SNC 1D1 – Characteristic Physical Properties

1. SNC 1D1 – Characteristic Physical Properties Certain physical properties are unique to each substance. Physical properties are unique due to the composition and structure of each substance. Characteristic physical properties can be used to identify a pure substance. Characteristic physical properties include; density, freezing/melting point, and boiling point.

2. Density: • The density of a substance is a ratio of its mass to its volume. Density = mass /volume D = m / V • The units for density include g/cm3, g/ml, kg/m3 • Density may be used to identify types of matter.

3. Problem: Calculate the density of a metal sample that is 18.0 cm long, 9.21cm wide and 4.45 cm high and that has a mass of 14.25 kg. What is the identity of the metal?

4. The density of a material is related to the mass of the particles that compose the materials. • Densities of gases are closely related to their temperature and pressure. • Gases at high pressure have higher densities, gases at lower pressures have lower densities. • Gases at higher temperatures are less dense than those at lower temperatures. • Pressure and temperature have less effect on liquids and solids making densities of liquids and solids characteristic physical properties.

5. Freezing, Melting and Boiling Points: • The freezing point is the temperature at which substances turn from a liquid into a solid. (water - 0ºC) • The melting point is the temperature at which the substance turns from solid to liquid. (water - 0ºC) • The boiling point is the temperature at which a substance goes from a liquid to a gas. (water - 100ºC) • All three of these points depend on the composition and structure of the substance and are thus characteristic properties.

6. Applications of Melting Points: • The melting points of metals can be used to help choose metals for specific purposes. • Tungsten is used in light bulbs because it has a very high melting point, low chemical activity and it is widely available. • Mercury melts at - 39º C. This makes it useful in thermostats because it conducts electricity but it is also sensitive to changes in temperature.

7. Salt and Ice: • Salt in water interferes with the freezing process and lowers the temperature at which water freezes. • If water contains a 20% mixture with salt it lowers the freezing point to -16ºC. • Salting can be used to prevent water on roads from freezing when temperatures go below 0ºC.

8. Water – An Unusual Molecule: • Most substances become more dense as they transition from a liquid to a solid. • Water actually becomes 10% less dense as it turns to ice. This is why ice floats. • The chemical structure of water gives clues as to why this is: • When water freezes it forms hexagonal spaces that trap air and forces the water to occupy a larger volume thus reducing the density.

9. This property of water means that lakes in the northern and southern hemisphere freeze from the top down providing winter habitats for animals. • Because water expands by 10% it will break pipes and containers if they are overfilled.

10. frozen waterliquid water

11. Homework: Page 198 # 1 -12