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NTA Abhyas NEET2020ChemistryGeneral Principles and Processes of Isolation of MetalsPractice

One of the processes used for concentration of ores is Froth floatation process. This process is generally used for concentration of sulphide ores. Sometimes in this process we add NaCN as a depressant. NaCN is generally added in case of ZnS and PbS minerals. What is the purpose of addition of NaCN during the process of Froth floatation ?

Options

  1. ANaCN causes reduction by precipitation
  2. BA soluble complex is formed by reaction between NaCN and ZnS while PbS forms froth
  3. CA soluble complex is formed by reaction between NaCN and PbS while ZnS forms froth
  4. DA precipitate of Pb(CN) 2 is produced while ZnS remain unaffected.

Correct answer

B. A soluble complex is formed by reaction between NaCN and ZnS while PbS forms froth

Step-by-step solution

NaCN + ZnS → Na 2 Zn CN 4 Soluble complex A layer of this zinc complex is formed on the surface of ZnS and due to this ZnS is prevented from the froth formation while PbS form froth. (i.e., NaCN is added as depressant for ZnS).

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