Physical and chemical properties of carbon
Carbon is an odourless, tasteless, hard-to-melt solid that does not dissolve in water; diamond melts at about 3550 °C. Charcoal and other carbons show adsorption: they take up gases and dissolved substances on their surface; activated carbon, whose surface is enlarged with steam, is used in gas masks and for purifying water and oils, and the gas mask was created by N.D. Zelinsky. At ordinary temperature carbon is fairly inactive, but when heated it burns: C + O₂ → CO₂ (with little oxygen 2C + O₂ → 2CO) and gives CS₂ with sulfur: C + 2S → CS₂. With metals it forms carbides: Ca + 2C → CaC₂; CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂ (acetylene), Al₄C₃ + 12HCl → 4AlCl₃ + 3CH₄. Carbon is a strong reducing agent: 2CuO + C → 2Cu + CO₂↑, 2Fe₂O₃ + 3C → 4Fe + 3CO₂↑. In Uzbekistan coal (brown coal and hard coal) is mined at Angren, Sharg‘un and Boysun. Carbon monoxide CO formed when coal burns is extremely poisonous, so coal must never be burned in a closed room.
Observation (teacher demonstration only): the teacher shows adsorption with coloured water and an activated-carbon tablet (or filter). Students watch the colour fade and discuss why a larger carbon surface adsorbs better. Burning coal or experimenting with gases at home is forbidden.