Nature — Our Science Laboratory

The world around us acts as a vast science laboratory. Simple activities, like the one witnessed by Ashwin and Keerthi at the science fair where words appeared upon being sprayed with a liquid, demonstrate the hidden chemical nature of everyday substances.

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1. Indicators: The Chemical Messengers

Substances that are used to test whether a substance is acidic or basic are called indicators. These indicators change their colour when added to a solution containing an acidic or a basic substance.

• Natural Indicators: Derived from nature, such as Litmus, Turmeric, Red Rose petals, and China Rose.
• Synthetic Indicators: Prepared in laboratories (e.g., Phenolphthalein, Methyl orange).

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2. Litmus: A Natural Dye from Lichens

The most commonly used natural indicator is Litmus. Its properties and origins are detailed below:

• Origin: It is extracted from Lichens.
• Composition: Lichens are a symbiotic association of two living organisms: a Fungus and an Alga.
• Availability: It is available as a mauve (purple) coloured solution or as paper strips (Red and Blue litmus paper).
• Environmental Indicator: Lichens generally grow in regions with clean air and abundant rainfall; their absence can indicate air pollution.

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3. Classification of Substances

Based on their interaction with indicators, substances are classified into three primary groups:

A. Acidic Substances

• Taste: They generally taste sour.
• Litmus Test: They turn Blue Litmus paper to Red.
• Examples: Lemon juice, Vinegar, and Amla juice.

B. Basic Substances

• Taste: They generally taste bitter.
• Texture: They feel soapy or slippery when rubbed between fingers.
• Litmus Test: They turn Red Litmus paper to Blue.
• Examples: Soap solution, Baking soda solution, and Lime water.

C. Neutral Substances

• Nature: They are neither acidic nor basic.
• Litmus Test: They do not change the colour of either Red or Blue litmus paper.
• Examples: Sugar solution, Salt solution, and Distilled water.

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4. Observation Data: Testing Common Samples

The following table summarizes the behavior of various household samples when tested with litmus paper:

S.No.	Name of the Sample	Blue Litmus	Red Litmus	Nature
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.	Baking soda solution	No change	Turns Blue	Basic
5.	Sugar solution	No change	No change	Neutral
6.	Lime water (Chuna)	No change	Turns Blue	Basic

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5. Preparation of Lime Water (Chuna Water)

In the Indian context, Chuna (Calcium Oxide) is frequently used. Lime water is a chemical solution of Calcium Hydroxide and is prepared as follows:

1. Take a small amount of Calcium Oxide ($CaO$) and mix it with water.
2. Leave the mixture undisturbed for about an hour to allow the Calcium Hydroxide to form and settle.
3. Filter the liquid to remove the undissolved particles.
4. The clear filtrate is Lime Water ($Ca(OH)_2$).

Chemical Formula for Preparation:

$\text{Calcium Oxide} (CaO) + \text{Water} (H_2O) \rightarrow \text{Calcium Hydroxide} [Ca(OH)_2]$

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6. Common Acids in Edible Substances

Many foods we consume contain natural acids. The following list identifies the specific acid present in common Indian food items:

• Vinegar (Sirka): Contains Acetic acid.
• Curd (Dahi): Contains Lactic acid.
• Lemon / Orange: Contains Citric acid.
• Tamarind (Imli) / Grapes: Contains Tartaric acid.
• Amla: Contains Ascorbic acid (Vitamin C).
• Spinach (Palak) / Tomato: Contains Oxalic acid.

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Answer:

Natural Indicators: Red Rose and Turmeric

Apart from Litmus, nature provides a variety of substances that change colour depending on whether they are in an acidic or basic medium. These are called Natural Indicators and are easily accessible in an Indian kitchen or garden.

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1. Red Rose as an Indicator

Petals of the Red Rose can be processed to create a sensitive liquid indicator. The steps and observations are as follows:

Preparation Method:

• Collect fallen petals of red roses (avoid plucking).
• Crush the petals using a mortar and pestle.
• Add hot water and let it sit for $5$ to $10$ minutes until the water becomes deeply coloured.
• Filter the solution to obtain the Red Rose extract.

