The first estimation of the mass of a carbon atom was accomplished through a series of experiments conducted by the chemist and physicist Amedeo Avogadro in the early 19th century. Avogadro is best known for his contributions to the development of Avogadro's law and the concept of Avogadro's number.
Avogadro's work was based on the hypothesis that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. Using this idea, Avogadro proposed that the relative atomic masses of elements could be determined by comparing the densities of their gases.
To estimate the mass of a carbon atom, Avogadro focused on carbon dioxide (CO2) gas. He performed experiments in which he measured the densities of carbon dioxide and hydrogen gases. By comparing the densities, Avogadro was able to determine the ratio of the masses of equal volumes of the two gases.
Avogadro's key insight was that in one mole of any gas at standard temperature and pressure (STP), there are 22.4 liters of the gas. He observed that at STP, one liter of hydrogen gas weighs around 0.0899 grams, while one liter of carbon dioxide gas weighs around 1.977 grams.
Based on these measurements, Avogadro found that the ratio of the masses of equal volumes of hydrogen gas to carbon dioxide gas was approximately 1:22. Using this ratio and the known atomic mass of hydrogen (approximately 1 gram per mole), he could estimate the atomic mass of carbon.
Since the ratio of the masses of hydrogen to carbon in carbon dioxide is 1:22, and the atomic mass of hydrogen is 1 gram per mole, Avogadro concluded that the atomic mass of carbon should be around 12 grams per mole.
This estimation was a crucial step in the development of the concept of Avogadro's number and the determination of atomic masses. Over time, more precise methods and techniques have been developed to measure atomic masses, including mass spectrometry and advanced spectroscopic methods.