Question

Write short notes on the following:
(i) Tyndall effect
(ii) Activity and selectivity of catalysts.

Answer 1

(i) Tyndall Effect:
It is the phenomenon of light scattering by colloidal particles due to which the path of light through colloidal dispersion becomes visible.
It is not shown by true solutions due to smaller particle size.
Examples of Tyndall Effect:
1) The scattering of automobile headlight by fog and mist.
2) In movie theater, the light coming out from the projector appears bright because the dust particles scatter light.

(ii) Activity and selectivity of catalysts.

The strength of chemisorption determines catalyst activity. The catalyst activity first increases with strength of chemisorption and then decreases. Most active catalysts are the metals present in the middle of d-block.
Catalysts are selective in their action. When different products are possible in a reaction, a particular catalyst can be used to produce a particular product.
$CO\left(g\right)+2H_2\left(g\right)\stackrel{Cu/ZnO}{\to }C{H}_{3}OH$
$CO\left(g\right)+3H_2\left(g\right)\stackrel{Ni/A{l}_2{O}_3}{\to }C{H}_4+H_{2}O$