Examples of Mass-relation Calculations

as shown above, the state of aggregation of a substance is represented by appended letters Cu(c) refers to crystalline copper (c standing for crystal sometimes, for solid, s is used), Cu(l) to liquid copper, and Cu(g) to gaseous copper. A substance in solution is sometimes represented by its formula followed by the name of the solvent in parentheses (aq) is used for aqueous solutions. 

7 he way to work a mass-relation problem is to think about the problem, in terms of atoms and molecules, and then to decide how to carry out the calculations. You should not memorize any rule about these problems — such rules are apt to confuse you and to cause you to make mistakes. 

The way to work these problems is best indicated by some examples. 

In general, chemical problems may be solved by using a slide rule for the numerical work. This gives about three reliable figures in the answer, which is often all that is justified by the accuracy of the data. Sometimes the data are more reliable, and logarithms or long-hand calculations might be used to obtain the answer with the accuracy required. Unless the problem requires unusual accuracy, you may round values of atomic mass off to the first decimal point. 

Example 4-1. What is the percentage of lead in galena, PbS Calculate to 0.1%. 

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