How to Determine the Ratio Between the Elements in a Compound

By Mara Pesacreta
Using a molecular model to determine the ratio between elements in a compound.

A compound is a combination or two or more elements held together by chemical bonds. Compounds can only be separated by chemical processes. Since chemicals are composed of different elements, determining the ratio between the elements can allow you to analyze how much of each compound is present. Such a process is also useful for analyzing chemical reactions that are being performed in chemistry experiments. Making connections between units and how elements combine to form compounds can help you to better understand their ratios.

Understand the coefficients of a chemical formula. In a chemical formula, the number at the beginning of the compound can either be one, which is not written, or another positive whole number. This number is known as the coefficient. It indicates how many moles of the compound are present. For example, 2NO2 indicates that there are two moles of nitrogen dioxide.

Understand the meaning of the subscripts that are present within a chemical formula. The subscripts are the small numbers that are written to the bottom right of the elements. If the subscript is one, then it is not written. The subscripts indicate how many moles of each element is present. For example, in the chemical formula NO2, there is one mole of nitrogen and two moles of oxygen.

Write the number of moles of each element over the number of moles of the compound. For example, the ratio for the amount of nitrogen in two moles of nitrogen dioxide, 2NO2, is 1-to-2. The ratio for the amount of oxygen in two moles of nitrogen dioxide is 2-to-2.

Compare the amount of the each element in the compound. Writing the ratio for the elements in the compound can help you to determine which element is present in the larger amount of moles. For example, in two moles of nitrogen dioxide there is one mole of nitrogen for every two moles of oxygen.

About the Author

Mara Pesacreta has been writing for over seven years. She has been published on various websites and currently attends the Polytechnic Institute of New York University.