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NTA Abhyas JEE Main2020ChemistryGeneral Principles and Processes of Isolation of MetalsPractice

Sometimes it is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using depressants in froth flotation. When a depressant NaCN is added to an ore containing ZnS and PbS, what is the correct observation?

Options

  1. ANaCN prevents PbS from coming to the froth but allows ZnS to come with froth
  2. BNaCN prevents ZnS from coming to the froth but allows PbS to come with froth
  3. CNaCN prevents frothing of both ZnS and PbS, hence no froth is formed
  4. DNaCN does not act as depressant hence a mixture of PbS and ZnS is found in froth

Correct answer

B. NaCN prevents ZnS from coming to the froth but allows PbS to come with froth

Step-by-step solution

NaCN acts as a depressant, it selectivley prevents ZnS from coming to froth by forming a complex N a 2 [ Z n ( C N ) 4 ] but allows PbS to come with froth.

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