(a) A colloidal solution of AgI is prepared by adding AgNO₃ solutiondrop-by-drop to excess of KI solution. What will be the charge onthe sol so formed ? What is the cause of the charge ?

(b) Which of the following adsorption isobars represents

physisorption ? Justify the answer.

(x/m-Extent of adsorption; t-temperature)

(c) Two gases A and B have critical temperatures 430 K and 190 K respectively. Which gas will be readily adsorbed and why ?

(a) The reaction which takes place between KI and AgNO₃ is a double displacement reaction, it is shown as:

The precipitated AgI adsorbs I^- ions from the dispersion medium,and as a result negatively charged colloidal solution is formed. When KI is taken in excess, I^- ions, from KI, will be adsorbed on the surface of AgI particles, giving them a negative charge.

So, a negative sol is formed.

(b) In physisorption, the extent of adsorption (x/m) decreases with temperature.

Whereas in chemisorption, as it involves high activation energy, the extent adsorption (x/m), first increases then decreases with increase in temperature.

So, the graph representing physisorption would be:

(c) First of all, we see what does critical temperature mean.

Critical temperature of a substance is defined as the temperature at or above which the vapor of the substance cannot be liquefied. So, gases with lower critical temperature than room temperature (298 K), will exist in gaseous form at room temperature.

Or in other words,those gases will be liquefy easily whose critical temperature will be arrived first at room temperature, that is with higher critical temperature.

Thus, gas A with critical temperature, 270 K will be readily adsorbed than the gas B with critical temperature 250 K.