What would be the mass of 1000ml of aluminum?

The density of something is mass/volume (this is a constant)

The density of Aluminium is 2,700 kg/m3 at STP

Therefore knowing the density and the volume you can work out the mass

If D = M/V then M = D*V

1m3 = 1000000 ml

But we have only 1000 ml or 1000/1000000 of a 1m3 = 0.001m3

Therefore 0.001 * 2700 = 2.7 kg