Practice MCQ Questions and answers on Chemistry-GK

Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates, the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO₂ shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass. Cement sets when mixed with water by way of a complex series of chemical reactions still only partly understood. The different constituents slowly crystallise and the interlocking of their crystals gives cement its strength. Carbon dioxide is slowly absorbed to convert the portlandite (Ca(OH)₂) into insoluble calcium carbonate. After the initial setting, immersion in warm water will speed up setting. Gypsum is added as an inhibitor to prevent flash setting.

Nitrogen (N₂) is most stable at room temperature.

Sodium metabisulphite is used as a preservative to protect processed food.

Chemical composition of cement is Limestone, Clay and Gypsum.

Nitrogen, phosphorus and potassium are the three most common bases of fertilizers. Potash can be used to make potassium (K) fertilizers. All commercial potash deposits come originally from marine deposits and are often buried deep in the earth.

Asbestos is formed of Calcium and Magnesium.

Baeyer's reagent is an alkaline solution of cold potassium permanganate of violet colour solution. It is a strong oxidizing agent. As this solution interacts with a double bond compound the colour disappears and becomes colourless.

Bone ash is a white material produced by the calcination of bones. It is primarily composed of calcium phosphate. It is commonly used in fertilizers, polishing compounds and in making ceramics such as bone china. It also has historical uses in the manufacture of baking powders and assay cupels.

Cements (e.g., Portland cement) harden because of hydration, chemical reactions that occur independently of the mixture’s water content; they can harden even underwater or when constantly exposed to wet weather. The chemical reaction that results when the anhydrous cement powder is mixed with water produces hydrates that are not watersoluble.

Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting, and can be easily manipulated with metal tools or even sandpaper. These characteristics make plaster suitable for a finishing, rather than a load-bearing material. The term plaster can refer to gypsum plaster (also known as plaster of Paris), lime plaster, or cement plaster. Plaster of Paris can be used to impregnate gauze bandages to make a sculpting material called modroc. It is used similarly to clay, as it is easily shaped when wet, yet sets into a resilient and lightweight structure.