Gas-Formation Reactions

Will a precipitate form when aqueous solutions of Ca(N03)2 and NaCl are mixed in reasonable concentrations Write balanced formula unit, total ionic, and net ionic equations for any reaction. 

We recognize that both Ca(N03)2 (solubility guideline 3) and NaCl (solubility guidelines 2 and 4) are soluble compounds. We use the solubility guidelines to determine whether any of the possible products are insoluble. 

At the instant of mixing, the resulting solution contains four ions  

New combinations of ions could be CaCl2 and NaN03. But solubility guideline 4 tells us that CaCl2 is a soluble compound, and solubility guidelines 2 and 3 tell us that NaN03 is a soluble compound. Therefore, no precipitate forms in this solution. 

Seashells, which are formed in very siow precipitation reactions, are mostiy caicium carhonate (CaCOa) a white compound. Traces of transition metai ions give them coior. 

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We now discuss chemical reactions in further detail. We classify them as oxidation-reduction reactions, combination reactions, decomposition reactions, displacement reactions, and metathesis reactions. The last type can be further described as precipitation reactions, acid-base (neutralization) reactions, and gas-formation reactions. We will see that many reactions, especially oxidation-reduction reactions, fit into more than one category, and that some reactions do not fit neatly into any of them. As we study different kinds of chemical reactions, we will learn to predict the products of other similar reactions. In Chapter 6 we will describe typical reactions of hydrogen, oxygen, and their compounds. These reactions will illustrate periodic relationships with respect to chemical properties. It should be emphasized that our system is not an attempt to transform nature so that it fits into small categories but rather an effort to give some order to our many observations of nature. 

The formation of an insoluble or slightly soluble gas provides a driving force for a third type of metathesis reaction that we call a gas-formation reaction. The only common gases that are very soluble in water are HCl(g) and NH3(g). All other gases are sufficiently insoluble to force a reaction to proceed if they are formed as a reaction product. 

Gas-formation reaction A metathesis reaction in which an insoluble or slightly soluble gas is formed as a product. 

An important route to the production of foamed polysiloxane rubbers relies on the use of a low molecular weight silicone gum and on a series of tin catalysed cure and gas formation reactions. Normally, a dihydroxy terminated poly dimethylsiloxane containing a small amount of silica filler, together with a polyfunctional crosslinking agent (e.g. tetrapropylsilicate), is used as the starting material. 

Evaluation of gas formation, reactions in contact with water, and - at higher organic matter contents - degradability of organic substances. 

Precipitation Reactions 6-10 Gas-Formation Reactions 6-11 Summary of Reaction Types... 

Recognize and describe ciasses of reactions decomposition reactions, displacement reactions, various types of metathesis reactions, and gas-formation reactions... 

Hydrogen sulfide, HjS, is responsible for the smell of rotten eggs.This gas-formation reaction Is also a metathesis reaction. 

Displacement reactions in which an active metal displaces hydrogen from an acid or from water (see Section 6-8, Part 2) are gas-formation reactions, but they are not metathesis reactions. 

Chapter 6, Same Types of Chemical Reactions, s) tematizes chemical reaction types and relates them to the periodic table. Reactions are classified as (a) oxidation-reduction reactions, (b) combination reactions, (c) decomposition reactions, (d) displacement reactions, (e) metathesis reactions (two types), and (f) gas-formation reactions. If desired, the material in this chapter can be presented at any later point in the course. 

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