Stoichiometry problem-solving procedure

You can use pattern puzzles to help you remember sequential information. Pattern puzzles are not just a tool for memorization. They also promote a greater understanding of a variety of chemical processes, from the steps in solving a mass-mass stoichiometry problem to the procedure for making a solution of specified molarity. 

Sketch the titration curve for a weak acid titrated by a strong base. When performing calculations concerning weak acid-strong base titrations, the general two-step procedure is to solve a stoichiometry problem first, then to solve an equilibrium problem to determine the pH. What reaction takes place in the stoichiometry part of the problem What is assumed about this reaction ... 

A Figure 4.18 Outline of the procedure used to solve stoichiometry problems that involve measured (laboratory) units of mass, solution concentration (molarity), or volume. 

Five examples from the chapter are repeated here. Each example represents one kind of stoichiometry problem. If you can classify a problem as one of these types, you will find it easier to select the correct procedure for solving it. The problem types are summarized in Table 10.1, Summary of Stoichiometry Classifications, immediately following the examples. Exercises follow the table. 

In the ideal gas equation method, there are two procedures (1) If the given quantity is a gas, the ideal gas equation is solved for n to change the given volume to moles. The problem is completed by the second and third steps in the stoichiometry path. (2) If the wanted quantity is a gas, the moles of wanted quantity are calculated by the first and second steps in the stoichiometry path. The ideal gas equation is then solved for V to convert the moles of gas to liters. The section describing the ideal gas equation method is identified by a green bar in the inside margin, as next to this paragraph. 

The two steps in the procedure can be combined so you can solve the problem in a single setup. The conversion factor between liters and moles is the molar volume at the temperature and pressure of the problem (see Section 14.5, particularly Example 14.9). From the ideal gas equation, molar volume is V/n, which, according to Equation 14.10, is RT/P. Thus, if you need to change moles to liters, multiply by V/n in the form RT/P. To change liters to moles, divide by RT/P, or multiply by its inverse, P/RT. This can be done in the same setup as the two steps in the stoichiometry path. The single setup for Example 14.14 becomes... 

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