Colour Changes:

• In Acidic Solutions: The extract changes to a shade of red or dark pink (e.g., when Lemon juice is added).
• In Basic Solutions: The extract changes to a shade of green (e.g., when Soap solution is added).
• In Neutral Solutions: There is no change in the colour of the extract.

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2. Turmeric (Haldi) as an Indicator

Known as the 'Golden Spice', Turmeric is a member of the ginger family and is a staple in Indian households. It serves as an excellent indicator, especially for detecting bases.

Properties and Preparation:

• Make a turmeric paste by adding a little water to turmeric powder.
• Apply this paste on filter paper or plain white paper and allow it to dry.
• Cut the yellow paper into thin Turmeric paper strips.

Reaction Summary:

• Basic Medium: The yellow turmeric paper turns Red. This is why a yellow haldi stain on a white shirt turns red when rubbed with soap.
• Acidic Medium: The yellow colour remains unchanged (remains Yellow).
• Neutral Medium: The colour remains unchanged (remains Yellow).

Answer:

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3. Olfactory Indicators

Some substances do not change colour, but their odour (smell) changes when added to an acidic or basic medium. These are known as Olfactory Indicators.

• Onion:
  • In Acidic medium (like Tamarind water): The characteristic smell of onion remains.
  • In Basic medium (like Baking soda): The characteristic smell of onion vanishes.
• Vanilla Essence: The pleasant smell of vanilla disappears when mixed with a base.

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4. Other Natural Indicators in Nature

Various fruits, flowers, and vegetables exhibit indicator properties:

• Hydrangea: A plant found in the Himalayan region.
  • Produces Blue flowers in acidic soil.
  • Produces Pink or Red flowers in basic soil.
• Red Hibiscus (Gudhal): The extract of this flower also changes colour in acids and bases.
• Purple Cabbage & Beetroot: Their juices act as powerful pH indicators.
• Jamun (Indian Blackberry): The deep purple pigment can also be used to test the nature of substances.

Summary Table of Indicator Colours

Indicator	Acidic Solution	Basic Solution	Neutral Solution
Blue Litmus	Red	Blue (No change)	Blue
Red Litmus	Red (No change)	Blue	Red
Turmeric Paper	Yellow (No change)	Red	Yellow
Red Rose Extract	Red / Dark Pink	Green	No change

What Happens When Acidic Substances Mix with Basic Substances?

When we mix an acidic solution with a basic solution in appropriate amounts, a fascinating chemical transformation occurs. The two substances work against each other to nullify their individual properties.

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The Process of Neutralisation

The reaction between an acid and a base is known as a Neutralisation Reaction. The key characteristics of this process are:

• Loss of Identity: The acidic nature of the acid and the basic nature of the base are both destroyed.
• New Product Formation: A completely new substance called Salt is produced. This salt may be acidic, basic, or neutral in nature.
• Byproduct: Water ($H_2O$) is always formed along with the salt.
• Energy Release: These reactions are exothermic, meaning Heat is evolved. This heat increases the temperature of the reaction mixture, making the test tube feel warm.

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Chemical Equation and Formula

The general representation of this reaction can be written as a word equation:

$\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water} + \text{(Heat)}$

Specific Chemical Example

A classic example involving common laboratory chemicals is the reaction between Hydrochloric Acid and Sodium Hydroxide:

$\text{HCl (Hydrochloric acid)} + \text{NaOH (Sodium hydroxide)} \rightarrow \text{NaCl (Sodium chloride)} + \text{H}_2\text{O (Water)} + \text{Heat}$

• NaCl: This is Sodium Chloride, commonly known in India as 'Namak' or table salt.
• Reaction State: If the acid and base are perfectly balanced, the resulting $NaCl$ solution will have a neutral pH.

