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Avogadro's number is a fundamental constant used in chemistry to calculate the number of entities, usually atoms or molecules, present in one mole of a substance. The value is approximately \(6.022 \times 10^{23}\) entities per mole. This profound number allows chemists to bridge the gap between the atomic scale and the macroscopic scale we observe. In our case of Freon-12, once we know the number of moles, we can easily determine the number of molecules by multiplying the number of moles by Avogadro's number. This conversion is essential for chemical calculations and offers insights into the massive quantity of molecules present even in seemingly small amounts of a substance. By using Avogadro's number as part of our calculations, we can determine that in 5.56 mg of Freon-12, there are approximately \(2.77 \times 10^{19}\) molecules.

Mass percentage is a way of describing the composition of a compound by dividing the mass of a particular element by the total molecular mass, then multiplying by 100 to get a percentage. This is very useful for understanding how much of a specific element, like chlorine in Freon-12, is present in a compound. To find the mass percentage of chlorine in Freon-12, we calculate the total mass of the chlorine atoms in the molecule and divide it by the molecular weight of Freon-12. In our case, Freon-12 has a mass percentage of chlorine of approximately 58.51%. This essentially means that 58.51% of the mass of Freon-12 is due to chlorine atoms. Knowing the mass percentage allows us to easily calculate the actual mass of chlorine in any given amount of Freon-12, such as the 5.56 mg discussed earlier, resulting in roughly 3.25 mg of chlorine.

Calculating the number of moles is a fundamental skill in chemistry that involves dividing the mass of a substance by its molecular weight. This is essential for linking the mass of a sample to the number of molecules or atoms contained within. In the context of Freon-12, after converting the mass from milligrams to grams, we divide by the molecular weight of 120.91 g/mol.The process results in a number of moles for the given mass, providing insight into the amount of substance in a measurable way. For the 5.56 mg of Freon-12, we calculated approximately \(4.6 \times 10^{-5}\) moles. Establishing the number of moles acts as a crucial step for further calculations, such as determining the total number of molecules using Avogadro's number.

Freon-12, chemically known as dichlorodifluoromethane and represented by the formula \(\text{CCl}_2\text{F}_2\), has been widely used as a refrigerant and as a propellant in aerosol cans. The compound consists of one carbon atom, two chlorine atoms, and two fluorine atoms. Each of these atoms contributes to the molecular weight and properties of Freon-12. The presence of chlorine contributes to the cooling properties and stability of the compound. Freon-12 was a popular choice in refrigeration because of its non-flammable and relatively non-toxic nature. However, Freon-12 is also known for its environmental impact, particularly its role in ozone layer depletion, leading to its phasedown under international regulations like the Montreal Protocol. Understanding the basic properties and structure of Freon-12 is essential for both its practical applications and environmental considerations. Its use and phase-out demonstrate the intersection of chemistry, industrial application, and environmental science.