Stoichiometry precipitation reactions

The stoichiometry between two reactants in a precipitation reaction is governed by a conservation of charge, requiring that the total cation charge and the total anion charge in the precipitate be equal. The reaction units in a precipitation reaction, therefore, are the absolute values of the charges on the cation and anion that make up the precipitate. Applying equation 2.3 to a precipitate of Ca3(P04)2 formed from the reaction of Ca and P04 , we write... 

In a gravimetric analysis a measurement of mass or change in mass provides quantitative information about the amount of analyte in a sample. The most common form of gravimetry uses a precipitation reaction to generate a product whose mass is proportional to the analyte. In many cases the precipitate includes the analyte however, an indirect analysis in which the analyte causes the precipitation of another compound also is possible. Precipitation gravimetric procedures must be carefully controlled to produce precipitates that are easily filterable, free from impurities, and of known stoichiometry. 

Quantitative Calculations The stoichiometry of a precipitation reaction is given by the conservation of charge between the titrant and analyte (see Section 2C) thus... 

A similar observation was made in the ionic precipitation of lead(ll) iodide. When aqueous solutions of potassium iodide and sodium iodide were separately added to aqueous leadfll) nitrate, 12% of students believed that the ionic equation for the precipitation reactions was different in the two instances even though the stoichiometry of the two chemical reactions had no influence on the ionic equation. 

Tables of amounts are useful in stoichiometry calculations for precipitation reactions. For example, a precipitate of Fe (OH) forms when 50.0 mL of 1.50 M NaOH is mixed with 35.0 mL of 1.00 M FeCl3 solution. We need a balanced chemical equation and amounts in moles to calculate how much precipitate forms. The balanced chemical equation is the net reaction for formation of Fe (OH)3 Fe (ag) + 3 OH (a g) Fe (OH)3 (. )...

Introduction and Orientation, Matter and Energy, Elements and Atoms, Compounds, The Nomenclature of Compounds, Moles and Molar Masses, Determination of Chemical Formulas, Mixtures and Solutions, Chemical Equations, Aqueous Solutions and Precipitation, Acids and Bases, Redox Reactions, Reaction Stoichiometry, Limiting Reactants... 

The initial product of the copper reaction is a brown precipitate of stoichiometry Cu(p-tol-NNNNN-tol-p)2, which, on heating, is reduced to deep red, air-stable Cu(p-tol-NNNNN-tol-p) j. The latter product, which is weakly paramagnetic [p ranges from 0.33 (113 K) to 1.52 BM (303 K)] and decomposes explosively at 160°C, has been found by X-ray diffraction methods to possess the trinuclear structure shown in Fig. 18. Three N, zig-zag chains coordinate three linearly arranged copper(I) ions through N-1, N-3, and N-5 atoms, such that each copper is in a trigonal-planar coordination environment. Mean copper-nitrogen distances are 2.036 A for the outer copper atoms and 1.945 A for the central copper atom. The copper-copper distances of 2.348 and 2.358 A are the shortest yet recorded for copper(I) complexes (6). 

Precipitation reactions have several applications in analysis in gravimetric methods, in precipitation titrations, and in separations. Gravimetry, which used to be a major l>art of analytical chemistry, has expanded less rapidly than other aspects of analysis and does not now occupy a prominent place. Precipitation titrimetry always has been restricted in application because most precipitation reactions fail to meet the requirements of rapid reaction rate and adequate stoichiometry. In separations, precipitation reactions are used in two ways in one the precipitate involved is of direct concern, and in the other it acts as a carrier for another substance of interest. The application of precipitation reactions to separations is described in Chapter 22. 

Teachers report that students get a much better idea of the role of chemistry in society. Contexts are effective in engaging the students. Students are confronted with a lot of knowledge in a short time. They learn a lot. There are still problems however. Using the knowledge gained in other contexts needs to be established more firmly. There is a need for more practice with skills like calculations in stoichiometry, writing equations in precipitation reactions or acid-base reactions. 

To illustrate this, let us consider the case of an aqueous system close to saturation with respect to calcite at rather high pH and low pc02, corresponding lo a classical natural situation. According to Eq. 5, the rate of dissolution is then controlled mainly by the hydration of the surface of calcite and the forward rate is a constant equal to /c3. The backward precipitation reaction corresponding to die stoichiometry of reaction 1 is given by... 

Solute transport, adsorption, and precipitation reactions can make it difficult to reconstruct decomposition stoichiometries from pore-water profiles alone, particularly within the bioturbated zone. Because the general trends and limits on N/P and N/C stoichiometry are evident from the previous considerations no further modeling will be done here. An adequate explanation for the higher NH//HPO4 -concentration ratios in the deeper pore water at inshore relative to offshore stations (Fig. 14) requires decomposition experiments below 10 cm, together with direct examination of the solid phase for phosphate compounds and solute transport modeling. 

The advantages of co-precipitation reactions are (i) homogeneity of components distribution, (ii) relatively low reaction temperature, (iii) fine and uniform particle size with weakly agglomerated particles, and (iv) low cost. However, these reactions are highly susceptible to the reaction conditions, and due to incomplete precipitation of the metal ions, a control over the stoichiometry of precursors is rather difficult. In addition, the co-precipitation reactions are not suited for certain oxides/hydroxides, for instance, in the case of amphoteric systems. 

We will now deal with the stoichiometry of acid-base reactions in aqueous solutions. The procedure is fundamentally the same as that used previously for precipitation reactions. 

Stoichiometry of a Precipitation Reaction, an Oxidation-Reduction Reaction, and a Compiexation Reaction... 

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