2. Exploring substances - Acidic, Basic, Neutral

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Lime water preparation

Lime water is a solution of calcium hydroxide in water. It can be prepared through the following steps:

Mixing: Combine lime (also known as chuna or calcium oxide) with water.
Settling: Leave the mixture undisturbed for about one hour.
Filtration: Filter the liquid into a separate container to obtain clear lime water.

Lime water should not be confused with the fruit called "lime," which is similar to a lemon.

Lichens

Lichens are formed by the association of 2 living organisms - Fungus and Algae.

Indicators

Litmus paper - Lichens
Red Rose
Turmeric - Golden spice, member of the Ginger family

Property	Acids	Bases	Change in Neutral Solution
Taste	Generally taste sour.	Generally taste bitter.
Touch	Not advisable to touch.	Feel soapy or slippery to the touch.
Blue Litmus	Turns blue litmus paper red.	No colour change.	No change
Red Litmus	No colour change.	Turns red litmus paper blue.	No change
Red Rose Extract	Turns a shade of red.	Turns a shade of green.	No change
Turmeric Paper	Remains yellow (unchanged).	Turns red.	Remains Yellow (Unchanged)

Beetroot, purple cabbage, turmeric, Indian blackberry (jamun) and red hibiscus (gudhal) flowers also act as acid base indicator.

Different types of acids

Formic acid: Injected into the skin during a red ant bite.
Citric acid: Found in lemons and amla juice.
Tartaric acid: Found in tamarind.
Ascorbic acid (Vitamin C): Found in amla juice.
Oxalic acid: Present in some eatable substances alongside citric acid.
Acetic acid: The primary component of vinegar.
Lactic acid: Present in curd.

Different Bases

Baking soda (Sodium hydrogen carbonate) solution: Used as a common household base for testing and to treat acidic ant bites.
Lime water: A solution used to demonstrate basic properties and neutralisation.
Soap solution and Washing powder solution: Everyday examples of basic substances

Neutralisation reactions

Neutralisation reactions occur when the solution of an acid is mixed with the solution of a base in sufficient quantity, resulting in a solution that is neither acidic nor basic.
In these reactions, the acid and base neutralise each other's effects to form salt and water, a process that also releases heat.

Neutralisation in Daily Life

Ant Bites: When a red ant bites, it injects an acidic liquid called formic acid into the skin, causing a stinging pain. This effect can be neutralised by rubbing moist baking soda (a base) on the affected area to relieve the pain.
Soil Treatment: Excessive use of chemical fertilisers can make soil too acidic, preventing plants from growing well. Such soil can be treated with lime, which is a base. Conversely, if soil is basic, organic matter like manure or composted leaves is added; these release acids that neutralise the soil's basic nature.
Industrial Waste: Factory wastes are often acidic and can be harmful to aquatic life, such as fish, if released directly into water bodies. To prevent this, industrial waste is neutralised by adding basic substances before it is discharged into lakes or rivers.

Olfactory indicators

Defined as substances whose odours change when they are in an acidic or basic medium. They are particularly useful when a person cannot rely on colour-based indicators.

Example: Chopped Onions

The chapter describes a detailed investigation using onions as a natural olfactory indicator:

Preparation: Finely chopped onions are placed in a container with strips of clean cotton cloth or filter paper and left tightly closed overnight. This allows the cloth strips to absorb the onion's odour.
Testing with Acid (Tamarind Water): When a few drops of an acidic substance like tamarind water are put on a strip, the characteristic odour of the onion is typically retained or does not disappear.
Testing with Base (Baking Soda Solution): When a few drops of a basic substance like baking soda solution are added to another strip, the onion's odour changes or disappears.

By observing whether the smell of the onion remains or vanishes, one can identify if a substance is acidic or basic without needing to see a colour change.

Table 2.1

S.No.	Name of the Sample	Colour of Blue Litmus Paper	Colour of Red Litmus Paper	Nature of the Substance
1	Lemon juice	Turns Red	No change	Acidic
2	Soap solution	No change	Turns Blue	Basic
3	Amla juice	Turns Red	No change	Acidic
4	Tamarind water	Turns Red	No change	Acidic
5	Vinegar	Turns Red	No change	Acidic
6	Baking soda solution	No change	Turns Blue	Basic
7	Lime water	No change	Turns Blue	Basic
8	Tap water	No change	No change	Neutral
9	Washing powder solution	No change	Turns Blue	Basic
10	Sugar solution	No change	No change	Neutral
11	Salt solution	No change	No change	Neutral

Table 2.3

S.No.	Name of the Sample	Colour of Red Rose Extract after adding the sample	Nature of the Substance
1	Lemon juice	Shade of Red	Acidic
2	Soap solution	Shade of Green	Basic
3	Amla juice	Shade of Red	Acidic
4	Baking soda solution	Shade of Green	Basic
5	Vinegar	Shade of Red	Acidic
6	Salt solution	No change (remains same)	Neutral

Table 2.4

S.No.	Name of the Sample	Colour of Turmeric Paper after adding the sample	Nature of the Substance
1	Lemon juice	Yellow (Unchanged)	Acidic
2	Soap solution	Turns Red	Basic
3	Amla juice	Yellow (Unchanged)	Acidic
4	Tamarind water	Yellow (Unchanged)	Acidic
5	Vinegar	Yellow (Unchanged)	Acidic
6	Baking soda solution	Turns Red	Basic
7	Lime water	Turns Red	Basic
8	Tap water	Yellow (Unchanged)	Neutral
9	Washing powder solution	Turns Red	Basic
10	Sugar solution	Yellow (Unchanged)	Neutral
11	Salt solution	Yellow (Unchanged)	Neutral