2. Exploring Substances

Visual Summary & Essential Science Concepts

What are Indicators?

CORE

We can't taste everything safely! Indicators are special substances that exhibit distinct, visible colour changes when introduced to acidic or basic environments.

Safety Caution:

Never taste unknown chemicals or substances in the laboratory without supervision!

Acid vs. Base Crash Course

Acids

  • Taste Sour
  • Contain hydrogen ions
  • Turn Blue Litmus → Red

Bases

  • Taste Bitter
  • Feel Soapy/Slippery
  • Turn Red Litmus → Blue
Neutral substances do not change either red or blue litmus papers.

Litmus: Sourced from Lichens

NATURAL

Litmus is a natural indicator extracted from Lichens (a fascinating symbiotic partnership of a fungus and an alga).

Blue Litmus → Red in Acid
Red Litmus → Blue in Base

Nature's Acids Gallery

Citric Acid

Lemons, Oranges

Tartaric Acid

Tamarind (Imli)

Acetic Acid

Vinegar (Sirka)

Oxalic Acid

Tomatoes, Spinach

Ascorbic Acid (Vit C)

Amla, Citrus Fruits

Other Natural Indicators

Red Rose Extract

Turns Red in acidic solutions and turns Green in basic solutions.

Turmeric (Haldi)

Stays Yellow in acidic/neutral. Turns Reddish-Brown in basic solutions (e.g., when soap meets a curry stain!).

Hydrangea: Soil pH alters its blooms! Gives blue flowers in acidic soil, pink/red in basic soil.

Olfactory Indicators

These substances change their smell/odour depending on whether they are mixed with an acid or a base!

Fun Experiment: Onion Cloth Strips

Onion-soaked cloth retains its signature strong odour in acidic media (e.g., tamarind water) but loses its smell in basic solutions (e.g., baking soda solution).

Neutralisation Reaction

EXOTHERMIC

When an acid mixes with a base in the correct quantities, they nullify each other's effects. This is a neutralisation reaction, yielding a salt, water, and heat!

Acid + Base → Salt + Water + Heat

Heat Generation

The mixture temperature rises as neutralisation reactions are exothermic (release energy).

What is Salt?

A new substance formed during neutralisation. It can be acidic, basic, or neutral in nature.

Scientist Spotlight

Acharya Prafulla Chandra Ray

"Father of Modern Indian Chemistry"

A legendary Indian chemist, academician, and visionary industrialist. He established India's first pharmaceutical company in 1901 and dedicated his efforts to advancing chemical research and education across India.

Everyday Neutralisation Remedies

1 Ant Bite Relief

An ant bite injects Formic Acid into the skin causing stinging pain.

Remedy: Rub moist baking soda (Sodium Hydrogen Carbonate) or calamine solution to neutralise the acid.

2 Healthy Soil Management

Excess fertilizers make soil highly acidic, stunted crops.

Remedy: Add quicklime (calcium oxide) or slaked lime (calcium hydroxide). If basic, organic manure releases organic acids!

3 Saving Aquatic Ecosystems

Many factory wastes are heavily acidic and harmful to fish if dumped directly.

Remedy: Neutralise factory effluent with basic chemicals prior to discharging them into rivers.