The element nickel (Ni) has a density of 8.91 g/cm3. How many moles of nickel are there in 5.0 L of nickel. (molar mass 58.69 g/mol)?

Volume nickel = 5.0 L = 5000 cm³

Mass of nickel = Volume × Density = (5000 cm³) × (8.91 g/cm³) = 44550 g

No. of moles of nickel = Mass / Molar mass = (44550 g) / (58.69 g/mol) = 759.1 mol

d = m/V

8.91 g/cm3 = m/V = m/5000
m = 44550 g

so

M = m/n
n = m/M = 44550/58.7 mol =758.9 moles

1 L = 1 dm3 = 1000 cm3

Hope that helps