Observation of a Candle

= Observation of a Candle

CHEMLAB 1.1

Chemistry: Concepts and Applica= tions

You have seen candles burn, perhaps on a birthday cake. But you probably have never considered the burning of a candle from a chemist’s point of view.

Michael Faraday, a 19th-century chemist, found m= uch to observe as a candle burns. He wrote a book and gave talks on the subject. In this ChemLab, you will investigate the burning of a candle and the products= of combustion.

PROBLEM (change to become hypothesis)

What are the requirements for and characteristic= s of a candle flame? What are the products of the combustion of the candle?

OBJECTIVES

• Observe a candle flame and perform several tests.

• Interpret observations and the results of the tests.

MATERIALS

large birthday candles

matches or lighter

shallow metal dish or plastic container

glass 3 X 3 plate

25 mL of limewater solution

250-mL beaker

500-mL Erlenmeyer flask

solid rubber stopper to fit the flask=

wire gauze square

tongs

SAFETY PRECAUTIONS

Wear an apron and goggles. Keep all combustible materials, including clothing, away from the match and candle flames. Do not allow the limewater to splash into your eyes.

If it does, immediately rinse your eyes for 15 m= inutes and notify your teacher.

PROCEDURE

1. Light a candle and allow a drop or two of liquid= wax to fall into the center of the glass plate. Press the candle upright onto t= he melted wax before it can solidify. If the candle burns too low during the following procedures, repeat this step with a new candle.=

2. Observe the flame of the burning candle for a few minutes. Try to observe what is burning and where the burning takes place. Observe the different regions of the flame. Make at least eight observation= s, and record them in the data table.

3. Light a second candle and hold the flame about 2= cm to 4 cm to the side of the first candle flame. Gently blow out the first candle flame, and then quickly move the flame of the second candle into the smoke = from the first flame. Record your observations.

4. Relight the standing candle. With tongs, hold th= e wire gauze over the flame, perpendicular to the candle. Slowly lower the gauze o= nto the flame. Do not allow the gauze to touch the candle wax. If the flame goes out, quickly move the wire gauze off to the side. Record your observations.=

5. Fill the 250-mL beaker with cold tap water, dry = the outside of the beaker, and hold it about 3 cm to 5 cm above the candle flam= e. Record your observations.

6. Pour tap water into the plastic container or dis= h to a depth of about 1 cm. Place the glass plate with the candle attached into wa= ter.

7. Quickly lower an Erlenmeyer flask over he candle= so that the mouth of the flask is below the surface of the water. Allow the fl= ask to remain in place for approximately one minute. Record your observations.<= o:p>

8. Lift the flask out of the water, turn it upright= , and add about 25 mL of limewater. Stopper the flask and swirl the solution for approximately one minute. Record your observations. If the solution becomes cloudy or chalky, calcium carbonate was formed, indicating the presence of carbon dioxide in the flask. Record your observations.

DATA AND OBSERVATIONS

ANALYZE AND CONCLUDE

1. Classifying &nb= sp;

Which changes that you noted in step 2 were physical?

Which were chemical? =

2. Making Inferences

Do your results in st= ep 3 indicate that the candle wax burns as a solid, a liquid, or a vapor?

Explain.

3. Interpreting Data

One requirement for combustion is the presence of fuel. Interpret your results from steps 4 and= 7 to determine the other requirements.

4. Interpreting Data

Based upon your analy= sis of the observations from steps 5 and 8, what are two products of the combustio= n of the candle?

APPLY AND ASSESS

1. Sir Humphry Davy invented a safety lamp for mine= rs in which a flame was surrounded by a wire gauze cylinder.

Can you explain the reason why the lamp was constructed in this way?

2. What change in water level occurred in procedure= 7?

Propose an explanation for this change.