Calculations and Chemical Formulas

All of these people ask questions that begin, How much...  

The presentation of information in this chapter assumes that you can already perform the tasks listed below. You can test your readiness to proceed by answering the Review Questions at the end of the chapter. This might also be a good time to read the Chapter Objectives, which precede the Review Questions. 

Describe the general structure of molecular and ionic compounds. (Sections 3.3 and 3.5) Convert between the names of compounds and their chemical formulas. (Section 5.3) 

Report the answers to calculations to the correct number of significant figures. (Section 8.2) 

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In a stoichiometry calculation, the weight of one substance involved in a chemical reaction (reactant or product) is converted to the weight of another substance (reactant or product) appearing in the same reaction. The balanced equation is the basis for the calculation, and the formula weights of the reactant and product involved are needed. In the following general example,... 

Hertkorn et al. (2006) analyzed DOM that was isolated by ultrafiltration from surface and deep waters. They used ll and 13C NMR spectra and FTICR mass spectra to resolve DOM into three normative components heteropolysaccharides, carboxyl-rich alicyclic molecules (CRAM), and peptides (accounting for all N).They reported that surface DOM contains 60.1% heteropolysacharides, 22.9% CRAM, and 23.6% peptides and that deep DOM contains 27.1% heteropolysaccharides, 50.9% CRAM, and 20.7% peptides. Unlike Sannigrahi et al. (2005), who gave empirical formulae of the endmembers of the three-component model that was used to analyze their 13C NMR data, Hertkorn et al. (2006) did not provide empirical formulae for heteropolysaccharides, CRAM, and peptides. It is unclear how to calculate average chemical formulae of surface and deep DOM from their results. 

Several companies offer instruments capable of determining carbon, hydrogen, nitrogen and some other elements [72]. Such instruments feature an automatic sample injector. Samples are normally encased in sealed capsules. There is also a small computer which integrates peak areas and performs all the necessary calculations, which in some instances include the calculations of chemical formulae the computer also prints out the results. Finally, the new instruments feature advanced combustion and chromatographic separation systems. 

CHAPTER 3 Stoichiometry Calculations with Chemical Formulas and Equations... 

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