PROBLEM:
What is the difference between the two changes in the sugar. Why?
HYPOTHESIS:
MATERIALS:
100 mL of sugar crystals, two 100 mL beakers, two glass stirring
rods, go outdoors or under a fume hood!
PROCEDURE:
Fill
each beaker half full of sugar.
Add
about 40 mL of water to the first beaker and the same amount of
concentrated sulfuric acid to the second beaker.
Stir
and let it stand.
Observe
the difference between the two changes in the sugar.
Ask:
"In which beaker do the reactants still have the same properties?"
OBSERVATION:
CONCLUSION:
What is
the difference between the processes in beaker I and beaker II?
How can
we recognize or distinguish between a physical change and a chemical
change?
In which
of the two beakers could we get the sugar back as sugar?
What do
you think happened in the second beaker?
What property
do you think concentrated sulfuric acid has?
What do
you think the black material in beaker two is?
Change
There are
two types of change:
Physical
change
Chemical
change
In a physical
change there is only a change of state. The new substance has the same
properties as the old one. No new substance(s) are produced.
ice - water
- steam (They are all still water!) For example: ice melting to water
or water boiling.
**In all of these changes, you can get the original materials back!**
A physical change may also involve changing the shape of the substance.
paper cut into pieces is still paper, sloughing a field but the field
still remains as soil, cutting wood into pieces is still wood, and molding
a sculpture is still cement or marble!
In a chemical
change one or more NEW substances are created. The new substance is different
from the original. It has properties that are different than those of
the starting materials. Plus, you cannot get the original materials back
easily.
(Think about
an ordinary box of matches. A single match in a box can remain unchanged
forever. But if someone were to take the match and then light it...A flame
lights up and then burns out. What remains will have changed forever!
The match can never be lighted again. The match has undergone a chemical
reaction.)To view a quick movie of a chemical change, click the button
below!
Here are
some other examples of chemical reactions:
raw
egg becomes cooked egg
cake
mix
becomes cake
paper
becomes ash
steel
becomes rust
Can
you think of other chemical reactions that occur in everyday life?
Think about
these changes...
What
might be some clues that would help us know whether or not the change
is chemical?
1). Chemical Change or Physical Change?
State whether the following changes are chemical or physical.
boiling
water
tearing
clothes
tarnishing
silver
lighting
a match
chewing
a food
breaking
a stick
rusting
nail
burning
gas in a stove
melting
ice cream
sawing
wood
oxidizing
food for energy
stretching
a rubber band
2). Find
three examples of Chemical and Physical Changes in everyday life. Explain
why each of these changes are either chemical or physical.
LAB:
MELT IT!
Problem:
Which ice cube will melt the fastest? Why? A: The ice cube left
on the kitchen counter. B: The ice cube left in a hot spot. C: The
ice cube with salt on it. D: The ice cube crushed gently with a
heavy utensil or hammer.
Materials:
4 ice cubes, same size
4 small dishes
salt
hammer or heavy utensil
Procedure:
Put
an ice cube on each plate.
Leave
one on the kitchen counter.
Find
a hot spot around your lab or classroom. (On a windowsill or next
to a heater).
Put
one ice cube in the hot spot.
Pour
salt on the third ice cube.
Put
this ice cube on a table or counter.
Crush
the last ice cube gently with a hammer or heavy utensil and leave
it on the counter.
Wait
a few minutes. Check your ice cubes and see what happened.
Which
ice cube melted the fastest? Compare how long it takes for the
ice cubes to melt.
Observations:
Observe
and record what happens.
Record
the time to the minute on your data sheet.
Translate
your collected data into a graph.
Conclusion:
To
make a connection to literacy, write a story to explain what happens to
a snowman who sits for two hours on a sunny day! Make sure you go into
detail following the steps you observed as the ice cube melted in the
lab.
Using
the data collection sheet provided, go through the various stations and
determine whether the change is physical or chemical. Make sure to indicate
the reasons or characteristics that helped you to decided if it was a
chemical or physical change.
Classify
the changes listed below as either physical or chemical, then give a reason
for your decision.
Change/Type/Reason:
Fill in the information about the type and the reason why it is a chemical
or physical change.
