1. Physical and Chemical Changes Lab
Station
Name
Observation
Physical or Chemical? 1
Toothpick
Broken into smaller pieces
Physical 2
HCl + Mg
Bubbles (gas formed)
Tube got hot (heat produced)
Chemical 3
NaCl + AgNO3
White solid appeared in the liquid (precipitate) 4
Sodium Chloride - Water
Disappeared in water (dissolved)
Physical*** 5
Candle
Wax melted
Wick burned
BOTH!
Burning=chemical
Melting=physical 6
Acetone and Styrofoam
Melted in the liquid (dissolved)

2. First, let’s review our definitions......
A physical change is a change in which the physical properties of a substance are altered. The change could be in the size or shape, for example. The same substance remains before and after the change.
A chemical change is a change in which one or more new substances are formed. The properties of the new substance will have a different composition from the original substance.

3. Analysis Questions:
Name 3 observations that indicate a physical change has taken place. Give specific examples from the experiment.
a) Breaking- The toothpick is still a toothpick.
b) Dissolving- The Styrofoam just dissolved in the acetone.
c) Melting- The solid wax became liquid wax.

4. 2. Name 3 observation that indicate a chemical change has taken place
2. Name 3 observation that indicate a chemical change has taken place. Give specific examples from the experiment.
a) Production of Gas- The solid Mg and liquid HCl produced a new substance (the gas bubbles were Hydrogen gas) Mg + 2 HCl  2 MgCl + H2
b) Formation of precipitate- The white solid in the NaCl solution was a new substance that formed from the reaction. NaCl + AgNO3  NaNO3 + AgCl
c) Burning – The wick burns and blackens, becoming ash (a new substance).

5. 3. Was the dissolving of salt in water a physical change or a chemical change? Explain why this one can easily be mistaken.
(If you said physical change, it makes sense. Dissolving is usually when a substance goes into a liquid solution, but it is still the same substance and it can be retrieved by physical methods.
If you said a chemical change it makes sense. Because the salt “disappears”, making it seem like a chemical reaction might have taken place. But was a new substance formed?)
To be continued….

6. ***Dissolving: Chemical or Physical?
In some cases, it may be hard to tell whether a chemical or physical change occurred.
For example, when you dissolve sugar in water, a physical change occurs. The form of the sugar changes, but it remains the same chemically (sucrose molecules).
However, when you dissolve salt in water the salt dissociates into its ions (from NaCl into Na+ and Cl-) so a bond is broken.
In both cases a white solid dissolves into a clear liquid and in both cases you can recover the starting material by removing the water, yet the processes are not the same.

7. Salt dissolved in water is a SPECIAL CASE.
This is why I chose it!
Sodium Chloride (NaCl) dissolving in water actually separates into Na+ and Cl-
This means the bond between Na and Cl brakes, and so it could be considered a chemical reaction
I didn’t want to trick you, but I want you learn and to remember. Did anyone look it up?
I want you to know that if we did that lab station with sugar, it would have been a simple physical change. The sugar molecules would stay in tact and no bonds made or broken.

8. Dissolution to Ions
Many scientists continue to argue this one to this day.
Ms. Mom sides with “physical”.
Why? Take a look at my rainbow experiment.
I just let the water naturally evaporate. Salt crystals remained. They aren’t the shape they started in, but they are still made of NaCl.
Though it has aspects of a chemical change, scientists would still classify the dissolution of salt as a physical change.

9. So How Should I Grade It?
I should grade you on your explanation and reasoning. Not whether you answered physical or chemical.
Science is not being about right or wrong.
Just follow the evidence and have a logical explanation.

10. 4. Does a change in temperature indicate a physical change or a chemical change? Explain your answer. (Hint: Think about the candle carefully.)
It can indicate either type of change. Burning is from the hot flame, which is a chemical change.
The wax melting is due to a temperature increase, but melting is a physical change.
The test tube reaction of HCl + Mg also had a temperature increase, which was a chemical change in that case.

11. Review: Evidence of………
physical chemical change both change

12. Choice of words for Venn Diagram
breaking
burning
new chemical
temperature change
phase changes
gas bubbles
Dissolving
Melting

13. Sec 3.2 Review: Evidence of………
physical chemical change both change
Dissolving
Temperature change
Burning
Gas bubbles
New chemical
Breaking
Phase changes
melting