Question

What is the mass of 5.00 x 10 21 formula units of aluminum hydroxide?

Answer 1

We are given with a compound, Aluminum Hydroxide (Al(OH)3), with a molar of 5.00 x $10^{21}$ formula units. We are tasked to solve for it's corresponding mass in g. We need to solve first the molecular weight of Aluminum Hydroxide, that is
Al=27 g/mol
O=16 g/mol
H=1g/mol

Al(OH)3= 27 g/mol +16(3) g/mol +1(3) g/mol= 78 g/mol

Not that 1 mol=6.022x10^{23} formula units, hence,

5.00 $10^{21}$ formula units x $\frac{1 mol }{6.022x10^{23} formula units}$ x$\frac{78 g}{1 mol}$
=0.648 g of Al(OH)3

Therefore, the mass of Aluminum Hydroxide is 0.648 g