Final answer:
31.2 g of magnesium chloride is equivalent to about 1.976 × 1023 formula units. This is determined by first calculating the number of moles from the given mass and the molar mass of MgCl2, and then multiplying by Avogadro's number.
Step-by-step explanation:
To calculate the number of formula units of magnesium chloride (MgCl2) that make up 31.2 g of the substance, we first need to find the molar mass of magnesium chloride. The molar mass of magnesium is 24.31 g/mol and that of chlorine is 35.45 g/mol. Therefore, the molar mass of MgCl2 (1 Mg atom and 2 Cl atoms) is 24.31 g/mol + (2 × 35.45 g/mol) = 95.21 g/mol.
Next, we convert the mass of MgCl2 to moles using its molar mass:
31.2 g MgCl2 ÷ 95.21 g/mol = 0.328 moles of MgCl2
Avogadro's number tells us that 1 mole of any substance contains 6.022 × 1023 formula units. Therefore, to find the number of formula units in 0.328 moles, we multiply this by Avogadro's number:
0.328 moles × 6.022 × 1023 formula units/mole = 1.976 × 1023 formula units of MgCl2