Exploring Substances: Acidic, Basic, and Neutral

CHAPTER 2: EXPLORING SUBSTANCES: ACIDIC, BASIC, AND NEUTRAL

2.1 NATURE — OUR SCIENCE LABORATORY

What is an Indicator?

**Indicator** = A substance that changes colour to show the nature (acidic, basic, or neutral) of other substances.

2.1.1 LITMUS AS AN INDICATOR

**What is Litmus?**

Litmus is a natural substance obtained from **lichens** (living organisms formed by the association of a fungus and an alga)

Available as:

Blue litmus paper strips (turns red in acidic solutions)

Red litmus paper strips (turns blue in basic solutions)

Also available as a solution

**Lichenology Fact**: Lichens grow on rocks and trees in regions with abundant rainfall and clean air. They are sensitive to air pollution.

Activity 2.1: Testing Substances with Litmus Paper

**Procedure**:

1. Collect samples: lemon juice, soap solution, amla juice, tamarind water, vinegar, baking soda solution, lime water, tap water, washing powder solution, sugar solution, salt solution

2. Cut blue litmus paper into small pieces and spread on a clean white tile

3. Using a dropper, put one drop of each sample on the litmus pieces

4. Observe and record colour changes in a table

5. Repeat the same process with red litmus paper pieces

6. Record all observations

**Key Observations**:

**Group A** (Turn blue litmus to red) = **ACIDIC** substances

Examples: Lemon juice, amla juice, tamarind water, vinegar

**Group B** (Turn red litmus to blue) = **BASIC** (or alkaline) substances

Examples: Soap solution, baking soda solution, lime water, washing powder solution

**Group C** (No colour change) = **NEUTRAL** substances

Examples: Tap water, sugar solution, salt solution

**Definition of Three Types**:

**Acidic substances**: Turn blue litmus paper to red. Taste sour. Examples: citric acid (lemon, tamarind), tartaric acid (grapes), ascorbic acid/Vitamin C (amla), oxalic acid (spinach)

**Basic substances**: Turn red litmus paper to blue. Feel soapy/slippery when rubbed. Taste bitter (but not all bitter things are basic). Examples: baking soda, lime water, soap

**Neutral substances**: Do not change the colour of either blue or red litmus paper. Neither acidic nor basic.

**Important Notes**:

**Acid-base indicator** = Any substance that shows different colours in acidic and basic solutions

Common edible acidic substances and their acids:

Lemon: Citric acid

Curd: Lactic acid

Tamarind: Tartaric acid

Vinegar: Acetic acid

Grapes: Tartaric acid

Amla: Ascorbic acid (Vitamin C) and Citric acid

**How to Prepare Lime Water** (Important!):

Lime (chuna/calcium oxide) + Water = Lime water (calcium hydroxide solution)

Leave undisturbed for about 1 hour

Filter the liquid before use

NOTE: Do not confuse with the fruit "lime" (nimbu)

2.1.2 RED ROSE AS AN INDICATOR

**Why use flowers as indicators?**

Natural indicators are readily available in the environment

Can be prepared easily at home

Activity 2.3: Preparing Red Rose Extract

**Procedure**:

1. Collect fallen red rose petals (do not pluck flowers from plants)

2. Wash the petals with water

3. Crush the petals using a mortar and pestle to break them down

4. Place crushed petals in a glass tumbler

5. Pour hot water (under adult supervision) until petals are completely immersed

6. Cover the glass tumbler with a lid

7. Wait 5-10 minutes until water becomes coloured

8. Filter the liquid to get the **flower extract** (called filtrate)

9. This coloured extract is used as an acid-base indicator

**Diagram to Draw**:

Test tube stand with test tube containing red/pink coloured liquid (red rose extract)

Labels: Test tube, Test tube stand, Red rose extract

Activity 2.4: Testing with Red Rose Extract

**Procedure**:

1. Pour 10-20 drops of red rose extract into two small transparent bottles (A and B)

2. Add 20-30 drops of lemon juice to bottle A

3. Add 20-30 drops of soap solution to bottle B

4. Observe colour changes

5. Test other samples and record observations in a table

**Key Observations**:

**Red rose extract + Acidic substances (e.g., lemon juice)** = **Red/Pink colour**

**Red rose extract + Basic substances (e.g., soap solution)** = **Green/Yellow-green colour**

**Red rose extract + Neutral substances** = **No change** (remains original colour)

**Comparison with Litmus**:

Red rose extract gives the same grouping as blue and red litmus papers

Acidic substances in Group A turn rose extract red

Basic substances in Group B turn rose extract green

Neutral substances in Group C show no colour change

**Other Natural Indicators**:

You can also use extracts from:

