What Are Chemical Properties?
Chemical Property
A chemical property tells how a substance reacts to create new substances. It contrasts with a physical property, which can be seen without altering the substance’s identity. Carbon compounds display their chemical properties in reactions like combustion, oxidation, addition and substitution.
Remember: chemical ≠ physical — one changes composition, the other doesn’t.
Source: NCERT Class 10 Science
Combustion Reaction
Combustion
A carbon compound rapidly combines with oxygen, releasing heat and light to form carbon dioxide and water.
Key Characteristics:
- Needs excess \(O_2\)
- Highly exothermic—gives heat & light
- Products: \(CO_2\) and \(H_2O\)
Example:
\( \text{Hydrocarbon} + O_2 \rightarrow CO_2 + H_2O + \text{energy} \)
Complete vs Incomplete Combustion
Blue flame = complete; yellow, sooty flame = incomplete; lime-water test confirms CO₂.
Oxygen supply decides flame colour and products
Complete combustion: hydrocarbon burns with plenty of O₂, giving a clean blue flame and only CO₂ + H₂O.
Incomplete combustion: limited O₂ causes a yellow luminous flame, forming toxic CO and black carbon soot.
Key Points:
- Blue, non-luminous flame + clear glassware → complete combustion observed.
- Yellow flame, soot deposit, possible CO detector alert → incomplete combustion.
- Bubble exhaust through lime water; milky precipitate confirms CO₂ from complete combustion.
Oxidation Reaction
Oxidation
In carbon compounds, oxidation means adding oxygen or removing hydrogen from the molecule, usually using a strong oxidising agent.
Key Characteristics:
- Alkaline KMnO₄ (purple) supplies nascent oxygen.
- Acidified K₂Cr₂O₇ (orange) is another common oxidiser.
Example:
\( \mathrm{CH_3CH_2OH + [O] \rightarrow CH_3COOH + H_2O} \)
Oxidation of Ethanol to Ethanoic Acid
Follow these ethanol oxidation steps to obtain ethanoic acid using alkaline \( \mathrm{KMnO_4} \).
Prepare Alkaline Mixture
Mix ethanol with dilute NaOH and add alkaline \( \mathrm{KMnO_4} \) slowly until the purple colour just disappears.
Gentle Heating
Heat the solution gently in a water bath to provide energy without evaporating ethanol.
Oxidation Reaction
Under heat, \( \mathrm{KMnO_4} \) oxidises ethanol to acetaldehyde and finally to ethanoic acid.
End-Point Observation
Persistent pale pink shows excess oxidant; stop heating and cool to collect ethanoic acid.
Pro Tip:
Always keep the mixture alkaline; acidic conditions reduce \( \mathrm{KMnO_4} \) before full oxidation occurs.
Addition Reaction
Addition Reaction
Two atoms or groups add across a carbon-carbon multiple bond, converting an unsaturated hydrocarbon into a saturated one.
Key Characteristics:
- Needs a C=C or C≡C multiple bond.
- Reactants join; no by-product is released.
- Product becomes a saturated hydrocarbon.
Example:
CH2=CH2 + H2 → CH3–CH3 (hydrogenation of ethene).
Hydrogenation of Vegetable Oil
Hydrogen gas + nickel converts liquid oil to solid fat.
Addition Reaction in Daily Life
Unsaturated vegetable oils contain C=C bonds that undergo hydrogenation, an addition reaction.
Industrially, hot oil is treated with hydrogen under pressure; finely divided nickel catalyses its conversion into semi-solid ghee or margarine.
Key Points:
- Industrial application: large-scale production of ghee and margarine.
- Nickel catalyst speeds the addition of H₂ and is recovered for reuse.
- Shows how chemical addition reactions impact everyday food.