Stoichiometry percent composition

Chemical stoichiometry is the area of study that considers the quantities of materials in chemical formulas and equations. Quite simply, it is chemical arithmetic. The word itself is derived from stoicheion, the Greek word for element and metron, the Greek word for measure. When based on chemical formulas, stoichiometry is used to convert between mass and moles, to calculate the number of atoms, to calculate percent composition, and to interpret the mole ratios expressed in a chemical formula. Most topics in chemical arithmetic depend on the interpretation of balanced chemical equations. Mass/mole conversions, calculation of limiting reagent and percent yield, and various relationships among reactants and products are commonly included in this topic area. 

Stoichiometry deals with the mass relationships between reactants and products in chemical reactions. The primary bases of stoichiometry are the balanced chemical equation and the mole concept. In this experiment the concepts of stoichiometry will be used to calculate the percent composition of a mixture composed of sodium hydrogen carbonate (sodium bicarbonate), NaHC03, and sodium carbonate, Na2C03. The number of moles of reactants and products will be calculated using only experimental mass measurements. When an analytical procedure that is used to determine the stoichiometry of a reaction involves only mass measurements, the analysis is called a... 

Stoichiometry is the series of calculations on the basis of formulas and chemical equations and will be covered in Chapter 4. The use of conversion factors is common even when the relative proportions are not fixed by a chemical formula. Consider a silver alloy used for jewelry production. (Alloys are mixtures of metals and, as mixtures, may be produced in differing ratios of the metals.) A particular alloy contains 86 percent silver. Factors based on this composition, such as... 

Consider the situation as one decreases the 0/R ratio, i.e., decreases the mole percent of the metallic oxide Mj Oy Between 100 and 66% there is little need for special modeling because the quadrivalency of silicon and the requirements of stoichiometry demand that the ionic species present he monomers of SiO tetrahedra. It is in the composition range of 66 to 10% M that the network model fails (see Section 5.13.7) in the face of facts. 

Both the low (B) and high (o) temperature polymorphs of NiS dissolve excess sulfur to form solid solutions. The B phase shows a limited range of homogeneity but the a phase shows a broad limit extending to approximately NiS (8). The o phase is normally designated o-Ni to emphasize this feature. However, the sulfur-poor limit of this phase has the stoichiometric composition to at least 873 K at 1070 K the deviation from stoichiometry is less than 0.05 weight percent nickel (8). Above 1079 K the deviation of the sulfur-poor limit from stoichiometry increases more rapidly and a material of stoichiometry NiS will exist as an equilibrium mixture of liquid NiyS. a hd solid a-Nij S (8). Thus, NiS melts incongruently. 

Elemental analysis is important in establishing the purity and identity of a known compound, or the empirical (stoichiometric) formulae of a new one. Elemental composition is usually quoted as percent by mass, from which the stoichiometry can be determined from atomic mass (RAM) values. Consider a compound (X) with the following composition by mass ... 

We have already discussed under practical stoichiometry how the air requirements can be estimated based on the fuel composition (ultimate analysis). The primary and secondary air requirements for combustion of pulverized coal or coke are best estimated by mass and heat balance at the mill. In Appendix 6A we show a calculation taken from Musto (1997) for the primary and secondary air required for coal pulverizer with 4.5 metric ton per hour (10,0(X)lb/hr) coal feed rate at initial moisture of 15 percent which is required to be ground and dried to 2 percent with a 200 HP mill. In order to estimate the actual primary and secondary air, one has to make some estimation of the evaporation rate, the amount of gas entering the coal mill, and the bleed air required so that the quantity of air that should be vented from the hood off-take can be properly estimated. It shows that for a take-off gas temperature of 315°C (600° F) and vent gas temperature of 76°C (170°F) and allowing ambient air infiltration of 10 percent at 15°C (60°F) the primary air will be about 22 percent of stoichiometric air and 21 percent of total air. The remaining air (about 79 percent) will be the secondary air. With this information we can size a burner using a burner pipe diameter based on a Craya-Curtet parameter of choice bearing in mind the conditions that ensure the desired jet recirculation patterns described in Chapter 3. 

Bulk samples of Sn-4.7Ag-l. 7Cu solder reflowed on pure Ni substrates were observed by Zribi et al. [36] to exhibit results distinctly different from Pb-Sn/Ni or Sn/Ni solder joints. Recall that in both Pb-Sn/Ni and Sn/Ni solder joints, NisSn was observed to grow first. In contrast, Cu-Ni-Sn compounds are observed to form at Sn-Ag-Cu/Ni interfaces. For instance. Fig. 22 is an SEM image of a Sn-4.7Ag-l.7Cu (Sn-5.lAg-3.lCu in atomic percent) solder/Ni interface, where WDS analysis identified the composition of the growing phase as Cu cNi Sn,45, where the Cu concentration x varied between 44 and 53 at.%, and the corresponding Ni concentration y between 10 and 1 at. %, respectively. These compositions are consistent with the stoichiometry of the compound, (Cu,Ni)6Sn5 [36]. 

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