Online labs include: Mixture Separation Living in a Thirsty World Matter and Change Why it Matters

Physical Properties and Physical Changes
A 
physical property
 is a characteristic that can be observed or measured 
without changing the identity of the substance.
We commonly use physical 
properties to describe a substance. Examples of physical properties are 
melting point and boiling point. For example, water melts from ice to 
liquid at 0°C (273 K or 32°F). Liquid water, as shown in 
Figure 2.2,
boils to 
vapor at 100°C (373 K or 212°F). Density is also another physical property. 
Water’s density at 4°C (277 K or 39°F) is about 1000 kg/m
3
. Unlike most 
substances, the density of water decreases when it freezes to become ice. 
As a result, a pond or lake that freezes in the winter does so from the top 
down, enabling some fish to survive in the water at the bottom.