Ch 2.3
Chemical Properties
When you describe the
candles at the left you
may talk about the
color, the size, the
smell, or the fact that
they float on water.
Those are all physical
properties….
You may also notice that
the candles are burning.
This is a Chemical property
because you cannot test it
without changing the
composition of the candle
The burning of the candle
creates new compounds
like ash and smoke.
• Chemical Properties –
any ability to produce
change in the make up
of matter.
This means that chemical
properties can only be
observed as the
chemical itself changes
into different materials.
Flammability and reactivity are both examples
of chemical properties.
Flammability
Flammability is a material’s
ability to burn when oxygen
is present.
Gasoline is burned to power
cars and wood is burned for heat and light.
Flammability is not always considered a good thing.
Cloth is often flammable but if your clothes are
burning they are not doing their intended job.
Reactivity
Reactivity is the ability to combine
chemically with other
substances. Oxygen is a very
reactive element, while Nitrogen
is has a very low reactivity.
Oxygen in the presence of water
and iron creates rust. Oxygen
with apples causes them to
brown.
What is the ability to produce a change in the
make up of matter called?
a. Chemical change
b. Chemical property
c. Physical change
d. Physical property
Answer : B
Which of the following is an example of a
chemical property?
a. Color
b. Density
c. Reactivity
d. Hardness
Answer: C
Which element is more reactive, Nitrogen or
Oxygen?
Answer: Oxygen
Other reactive elements are iron, sodium, and
chlorine
Chemical Changes
A chemical change is any change that cause the
substance to turn into a new and different
substance.
• Cutting an iron beam in half is not a chemical change, because you still
have iron, just in smaller pieces.
• Water and oxygen acting on iron to cause it to change to iron oxide, or rust
is a chemical change because rust is a new compound separate from the
iron we started with.
Which of the following is a chemical change?
A. Peeling a banana
B. Turning copper into a wire
C. Burning a log on a fire
D. Driving over a watermelon
Answer: C
Detecting Chemical Change
There are 3 main ways to detect chemical
change:
1. Change in color
2. Production of gas
3. Formation of a precipitate
Changes in color
Shiny silver left out and exposed to the air will
dull and darken
A lit match will turn dark black.
Copper turns green with time and air.
Banana peels turn brown with spots as they
ripen.
These are all changes of color from chemical
change.
Production of a Gas
Think about mixing vinegar with baking soda.
The foaming bubbles produced are the result of
a chemical change. This is similar to what
happens when baking soda or yeast is used in
baking. The gas produced creates bubbles of
carbon dioxide that causes the bread or cake
to rise.
Formation of a Precipitate
A precipitate is any
solid that forms and
then separates when
liquids mix.
When an acid is added
to milk, the proteins
and fat in the milk
undergo a chemical
change to form
cottage cheese as a
precipitate.
When a marshmallow is held over a camp fire
but doesn’t catch fire, what tells you a
chemical change has occurred on the outside?
Answer: The marshmallow changes color as it
cooks on the outside.
What tells you a candle wick is undergoing a
chemical change?
a. It changes color as ash forms on it
b. A small trail of smoke rises from the wick
c. The wick begins to grow shorter
d. Both a and b
Physical and Chemical Change
Gas, color change, and even precipitate does not
always mean a chemical change. A hot piece
of iron is still iron though it turns orange or
white. Water releases steam as it boils, but it
is still water.
A chemical change always produces new
substances. The composition of matter
changes whenever a chemical change occurs.
A pad of butter is put in a hot pan and begins to
melt. Is this a chemical or physical change?
Answer: Physical, it is still butter, just melted.
The butter then begins to burn and smokes and
turns to a brown ash on the pan. Is this a
chemical or physical change?
Answer: Chemical the butter is changed into a
gas and a carbon residue left behind.