Practice MCQ Questions and answers on Chemistry-GK

CaSO₄.2H₂O (Gypsum) is added to cement clinker to retard setting action of cement.

Stalactites and stalagmites are formed by water dripping or flowing from fractures on the ceiling of a cave. The dominant mineral in them is calcite (calcium carbonate) or CaCaO₃. Their largest displays are formed in caves of limestone and dolomite. Other minerals that may be deposited include other carbonates, opal, chalcedony, limonite, and some sulfides.

A pearl is a hard object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of a clam, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls (baroque pearls) occur. The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries, and because of this, the word pearl has become a metaphor for something very rare, fine, admirable, and valuable.

Seventy percent of bone consists of hydroxyapatite, a calcium phosphate mineral (known as bone mineral). Tooth enamel is composed of almost ninety percent hydroxylapatite.

Baryllium sulfate (BeSO₄) is a white crystalline solid. It was first isolated in 1815 by Jons Jakob Berzelius. Beryllium sulfate may be prepared by treating an aqueous solution of any beryllium salt with sulfuric acid, followed by evaporation of the solution and crystallization. The hydrated product may be converted to anhydrous salt by heating at 400°C. Baryllium Sulphate is less soluble in water due to High inflammable energy.

Sodium Nitrate (NaNO₃) is also known as Chile saltpeter or Peru saltpeter (due to the large deposits found in the Atacama desert in these countries) to distinguish it from ordinary saltpeter, potassium nitrate. Also known as soda niter, it is used in the production of fertilizers, pyrotechnics and smoke bombs, glass and pottery enamels, food preservatives, and solid rocket propellant.

The setting of plaster of Paris takes place by hydration due to the formation of a solid crystalline hydrate and hardening of Plaster of Paris is hydration reaction, which is reverse of the dehydration of gypsum. Plaster of Paris quickly sets to a hard mass when made into a thin paste with water. A slight expansion takes place in the process and heat is evolved. This process is exothermic.

Slaked lime is the odd one.

Plaster of Paris is the common name of Calcium Sulphate hemihydrate, with chemical formula: CaSO₄.1/2H₂O. Plaster of Paris is produced by heating gypsum to about 150°C.