Ch 11Adsorption and Colloids — Class 11 Chemistry, concept-first.

Adsorption is introduced through two everyday observations. First, when a metal spoon is dipped into milk and then withdrawn, a thin film of milk particles clings to the spoon's surface -- rinsing rem…

This section sets up the physical picture behind adsorption before splitting it into its two types (Section 11.3).

Every surface molecule of a liquid or every surface ion/molecule of a solid crystal is in a state of unsaturated or unbalanced force, because its bonding or attractive interactions are only satisfied…

Adsorption is driven by London dispersion forces (a component of the broader van der Waals forces) acting between the adsorbent's surface and the incoming molecules.

The book draws a first contrast with absorption before giving worked examples of adsorption itself: when cotton is dipped in water, the cotton becomes wet because water penetrates into the bulk of the…

Desorption is defined as the process of removing an adsorbed substance from the surface it was adsorbed onto -- it is, in effect, the reverse of adsorption.

Sorption is the name given to the situation where adsorption and absorption happen at the same time in the same system.

Adsorption is classified into two main types depending on the nature of the forces holding the adsorbate onto the adsorbent's surface: physical adsorption (physisorption), where the attraction is due…

Physisorption occurs when gas (or other adsorbate) molecules accumulate at a solid surface purely because of weak van der Waals forces, with no chemical bond forming between adsorbate and adsorbent.

Chemisorption, first investigated in 1916 by the American chemist Irving Langmuir (1881-1957), occurs when gas molecules accumulate on a solid surface by forming genuine chemical bonds -- covalent or…

All solids adsorb gases to some extent, and five factors together determine how much. (1) Nature of the adsorbate (the gas): gases with a high critical temperature liquefy more readily (see Chapter 10…

An adsorption isotherm is the relationship, at a fixed (constant) temperature, between the amount of a substance adsorbed per unit mass of adsorbent and either the equilibrium pressure of the gas (for…

Adsorption underlies a wide range of practical applications. (i) Catalysis: heterogeneous solid catalysts, whose action depends on adsorbing reactants onto their surface, are used throughout industry…

Catalysts matter both in the chemical industry and in living organisms: a large share of industrially manufactured chemicals rely on a catalyst to obtain a specific product, and using a catalyst also…

In homogeneous catalysis, the reactants and the catalyst are all present in the same phase. Four examples are given.

In heterogeneous catalysis, the reactant(s) and the catalyst are in different phases -- typically a solid catalyst with gaseous or liquid reactants.

Inhibitors are substances that decrease the rate of a chemical reaction -- the opposite effect of a catalyst. Two examples are given.

Because heterogeneous catalytic action occurs specifically on the surface of the solid catalyst, the adsorption theory explains that mechanism as a five-step cycle.

Three features determine how a solid catalyst behaves in practice. (a) Catalytic activity: a catalyst's activity depends on the strength of chemisorption between it and the reactant molecules -- if la…

Colloids are part of everyday life -- milk, butter, jelly, whipped cream and mayonnaise are all colloids, and colloid chemistry underlies the understanding of cement, bricks, pottery, porcelain, glass…

Several everyday phenomena are explained by colloid chemistry. (i) The blue colour of the sky: minute dust particles together with tiny water droplets dispersed in air scatter blue light preferentiall…

Colloids are classified in three independent ways. (a) By physical state of the dispersed phase and dispersion medium: Table 11.4 (attached to this section) lists eight combinations -- for example sol…

Colloids can be prepared by three broad methods. (a) Chemical methods: double decomposition, oxidation, reduction or hydrolysis reactions that produce a water-insoluble product whose molecules then ag…

A freshly prepared colloidal solution usually contains an excess of electrolytes and other soluble impurities left over from its preparation.

Colloidal dispersions show several characteristic properties beyond the general ones noted in Section 11.9.4.

Lyophobic sols can be coagulated in five ways. (i) By electrophoresis: the charged colloidal particles migrate toward the oppositely-charged electrode, are discharged on contact, and precipitate.

An emulsion is a colloidal system in which one liquid is dispersed as fine droplets throughout another, immiscible (or only partially miscible) liquid.

Colloids are put to use widely, in both industry and daily life. (i) Electrical precipitation of smoke: smoke is a colloidal dispersion of solid particles (carbon, arsenic compounds, dust, etc.) in ai…