Final answer:
To find the number of Al molecules in a piece of aluminum foil, one calculates the mass of the foil using its density and volume, then converts that mass into moles, and finally multiplies by Avogadro's number. The given volume and mass of a single molecule provide insufficient evidence to reach the provided answer of 1.27 × 10^23 molecules.
Step-by-step explanation:
To calculate the number of Al molecules in a piece of aluminium foil with a volume of 0.79 cm³, we need to use the molar mass of aluminum (which is 26.98 g/mol) as well as the mass of a single aluminum molecule (4.5 × 10^-23 g). First, we find the mass of the aluminium foil using its density, which is 2.70 g/cm³. Multiplying the density by the foil's volume (0.79 cm³) gives us a mass of 2.133 g.
Next, we convert the mass of the foil to moles by dividing by aluminum's molar mass (26.98 g/mol), which results in approximately 0.0791 mol of aluminum. To find the total number of molecules, we multiply 0.0791 mol by Avogadro's number (6.022 × 10^23 molecules/mol). This calculation yields approximately 4.76 × 10^22 molecules. Since this result is not one of the provided answers, there may be a mistake in the provided answers or the question itself.