Purple cabbage (turns different colours in different pH)

Beetroot

Turmeric

Indian blackberry (jamun)

Red hibiscus (gudhal) flowers

All can act as acid-base indicators

**Fascinating Fact - Hydrangea Flowers**:

Plant that grows in Himalayan region and North-eastern states

**Acidic soil** → Blue-coloured flowers

**Basic soil** → Pink or red-coloured flowers

Gardeners can change flower colours by adjusting soil acidity/basicity

2.1.3 TURMERIC AS AN INDICATOR

Activity 2.5: Preparing Turmeric Paper

**Procedure**:

1. Take a spoonful of turmeric (haldi) powder in a petri dish or container

2. Add a little water to make a yellow paste (or grind fresh turmeric)

3. Under adult supervision, carefully dip filter paper in turmeric paste until it gets yellow colour

4. Take it out and allow it to dry completely

5. Cut this yellow paper into thin strips called **turmeric paper**

6. Store for use as an indicator

**Diagram to Draw**:

(a) Petri dish with yellow turmeric paste

(b) Yellow strips of turmeric paper

Labels: Turmeric paste, Turmeric paper strips

Activity 2.6: Testing with Turmeric Paper

**Procedure**:

1. Put a drop of each sample on separate pieces of turmeric paper using a dropper

2. Record observations in a table for each sample

3. Note colour changes

4. Group samples and compare with Groups A, B, and C from litmus testing

**Key Observations**:

**Turmeric paper + Acidic substances** = **No colour change** (remains yellow)

**Turmeric paper + Basic substances** = **Colour changes from yellow to RED/BROWN/ORANGE**

**Turmeric paper + Neutral substances** = **No colour change** (remains yellow)

**Important Limitations of Turmeric Paper**:

Can be used to test **basic substances only**

**Cannot differentiate between acidic and neutral substances** (both show no colour change)

Therefore, it is not a complete acid-base indicator like litmus or red rose extract

**Fascinating Fact - Why is Turmeric Called the 'Golden Spice'?**

Member of the ginger family

Grown in India and other countries

Used as a common spice in Indian households

In Ayurvedic medicine, considered to have numerous health benefits

Used in traditional home remedies

Being researched for applications beyond taste and colour

**Creative Application - Greeting Card**:

Ashwin applied turmeric paste on white paper and dried it

To write a hidden message visible only when basic solution is applied

Could use soap solution or baking soda solution to write

Message appears in red colour on yellow background

Shows creative application of acid-base chemistry

2.1.4 OLFACTORY INDICATORS (SMELL INDICATORS)

**What are Olfactory Indicators?**

Substances whose **odour changes when mixed with acidic or basic substances**

"Olfactory" = related to sense of smell

Natural indicators that work through smell instead of colour

Activity 2.6: Investigating Olfactory Indicators

**Procedure**:

1. Take finely chopped onions in a container with clean cotton cloth or filter paper strips

2. Tightly close the container and leave overnight

3. The onion odour gets absorbed by the cloth strips

4. Take two strips and check their odour

5. Put a few drops of tamarind water (acidic) on one strip

6. Put a few drops of baking soda solution (basic) on the other strip

7. Allow drops to spread on the strips

8. Check the odour again after some time

9. Record observations of odour change

10. Repeat with other acidic and basic substances

**Key Observations**:

**With acidic substances**: Onion odour becomes **more pungent/sharper**

**With basic substances**: Onion odour becomes **milder/less sharp** or changes character

**With neutral substances**: Odour may remain unchanged

**Biological Explanation**:

Onion contains volatile sulphur compounds that give it strong smell

These compounds react differently with acids and bases

This changes how they smell to our nose

**Note on Scientist**: **Acharya Prafulla Chandra Ray (P.C. Ray)**

Known as the **'Father of Modern Indian Chemistry'**

Earned doctorate in chemistry from the United Kingdom

Returned to India and advanced scientific research

Established India's **first pharmaceutical company in 1901** (for medicines)

Was rooted in Indian culture and knowledge traditions

Through writings on history of chemistry in India, highlighted achievements of ancient Indian scientists

Advocated use of mother tongue as medium of instruction in educational institutions

Was both a scientist and social reformer

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2.2 WHAT HAPPENS WHEN ACIDIC SUBSTANCES MIX WITH BASIC SUBSTANCES?

