ADVENTURE #2

Physical and Chemical Changes

INTRODUCTION:

In chemistry it is important to learn to make careful observations to determine what types of changes you are observing. Chemists classify changes as chemical or physical. In a physical change the identity of the starting material does not change. Some examples of physical changes are: water boiling, a gas being compressed, sugar dissolving in water, and cutting up a piece of paper. In a chemical change the identity of the starting material changes. Chemical changes are usually accompanied by one or more physical changes such as a color change, the formation of a gas or a precipitate, or a change in temperature. Some examples of chemical changes are the rusting of iron, the digestion of food, and the change in color of leaves in the autumn.

In this lab you will perform tests on several different substances. By making careful observations, you will decide if the changes you observe are physical or chemical and justify your decisions.

PRE-AB ASSIGNMENT: Read Chapter 1 sections 1.4 through 1.8 in your textbook.

SUPPLIES:

table salt (NaCl - sodium chloride)

black construction paper

distilled water

piece of white paper or index card

q-tips

radish

household ammonia

vinegar (acetic acid)

aluminum foil

candle

baking soda (sodium bicarbonate)

baking powder

dry ice (optional)

 

EXPERIMENTAL:

A. Determining the type of change.

Perform each of the following tests, record your observations and decide if the change you observe is physical or chemical. Justify your answer. Record your results on your report sheet. (Each test is listed as a separate number.)

1. Dissolve some table salt in distilled water. Saturate a square of black construction paper with the salt water solution. Place the paper on a dish and allow the water to evaporate. Check on your experiment in a day or two. Record all changes.

2. A radish can be used as an acid/base indicator. Using a q-tip place some solutions on the index card. Rub the radish over the spot of solution and observe the color changes. Perform the experiments using distilled water (neutral), household ammonia (a base) and vinegar (an acid). Record all color changes for later use.

3. Cut a square of aluminum foil. Place a piece of candle wax on the foil. Heat the candle wax on the foil using a candle. Compare the changes that occur for the wax on the foil to what is happening to the candle wax in the burning candle. Are the changes the same? Why or why not? Can you design a way (experiment) to prove this?

4. Using the setup from test #3, place a drop of water on a new piece of foil and heat the water with the candle. Record your observations.

5. Get out three glasses. Place a small amount of baking soda in one and a small amount of baking powder in the other. Add warm distilled water to each beaker and observe what happens. Place a small amount of sodium bicarbonate (NaHCO3) in the third beaker and then add a few drops vinegar. Record all changes. Dispose of chemicals down the drain.

6. (Optional - do not worry about if you can not get dry ice.) Obtain two pieces of Dry Ice (solid CO2). Place a few drops of household ammonia in a glass of distilled water. (Recall the color of the test of this solution with a radish indicator.) Add one of your pieces of dry ice to this solution, wait until the carbon dioxide dissolves, and test the resulting solution with your radish indicator. Record all changes. Place the other piece of Dry Ice on the lab bench and record any changes. Dispose of all solutions down the drain.

B. Can you think of other chemical and physical changes? Design an experiments to explore one of these chemical or physical changes. Record your experiment and observations and post them to the list-serve. Do not post the type of change. Take the observations from your experiment and those of two other students from our class and decide if the changes were chemical or physical. Justify your answers.

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Adventure 2 Report Sheet

Name: ______________________________________

A. IDENTIFYING THE TYPE OF CHANGE

1. Salt in water

Changes in appearance:

 

 

Nature of change: _______________________________

Explanation:

 

 

 

 

 

2. Radish indicator

distilled water indicator color __________________________

household ammonia indicator color __________________________

vinegar indicator color __________________________

Are the chemical changes using the radish indicator chemical or physical? Explain.

 

 

 

 

3. Wax on foil

Changes in appearance for wax on foil:

 

Changes in appearance for candle wax:

 

 

 

Nature of changes:

for wax on foil:

 

Explanation:

 

 

 

for candle wax:

Explanation:

 

 

What might you do to prove if the change in the candle wax and the change in the wax on the foil are identical?

 

 

 

 

 

 

 

4. Water on foil

Changes in appearance of water:

 

 

Nature of change:

Explanation:

 

 

 

 

5a. Baking soda and water

Observations:

 

 

Chemical or physical change? Explain.

 

 

 

 

5b. Baking powder and water

Observations:

 

 

Chemical or physical change? Explain.

 

 

 

 

 

 

5c. Sodium bicarbonate plus acetic acid

Observations:

 

Chemical or physical change? Explain.

 

 

 

 

Briefly explain why 5 a, b and c behaved the way they did. (Hint: What are the ingredients in baking powder and baking soda?)

 

 

 

 

 

 

6a. Dry Ice and ammonia solution

Changes in appearance (changes in test with radish indicator):

 

Nature of change: __________________________________

Explanation:

 

 

 

 

6b. Dry ice on table top

Changes in appearance:

 

Nature of change:_____________________________

Explanation:

 

 

 

B.

(1) Description of your experiment and observations:

 

 

 

 

Nature of change and explanation

(2) Description of first student=s experiment and observations:

 

 

 

 

 

Nature of change and explanation:

 

 

 

 

 

 

 

 

(3) Description of second student=s experiment and observations:

 

 

 

 

 

 

Nature of change and explanation:

 

 

 

 

 

 

Additional Questions

1.Does a chemical change occur when carbon dioxide (dry ice) dissolves in water? Explain.

 

 

 

 

 

 

 

 

2. What is sublimation? Is it a chemical or physical change? Which of the experiments that you preformed are examples of sublimation?