Question

Calculate the number of moles 41.0 g of Ca(NO3)2  1.48 g of Ca(OH)2  3.40 g of CaSO4

Answer 1

First. moles is just a label for a number of things. just like a dozen = 12, a gross = 144, a mole = 6022 with another 20 zeros after the 2

next

moles = mass / molecular weight.

molecular weight = sum of atomic mass from the periodic table

atomic mass MnO2 = atomic mass Mn + 2 x atomic mass O
= 54.94 + 2 x 16 = 86.94 g/mole

so moles MnO2 = 98.0 grams / (86.94 g/mole) = 1.13 moles

notice that I only gave 3 digits? that because of sig figs read the link below if you don't understand....

mw C5H12 = 5 x 12 + 12 x 1 = 72 g/mole

so moles C5H12 = 12.0 g / 72.0 g/mole = 0.167 moles

mw XeF6 = 131.3+ 6 x 19.00 = 245.3

so moles XeF6 = 100 g / 245.3 g/mole = 0.4077 moles

I've also provided a link to a periodic table. if you need atomic weights click on any element and it will give you the
details.