Grade 9 Academic Science – Unit 3 Chemistry
Characteristic Properties
Section 5.6 Pages 192-198
By now, we should be able to define physical and chemical properties, as well as physical and chemical change.
Physical Property
A characteristic of a substance used to identify the substance. Physical Properties DO NOT change the chemical nature of matter. These include:
· Colour
· Odour (smell)
· Taste (sweet, salty, bitter, sour)
· Clarity (clear, cloudy, opaque)
· State (gas, liquid, solid)
· Lustre (dull, shiny)
· Hardness (resistance to being scratched or dented)
· Melting Point (temperature at which a solid melts)
· Boiling Point (temperature at which a liquid boils)
· Viscosity (measure of how easily a liquid flows)
· Solubility (ability of a substance to dissolve in a solvent)
· Density (ratio of mass to volume)
Chemical Property
It describes the behaviour of a substance as it becomes a new substance when it interacts with another substance. It is the potential to undergo chemical change. These include:
· Combustibility (ability of a substance to burn)
· Flammable (substance burns when exposed to a flame)
· Light sensitivity (change when a substance interacts with light)
· Oxidation (change when a substance interacts with air)
In your own words, define each of the following term AND provide an example of each.
· Physical Change
· Chemical Change
Characteristic Properties
A physical or chemical property that is unique to a substance AND that can be used to identify the substance
Temperatures at which physical changes such as freezing, melting and boiling take place are characteristic properties. Why?
· Freezing Point is the temperature at which a substance turns from liquid to solid.
· Melting Point is the temperature at which a substance turns from a solid to a liquid.
· Boiling Point is the temperature at which a substance forms bubbles of vapour that escape into the air. Pure water boils at 100OC.
For a pure substance, what do Freezing Point and Melting Point have in common?
Some facts
· Carbon has the highest melting point of any pure substance. It melts at 3550OC.
· Helium has the lowest melting point of any pure substance. It melts at -272.2OC.
· Gallium is a metal. It is so soft, it can be cut by a knife. Its melting point is 29.8OC. The human body temperature is 37OC. If you hold Gallium in your hand, what should happen?
NOTE: The Freezing Point and Melting Point of a MIXTURE is different that a pure substance. For example, a salt and water mixture has a Freezing Point of -10OC. Knowing this information, why is salt used to make icy roads safer for driving?
How do you think ANTIFREEZE works in a car?
Density is the mass in a given volume of a substance. It is expressed as mass per volume. For example, the density of pure water is 1 g/mL. In your own words, what does that mean?
· Each substance has its own unique density.
· The human body and water have about the same density. Thus, humans sink or float in water depending on how much air is in the lungs.
· A lifejacket contains a tiny cylinder of compressed CO2. When the ripcord is pulled, the gas rushes from the cylinder and inflates the lifejacket. The mass of the lifejacket does not change, but the volume of the lifejacket increases. Knowing this about the lifejacket, how does it keep you afloat?
Activity – How does salt impact the freezing point of water
Equipment
· 250 mL beaker
· Ice cubes
· Thread
· Teaspoon of salt
· Stirring rod
· Thermometer
· 125 mL H2O
Methods
· Put the H2O into the beaker
· Add the ice cubes to the beaker until full
· Place a thermometer into the beaker
· The temperature of the ice water will decrease. Wait until the temperature is near 0OC.
· Add salt to the ice water and stir gently
· Observe the temperature
HOMEWORK – PRACTICE
· Page 198, Questions 1,4-11