Explain the role of each of the following : (i) NaCN in the extraction of silver (ii) `SiO_(2)` in the extraction of copper

Explain the role of each of the following : (i) NaCN in the extraction

1.	Explain the role of each of the following : (i) NaCN in the extraction of silver (ii) `SiO_(2)` in the extraction of copper
Answer» (i) During roasting copper pyrites are converted in to mixture of FeO and `Cu_(2)O` To remvoe Fe(basic) an acidic flux silica is added during smelting .FeO then combines with Si `O_(2)` to form ferrous silicate `(Fe SiO_(3))` slag which floats over molten matter (ii) Role of Na CN in he extraction of silver is to do the leaching of silver ore in the presence of air from which the silver is obtained later by replacement `4Ag(s)+8CN^(-)(aq)+2H_(2)O(aq)+O_(2)(g)rarr4[Ag(CN)_(2)]^(-)(aq)+4OH^(-)(aq)` `2[Ag(CN_(2))^(-)](aq)+Zn(s)rarr2Ag(s)+[Z(CN)_(4)^(2-)(aq)]`

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(i) Arrange the following compounds in an increasing order of basic strength : `C_(6)H_(5)NH_(2), C_(6)H_(5)N(CN_(3))_(2), (C_(2)H_(5))_(2)NH and CH_(3)NH_(2)` (ii) Arrange the following compounds in a decreasing order of `pK_(b)` values: `C_(2)H_(5)NH_(2), C_(6)H_(5)NHCH_(3), (C_(2)H_(5))_(2) NH and C_(6)H_(5)NH_(2)`
Rerrange the following in an increasing order of their basic strengths: `C_(6)H_(5)NH_(2),C_(6)H_(5)N(CH_(3))_(2),(C_(6)H_(5))_(2)` NH and `CH_(3)NH_(2)`.
(b) Estimate the minimum potential difference needed to reduce `AI_(2)O_(3)` at `500^(@)C` The gibbs energy change for the decomposition reaction `2/3AI_(2)O_(3)rarr4/3AI+O_(2)`is 960 kJ (F=96500 C `mol^(-1))`

Explain the role of each of the following : (i) NaCN in the extraction of silver (ii) `SiO_(2)` in the extraction of copper

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