Sample Calculations for Notebook Records

Students frequently have difficulty in setting up Tables of Reactants and Products and calculating theoretical yields, so two hypothetical examples are provided for your reference. 

Problem Consider the reaction shown in Equation 1.2. Assume that you are to use 5 g (7.8 mL) of 1-pentene and 25 mL of concentrated HBr solution. Prepare a Table of Reactants and Products, determine the limiting reagent, and calculate the theoretical yield for the reaction. 

Answer First of all, note that the equation is balanced, because the 1 that signifies that 1 mole of each reactant will react to produce 1 mole of product is omitted by convention. Because an aqueous solution of HBr, rather than the pure acid, is being used, the amount of HBr present must be determined. Concentrated HBr is 47% by weight in the acid, and its density, d, is 1.49 g/mL, a value that would be recorded in the column headed Other Data. Consequently, 25 mL of this solution contains 17.5 g of HBr (25 mL X 1.49 g/mL X 0.47). The needed data can then be entered into Table 1.1. 

The limiting reagent is 1-pentene because theory requires that it and HBr react in a 1 1 molar ratio, yet they have been used in a ratio of 0.07 0.22. This means that no more than 0.07 mole of product can be formed, since theory dictates that the ratio between 2-bromopentane and 1-pentene also be 1 1. The calculation of the theoretical yield is then straightforward. 

You may find it convenient to use units of milligrams (mg), microliters ( xL), and milHmoles (mmol) instead of grams, milHHters, and moles, respectively, in performing measurements and calculations when small quantities of reagents are used, as is the case for microscale reactions. For example, let s consider how Table 1.1 would be modified if 0.1 g of 1-pentene and 0.5 mL of concentrated HBr solution 

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