How To Use This Molar Mass Calculator

Say you need to calculate the molar mass of H₂O. Simply type H2O into the textbox. Then press Go. The molar mass shows up in the green box. Below this, you'll see a table which breaks the calculation down step-by-step. The first column (Element) shows the symbols of the elements in the chemical given. In this case, it says H and O because H and O are the two elements found in the molecule H₂O, or water. The second column says (Average Atomic Mass). The average atomic mass is a weighted average of all of the isotopes of a given element. The average atomic mass is found on the periodic table of elements as the bottom number. The average atomic mass of hydrogen is 1.008, and the average atomic mass of oxygen is 15.999. The third column is (Atoms), which shows the number of each atom found in the given molecule. Since H₂O has 2 atoms of hydrogen and 1 atom of oxygen, it says 2 for H and 1 for O. The final column is (Mass). This is found by multiplying column two (Average Atomic Mass) by column three (Atoms). There are 2 atoms of hydrogen in 1 molecule of water, so we multiply 2 by 1.008, which equals 2.016. There is only 1 atom of oxygen in one 1 molecule of water, so we multiply 1 by 15.999, which equals 15.999. The bottom of the table says (Molar Mass). This is the sum of all masses (2.016 + 15.999) in this case, which equals 18.02. So 1 atom of hydrogen weighs 1.008 amu (a unit used to measure weight of atoms). 1 atom of oxygen weighs 15.999 amu. Therefore, 1 molecule of H₂O weighs 18.02 g/mol (g/mol is the unit used for molar mass). The molar mass of water is 18.02 g/mol.

How To Calculate Molar Mass By Hand

In order to calculate molar mass by hand, you need to look up average atomic mass for each element in your compound. You can find the average atomic mass for any element on the periodic table of elements. Hydrogen has an average atomic mass of 1.008. Oxygen has an average atomic mass of 15.999. 1 molecule of H₂O has 2 atoms of hydrogen and 1 atom of oxygen. So we multiply 2 by 1.008, then we multiply 1 by 15.999, and finally add up the two resulting numbers. Here's how you calculate the molar mass of H₂O by hand:

$$\begin{aligned} Molar\ Mass\ &=\ (2\times average\ atomic\ mass\ of\ H) + (1\times average\ atomic\ mass\ of\ O) \\ &=\ (2\times 1.008) + (1\times 15.999) \\ &=\ (2.016) + (15.999) \\ &=\ 18.02\ \frac{g}{mol} \end{aligned}$$

What Is Average Atomic Mass?

As an example, the average atomic mass of H is 1.008. This means that if you take a weighted average of all of the Hydrogen isotopes, you'll get 1.008. Hydrogen has 3 different isotopes: H-1 (Hydrogen), H-2 (Deuterium), and H-3 (Tritium). All three isotopes have the same number of protons (1 in this case because the atomic number for Hydrogen is 1). The atomic number is the top number on the periodic table of elements. Even though all three isotopes of Hydrogen have the same number of protons, they each have a different number of neutrons. H-1 has 0 neutrons, H-2 has 1 neutron, and H-3 has 2 neutrons. This is because the number after the H- is the number of protons+neutrons, also known as the mass number. So for H-1, the number of protons+neutrons adds up to 1. Since H always has 1 proton, it must have 0 neutrons. For H-2, the number of protons+neutrons adds up to 2. Since H always has 1 proton, it must have 1 neutron. For H-3, the number of protons+neutrons adds up to 3. Since H has 1 proton, H-3 has 2 neutrons. The mass of H-1 is 1.007825 amu, the mass of H-2 is 2.014102 amu, and the mass of H-3 is 3.016049 amu. Which of those 3 numbers should be used as the mass of hydrogen on the periodic table of elements? The answer requires taking a weighted average. Since H-1 is the most common isotope of the 3, the average atomic mass should be closest to 1.007825 which is the mass of H-1. H-1 has an abundance of 99.9885%, H-2 has an abundance of 0.0115%, and H-3 has an abundance of close to 0%. In order to find the average atomic mass of hydrogen, simply find the weighted average as shown below:

$$\begin{aligned} Average\ Atomic\ Mass\ &=\ (abundance\ of\ ^{1}H\times mass\ of\ ^{1}H) + (abundance\ of\ ^{2}H\times mass\ of\ ^{2}H) + (abundance\ of\ ^{3}H\times mass\ of\ ^{3}H) \\ &=\ (99.9885\%\times 1.007825) + (0.0115\%\times 2.014102) + (0\%\times 3.016049) \\ &=\ (0.999885\times 1.007825) + (0.000115\times 2.014102) + (0\times 3.016049) \\ &=\ (1.00771) + (0.000232) + (0) \\ &=\ 1.008\ amu \end{aligned}$$