To determine the number of molecules of PCI5, we need to use the following steps:
Convert the given mass of PCI5 to moles using the molar mass of PCI5.
Use Avogadro's number to convert the number of moles to molecules.
The molar mass of PCI5 can be calculated as follows:
P = 1 x 30.97 = 30.97
C = 1 x 12.01 = 12.01
I = 5 x 126.90 = 634.50
Molar mass of PCI5 = 30.97 + 12.01 + 634.50 = 677.48 g/mol
Mass to moles:
moles = mass / molar mass
moles = 77.4 g / 677.48 g/mol
moles = 0.114 moles
Moles to molecules:
One mole of any substance contains 6.022 x 10^23 particles (Avogadro's number).
Number of molecules = moles x Avogadro's number
Number of molecules = 0.114 mol x 6.022 x 10^23 mol^-1
Number of molecules = 6.87 x 10^22 molecules
Therefore, there are 6.87 x 10^22 molecules of PCI5 in 77.4g of PCI5.