What is [Ag^+] when 25.0 mL each of 0.044 M AgNO3 and 0.57 M Na2 S2 O3 are mixed [Kf. of .Ag(S2

What is [Ag^+] when 25.0 mL each of 0.044 M AgNO3 and 0.57...

Key Concepts

Complex Ion Formation

Complex ion formation involves the interaction between a metal ion and one or more ligands to form a coordinated complex. In the context of this problem, silver ions combine with thiosulfate ligands to form a complex ion, demonstrating how coordination compounds are generated, which is a key aspect in understanding their equilibrium behavior.

Formation Constant (Kf)

The formation constant, denoted as Kf, quantifies the stability of a complex ion in solution. A high Kf value indicates that the formation of the complex is heavily favored, meaning the reaction proceeds almost to completion. This concept is crucial when analyzing systems where complexation significantly shifts equilibrium, affecting the concentrations of free metal ions.

Stoichiometry and Limiting Reagent

Stoichiometry, the quantitative relationship between reactants and products in a chemical reaction, is essential for determining which reactant is present in limiting quantity. Identifying the limiting reagent allows for accurate computation of the substances remaining in the mixture after the reaction, which directly influences the equilibrium concentrations.

Equilibrium Approximations

In reactions with extremely favorable equilibria, approximations can be made by assuming that nearly all of the reactant is converted to product. Such approximations simplify calculations by neglecting minor amounts of unreacted species, yet they require an understanding of the conditions under which such approximations are valid.

Concentration Calculations in Mixed Solutions

When different solutions are mixed, the overall concentrations of the species are affected by the dilution factor resulting from the combined volumes. Understanding how to recalculate concentrations post-mixing is fundamental to solving equilibrium problems, as it ensures that subsequent calculations reflect the true conditions of the solution.

Transcript

00:01 Question 99 is a rather lengthy question that requires you to include in your calculations concepts associated with limiting reactants.

00:13 Ultimately, it wants you to determine the silver ion concentration after a solution containing silver nitrate has been mixed with a solution containing sodium thiosulfate, forming the precipitate or forming the complex ion, silver thiosulfate.

00:37 So after a reaction has occurred, we will have some silver left over and some thiosulfate left over according to this equilibrium.

00:48 However, before understanding equilibrium, we would assume that the reactant that produces the least amount of product would be the limiting reactant and consumed completely, and we still need to include some of this understanding in solving this problem.

01:09 The kf expression, then, for this equilibrium would be, as shown here, the product concentration of the complex ion, divided by the reactant concentrations, each raised to their coefficient, and that is equal to 4 .7 times 10 to the 13, as given in the problem.

01:29 So how i would approach this problem is to first determine the limiting reactant in the traditional way assuming this reaction goes to completion and it goes pretty darn close to completion because it has a very large equilibrium constant.

01:44 So if we start with 25 milliliters of the silver nitrate solution at 0 .44 molar we can convert the 25 milliliters into liters, multiply this by the molarity of the silver nitrate solution to get the moles of the silver ion.

02:05 Then we see that one mole of silver ion produces one mole of product.

02:12 So this will tell us now the moles of product that can be created if all of the silver were consumed.

02:19 Let's do the same thing now with the thiosulfate.

02:23 We also have 25 milliliters at a concentration of .57 molar.

02:29 So we'll take our 25 milliliters converted to liters, multiply by the molarity to get the moles of the thiosulfate, and then recognize that two moles of thiosulfate make one mole of product.

02:46 This would then be the moles of product that could be produced if all of the thiosulfate reacts.

02:53 We see that it is significantly more than the amount that can be created with the silver...

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