Case Study:

In many Indian cities, old marble monuments and statues are slowly losing their smooth surface and natural shine. Environmental scientists observed that some buildings located near busy industrial areas developed rough patches and tiny holes over the last 15 years. During a survey near a historic marble structure, rainwater samples showed a pH value of 5.2, which is lower than normal rainwater.

If you’re finding it tricky to distinguish between these different chemical levels, check out our guide on how to easily identify acids, bases, and salts for some quick CBSE shortcuts.

Experts linked this change to acid rain formed due to pollutants like sulphur dioxide and nitrogen oxides released from factories and vehicles.

Marble mainly contains calcium carbonate (CaCO₃). When acid rain falls on the surface of marble, a chemical reaction takes place between the acids and calcium carbonate. This reaction slowly damages the stone and produces carbon dioxide gas, water, and soluble salts. Due to this process, the outer layer of the monument becomes weak and loses its polish over time.

Researchers also noticed that areas receiving more rainfall showed faster damage compared to drier regions. In one experiment, two marble samples were kept under different conditions. Sample A was sprayed with normal water for 30 days, while Sample B was sprayed with weak acidic water of pH 5.0. After one month, Sample B showed visible roughness and a small decrease in mass.

This investigation helped students understand how the reaction of acids with metal carbonates and metal hydrogen carbonates affects historical buildings in real life.

Want to see how these same reactions happen in your kitchen? Explore the science behind lemon juice and baking soda to see chemistry in action at home.

CASE-BASED QUESTIONS

 MCQ 

Q1. Why did the marble surface become rough after long exposure to acid rain?
A. Marble absorbed water and expanded
B. Acids reacted with calcium carbonate present in marble
C. Sunlight melted the outer layer of marble
D. Dust particles scratched the marble surface

Q2. Which gas is released when acids react with metal carbonates like calcium carbonate?
A. Oxygen
B. Hydrogen
C. Carbon dioxide
D. Nitrogen

 Assertion–Reason 

Q3. Assertion (A): Acid rain damages marble monuments over time.
Reason (R): Marble contains calcium carbonate which reacts with acids to form salts, water, and carbon dioxide.
A. Both A and R are true, and R is the correct explanation of A
B. Both A and R are true, but R is not the correct explanation of A
C. A is true, but R is false
D. A is false, but R is true

 Application-Based 

Q4. A student puts a few drops of dilute hydrochloric acid on marble chips and notices bubbles forming. What do these bubbles indicate?

Q5. Why were monuments in areas with higher rainfall damaged more quickly than monuments in dry regions?

 Data/Logic-Based 

Q6. Two marble samples were tested:

Based on the data, what conclusion can be drawn about the effect of acidic water on marble?

 Application + Reasoning 

Q7. If the pollution level around a marble monument decreases in the future, predict how it may affect the condition of the monument over time.

ANSWER KEY WITH EXPLANATION

A1. B. Acids reacted with the calcium carbonate present in marble
Explanation: Marble contains calcium carbonate. Acids present in acid rain react with it, causing slow erosion and roughness on the surface.

A2. C. Carbon dioxide
Explanation: When acids react with metal carbonates, carbon dioxide gas is released along with salt and water.

A3. A. Both A and R are true, and R is the correct explanation of A
Explanation: Calcium carbonate present in marble reacts chemically with acids present in acid rain, which damages the monument slowly.

A4. The bubbles indicate the release of carbon dioxide gas.
Explanation: Acids react with calcium carbonate in marble chips to produce carbon dioxide gas, causing bubbles.

A5. Higher rainfall increases the contact of acidic water with marble surfaces.
Explanation: More acidic rain means faster chemical reactions and greater damage to marble monuments.

A6. Acidic water reacts with marble and damages it gradually.
Explanation: The rough surface and decrease in mass show that acidic water chemically reacts with calcium carbonate.

A7. The rate of damage to the monument may decrease over time.
Explanation: Lower pollution means less acid rain formation, reducing chemical reactions with marble surfaces.

 Ready to test your knowledge further?  We've compiled the top 10 exam questions from Acids, Bases, and Salts with full solutions to help you ace your next test

 Practice Corner 
Mastering this topic requires practice. You can download our Class 10 Chemistry Worksheets to reinforce these concepts, or challenge yourself with our Solved and Unsolved Practice Papers designed specifically for the latest board pattern.

HOTS EXTENSION QUESTIONS

Q1. Suppose a protective coating is applied to marble monuments. How can this coating reduce damage caused by acid rain?

Q2. If pollution levels continue increasing for the next 20 years, predict how the appearance and strength of marble monuments may change.

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