How many atoms of silicon are in 535gm of Na8[Cl2(AlSiO4)6]?

Question

an explanation of how you got the answer would be nice. thanks

Answer 1

To get number of atoms, you need number of moles.

moles = mass / Molar mass

Molar mass = 8 Na + 2 Cl + 6 (AlSiO4)
= 8 (22.99g/mol) + 2(35.35g/mol) + 6 (26.98g/mol+28.09g/mol+ 4*16.00g/mol)
=969.24g/mol

therefore
moles = 535g/969.24g/mol = 0.552 mol of your total compound.

for every moles of your compound, there are 6 moles of Si.

Therefore there are 6*0.552 = 3.31 mol of Si in this compound

atoms of Si = moles x Nv (Avagrado's number)
=3.31 x 6.02x10^23
=1.99x10^24 atoms of Si

Answer 2

MW = 8*23 + 2* 35.5 + 6*27 + 6*28 + 24*16 = 969

535 g/ 969 g/mole = 0.552 moles

0.552 moles * 6.022 *10^23 molecules/mole * 6 atoms Si/molecule = 19.9 * 10^24 atoms