Knowns

Material	Accepted Density (g/mL)
Steel	7.8
Carbon	1.8
Brass	8.5
Lead	11.35
Styrofoam	0.01*
Cast Iron	7.87
Aluminum	2.70
Wood (pine)	0.5*
Plastic	1.2
Water	1.00
Salt Water	1.08
Methyl Alcohol	0.791
Ethylene Glycol	1.113

Unknowns

Material	Accepted Density (g/mL)
Phosphorus	1.82
Silicon	2.33
Titanium	4.50
Iron Sulfide	5.1
Vanadium	5.8
Zinc	7.14
Tin	7.31
Nickel	8.90
Copper	8.96
Bismuth	9.8
Technetium	11.5
Hafnium	13.1
Tungsten	19.3

Pick the substance that is closest to your experimental density and use that accepted density to calculate the experimental error.
Click here to learn how to calculate experimental error.