The apparent discrepancy between the atomic mass of aluminum (26.98 g/mol) and the mass of an aluminum coin (0.75 g) can be explained by considering the different scales involved in these measurements.
Atomic Mass: The atomic mass of an element, such as aluminum, is given in atomic mass units (amu) or grams per mole (g/mol). It represents the average mass of one atom of that element compared to the mass of one-twelfth of a carbon-12 atom. The atomic mass takes into account the relative abundances of different isotopes of the element and their respective masses. In the case of aluminum, it has several isotopes with different masses, including aluminum-27 being the most abundant.
Mass of an Aluminum Coin: On the other hand, the mass of an aluminum coin is measured in grams (g) and represents the total mass of the entire coin. Coins are made up of a mixture of elements, including aluminum and other metals. The mass of the coin includes not only the aluminum content but also the other components such as alloying metals, potential impurities, and any design features or coatings on the surface.
The mass of an aluminum coin is significantly lower than the atomic mass of aluminum because the coin is composed of a large number of atoms, each with its own atomic mass. The coin's mass is determined by factors such as its size, thickness, and the specific composition of the alloy used to make it.
Therefore, it's important to differentiate between the atomic mass of an element, which refers to the average mass of one atom of that element, and the mass of an object composed of that element, which takes into account the total mass of all the atoms within that object. The mass of a macroscopic object like an aluminum coin will be significantly higher than the mass of a single atom of aluminum.