Question

What is the mass of 2.90 ×10^22 formula units of NaOH (Molar mass = 40.0 g/mol)?

Answer 1

Considering the Avogadro number, we know that there is 6,022 x 10^23 molecules of NaOH in 1 mol of NaOH, and we need to calculate how much in mols we would have for 2.90 ×10^22 molecules:

6,022 x 10^23 molecules ------- 1 mol

2.90 ×10^22 molecules ---------- x

`x\text{ = }\frac{\text{1 mol of NaOH}*(2.90*10^(22)\text{molecules of NaOH)}}{(6.022*10^(23)\text{ molecules of NaOH)}}`

Solving for x, we have 0.048 mol of NaOH.

Now we calculate how much, in mass, 0.048 mol of NaOH is:

1 mol ---------- 40.0 g

0.048 mol ---------- y

Solving for y, we have 1.92 g of NaOH