how many molecules are in 25.5g of iron (iii) hydroxide?

Question

How many molecules are in 25.5g of iron (iii) hydroxide?

Answer 1

The first step I would use on this one is converting the grams into moles by dividing by the molar mass

Moles = Mass / Molar Mass = 25.5g / 106.866 g/mol = 0.2386 moles

From there then you can convert over into Molecules by multiplying by Avogadro's Number

0.2386 moles x (6.022 x 10^23 molecules/mole) = 1.44 x 10^23 molecules

Answer 2

Iron(III) hydroxide = Fe(OH)₃

Molar mass of Fe(OH)₃ = 55.9 = 3x16 + 3x1 = 55.9 + 48 + 3 = 106.9 g/mol

Moles of Fe(OH)₃ in 25.5 g = 25.5 g x 1 mol / 106.9 g = 0.2385 moles

Molecules of Fe(OH)₃ = 0.2385 mols x 6.022x10²³ molecules / mole = 1.44x10²³ molecules (3 sig.figs.)