Activity 2.7: The Neutralisation Experiment

**Procedure**:

1. Take one drop of lemon juice in a test tube

2. Add around 20 drops of water to dilute it

3. Observe the colour

4. Add a drop of blue litmus solution to the diluted lemon juice

5. Observe: The solution turns **RED** (showing it's acidic)

6. Slowly add drops of lime water using a dropper while swirling well

7. Continue adding lime water drop by drop

8. Observe: Gradually the red colour fades and eventually turns **BLUE**

9. The solution is no longer acidic

10. Add one more drop of lemon juice and observe what happens

11. Record all colour changes

**Diagram to Draw**:

Test tube with red solution after adding blue litmus to lemon juice (Fig. 2.10a)

Test tube showing gradual colour change from red to blue after adding lime water (Fig. 2.10b)

Labels: Lemon juice solution, Blue litmus solution, Lime water, Colour change sequence

What is NEUTRALISATION?

**Definition**: When a solution of an **acid** is mixed with a solution of a **base** in sufficient quantity, the resulting solution is **neither acidic nor basic**. This process is called **neutralisation reaction**.

**Chemical Equation**:

**Acid + Base → Salt + Water + Heat**

**Key Points About Neutralisation**:

1. Acid and base cancel each other's effects

2. Products formed: **Salt** and **Water**

3. **Heat is evolved** (released) in this process (exothermic reaction)

4. The resulting solution becomes neutral (pH = 7)

5. Litmus paper shows no colour change in the final neutral solution

**Example from Activity 2.7**:

Lemon juice (acid) + Lime water (base) → Salt (calcium citrate) + Water + Heat

Initial solution: Red (acidic)

Final solution: Blue changes back to purple/neutral when more acid is added (showing the balance point)

**Important Concept**:

Neutralisation is not just a colour change

It's a **chemical reaction** where the properties of both acid and base are destroyed

The resulting salt has properties different from both the original acid and base

Heat is released, showing chemical change is occurring

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2.3 NEUTRALISATION IN DAILY LIFE

**Real-Life Applications of Neutralisation Reactions**:

Situation 1: Treatment of Ant Bites

**Problem**:

Red ants inject an **acidic liquid called formic acid** into the skin when they bite

This causes stinging pain and redness

**Solution**:

Apply **moist baking soda** (which is basic/alkaline) to the affected area

The base (baking soda) neutralises the acid (formic acid) injected by the ant

**Acid (formic acid) + Base (baking soda) → Salt + Water + Heat**

Pain and redness are relieved

**Chemical Explanation**:

Formic acid causes the burning sensation

Baking soda is basic in nature

When mixed, they form calcium salt and water

The neutralisation reaction relieves the pain

**Indian Context**:

In many Indian regions, different remedies are used:

Some apply toothpaste (which is basic)

Some use paste of flour and water

Some use lime paste

Ask students what remedies are used in their region

Situation 2: Treating Acidic Soil

**Problem**:

Farmers use chemical fertilisers to help plants grow

Excessive use of chemical fertilisers makes the **soil too acidic**

Acidic soil: Plants cannot absorb nutrients properly, so they don't grow well

**Solution - When Soil is Acidic**:

Add **lime (chuna)**, which is **basic/alkaline in nature**

**Acid (in soil) + Base (lime) → Salt + Water + Heat**

This neutralises the soil, making it suitable for plant growth

Lime is calcium oxide (CaO), when mixed with water becomes calcium hydroxide, which is basic

**Solution - When Soil is Basic**:

If soil becomes too basic, add **organic matter** like:

