Experiment-Simple Chemical Reactions (1).doc - Experiment 32 SIMPLE CHEMICAL REACTIONS BACKGROUND One of the most important aspects of the study of

Experiment-Simple Chemical Reactions (1).doc - Experiment...

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Experiment 32 - SIMPLE CHEMICAL REACTIONSBACKGROUND:One of the most important aspects of the study of chemistry is to understand how chemicals react, what products are formed, and how much yield of each product is obtained. The evidence that a chemical reaction has occurred is often seen from one ormore of the following changes:evolution of a gas formation of a precipitate change in colorrelease of heat and/or sometimes other energy (e.g., sound or light)emission of an odor.In classifying chemical reactions, there are four basic types (and their general equations):[Reminder: s = solid phase, aq = aqueous solution, g = gas phase, l = liquid phase]Combination: A + B –> Ce.g., 2 Fe(s) + 3 O2(g) –> 2 Fe2O3(s)Decomposition: AB –> A + B e.g., CaCO3(s) –> CaO(s) + CO2(g)Replacement: A + BC –> B + ACe.g., Zn(s) + 2 AgNO3(aq)–> 2 Ag(s) + Zn(NO3)2(aq)Ion Exchange: AB + CD –> AC + BDe.g., PbCl2(aq) + Na2SO4(aq) –> PbSO4(s) + 2 NaCl(aq)There is a special type of combination reaction, called a “complexation reaction,” in which a complex ion or molecule is formed from two or more simple ions or molecules. These complexes have a central metal atom that covalently bonds to the surrounding molecules or ions by accepting unshared electron pairs into its previously unfilled outer orbitals. The representation of the complex ion or molecule is often surrounded by brackets, [ ]. Complexation reactions can be categorized as the above-described simple reaction type, or sometimes they may be slightly more complicated, often as a combination of two simple types. These reactions usually involve a transition metal ion, and frequently they exhibit dramatic color changes.For example: CoCl2(aq) + 2HCl(aq) –> H2[CoCl4](aq)pale pinkcolorlessdeep blueThere are thousands of known complexes, and they can exist as neutral molecules, as positively charged ions (cations), or as negatively charged ions (anions). Some
biologically active complexes are chlorophyll, hemoglobin, and cobalomin (vitamin B-12), whose central metal atoms are magnesium, iron, and cobalt, respectively].

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