Molar mass is the mass of one mole of a substance, which contains Avogadro’s number of atoms or molecules. Atoms have protons, neutrons, and electrons, and a mole is a scientific measurement in chemistry. The mass number is the sum of protons and neutrons, and isotopes are atoms of the same element with different masses. Carbon-12 is the basis for mole measurements, and chemists use molar mass to measure the mass and concentration of a substance.
Molar mass is the mass of one mole of a substance. One mole is defined as the number of atoms in 12 grams of the carbon-12 isotope. This is always a fixed number, known as Avogadro’s number. Therefore, the molar mass of a substance is the mass of Avogadro’s number of molecules of that substance. Molar mass is used to calculate concentrations of a substance in chemistry.
Atoms contain at least two and usually three types of particles. These are the proton, the neutron and the electron. A proton is roughly equivalent to a neutron in terms of mass. The electron is much lighter, so much so that it is almost negligible in the calculation of the mass.
A mole is a scientific form of measurement in chemistry. Elements must have equal amounts of protons and electrons to be stable, but they can vary in the amount of neutrons they contain. The amount of protons in the element is the atomic number.
The amount of protons and neutrons together is the mass number because electrons are so light. The atomic number indicates the element. The mass number can change depending on the amount of neutrons contained in the atom. Atoms that are the same element but have different masses are isotopes.
A carbon atom always has six protons. If it has even six neutrons, it is called an isotope of carbon-12. Made with eight neutrons, it is an isotope of carbon-14.
Scientists have chosen the carbon-12 isotope as the basis for mole measurements. Twelve grams of carbon-12 contain 6.022 x 1023 atoms. This is known as Avogadro’s number. One mole of any substance is defined as this number of atoms or molecules.
Cleverly speaking, the mass of one mole of a substance refers to the individual mass number of the atoms in that substance. For example, one mole of oxygen has a mass of 16 grams. This is because the most common type of oxygen atom contains eight protons, eight neutrons and eight electrons and, therefore, has a mass number of 16.
Measurement by molar mass is also possible with a compound molecule. Water is a molecule that has two atoms of hydrogen and one of oxygen attached together. Adding up all their mass numbers gives the mass of a water molecule. This number is equivalent to the mass in grams of one mole of water.
Chemists use the mole as a measure of the mass and concentration of a substance. Since a mole can contain trillions of atoms and a given number of grams of one substance is not necessarily the same strength as the same number of grams of another substance, it is a very useful method for measuring chemicals in a relatively simple way. The molar mass of a substance is also equal to the mass number of the substance, so chemists can easily use this known quantity to weigh out how much chemical they need to use.
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