ChemistryMediumClass 11

Carbon Compounds — CO, CO₂, carbonate reactions

p-block Elements (Class 11 — Groups 13 & 14)

JEE Qs

Hard

min

Focus on distinguishing properties and reactions of CO, CO₂, and carbonates under various conditions, especially thermal stability and reactions with acids/bases.

🧮 Key Formulas

C(s) + H₂O(g) --(1200°C)--> CO(g) + H₂(g) (Water gas)

2C(s) + O₂(g, limited) --> 2CO(g)

C(s) + O₂(g, excess) --> CO₂(g)

Fe₂O₃(s) + 3CO(g) --> 2Fe(s) + 3CO₂(g) (Reduction in blast furnace)

CO₂(g) + H₂O(l) <=> H₂CO₃(aq) (Carbonic acid formation)

CO₂(g) + Ca(OH)₂(aq) --> CaCO₃(s) + H₂O(l) (Limewater test, white ppt)

CaCO₃(s) + CO₂(g) + H₂O(l) --> Ca(HCO₃)₂(aq) (Soluble, temporary hardness)

MCO₃(s) --(Heat)--> MO(s) + CO₂(g) (Decomposition of carbonates)

MCO₃(s) + 2HX(aq) --> MX₂(aq) + H₂O(l) + CO₂(g) (Reaction with acids)

✅ Key Points for JEE

1Carbon monoxide (CO) is a colorless, odorless, highly toxic gas, acts as a strong reducing agent (due to high bond dissociation enthalpy of CO₂ formation), and is isoelectronic with N₂.
2Carbon dioxide (CO₂) is a colorless, odorless, non-toxic gas (at typical ambient concentrations), acidic in nature, dissolves in water to form carbonic acid (H₂CO₃), and has a linear structure with sp hybridization at carbon.
3The limewater test (CO₂ with Ca(OH)₂) produces a white precipitate of CaCO₃, which redissolves in excess CO₂ to form soluble Ca(HCO₃)₂.
4The thermal stability of metal carbonates generally increases down a group (e.g., Group 2 carbonates) and decreases with increasing polarizing power of the cation for transition metals.
5The structure of CO features a triple bond with one dative bond (C←O), making it polar, while CO₂ has two C=O double bonds and is non-polar due to its linear symmetric structure.

⚠️ Common Mistakes

✕Confusing the properties of CO (toxic, reducing, neutral oxide) with CO₂ (non-toxic, acidic oxide, non-reducing).
✕Incorrectly predicting the products of carbonate reactions, especially with excess CO₂ or prolonged heating.
✕Failing to understand the structural implications (hybridization, polarity) for CO and CO₂ and their respective chemical behaviors.

NCERT Chapters

Class 11 Chemistry Ch 11: The p-Block Elements (Groups 13 & 14)
Class 11 Chemistry Ch 4: Chemical Bonding and Molecular Structure