Welcome to another chemistry tip for another day. How is your chemistry? If you are still struggling with chemistry, you should seriously consider to change the way how you study chemistry - understanding the concepts and mastering the problem-solving. These are the core skills I teach in the Chemistry Survival Guide and our Survival Coaching Program.
Today's topic is Empirical Formula vs Molecular Formula. Determination of a formula is the most basic and frequent calculation in chemistry. In some cases, the molecular formula and empirical formula of a given molecule are identical. However, in many cases, the molecular formula is different from the empirical formula. For example, CH is the empirical formula and C6H6 is the molecular formula. Be aware.
Empirical Formula: The simplest chemical formula that expresses the relative number of moles of elements in a compound using the smallest whole numbers. It can be easily calculated with a simple six-step process:
(1) Determine the percent composition of each element;
(2) Assume 100 grams of sample, which automatically converts percent from the previous step to grams;
(3) Calculate the moles for each element by dividing its weight from previous step by its atomic weight;
(4) Set up a formula with the number of moles of each element as subscripts;
(5) Normalize the subscripts by dividing through by the smallest number of moles;
(6) Round up the fractional to whole numbers.
Molecular Formula: A formula indicating the actual number of atoms of each element making up a molecule. In other words, the molecular formula must accurately state the exact number of atoms of all of the elements in one molecule of the substance. Given the empirical formula is known, its molecular formula can be determined via the four-step process:
(1) Determine the molecular mass in grams;
(2) Divide the molecular mass of the compound by the molecular mass of the empirical formula;
(3) Round the quotient to the closest integer;
(4) Multiply the rounded whole number by all the subscripts. The result is the new molecular formula.
That wraps up today's tip. Tomorrow, I will switch gear and talk about your professors/teachers.
Until then, student, keep up your study!
Committed to Your Success
Wayne Huang, PhD
"The Chemistry Survival Coach"
http://www.ChemistrySurvival.com
PS: This chemistry tip, and many others like it, are part of the "Chemistry Survival Guide", available at: http://www.ChemistrySurvival.com. Systemize your study with the template-based ChemMastery system and learn the secrets of how to master chemistry the easy way.
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