Using Solutions in Chemical Reactions

When we plan to carry out a reaction in a solution, we must calculate the amount of solution that we need. If we know the molarity of a solution, we can calculate the amount of solute contained in a specified volume of that solution. This procedure is 

Calculate (a) the number of moles of H2SO4 and (b) the number of grams of H2SO4 in 500. mL of 0.324M H2SO4 solution. 

Because we have two parallel calculations in this example, we state the plan for each step just before the calculation is done. 

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We have less than one liter of solution, and the molarity tells us that there is less than one mole in each liter of solution.Thus it is reasonable that (a) the number of moles of H2SO4 present is less than one, so (b) the mass of H2SO4 present is less than the formula weight (98.1 g/mol). 

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The Limiting Reactant Concept 3-4 Percent Yields from Chemical Reactions 3-8 Using Solutions in Chemical Reactions... 

Carry out calculations related to the use of solutions in chemical reactions... 

Calculating Solution Concentration 406 Using Concentration to Calculate Mass or Volume 409 Calculating Dilution Quantities 413 Calculations Involving Solutions in Chemical Reactions 414 Calculating Molality 420 Using Molality 422... 

Serious science started in Russian empire in the middle of the XVIII century. The first known Russian scientist M.V. Lomonosov obtained (in the I750sJ experimental data on the preservation of the mass of substances in chemical reactions. T.E. Lovits discovered adsorption from solutions he used wood carbon as an adsorbent. Among other scientists, Lovits detected compounds using characteristic forms of their crystals. V.M. Severgin published a book on analysis of mineral raw materials. 

Now let s take a more detailed look into the electrochemical cell. Figure 12-5 shows a cross-section of a cell that uses the same chemical reaction as that depicted in Figure 12-1. The only difference is that the two solutions are connected differently. In Figure 12-1 a tube containing a solution of an electrolyte (such as KNOa) provides a conducting path. In Figure 12-5 the silver nitrate is placed in a porous porcelain cup. Since the silver nitrate and copper sulfate solutions can seep through the porous cup, they provide their own connection to each other. 

These early observations have evolved into the branch of chemistry called electrochemistry. This subject deals not only with the use of spontaneous chemical reactions to produce electricity but also with the use of electricity to drive non-spontaneous reactions forward. Electrochemistry also provides techniques for monitoring chemical reactions and measuring properties of solutions such as the pK, of an acid. Electrochemistry even allows us to monitor the activity of our brain and heart (perhaps while we are trying to master chemistry), the pH of our blood, and the presence of pollutants in our water supply. 

Balancing the chemical equation for a redox reaction by inspection can be a real challenge, especially for one taking place in aqueous solution, when water may participate and we must include HzO and either H+ or OH. In such cases, it is easier to simplify the equation by separating it into its reduction and oxidation half-reactions, balance the half-reactions separately, and then add them together to obtain the balanced equation for the overall reaction. When adding the equations for half-reactions, we match the number of electrons released by oxidation with the number used in reduction, because electrons are neither created nor destroyed in chemical reactions. The procedure is outlined in Toolbox 12.1 and illustrated in Examples 12.1 and 12.2. 

Since 1986, when the very first reports on the use of microwave heating to chemical transformations appeared [147,148], microwave-assisted synthesis has been shown to accelerate most solution-phase chemical reactions [24-27,32,35]. The first application of microwave irradiation for the acceleration of reaction rate of a substrate attached to a solid support (SPPS) was performed in 1992 [36]. Despite the promising results, microwave-assisted soHd-phase synthesis was not pursued following its initial appearance, most probably as a result of the lack of suitable instriunentation. Reproducing reaction conditions was nearly impossible because of the differences between domestic microwave ovens and the difficulties associated with temperature measurement. The technique became a Sleeping Beauty interest awoke almost a decade later with the publication of several microwave-assisted SPOS protocols [37,38,73,139,144]. There has been an extensive... 

To make QM studies of chemical reactions in the condensed phase computationally more feasible combined quantum me-chanical/molecular mechanical (QM/MM) methods have been developed. The idea of combined QM/MM methods, introduced first by Levitt and Warshell [17] in 1976, is to divide the system into a part which is treated accurately by means of quantum mechanics and a part whose properties are approximated by use of QM methods (Fig. 5.1). Typically, QM methods are used to describe chemical processes in which bonds are broken and formed, or electron-transfer and excitation processes, which cannot be treated with MM methods. Combined QM and MM methods have been extensively used to study chemical reactions in solution and the mechanisms of enzyme-catalyzed reactions. When the system is partitioned into the QM and MM parts it is assumed that the process requiring QM treatment is localized in that region. The MM methods are then used to approximate the effects of the environment on the QM part of the system, which, via steric and electrostatic interactions, can be substantial. The... 

When QM/MM methods are used to study chemical reactions in solution and the reacting species are small enough to be treated completely with QM methods it is straightforward to separate... 

Spectra of carbenes are very useful sources of information on the structure of the free carbenes, e,g. the R—C—R angle, or the multiplicity of their lowest state. However, these data were mostly obtained under conditions different from those in solution, where chemical reactions normally occur. The spectra are usually recorded either in matrices at low temperatures, say at 4 or 77 °K, or in the gas phase. Only very few investigations of that type have been carried out in solution. The most important spectroscopic technique used in the investigations of carbenes is ESR. Other spectroscopic methods, such as flash photolysis which produces electronic spectra of carbenes, and infrared and lately CIDNP spectroscopy have been successfully employed. 

In some chemical reactions, the use uf concentrations does not give calculated results that agree with those observed, because of the departure from ideality hi real gases and solutions. In such reactions, concentrations are replaced hy apparent effective concentrations, ot activities, as explained in that entry. 

GO often is used in solution phase chemical reactions as well as being immobilized on dip-sticks and electrodes. Although its overall clinical usage is widespread, its use as conjugated to antibodies in enzyme-linked assay systems is minor compared to the popularity of other enzymes like horseradish peroxidase and alkaline phosphatase. 

The class of methods used for preparing colloidal dispersions in which precipitation from either solution or chemical reaction is used to create colloidal species. The colloidal species are built up by deposition on nuclei that may be of the same or different chemical species. If the nuclei are of the same chemical species, the process is referred to as homogeneous nucleation if the nuclei are of different chemical species, the process is referred to as heterogeneous nucleation. See also Dispersion Methods. An empirical or qualitative term referring to the relative ease with which a material can be deformed or made to flow. It is a reflection of the cohesive and adhesive forces in a mixture or dispersion. See also Atterberg Limits. 

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