Changes in a Burning Candle pdfs... · chemical changes in a burning candle. In one part of the...

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Changes in a Burning Candle• Pre-Lab DiscussionWhat do you observe as you watch a candle burning? You see a bright flame and feel theheat. You may notice an odor if it is a scented candle. As you watch, the candle becomessmaller until, eventually, it is just a small stub. Some changes that occur are physical,and others are chemical. In this investigation, you will determine the physical andchemical changes in a burning candle. In one part of the investigation, you will test forcarbon dioxide, using limewater. Limewater is a mixture of water and calcium hydroxidethat turns cloudy when carbon dioxide is added.1. What is a physical change?

2. What is a chemical change?

•Materials (per group)birthday candle shallow metal dish 20 mL of limewater solution150-mL beaker solid rubber stopper 500-mL Erlenmeyer flask

• Safety Review the safety guidelines in the back of your book. Use caution whenworking around an open flame. Tie back long hair and loose clothing. Keep the

limewater away from your eyes. If you get some in your eyes,immediately tell the teacher and rinse your eyes for 15 minutes.

• Procedure1. Light a candle and allow two or three drops of the melted wax to fall on the center ofthe metal dish. Press the candle upright onto the melted wax before the wax hardens. Ifthe candle burns too low during the following steps, repeat this step with a new candle.2. Observe the flame of the burning candle for a few minutes. Observe what is burningand where the burning takes place. Note the different regions of the flame. Record yourobservations in the Data Table.3. Fill a 150-mL beaker with cold tap water, dry the outside, and use tongs carefully tohold it 3 cm to 5 cm above the candle flame for about 10 seconds. Record yourobservations.4. Pour tap water into the metal dish to a depth of about 1cm. Quickly lower a 500-mL Erlenmeyer flask over thecandle so that the mouth of the flask is below the surface ofthe water. See Figure 1. Leave the flask in place for about aminute. Record your observations.5. Hold the flask by its neck and lift it out of the water.CAUTION: Lift the flask by its neck because the base of theflask may be hot. Turn it upright, and add about 20 mL oflimewater. Stopper the flask and swirl the solution for abouta minute. Record your observations.

•ObservationsData TableProcedure ObservationsCandle burning(Step 2)

Beaker above flame(Step 3)

Flask over candle(Step 4)

Limewater in flask(Step 5)

• Analyze and Conclude1. Which of the changes that you observed were physical?

2. Which of the changes that you observed were chemical?

3. One of the requirements for combustion is fuel. From your observations, whatare the other requirements? Explain.

4. What are the two chemical products of combustion of the candle? How doyou know?

• Critical Thinking and Applications1. Why was water needed when the Erlenmeyer flask was placed over the candle?

2. You can use an equation to describe a chemical reaction. For a one-way reaction, thepart of the equation to the left of the arrow gives the ingredients, and the part of theequation to the right of the arrow gives the products. For example, an equation for thechemical reaction that produces mayonnaise isEggs + Vinegar + Salad Oil -> Mayonnaise.Write an equation for the combustion of a candle in oxygen. Hint: There are twoingredients and two products.