Discussion Forum

1)

 Galena (an ore) is  partially oxidised by passing air through it at high temperature. After some time , the passage of air is stopped, but the heating is continued in a closed furnace such that the content undergo self- reduction. The weight (in kg)of Pb produced per kg of O₂  consumed is............  ( Atomic weights in g mol^-1 O= 16, S =32, Pb= 207)

 

Answer:

Option D

Explanation:

The equations of chemical reactions occurring  during the process are-

  In the presence of oxygen

 $2PbS+3O_{2}\rightarrow 2PbO+2SO_{2}.....(i)$

   By self reduction

        $2PbO+PbS_{}\rightarrow 3Pb+SO_{2}$

Thus 3 moles of 0₂ produces 3 moles of Pb 

    i.e.,

  32 × 3=96 g of O₂ produces

  3 × 207 =621 g of Pb

So 1000 g (1kg) of oxygen will produce  $\frac{621}{96}\times 1000= 646815 g$

                                   = 6.4687 kg = 6.47 kg

Alternatively 

       From the direct equation,

        $Pb S+O_{2}\rightarrow Pb +SO_{2}$

                     32g        207g

So,   32g of O₂  gives 207 g of Pb

1 g of O₂ will give  $\frac{207}{32}$ g of Pb

1000g of O₂  will give    $\frac{207}{32}\times 1000$

                            = 6468.75g= 6.46875 kg

                            =6.47 kg