Surface Chemistry Test

Consider the following sequence of reactions:

Red Hot Coke$$\ +\ $$Steam $$\xrightarrow {\displaystyle \text{Y}{(\text{catalyst})}} X \longrightarrow Z \xrightarrow [\displaystyle \text{cold water}]{\displaystyle \text{pressure}}\ $$W(gas)

Directions For Questions

The catalytic activity and collodial nature of a substance are surface phenomenon. Both these properties depend upon the property of adsorption. Adsorption may be physisorption or chemisorption. Adsorption is spontaneous and always leads to decrease in entropy and evolution of heat. Chemisorption is irreversible with temperature, unilayer, specific and directional. Adsorbate molecules adsorbs on cataylst surface and thus, lower energy of activation of reaction to provide a new path way for reaction. In colloidal state, dispersed phase particles possess the adsorption characteristics at the interface.

...view full instructions

Mention catalyst in the following reaction:

Directions For Questions

In macromolecular type of colloids, the dispersed particles are themselves large molecules (usually polymers). Since these molecules have dimensions comparable to those of colloidal particles, their dispersions are called macromolecular colloids. Most lyophilic sols belong to this category. There are certain colloids which behave as normal strong electrolytes at low concentrations but exhibit colloidal properties at higher concentrations due to the formation of aggregate particles. These are known as micelles or associated colloids. Surface active agents like soaps and synthetic detergent belong to this class.

Critical micelle concentration (CMC) is the lowest concentration at which micelle formation appears. CMC increases with the total surfactant concentration. At a concentration higher than CMC, they form extended parallel sheets known as lamellar micelles which resemble biological membranes. With two molecules thick, the individual molecule is perpendicular to the sheets such that hydrophilic groups are on the outside in aqueous solution and on the inside in a non-polar medium.

In concentrated solution, micelles take the form of long cylinders packed in hexagonal arrays and are called lyotropic mesomorphs.

In an aqueous solution (polar medium), the polar group points towards the periphery and the hydrophobic hydrocarbon chains point towards the center forming the core of the micelle. Micelles from the ionic surfactants can be formed only above a certain temperature called the Kraft temperature. They are capable of forming ions. Molecules of soaps and detergents consist of lyophilic as well as lyophobic parts which associate together to form micelles. Micelles may contain as many as $$100$$ molecules or more.

...view full instructions

Directions For Questions

Transition metal and their compounds are used as catalysts in industry and in biological system. For example, in the contact process, vanadium compounds in the +5 state ($$V_2O_5$$ or $$VO_3{^-}$$) are used to oxidise $$SO_2$$ to $$SO_3$$ : $$SO_2$$ + $$\displaystyle{\frac{1}{2}}O_2 \overset{V_2O_5} {\rightarrow}$$ $$SO_3$$. It is thought that the actual oxidation process takes place in two stages. In the first step, $$V^{5+}$$ in the presence of oxide ions converts $$SO_2$$ to $$SO_3$$. At the same time, $$V^{5+}$$ is reduced to $$V^{4+}$$. $$2V^{5+} + O^{2-} + SO_2 \rightarrow 2V^{4+} + SO_3$$. In the second step, $$V^{5+}$$ is regenerated from $$V^{4+}$$ by oxygen : $$2V^{4+} + \displaystyle{\frac{1}{2}O_2 \rightarrow} 2V^{5+} + O^{2-}$$. The overall process is, of course, the sum of these two steps: $$SO_2 + \displaystyle{\frac{1}{2}}O_2 \rightarrow SO_3$$.

...view full instructions