Sample Paper 2 for Class XII

UNIT 6

General Principles & Processes of Isolation of Elements

M.M.20

 

  1. Give reasons for the following:                                                                                                             3
  • Cryolite is added to alumina before its reduction.
  • Reduction of a metal oxide is easier if the metal formed is in liquid state at the temperature of reduction.
  • Copper can be extracted by hydrometallurgy but not zinc.

 

  1. Explain the cyanide process for isolation of silver.             2

 

  1. Differentiate between calcination and roasting.                                                                                    2

 

  1. Outline the principles of the following processes :             3
  • Froth floatation process
  • Zone refining method.

 

  1. Explain the process for refining of nickel metal.             2

 

  1. Explain the role of :             2
  • SiO2 in the metallurgy of Cu.
  • Depressant in froth floatation process.

 

  1. Name the ores of following metals from which extraction taken place – Aluminium and Zinc. 1

 

  1. Consider the following reaction at 10000C                                                                               2

2  Zn(s) + ½ O2 (g) → ZnO (s)          ΔG ̊ = – 360 KJmol-1

C (s) + ½ O2 (g) →  Co(g)           ΔG ̊  = – 460 KJmol-1

Predict whether C can be used as reducing agent for ZnO?

 

  1. Name of the following:             3
  • Two metals which never exist in native state.
  • Two metals which can exist in native as well as combined state.
  • Two metals which always occur in native state.
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