Chemistry MCQs with answers Page - 39

Liquid dishwashing detergents are of non-ionic type. Non-ionic detergents do not contain any ion in their constitution.

The German silver has long been in existence as it could be traced back to as far back as early 18th century. This Silver was developed in Germany by the German metalworkers in imitation of the Chinese alloys to be used as a substitute for silver since silver is highly expensive. The German silver is also known as the Nickel silver. These terms “German silver” and “Nickel silver” could be used interchangeably. It is a silver-white alloy of Copper, Zinc and Nickel. The German silver does not contain any trace of silver. The German silver is composed of three major elements Copper, Zinc and Nickel and sometimes with a trace of Tin and Lead. These elements vary in percentage with a range of Copper from approximately 50% – 61.6%, Zinc with an approximate range of 17.2& – 19% and Nickel with an approximate range of 21.1% – 30%. Theses compositions are always specified when it comes to commercial alloys. German silver is extensively used because of its hardness, toughness, and resistance to corrosion for articles such as tableware (commonly silver plated), marine fittings, and plumbing fixtures. Because of its high electrical resistance, it is used also in heating coils. It was discovered (early 19th cent.) by a German industrial chemist, E. A. Geitner.

Vulcanization is a chemical process that converts natural rubber and other polydiene elastomers into cross-linked polymers. The most common vulcanization agent is sulfur. It forms bridges between individual polymer molecules when heated with rubber. Often a catalyst and initiator are added to accelerate the vulcanization process. The cross-linked elastomers have many improved mechanical properties. In fact, unvulcanized rubber has poor mechanical properties and is not very durable. In order to give more strength and more elasticity, natural rubber is heated with sulphur or sulphur compounds at 150°C temperature. Vulcanized rubber has good tensile strength.