Manure

Composted leaves

Decomposed plant matter

Organic matter releases **acids that neutralise the basic soil**

**Acid (from organic matter) + Base (in soil) → Salt + Water + Heat**

**Solution - When Soil is Neutral but Plants Still Unhealthy**:

The problem may be **nutrient deficiency**

Add fertilisers containing required nutrients (nitrogen, phosphorus, potassium)

Not an acid-base problem, but a nutritional problem

**Indian Agricultural Context**:

This is a common problem in Indian farming

The **Farmer's Portal** (online platform from Department of Agriculture, Cooperation and Farmers Welfare) provides such guidance

Soil testing is important before deciding what to add

Different crops prefer different soil pH levels

Situation 3: Treating Industrial Waste

**Problem**:

Factories release industrial waste into lakes and rivers

Fish population in the lake near industrial areas is declining

Factory waste may contain **acidic substances** (from chemical manufacturing, metal processing, etc.)

Acidic waste changes the pH of water, making it unsuitable for aquatic life

Fish cannot survive in water that is too acidic

**Solution**:

Before releasing factory waste into the lake, treat it with **basic substances**

**Acid (in factory waste) + Base (added substance) → Salt + Water + Heat**

This neutralises the acidic waste

The water becomes neutral or slightly basic, suitable for aquatic life

Common basic substances used:

Lime (calcium oxide)

Calcium hydroxide

Sodium hydroxide (caustic soda)

**Environmental Protection**:

This is part of **environmental conservation**

Factories must follow government regulations about waste treatment

Protecting water bodies ensures survival of fish and other aquatic organisms

Protects the livelihood of fishermen and communities depending on fishing

**Indian Context**:

Many lakes in India near industrial areas face such pollution

Government regulations require industries to treat waste before disposal

Water pollution control boards monitor factory waste

Students should be aware of environmental responsibility

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SUMMARY OF INDICATORS AND THEIR BEHAVIOUR

Table: Comparison of Different Indicators

| Indicator | Acidic Substances | Basic Substances | Neutral Substances |

|-----------|------------------|-----------------|-------------------|

| **Blue Litmus Paper** | Turns RED | No change | No change |

| **Red Litmus Paper** | No change | Turns BLUE | No change |

| **Red Rose Extract** | RED/PINK colour | GREEN/YELLOW-GREEN colour | No colour change |

| **Turmeric Paper** | No change (yellow) | Turns RED/BROWN/ORANGE | No change (yellow) |

| **Turmeric Extract** | No change (yellow) | Turns RED/BROWN | No change |

| **Olfactory Indicators (Onion)** | Odour becomes sharper/pungent | Odour becomes milder | Odour unchanged |

Important Characteristics

**Acidic Substances**:

Turn blue litmus to red

Turn red rose extract red/pink

Taste **sour** (but don't taste unknown substances)

Examples: Lemon juice, vinegar, tamarind water, amla juice

Contain acids like citric acid, acetic acid, tartaric acid, ascorbic acid

**Basic Substances**:

Turn red litmus to blue

Turn red rose extract green

Turn turmeric yellow paper to red/brown

Feel **soapy or slippery** to touch when rubbed between fingers

Taste **bitter** (but not all bitter things are basic)

Examples: Soap solution, baking soda solution, lime water, washing powder solution

**Neutral Substances**:

Do not change colour of blue or red litmus paper

Do not change colour of red rose extract

Do not change colour of turmeric paper

Neither acidic nor basic properties

Examples: Tap water, sugar solution, salt solution, pure distilled water

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ANSWERS TO THE OPENING QUESTION

**Why did words appear on the paper at the science fair?**

The words 'Welcome to the Wonderful World of Science' appeared because of the use of **acid-base indicators**.

