Key Concept: Characteristic Properties

Sample Questions:

1. (JUNE 1999)Which of the following is a characteristic property of a liquid sample of a pure substance?

1. mass: 211 g
2. density: 0.98g/mL
3. volume: 215 mL
4. temperature: 23^oC

Answer B

1. (JUNE 1996) A student made the following observations in the laboratory. Which observation is a characteristic property of a substance?

1. Mass of iron: 250 g
2. Volume of lead: 50 cm3.
3. Melting point of copper: 1083 ^oC.
4. Temperature of water: 60 ^oC.

Answer C

1. (JUNE 1995: 416/436: Part B)While at a flea market, you purchased a ring that was supposedly pure gold, Au. You want to determine experimentally whether it is real gold or not. You already know the density of pure gold.

Explain in detail the experimental procedure you will carry out to determine whether the ring is pure gold.

Answer Weigh the gold ring. Measure 30ml of water. Add ring to water. Find the new volume of ring + gold. By subtracting the two volumes, we will get the volume of the ring. Then density = mass/volume.

Notes:

Characteristic Properties

A characteristic property helps you identify a substance. Out of all the elements, only copper melts at 1083 ^oC. Out of all common compounds, only H₂O has, at a specific temperature, a density of 0.98g/ml (usually rounded to 1). To say that I have 215 g of a substance in my pocket will not help you guess what it is. It may be a diamond, tangerine peels or a bunch of Kleenex. So mass is not characteristic.

Here is a list of physical properties that are characteristic:

• Density
• Melting or freezing point
• Boiling point
• Electrical conductivity, if expressed as a certain number
• Refractive index ( though I’ve never seen them use this one on provincial exams)

Here is a list of chemical properties that are characteristic for certain substances. Know all of them.

TEST	RESULT	INDICATES PRESENCE OF:
Cobalt chloride	Turns from blue to pink	Water = H2O
Glowing splint	Bursts into flames	Oxygen gas = O2
Limewater	Turns cloudy because of CaCO3	Carbon dioxide gas = CO2
Flaming splint	Popping sound and only water is left behind	Hydrogen = H2

 Properties also help distinguish groups of elements or compunds from other groups. Such a property is known as a group characteristic property. Here are some examples, many of which will be seen again later in the course, so you don't have to learn the specifics yet, but understand the general idea.

Group	Group Characteristic Properties
alkali metals	Soft, low-melting metals
acids	Conduct electricity (electrolytes) and turn blue litmus red
bases	Conduct electricity (electrolytes) and turn red litmus blue