Tag: science & technology

Brass (an alloy of copper and zinc) discolours in air due to reaction with hydrogen sulphide, forming a dark layer of copper sulphide on the surface. Oxygen, carbon dioxide, and nitrogen do not cause this discolouration. This is a common chemistry phenomenon observed in brass objects.

Bromine is the only non-metal that exists as a liquid at room temperature (25°C). It has a melting point of -7.2°C and boiling point of 58.8°C. Phosphorous and chlorine are non-metals but are solids and gases respectively at room temperature. Helium is a noble gas.

Chlorophyll is a chelate compound where magnesium is the central metal ion, coordinated to a porphyrin ring. This is similar to heme in blood where iron is the central metal. Copper, iron, and calcium are not the central metal in chlorophyll.

Graphite is used in pencil cores mixed with clay - the material we call pencil 'lead' contains no actual lead. Charcoal is used in charcoal pencils but not standard writing pencils. Silicon and phosphorus have no role in pencil manufacturing.

Mercury is the only metal liquid at room temperature and uniquely forms alloys called amalgams with most other metals. Amalgams have been used in dentistry and gold extraction. Tin, lead and zinc are solid metals that don't form amalgams in the same way.

Water's chemical formula is H2O, meaning two hydrogen atoms bonded to one oxygen atom. NaAlO2 is sodium aluminate, Al2O3 is aluminum oxide, and CaSiO3 is calcium silicate - none of these represent water.

Nitrogen gas is filled in electric bulbs because it is inert and prevents the filament from oxidizing at high temperatures. Hydrogen is reactive and would damage the filament. Oxygen would cause burning and carbon dioxide is not used for this purpose.

Washing soda is sodium carbonate decahydrate (Na2CO3·10H2O), used in washing and water softening. Calcium bicarbonate and calcium carbonate are different compounds. Sodium bicarbonate is baking soda, not washing soda.

Quartz is crystalline silicon dioxide (SiO2), the most abundant mineral in Earth's crust. It is piezoelectric, making it ideal for oscillating in quartz clocks. Germanium oxide and sodium silicate are chemically different substances.

Hydrogen is not classified as a greenhouse gas because it doesn't absorb infrared radiation in the atmospheric window. Methane, nitrous oxide and carbon dioxide are all well-known greenhouse gases that trap heat in Earth's atmosphere.