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Experimental Observation of Neutralisation

We can observe the transition from acidic to neutral using indicators like Blue Litmus solution or Phenolphthalein (a synthetic indicator). In Activity 2.7, the following sequence is observed:

Stage	Action Performed	Observed Colour	Resulting Nature
1	Blue Litmus added to Lemon Juice	Red	Acidic
2	Slowly adding Lime Water (Base)	Red (gradually fades)	Less Acidic
3	Perfect balance reached	Purple/No distinct change	Neutral
4	Excess Lime Water added	Blue	Basic

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Answer:

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Acharya Prafulla Chandra Ray (P.C. Ray)

India has a rich tradition in chemistry, and Acharya P.C. Ray is a towering figure in its modern history. His life and work can be summarized as follows:

• Title: Known as the 'Father of Modern Indian Chemistry'.
• Education: Earned a doctorate in chemistry from the United Kingdom before returning to serve India.
• Industrial Contribution: Established India’s first pharmaceutical company (Bengal Chemicals & Pharmaceuticals) in $1901$.
• Cultural Rooting: He was deeply rooted in Indian culture and wrote extensively on the History of Hindu Chemistry to highlight ancient Indian scientific expertise to the modern world.
• Social Reform: He advocated for instruction in the mother tongue within educational institutions to make science more accessible to the masses.

Neutralisation in Daily Life

The chemical process of neutralisation is not restricted to science laboratories. It plays a vital role in our day-to-day survival, agriculture, and environmental protection. By balancing acids and bases, we can treat stings, improve crop yields, and protect aquatic life.

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1. Treatment of Insect Bites (Ant Bites)

In Indian gardens and households, red ant bites are common. The science behind the pain and its cure involves:

• The Cause: When an ant bites, it injects an acidic liquid known as Formic Acid into the skin.
• The Symptoms: This results in redness, itching, and a sharp stinging pain.
• The Remedy:
  • Applying moist baking soda (Sodium hydrogen carbonate).
  • Applying Calamine solution, which contains Zinc carbonate.
• The Scientific Reason: Since baking soda and calamine are basic in nature, they neutralise the effect of the formic acid, providing immediate relief.

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2. Agriculture: Soil Treatment

For a farmer, the health of the soil is paramount. Plants are very sensitive to the pH level of the soil. They do not thrive if the soil is extremely acidic or extremely basic.

A. Managing Acidic Soil

• Cause: Excessive and continuous use of chemical fertilisers often makes the soil acidic.
• Treatment: Farmers add basic substances like Quick Lime (Calcium oxide) or Slaked Lime (Calcium hydroxide). In local Indian terms, this is often referred to as adding Chuna to the fields.

B. Managing Basic Soil

• Cause: Natural soil composition or specific mineral deposits.
• Treatment: Organic matter (like manure or composted leaves) is added.
• Mechanism: The organic matter releases acids as it decomposes, which neutralises the basic nature of the soil.

Soil Condition	Remedy / Material Used	Nature of Substance
Too Acidic	Quick Lime (Chuna) / Slaked Lime	Basic
Too Basic	Manure / Organic Compost	Acidic
Ideal Condition	Balanced / Neutralised Soil	Neutral

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3. Environmental Protection: Factory Waste

Many industrial units release liquid waste (effluents) that are highly acidic. If these wastes are discharged directly into rivers or lakes:

• The acidic content can be fatal to fish and other aquatic organisms.
• It disrupts the ecological balance of the water body.

Solution: Factories are required to neutralise their waste by adding basic substances before disposing of it in the environment.

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Economic and Social Perspective

Environmental safety comes with an economic cost, but it protects the livelihood of society (like fishermen). For example, if a small-scale industry in India spends money on neutralising agents:

Let the cost of basic neutralising agents be $C = \text{₹} \ 450 \text{/}$ per unit of waste. If there are $20$ units of waste produced daily:

$\text{Daily Expenditure} = 20 \times 450 = \text{₹} \ 9,000 \text{/}$

$\text{Monthly Expenditure (30 days)} = 30 \times 9,000 = \text{₹} \ 2,70,000 \text{/}$

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