Discussion Forum

 The molecular formula  of a commercial  resin used  for exchanging  ions in water softening is  $C_{8}H_{7}SO_{3}Na$    (mol.wt.=206) . What would be the maximum uptake of Ca²⁺ ions  by the resin  when expressed in mole per gram resin?

Answer:

Explanation:

 We know that the molecules weight of  $C_{8}H_{7}SO_{3}Na$ 

=  $12\times 8+1\times7+32+16\times 3+23=206$  We have to find  mole per gram  of resin.

  $\therefore$  1g of  $C_{8}H_{7}SO_{3}Na$   has number of mole

                     =   weight og given resin / molecular weight of resin

             = $\frac{1}{206}$  mol

 Now, reaction looks like

$2C_{8}H_{7}SO_{3}Na+Ca^{2+}\rightarrow (C_{8}H_{7}SO_{3})_{2}Ca+2Na^{+}$

 $\because$ 2 moles of  $C_{8}H_{7}SO_{3}Na$  combines with 1 mol Ca²⁺

 $\because$  1 mole of   $C_{8}H_{7}SO_{3}Na$ will combine  with   $\frac{1}{2}$ mol Ca²⁺

$\because$   $\frac{1}{206}$  mole of   $C_{8}H_{7}SO_{3}Na$  will combine with

$\frac{1}{2}\times\frac{1}{206}$ mol Ca²⁺   =   $\frac{1}{412}$  mol Ca²⁺