Chemistry Quiz 3

Oxygen is the most abundant element in the human body accounting for approximately 65% of a person's mass. Each water molecule consists of two hydrogen atoms bonded to one oxygen atom, but the mass of each oxygen atom is much higher than the combined mass of the hydrogen.

Plaster of Paris ((CaSO₄) H₂O) is made by partial dehydration of gypsum salt. Plaster of Paris is prepared by heating calcium sulphate dihydrate, or gypsum, to 120–180°C. With an additive to retard the set, it is called wall, or hard wall, plaster, which can provide passive fire protection for interior surfaces.

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.

Biological oxygen demand (BOD) generally represents how much oxygen is needed to break down organic matter in water. Clean water has BOD which is less than 5 ppm.

Copper sulphate (CuSO₄) is used for destroying Fungi in water tanks. It can kill bacteria, algae, roots, plants, snails and fungi.

Hydrogen peroxide (H₂O₂) is water (H₂O) with an extra oxygen molecule. H₂O₂ contains a single oxygen-oxygen bond. When its oxygen-oxygen bond breaks, hydrogen peroxide decomposes into water and oxygen.

Nucleus of an atom consists of protons and neutrons. The atom consists of a tiny nucleus surrounded by moving electrons. The nucleus contains protons, which have a positive charge equal in magnitude to the electron's negative charge. The nucleus may also contain neutrons, which have virtually the same mass but no charge.

Solar technologies convert sunlight into electrical energy either through photovoltaic (PV) panels or through mirrors that concentrate solar radiation. Silicon is the most common semiconductor material used in photovoltaic panels.

The bleaching of Sulphur dioxide (SO₂) is mainly due to its reduction property and its temporary reaction as soon as it gains the required oxygen helps to regenerate its initial property.

German Silver is an alloy of copper (60%), zinc (20%) and nickel (20%). It is used for making daily utensils and jewellery.