Chemistry: Reversible Chemical Reactions

Introduction;

Most chemical reactions are reversible which means that they react both forwards and backwards. A forward reaction is generically A + B -> C + D and a backward reaction is C + D -> A + B. Higher concentrations of A and B at the beginning of the reaction cause it to shift right towards C and D before beginning to slow down as more C and D are created. Eventually, the amount of A and B being formed is the same as the amount of A and B being used, which results in chemical equilibrium, denoted with Keq. From this reaction, the equilibrium constant can be calculated by using the ratio of the product of the products over the product of the reactants. Thus Keq= [C]*[D] / [A] * [B].

Some reversible reactions reach equilibrium faster than others such as that of Iron (III) ion (Fe3+) with thiocyanate ion (SCN-) that forms thiocyanatoiron(III) (FeSCN2+). In this reversible reaction Fe3+ reacts with SCN- to produce FeSCN2+ in water. For this reaction A is the iron (III) ion, B is the thiocyanate ion and C is the thiocyanato iron (III). Its Keq value is equal to

K=([Fe(SCN)^(2-)])/([Fe^(3+) ][SCN^-])

and this may now be used to find the equilibrium constant with known or calculated concentrations.

Methods;

Standard Curve;

Five clean and dry test tubes are obtained and labeled 1-5. Each is filled with exactly 2.50 mL of .200 M Fe(NO3)3 using a burette. Then 0.50 mL of 0.002 M KSCN solution is added to test tube 1. 0.75 mL of 0.00200 M KSCN is added to test tube 2 and so on in increments of 0.25 mL. Finally, enough 0.5 M HNO3 is added to each test tube so that the final volume is equal to 10.0 mL. Each test tube is mixed and then the contents of each are added to a cuvette and tested within a spectrophoto...

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...imary productivity in large regions of the global open ocean. Copper (Cu), on the other hand, is a common anthropogenic contaminant to estuarine and coastal oceans that can act as a toxicant to microorganisms at elevated concentrations. The organic complexation of dissolved iron and copper by largely uncharacterized natural ligands in seawater has proven to be an integral component in the oceanic biogeochemistry of these metals, governing aspects of their solubility, supply and bioavailability in the marine environment. Recent research projects in the Buck lab have examined the distributions, sources and sinks of natural iron- and copper-binding organic ligands in seawater, biological transformations of iron and copper species, and the influence of copper-binding ligands on bioavailability and toxicity of copper in contaminated coastal and estuarine environments.