This Molecular Formula Calculator finds the molecular formula corresponding to the given compound molar mass and its chemical composition. Enter the molar mass of the compound under study (in g/mol), the symbols of the chemical elements that make up this compound, and their masses into the appropriate fields of the calculator. To add an element to the list of constituents of the chemical compound you can click the “+” symbol on the right hand side to get additional fields. You can also click the “–” symbol to delete the redundant lines. The masses of the elements must be presented in the same mass units or as percentages.
How to Find Molecular Formula
The molecular formula describes the exact number and type of atoms in a single molecule of a compound. The molecular formula should be distinguished from the empirical formula.
The empirical formula of a chemical compound is the simplest whole number ratio of atoms present in the compound. To find the empirical formula of a substance you can use our Empirical Formula Calculator.
The most common approach to determining a compound’s chemical composition is to measure first the masses of its constituent elements. So, any experimental data involving masses must be used to derive the corresponding numbers of atoms in the compound. The easiest way to express the number of atoms is in moles.
For this, we have to use molar masses to convert the mass of each element to a number of moles. Then we consider the number of moles of each element relative to each other, converting these numbers into a whole-number ratio that can be used to derive the empirical formula of the substance.
The molecular formula of a substance is always the empirical formula of that substance whose indices are all multiplied by the same integer n, which can be symbolically expressed as the following formula:
Example of molecular formula calculation
Let’s consider an example of molecular formula calculation. A sample of a substance contains 2 g of carbon, 0.336 g of hydrogen and 2.67 g of oxygen. We know the molar masses of these elements: C – 12.011 g/mol, H – 1.008 g/mol, O – 16 g/mol. The corresponding numbers of moles are:
0.336 g H / 1.008 (g/mol) H = 0.3333 mol H
2.67 g O / 16 (g/mol) O = 0.1669 mol O
If we now divide the found numbers of moles by the minimum value of 0.1665 and round to whole values, then we get the following indices for the empirical formula: 1, 2, 1. So the empirical formula will be CH2O.
Now, if we know that the molar mass of the compound under study is 180.16 g/mol, we can find the molecular formula of this compound.
To this end, we first find the molecular weight of the empirical formula, that is, the weight in grams of one mole of a substance having the chemical formula CH2O. Using our Molecular Weight Calculator we can easily get 30.026 g/mol.
Next, we divide the molecular weight of the substance under study by the just found molecular weight of the empirical formula and obtain: 180.16 / 30.026 = 5.954. After rounding this result to a whole number we have n = 6, and obtain the molecular formula of glucose: C6H12O6.
This same result we can get in no time simply plugging the masses of the elements into our Molecular Formula Calculator. Note that to calculate the molecular formula we can also use percentages instead of masses in grams.
Using Molecular Formula Calculator
The symbols of chemical elements should be entered using the upper case for the first character and the lower case for the second character (if any). Compare: Co – cobalt is a chemical element and CO – carbon monoxide is a chemical compound.
Using the appropriate drop-down menu you can choose an output format for the molecular formula:
• Html – The molecular formula is represented using html tags for indices. For example, CO2. Clicking the ‘Copy to clipboard’ button ( ) you can copy the result ‘as is’, including all the tags, and then you can paste it to any html-page. However, clicking Ctrl-A and Ctrl-C you can copy the result without the tags and paste it to a DOC document keeping duly formatted indices.
• Small indices – The molecular formula is represented using ‘tiny’ symbols for indices. For example, CO₂ where unicode character is used: ₂ = (\u2082).
• Normal – The molecular formula is represented using ‘normal’ numbers for indices. For example, CO2.
Related calculators
Check out our other chemistry calculators such as Empirical Formula Calculator or Stoichiometry Calculator.