**Possible Explanation**:

1. The white sheet of paper was treated with a **turmeric solution** (yellow colour)

2. The liquid sprayed on it was a **basic substance** like soap solution or baking soda solution

3. When the basic solution touched the turmeric-treated paper, it turned **red/brown/orange**

4. The letters of the message written with the basic substance would show up in the colour change

5. Where the basic solution was applied, the yellow turmeric turned red, revealing the message

**Alternative Explanation**:

The paper could have been treated with red rose extract (pink colour)

The sprayed liquid could be acidic (like lemon juice)

The message would then appear in red colour where the acid touched the pink rose extract

**Key Concept**: This demonstrates the practical and creative use of acid-base indicators in everyday life.

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IN A NUTSHELL (CHAPTER SUMMARY)

1. **Classification of Substances**: All substances can be classified as:

**Acidic** (turn blue litmus red, taste sour)

**Basic** (turn red litmus blue, feel soapy, taste bitter)

**Neutral** (no effect on litmus paper)

2. **Indicators**: Substances that show different colours in acidic and basic solutions

**Natural indicators**: Litmus (from lichens), red rose, purple cabbage, turmeric, jamun, hibiscus

**Synthetic indicators**: Made in laboratories (studied in higher grades)

3. **Litmus Paper**:

**Blue litmus paper**: Turns red in acidic solutions

**Red litmus paper**: Turns blue in basic solutions

4. **Red Rose Extract**:

**Red/Pink colour** in acidic solutions

**Green/Yellow-green colour** in basic solutions

5. **Turmeric Indicator**:

**Yellow colour remains yellow** in acidic and neutral solutions

**Yellow colour turns red/brown/orange** in basic solutions

Cannot distinguish between acidic and neutral

6. **Olfactory Indicators**:

Substances whose odour changes with acids or bases

Example: Onion strips (smell becomes sharper with acids, milder with bases)

7. **Neutralisation Reaction**:

**Acid + Base → Salt + Water + Heat**

When acidic and basic substances mix in right proportions, they form a neutral solution

Heat is released in the process

8. **Real-Life Applications**:

**Ant bites**: Acidic formic acid neutralised by basic baking soda

**Acidic soil**: Neutralised by adding lime (base)

**Basic soil**: Neutralised by adding organic matter (contains acids)

**Industrial waste**: Acidic waste neutralised before release into water bodies

**Medical treatment**: Antacids (basic) neutralise excess stomach acid

9. **Properties of Acids and Bases** (without going into deep chemistry):

Acids: Sour taste, turn blue litmus red

Bases: Soapy feel, bitter taste, turn red litmus blue

Neutral: Neither acidic nor basic properties

10. **Environmental Significance**:

Understanding acid-base chemistry helps protect environment

Proper soil management ensures good crop production

Treating industrial waste protects water bodies and aquatic life

pH balance is important for ecosystems to function properly

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KEY TERMS TO REMEMBER

**Indicator**: A substance that changes colour to show if something is acidic, basic, or neutral

**Acid**: A substance that tastes sour and turns blue litmus paper red

**Base** (or Alkaline): A substance that feels soapy and turns red litmus paper blue

**Neutral**: A substance that is neither acidic nor basic

**Litmus**: A natural indicator obtained from lichens

**Acidic**: Having the properties of an acid (pH < 7)

**Basic**: Having the properties of a base (pH > 7)

**Filtrate**: The liquid obtained after filtering a mixture

**Neutralisation**: The reaction in which an acid and base combine to form salt and water

**Salt**: A compound formed when an acid reacts with a base

**Olfactory indicator**: A substance whose smell changes in acidic or basic solutions

**pH**: Measurement of how acidic or basic a substance is (0-14 scale; 7 = neutral)

**Lime water**: Solution of calcium hydroxide in water

**Turmeric paper**: Filter paper dipped in turmeric paste, used to test for bases

**Lichens**: Living organisms formed by association of fungus and alga

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IMPORTANT FACTS FOR EXAMS

1. **Litmus is the most reliable indicator** because it works for both acids and bases

2. **Red rose extract is better than turmeric paper** because it can detect both acids and bases, while turmeric paper can only detect bases

3. **Neutralisation produces heat** (exothermic reaction) — this is important

4. **Common acids in food items**:

Citric acid: Lemon, tamarind, amla, grapes

Acetic acid: Vinegar

Lactic acid: Curd, buttermilk

Tartaric acid: Grapes, tamarind

5. **Common bases**:

Baking soda (sodium bicarbonate)

Soap solution

Lime water (calcium hydroxide)

Washing powder solution

6. **Practical application**: Using the right indicator for the right purpose

Litmus/Rose extract: For general testing

Turmeric paper: When you only need to detect bases

Olfactory indicators: When colour is not visible or as an alternative method