Have you ever thought about what happens when you put an eggshell into nitric acid? This is a chemistry experiment that you often see in JEE questions about acids, bases and salts.
As someone who wants to ace the JEE Main Exam, knowing these reactions can get you marks in physical chemistry when it comes to acids, bases and salts and especially in JEE questions, about acids, bases and salts.
Eggshell Composition Basics
Egg shells aren’t just trash; they’re mostly calcium carbonate, or CaCO₃, about 95% of their makeup. That’s the key player here.
Calcium carbonate behaves as a basic salt because the carbonate ion reacts with acids. In JEE, remember CaCO₃ shows up in chapters on acids reacting with carbonates.
Farmers even grind shells for soil to neutralise acidity, but for us, it’s pure exam gold.
Nitric Acid Properties Quick Look
Nitric acid, HNO3, is a strong acid, fully dissociating in water to give H+ and NO₃- ions. It’s corrosive and oxidising, but in this reaction, it’s the acidity that drives things.
In JEE Main, questions often test strong acids like HNO₃, HCl, or H₂SO₄ versus weak ones. HNO₃ completely ionises in water, producing a highly acidic solution with low pH.
Handle it with gloves; real lab safety matters for practicals too.
The Chemical Reaction Step-by-Step
Drop crushed eggshell into dilute nitric acid, and watch bubbles form fast. That’s CO₂ gas escaping, causing brisk effervescence.
The balanced equation is straightforward:
CaCO₃ + 2HNO₃ → Ca(NO₃)₂ +CO₂ + H₂O
Calcium carbonate from the shell swaps with hydrogen ions, forming soluble calcium nitrate, water, and gas.
This is primarily an acid–carbonate reaction producing salt, water, and carbon dioxide. Carbonic acid (H₂CO₃) forms momentarily and decomposes into CO₂ and H₂O.
The shell dissolves slowly as CaCO₃ reacts away, leaving a clear solution if excess acid.
Observation in Lab and Why It Matters
First sign? Fizzing like a soda bottle shaken up. Pass the gas through limewater; it turns milky due to the formation of CaCO₃ precipitate. Classic test for CO₂ in JEE syllabi.
Solution heats a bit, an exothermic reaction. Color? Nitric acid might tint yellow, but products stay colourless.
For JEE preparation, sketch this: solid dissolving, gas evolving. Questions ask “brisk effervescence due to?” Answer: CO₂ from carbonate-acid reaction.
Reaction Type for JEE Scoring
This is an acid-carbonate reaction, under double displacement or neutralisation broadly. Carbonate + acid always gives salt, water, and CO₂.
In the acids, bases, and salts chapter (Class 10 base, but JEE revisits), it’s decomposition too for unstable H₂CO₃.
Compare with HCl: same products except CaCl₂. HNO₃ is specific because nitrate is soluble, no ppt. JEE twists: Concentrated nitric acid is a strong oxidising agent and may produce nitrogen oxides (NO₂) instead of behaving only as a simple acid.
JEE Exam Relevance Deep Dive
Similar questions are frequently asked in JEE Main and NCERT-based MCQs: “Eggshell + dil acid observes?” Options: effervescence, no reaction, etc. Straight from NCERT.
Net ionic skips spectators.
CaCO3(s)+2H+(aq)→Ca2+(aq)+CO2(g)+H2O(l)
Links to p-block (carbonates), coordination (nitrates). PYQs test observation, equation, gas test. Search “acids, bases, salts JEE PYQ” for mocks.
Chapter weightage: 4-5% in Main, builds for equilibrium (solubility).
Real-World Ties for Better Recall
Calcium nitrate from this? Fertiliser boosts plant calcium and nitrogen. Eggshell waste is recycled industrially.
Caveats: use dilute acid; conc HNO₃ is violent, brown NOx gases. JEE practicals stress dilution.
Eco angle: ocean acidification dissolves shells like this, harming marine life. Ties to current affairs MCQs.
Safety and Lab Hacks
Wear goggles and gloves; acid splashes burn. Do in a fume hood if conc. Neutralise waste with base.
Hack: Crush the shell fine for faster reaction. Test CO₂ with a burning splint? No, but limewater, yes.
For home demo, vinegar on the shell is safer, same idea minus nitrate.
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