The choice to use 1/12 of the mass of a carbon-12 (C-12) atom as a reference is based on historical conventions and practical considerations in atomic mass calculations.
The atomic mass unit (amu) is a unit of mass commonly used in chemistry to express the masses of atoms and molecules. Initially, scientists needed a reference point to establish a scale for atomic masses. They chose the carbon-12 isotope as the reference because it is the most abundant and stable isotope of carbon.
The mass of a carbon-12 atom is approximately 12 atomic mass units (amu). However, it is important to note that the amu is not equal to the mass of an individual carbon-12 atom. Rather, it is defined as 1/12 of the mass of a carbon-12 atom. This choice was made to ensure consistency and to simplify calculations.
Using carbon-12 as the reference allows scientists to compare the masses of different atoms and isotopes relative to a known value. For example, if an atom has an atomic mass of 20 amu, it means that it is approximately 20 times heavier than 1/12 of a carbon-12 atom.
This reference point is also practical because carbon is a common element in organic compounds and is widely used in chemical reactions and measurements. Therefore, it provides a convenient baseline for comparing atomic masses across different elements.