15) How many grams do 4.3times 10^21 molecules of UF_(6) weigh?

To solve this problem, we need to find the molar mass of UF6 and then use it to calculate the weight of 4.3 x 10^21 molecules of UF6.<br /><br />Step 1: Find the molar mass of UF6.<br />The molar mass of UF6 is the sum of the molar masses of uranium (U) and fluorine (F).<br />Molar mass of U = 238.03 g/mol<br />Molar mass of F = 18.998 g/mol<br /><br />Molar mass of UF6 = Molar mass of U + 6 * Molar mass of F<br />Molar mass of UF6 = 238.03 g/mol + 6 * 18.998 g/mol<br />Molar mass of UF6 = 352.03 g/mol<br /><br />Step 2: Calculate the weight of 4.3 x 10^21 molecules of UF6.<br />To find the weight of 4.3 x 10^21 molecules of UF6, we need to use Avogadro's number, which is 6.022 x 10^23 molecules/mol.<br /><br />Weight = (4.3 x 10^21 molecules) * (352.03 g/mol) / (6.022 x 10^23 molecules/mol)<br />Weight = 2.57 x 10^3 g<br /><br />Therefore, 4.3 x 10^21 molecules of UF6 weigh approximately 2.57 x 10^3 grams.