Name: ______Date: ______Pd: ______Day: ______

Physical vs. Chemical Changes Lab

Studying changes in matter is an important aspect of chemistry. The term “change” indicates an alteration to some aspect of matter that is being studied. These changes to matter can be classified as physical or chemical changes. Physical changes are those where the composition of the components DOES NOT change. On the other end, chemical changes are those where the composition of the components DO change and result in NEW substances being formed. Generally, the physical properties of the NEWLY formed substance are significantly different from the component elements. Remember again that in order to indicate a change, you must know the condition BEFORE and AFTER some action has taken place. Therefore it is important to indicate your observation both before and after you perform a specific task, in order to help determine the type of change.

There are common observations that are generally used to identify whether a change is physical or chemical. In today’s lab, you will perform a series of short experiments to help identify physical vs. chemical changes. Read and follow the step by step directions to help determine type of change.

PRELAB QUESTIONS:

1.  Indicate whether each of the following is a physical or chemical change. Write a one sentence explanation for why.

a.  Melting ice

b.  Litmus paper turns pink in the presence of sulfuric acid

c.  Hydrogen gas makes a popping noise when a lit splint is brought to it

d.  Throwing a rock at a glass window shatters the glass

2.  List five observations that indicate that a chemical change is taking place.

3.  What is the only way to determine whether a chemical change has in fact taken place?

4.  Based on the procedures given, is this a qualitative or quantitative lab? How do you know?

DATA TABLE:

Each column provides different information. Column 1 and 2 are filled for you (you may copy this as given). You are responsible for filling in column 3, 4 and 5

1.  List of Substances/Mixtures needed

2.  Procedure—this is the most important step. Follow directions CAREFULLY

3.  Your Prediction: Do you think this is a physical or chemical change? Write down (P=physical) or
(C=chemical)

4.  Observations: List your observations here.

5.  Evidence: Analysis of data.

a.  Is your prediction correct?

b.  Indicate the type of change that actually occurred.

c.  If a physical change occurred, indicate type of change (reversible or irreversible)

d.  If a mixture formed, indicate type of mixture (homogeneous or heterogenous)

e.  What evidence do you have to indicate whether a physical or chemical change has taken place. Write a statement about the scientific evidence you have that your analysis is accurate. Additionally, write a statement about what you can do to VERIFY that your analysis is correct (such as further test, separation of mixture etc.)


Data Table: Identifying Physical vs. Chemical Changes

At each station, you will find the materials needed for this portion of the lab. Use the materials as required. Clean up after you are done, leaving the station as clean or cleaner than you found it. You will have approximately 5-7 minutes at each station. Work diligently so you can finish in time. Remember again, the goal of the time in lab is to finish the experiment. You should use this time to perform lab and record observations. This is not the time to finish writing your analysis.

1 / 2 / 3 / 4 / 5
Substances/Setup / Procedure / Your Prediction / Observations / Evidence / Analysis
1. Salt and Water / 1. Place 10 mL of water in a beaker.
2. Sprinkle 1 scoopula tip full of salt on it.
3. Stir with a stirring rod / BEFORE
AFTER
2. Wood Splint / 1. Break wood splint into very small pieces / / BEFORE
AFTER
3. Wood Splint / 1. Light a Bunsen burner.
2. Hold wood splint in burner for 15-20 seconds
3. Remove and blow out flame if splint is lit / BEFORE
AFTER
4. Magnesium in HCl / 1. Place small testtube in testtube rack.
2. Place about 1 mL (approximately 1 small finger width) of Hydrochloric acid in the testtube.
3. Check temperature of HCl using a thermometer. Rinse thermometer in water.
4. . Place Mg (cut 1 inch piece Mg into small pieces) into testtube.
5. After 1 minute, check temperature inside testtube again. Rinse thermometer / BEFORE
AFTER
5. Milk / 1. Place small quantity of milk in a testtube.
2. Waft for smell.
3. Test temperature.
4. Using a testtube clamp, attach to ring stand and heat (Bunsen burner) for 2-3 minutes, until the milk boils
5. Test temperature again / BEFORE
AFTER
6. Milk (Continuation of #5—you do not need NEW milk for this) / 1. Place small quantity of milk in a testtube.
2. Using a testtube clamp, attach to ring stand and heat for 2-3 minutes, until the milk boils. Turn off Bunsen burner.
3. Add 10 drops of vinegar to the hot milk
4. Waft for smell. / BEFORE
AFTER
7. Heating Magnesium / 1. Take a strip to Mg ribbon approximately 5 cm long.
2. Light a Bunsen burner
3. Using crucible tongs, hold Mg ribbon in flame until you observe a change.
NOTE: DO NOT LOOK DIRECTLY AT Mg
4. Remove from flame and hold over a watch glass to collect any product. Continue holding until no more change occurs.
NOTE: BE CAREFUL TO NOT DROP Mg ONTO WATCH GLASS WHILE ANY CHANGE IS TAKING
/ BEFORE
AFTER
8. Mg product and HCl (continued from 7) / 1. Collect any product formed in step 7 on a clear watch glass.
2. Add 2-3 drops of HCl to Mg product.
3. Compare to results from step 4 / BEFORE
AFTER
9. Calcium chloride vs. Silver nitrate / 1. Transfer 1-2 mL (about 1pipette full) of Calcium chloride to a clean testtube.
2. Add 1-2 mL of Silver nitrate to testtube. / BEFORE
AFTER

POST LAB QUESTIONS

1.  Write a general statement about the difference between a physical and a chemical change.

2.  Classify each of the following as a physical or chemical change and give a specific reason why.

  1. Mothballs gradually vaporize in a closet.
  2. Hydrochloric acid attacks glass and is used to etch calibration marks on lab glassware
  3. Baking soda fizzes when mixed with vinegar
  4. A piece of rubber stretches when you pull on it.

3.  What does it mean when we say that the “composition of matter has changed during a chemical reaction”?

4.  List three specific tests you could do, or properties you could test to verify whether the composition of matter has actually changed during a chemical reaction.