CBSE Class 10 Chemistry Carbon and its Compounds Notes Set 03

Chemical Properties of Carbon Compounds

1. Combustion: carbon compounds burn in air to give carbon dioxide, water, heat and light. \( \ce{CH4 + 2O2 -> CO2 + 2H2O} \). Saturated hydrocarbons burn with a clean blue flame, unsaturated ones with a yellow sooty flame.
2. Oxidation: alkaline \( \ce{KMnO4} \) or acidified \( \ce{K2Cr2O7} \) oxidises ethanol to ethanoic acid.
3. Addition: unsaturated hydrocarbons add hydrogen in the presence of nickel or palladium. \( \ce{CH2=CH2 + H2 -> CH3-CH3} \). This is how vegetable oils are hydrogenated.
4. Substitution: alkanes react with chlorine in sunlight, replacing hydrogen atoms one by one. \( \ce{CH4 + Cl2 -> CH3Cl + HCl} \).

Ethanol and Ethanoic Acid

Pure ethanoic acid freezes at about 290 K and is called glacial acetic acid. A 5 to 8 percent solution in water is vinegar. Esters on heating with an alkali give back the alcohol and the sodium salt of the acid, which is called saponification and is the way soap is made from fats.

Soaps and Hard Water

1. Soap is a sodium or potassium salt of a long chain fatty acid. Its molecule has a water-loving head and a hydrocarbon tail that dissolves in oil, so it removes grease by forming micelles.
2. Hard water contains calcium and magnesium salts. Soap forms scum with such water, so more soap is needed.
3. Detergents are sodium salts of sulphonic acids and give lather even in hard water.