Properties of matter and solutions
A physical property can be measured without changing the substance; a chemical property only shows when the substance becomes something else.
A worked example
Dissolving 24 g of salt to make 400 g of solution gives 24 / 400 x 100 = 6% by mass, and 90 g of metal filling 30 cm3 has a density of 90 / 30 = 3.0 g/cm3.
The mistake people actually make
Mass percent divides by the mass of the whole solution, not by the mass of the solvent alone, and the same holds for a dilution measured by total volume. A WHMIS pictogram names the hazard; the safety data sheet is what tells you how to handle it.