Cookbook Dimensional Analysis Most chemical educators use dimensional analysis and most students can easily follow its logic when solving problems. These same students, however, stumble with dimensional analysis when left on their own. A frequent comment is, "It looks easy when you do it, hut I don't know where to start when I try i t on my own." To counter this, I have developed faur steps applicable to the majority of problems encountered in chemistry as well as other areas. These were designed to help the student get started. 1) Write down the given number with its units. 2) Write a ratio with the given unit in the denominator and the unit sought in the numerator. 3) Insert numbers into the ratio so that the numerator and denominator become equivalent. 4) Multiply (1) and (3) together. Step four is permissible because one can always multiply by unity. Step three ensures that the ratio is, in a sense, unity since bath numerator and denominator are equivalent. To illustrate the method, consider the following problem: What volume would 64 g of oxygen occupy a t STP? 1 ) 64 g oxygen 2) 1oxygenlg oxygen 3) 22.4 1oxygen132 g oxygen 4). (64 . e ..oxveen) ., (22.4 1oxveenl32 e.. oxveen) = 44.8 1oxveen. . .. Alrhouyh thr metnod li preamred in a cwkhoc,k fashion, with time nnd axperirncr srtdrntr bctrme p n i ~ i r n in t using d i m e n s ~ ~ nm a la l y i i ~in sd\,ing prohlrrns and rely lecs on mrmmzing rhrir uav thrcjugh their rotlrje\. Middle Georgia College Coehran, 31014
Ronald DeLorenzo
Volume 53,Number 10, October 1976 / 633
