Acids, Bases, and Natural Indicators

• Many daily substances like lemon, tamarind, salt, sugar, and vinegar have different tastes

Acids and Bases

• Acids taste sour, giving substances like curd, lemon juice, orange juice, and vinegar their tartness
• The word "acid" originates from the Latin word "acere," meaning sour
• Bases generally taste bitter and feel soapy
• Indicators are substances used to test if a substance is acidic or basic
• Indicators change color when added to acidic or basic solutions
• Examples of naturally occurring indicators include turmeric, litmus, and China rose petals (Gudhal)

Natural Indicators Around Us - Litmus

• Litmus is a common natural indicator extracted from lichens
• Litmus has a mauve (purple) color in distilled water
• Litmus turns red in acidic solutions and blue in basic solutions
• Litmus is available as a solution or as strips of paper called litmus paper

Activity 4.1

• Mix lemon juice and water in a plastic cup
• Put a drop of the lemon juice solution on a strip of red litmus paper
• Note any color change
• Repeat the experiment with blue litmus paper and other substances (tap water, detergent, soap, shampoo, salt, sugar, vinegar, baking and washing soda , milk of magnesia, lime water)

Neutral Solutions

• Solutions that do not change the color of either red or blue litmus paper are of neutral solutions
• Neutral substances are neither acidic nor basic

Turmeric as Indicator

• Turmeric can be used as a natural indicator
• Create turmeric paper by applying a turmeric paste on blotting/filter paper and let it dry
• Apply a drop of soap solution on the turmeric paper
• Turmeric paper turns red in soap solution

China Rose as Indicator

• Collect China rose (Gudhal) petals
• Immerse it in mixture of warm water until water it colored
• Use the colored warm water as a indicator
• China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green

Table 4.4

• Shampoo (dilute solution), lemon juice soda water, sodium hydrogencarbonate solution, vinegar, sugar and common salt solution can be tested as shown in the the table
• Keep the mixture for some time till water becomes colored.
• Use the coloured water as an indicator and add five drops of the indicator to each of the solutions

Table 4.5

• Dilute hydrochloric acid can be tested as shown in the table
• Record the effect on litmus paper, on tumeric papaer and China rose solution for this acid

Acid Rain

• Acid rain contains excessive acids and can damage buildings, historical monuments, plants, and animals
• Acid rain forms when carbon dioxide, sulfur dioxide, and nitrogen dioxide (pollutants) dissolve in rain, producing carbonic acid, sulfuric acid, and nitric acid

Neutralisation

• Acids turn blue litmus red
• Bases turn red litmus blue
• Neutralization occurs when an acid and base react, canceling each other's effects
• Mixing an acid solution with a basic solution neutralizes the effect of each of the solutions
• In neutralization, heat is produced, raising the temperature of the reaction mixture
• A new substance, called salt, is formed during neutralization
• Salt may be acidic, basic, or neutral
• Neutralisation salt and water are produced with the evolution of heat:
• Acid + Base -> Salt + Water (+ Heat)
• Example: Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) -> Sodium chloride (NaCl) + Water (H2O)

Neutralisation in Everyday Life - Indigestion

• The stomach contains hydrochloric acid to aid digestion
• Too much acid leads to indigestion, which can be relieved by taking an antacid like milk of magnesia (magnesium hydroxide), which neutralizes the excessive acid

Ant Bite

• Ants inject formic acid into the skin when they bite
• The acid's effect can be neutralized by rubbing moist baking soda (sodium hydrogencarbonate) or calamine solution (zinc carbonate) on the affected area

Soil Treatment

• Excessive use of chemical fertilizers makes the soil acidic, hindering plant growth
• Acidic soil is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide)
• Basic soil is treated with organic matter (compost), which releases acids that neutralize the soil

Factory Wastes

• Many factory wastes contain acids
• These wastes must be neutralized by adding basic substances before being released into water bodies to prevent harm to aquatic life

Keywords

• Main terms to remember are Acid, Acidic, Base Basic, Indicator, Neutral and Neutralisation

Explore acids, bases, and natural indicators like litmus. Acids taste sour and bases taste bitter. Indicators like litmus change color to identify acids and bases, turning red in acidic solutions and blue in basic solutions.