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16.9: Demonstrations for Chapter 16

Difficulty Level: At Grade Created by: CK-12

Boiling Water in a Paper Cup

Brief description of demonstration

Water is placed in a non – waxed paper cup. A Bunsen burner is placed underneath the cup with a medium flame. The water in the cup will boil without the paper igniting.

Materials

• Non – waxed paper cup (the conical ones used with water coolers work very well)
• Bunsen burner
• Ring Stand and Ring
• Water

Procedure(s)

Fill the cup to within 1cm of the top with tap water. Place the cup so that it is held firmly onto the iron ring: the closer the ring is to the top of the cup the better. Small diameter ring stands (about 6 to $7\ cm$) work well for this. Light the Bunsen burner and adjust the flame so that it is relatively cool (with the air vents shut). Position the tip of the flame so that it directly underneath and just touching the lower tip of the cup. Depending on the intensity of the flame the water will start boiling within $2-3 \ minutes$, without the cup igniting.

Hazards

Boiling hot water can cause severe burns. The cup may ignite if the flame touches the portion of the cup not in direct contact with the water. The cup may scorch slightly.

Disposal

Let the water cool, and dispose of the water down the sink, and the paper in the trash can.

Discussion

The heat capacity of water is enormous in comparison to other materials $- 4.18 \ J/g \cdot ^\circ C$ vs. less than $1 \ J/g \cdot ^\circ C$ for other materials. Thus it can absorb a lot of heat energy before changing its temperature. Once it reaches its boiling point of $100^\circ C$, it will stay there until all of the liquid water is gone, and the paper in contact with the water will stay at that temperature too. The temperature at which paper catches fire is $233^\circ C$, which is far above the temperature of the water, so the paper cannot catch on fire. The instant the water is no longer in contact with the paper, however, the temperature of the paper will rise very quickly, so watch it carefully so the paper does not ignite and spill it’s hot contents.

Aug 18, 2012

Aug 13, 2014