmeric is a natural indicator.
• It is yellow and turns red in basic solutions.
• It does not change color in acidic solutions.
• Turmeric stains turn red when washed with detergent because detergents are basic.

China Rose

• China rose petals extract can act as indicator.
• China rose indicator exhibits dark pink (magenta) in acidic media and green in basic.
• To prepare the indicator, soak China rose petals in warm water until the water is colored.

Acids

• Acids are naturally occurring from plants and animals, except hydrochloric acid, are called organic acids.
• Mineral acids are prepared from minerals (e.g., nitric, sulphuric, hydrochloric acids).
• Acids taste sour.
• Examples acids in daily life: acetic (vinegar), malic (apple), oxalic (spinach), ascorbic (Vitamin C), citric (citrus fruits), tartaric (grapes, tamarind), lactic (curd).
• The stomach produces hydrochloric acid and muscles produce lactic acid.
• Acids turn blue litmus paper red.
• China rose solution turns dark pink in acids.
• Acids do not affect turmeric paper.
• Acids are generally soluble in water.

Uses of Acids

• Hydrochloric acid cleans sanitary ware and is a laboratory reagent.
• Sulphuric acid is used in automobile batteries and in industries.
• Nitric acid is used by goldsmiths to clean jewelry.

Bases

• Bases are bitter and feel soapy.
• Bases includes baking soda, soap solution, and washing soda.
• Solutions containing a base are considered basic.
• Common bases include calcium hydroxide (lime water), sodium or potassium hydroxide (soap), ammonium hydroxide (window cleaner), magnesium hydroxide (milk of magnesia).
• Bases that dissolve in water are called alkalies.
• All alkalies are bases, but not all bases are alkalies.
• Bases turn red litmus paper blue.
• China rose solution turns green in bases.
• Turmeric paper turns red in bases.
• Solubility in water varies between bases.

Uses of Bases

• Used soap, textile, and plastic production
• Used in petroleum refining
• Used in cleaning processes
• Used as Antacids

Neutralization

• When an acidic solution and basic solution are mixed both neutralize each other.
• A salt and water are formed.
• The product may be acidic or basic depending on the starting salt and base mix.
• Acid + Base -> Salt + Water
• Acid + Alkali gives a salt
• The process is called neutralisation

Activity-2

• Demonstrating Neutralization Reaction:
• Materials: test tubes, dropper, phenolphthalein, dilute solutions of hydrochloric acid and sodium hydroxide.
• Procedure:
  • Take 5mL of sodium hydroxide in a test tube and add 2 drops of phenolphthalein (turns pink).
  • Add hydrochloric acid dropwise.
  • Stop adding when the pink color disappears.
  • Add a drop of sodium hydroxide again (solution turns pink).
  • Alternate additions, observe changes
• Observation: The solution turns pink; color disappears when HCl added. Test tube warms.
• Conclusion: The acid cancels the effect of sodium hydroxide/vice versa.

Neutralization in daily life

• In indigestion, excess hydrochloric acid in the stomach can be neutralized by taking an antacid (milk of magnesia).
• Bee stings inject formic acid, and can be treated by baking soda.
• Soil acidity: Soil can be treated with calcium hydroxide (slaked lime) or calcium oxide (quick lime).
• Organic matter is used to neutralize basic soil.
• Factory water is neutralized to protect the environment.

Exothermic/Endothermic Reactions

• Heat is given out in neutralization reaction called exothermic reactions.
• Reaction in which heat is absorbed are called endothermic reaction.

Characteristics of Acids and Bases

• Acids taste sour.
• Acids feel abrasive/rough.
• Acids turn blue litmus paper red.
• Acids turn China rose solution dark pink.
• Acids do not affect turmeric paper.
• Acids keep phenolphthalein colorless.
• Acids turn methyl orange red.
• Acids are usually soluble in water.
• Bases taste bitter.
• Bases feel slippery/soapy.
• Bases turn red litmus paper blue.
• Bases turn China rose solution green.
• Bases turn turmeric paper red.
• Bases turn phenolphthalein pink.
• Bases turn methyl orange yellow.
• Base solubility is variable.

Acid Rain

• Air pollutants like carbon, sulphur and nitrogen dioxides mixing with rain.
• Damages buildings and threatens animal and plant life.
• The Taj Mahal is affected damage due to acid rain.