![]() However, while this equality can be assumed for practical purposes, it is only approximate, because of the 2019 redefinition of the mole. A protein whose molecule has an average mass of 64 kDa would have a molar mass of 64 kg/mol. For example, the average mass of one molecule of water is about 18.0153 daltons, and one mole of water is about 18.0153 grams. ![]() ![]() That is, the molar mass of a chemical compound is meant to be numerically equal to its average molecular mass. The mole is a unit of amount of substance used in chemistry and physics, which defines the mass of one mole of a substance in grams as numerically equal to the average mass of one of its particles in daltons. The DNA of chromosome 1 in the human genome has about 249 million base pairs, each with an average mass of about 650 Da, or 156 GDa total. Titin, one of the largest known proteins, has a molecular mass of between 3 and 3.7 megadaltons. The molecular masses of proteins, nucleic acids, and other large polymers are often expressed with the units kilodalton (kDa) and megadalton (MDa). The two most common masses of individual acetylsalicylic acid molecules are 180.0423 Da, having the most common isotopes, and 181.0456 Da, in which one carbon is carbon-13. However, there are no acetylsalicylic acid molecules with this mass. Acetylsalicylic acid ( aspirin), CĤ, has an average mass of about 180.157 Da. This is an intrinsic property of the isotope and all helium-4 atoms have the same mass. For example, an atom of helium-4 has a mass of 4.0026 Da. This unit is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles, both for discrete instances and multiple types of ensemble averages. The atomic mass constant, denoted m u, is defined identically, giving m u = 1 / 12 m( 12C) = 1 Da. The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass defined as 1 / 12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest.
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