The process in which metal surface is made inactive is called
passivation
galvanising
corrosion
pickling
Which among the following alloys is used in making instruments for electrical measurements?
Stainless steel
Manganin
Spiegeleisen
Duralumin
Name the metal that is purified by placing the impure metal on sloping hearth of a reverberatory furnace and heating that above its melting point in the absence of air.
Mercury
Gallium
Zirconium
Copper
How is ore of aluminium concentrated?
Roasting
Leaching
Froth floatation
Using Wilfley table
B.
Leaching
Leaching is the method of extraction of aluminium from its ore (bauxite). By the treatment of powdered ore with a concentrated solution of NaOH resulting in dissolution of Al2O3, leaving impurities behind as,
Al2O3 (s) + 2OH- (aq) + 3H2O → 2[Al(OH)4]- (aq)
This process is known as Baeyer's process.
Name the reagent that is used in leaching of gold.
Carbon
Sodium cyanide
Carbon monoxide
Iodine
Name the process that is employed to refine aluminium.
Hall's process
Mond process
Hoope's process
Serperck's process
Purification of aluminium by electrolytic refining is called
Hall's process
Froth flotation process
Bayer's process
Hoop's process