Chemistry Quiz 6

Radioactive disintegration of uranium ultimately results in formation of lead. The half-life of uranium-238 is 4.5 billion years. It decays into radium-226, which in turn decays into radon-222. Radon-222 becomes polonium-210, which finally decays into a stable nuclide, lead.

In a lead-acid battery, the cathode is made of lead dioxide, and the anode is made of metallic lead. The two electrodes are separated by an electrolyte of sulfuric acid.

Peroxyacetyl nitrate is a secondary pollutant present in photochemical smog. It is thermally unstable and decomposes into peroxyethanoyl radicals and nitrogen dioxide gas. It is a lachrymatory substance, meaning that it irritates the lungs and eyes.

The main gases responsible for the greenhouse effect include water vapor, carbon dioxide, methane, nitrous oxide, and water vapor (which all occur naturally), and fluorinated gases (which are synthetic) chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, bromofluorocarbons (halons), perfluorcarbons, nitrogen trifluoride, and sulphur hexafluoride.

Oxyacetylene flame is commonly known as gas welding. It is a process which relies on combustion of oxygen and acetylene. When mixed together in correct proportions within a hand-held torch or blowpipe, a relatively hot flame is produced with a temperature of about 3200°C.

Heavy water (D₂O) is water that contains heavy hydrogen - also known as deuterium - in place of regular hydrogen. The boiling point of heavy water (101.4°C ) is higher than that of ordinary water (100°C). The density of heavy water (1.11 g/cm³) is higher than that of ordinary water (1.00 g/cm³). The freezing point of heavy water (3.8°C) is higher than that of ordinary water (0°C).

Silver halides are used in photographic plates because they are reduced by light. Silver halides are photosensitive as they react with light to form the image. A silver halide is a compound of silver and a halogen; for example, silver bromide (AgBr), silver chloride (AgCl), silver fluoride (AgF), and silver iodide (AgI).

Water can lie separated from alcohol-water mixture by fractional distillation. This technique relies on the fact that the compounds in the mixture have different boiling points. Since ethanol boils at a lower temperature (78.5°C) than water, the alcohol vaporizes while most of the water remains a liquid.

The ratio of pure gold in 18-carat gold is 75 percent. 'Caratage' is the measurement of purity of gold alloyed with other metals. 24 carat is pure gold with no other metals. Lower caratages contain less gold; 18-carat gold contains 75 percent gold and 25 percent other metals, often copper or silver.

Brass is a metal alloy primarily composed of copper and zinc. The composition of brass is generally 67% copper and 37% zinc. By varying the amount of copper and zinc, brass can be made harder or softer.