Mass Percentages from the Formula

Hydrogen cyanide, HCN, is a volatile, colorless liquid with the odor of certain fruit pits (such as peach and cherry pits). The compound is highly poisonous. How many molecules are there in 56 mg HCN, the average toxic dose  

When a chemist has discovered a new compound, the first question to answer is. What is the formula To answer, you begin by analyzing the compound to determine amounts of the elements for a given amount of compound. This is conveniently expressed as percentage composition—that is, as the mass percentages of each element in the compound. You then determine the formula from this percentage composition. If the compound is a molecular substance, you must also find the molecular weight of the compound in order to determine the molecular formula. 

The next section describes the calculation of mass percentages. Then, in two following sections, we describe how to determine a chemical formula. 

Suppose that A is a part of something—that is, part of a whole. It could be an element in a compound or one substance in a mixture. We define the mass percentage 

The next example will provide practice with the concept of mass percentage. In this example we will start with a compound (formaldehyde, CH2O) whose formula is given and obtain the percentage composition. 

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