Stoichiometry - chemical calculations

Study, the students are taught the basic concepts of chemistry such as the kinetic theory of matter, atomic stmcture, chemical bonding, stoichiometry and chemical calculations, kinetics, energetics, oxidation-reduction, electrochemistry, as well as introductory inorgarric and organic chemistry. They also acquire basic laboratory skills as they carry out simple experiments on rates of reaction and heat of reaction, as well as volrrmetric analysis and qualitative analysis in their laboratory sessions. 

This balanced equation can be read as 4 iron atoms react with 3 oxygen molecules to produce 2 iron(III) oxide units. However, the coefficients can stand not only for the number of atoms or molecules (microscopic level) but they can also stand for the number of moles of reactants or products. So the equation can also be read as 4 mol of iron react with 3 mol of oxygen to produce 2 mol ofiron(III) oxide. In addition, if we know the number of moles, the number of grams or molecules may be calculated. This is stoichiometry, the calculation of the amount (mass, moles, particles) of one substance in the chemical equation from another. The coefficients in the balanced chemical equation define the mathematical relationship between the reactants and products and allow the conversion from moles of one chemical species in the reaction to another. 

Most of the reactions that you have studied have essentially gone to completion. You can use stoichiometry to calculate the amounts of products formed, assuming that the chemical reaction proceeds only from left to right. In many chemical reactions, however, a mixture of reactants and products form because the reaction can also proceed from right to left. In this unit, you will study the concepts that describe reversible reactions. 

Solutions often are involved in reactions used to prepare compounds or to perform chemical analyses In either case, you will be faced with Stoichiometri-cal calculations similar to those in Chapters 10 and 12, but you must also consider the concentrations and volumes of the solutions that are used We shall use the "three simple steps" as outlined on p 173... 

Step 2 Calculate the moles of OH- ions in the volume of titrant added. Step 3 Write the chemical equation for the reaction between acid and base and use the reaction stoichiometry to calculate the number of moles of conjugate base (in this case, HC02- ions) formed by the reaction of the add with added base and the moles of weak acid (in this case, HCOOH) remaining. 

For work in the laboratory, it s necessary to weigh reactants rather than just know numbers of moles. Thus, it s necessary to convert between numbers of moles and numbers of grams by using molar mass as the conversion factor. The molar mass of any substance is the amount in grams numerically equal to the substance s molecular or formula mass. Carrying out chemical calculations using these relationships is called stoichiometry. 

Recall that stoichiometry involves calculating the amounts of reactants and products in chemical reactions. If you know the atoms or ions in a formula or a reaction, you can use stoichiometry to determine the amounts of these atoms or ions that react. Solving stoichiometry problems in solution chemistry involves the same strategies you learned in Unit 2. Calculations involving solutions sometimes require a few additional steps, however. For example, if a precipitate forms, the net ionic equation may be easier to use than the chemical equation. Also, some problems may require you to calculate the amount of a reactant, given the volume and concentration of the solution. 

Mikheikin et al. (11) have formulated an alternative approach where terminal valencies are saturated by monovalent atoms whose quantum-chemical parameters (the shape of AO, electronegativity, etc.) are specially adjusted for the better reproduction of given characteristics of the electron structure of the solid (the stoichiometry of the charge distribution, the band gap, the valence band structure, some experimental properties of the surface groups, etc.). Such atoms were termed pseudo-atoms and the procedure itself was called the method of a cluster with terminal pseudo-atoms (CTP). The corresponding scheme of quantum-chemical calculations was realized within the frames of CNDO/BW (77), MINDO/3 (13), and CNDO/2 (30) as well as within the scope of the nonempirical approach (16). 

Chemical stoichiometry the calculation of the quantities of material consumed and produced in chemical reactions. (3) Chirality the quality of having nonsuperimposable mirror images. (20.4)... 

Stoichiometry is defined as the quantitative relationship among reacting chemical species. This section provides a brief review of stoichiometry and its applications to chemical calculations. 

Stoichiometry concerns calculations based on balanced chemical equations, a topic that was presented in Chapter 8. Remember that the coefficients in the balanced equations indicate the number of moles of each reactant and product. Because many reactions take place in solution, and because the molarity of solutions relates to moles of solute and volumes, it is possible to extend stoichiometric calculations to reactions involving solutions of reactants and products. The calculations involving balanced equations are the same as those done in Chapter 8, but with the additional need to do some molarity calculations. Let s get our feet wet by working a couple of problems involving solutions in chemical reactions. 

Alkaline digestion reagent, 0.28M Na2CO3/0.5M NaOH Use your knowledge of chemical stoichiometry to calculate the amount of each base needed to prepare a solution of the molarity desired. 

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