How many moles are there in 1.09 kg of Al (OH) 3?

How many formula units are there in 2.55 g of Pb (CO3) 2?

question 1

moles = mass/molar mass of Al (OH) 3

convert Kg to g

that is 1.09 x 1000=1090g

moles is therefore=1090g/78 (molar mass of Al (OH) 3) = 13.974 moles

question 2

moles=2.55g/327.2 (molar mass of Pb (CO3) 2 = 7.79 x 10^-3 moles

from avogadro constant

1moles=6.02 x10^23 formula units

what about 7.79 x 10 ^-3

={ (7.79 x 10^-3) moles x (6.02 x10^23) } / 1 mole=4.69 x10^21 formula units