The three gas laws discover the relationship of pressure, temperature, volume, and amount of gas. Boyle’s Law tells us that the volume of gas increases as the pressure decreases. Charles’ Law tells us that the volume of gas increases as the temperature increases. A third gas law may be derived as a corollary to Boyle’s and Charles’ laws. According to Gay-Lussac’s Law, for a given amount of gas held at constant volume, the pressure is proportional to the absolute temperature. Methodology
* Materials
We will need several materials for the three demonstrations of gas laws. For Part 1, the Cartesian Diver, we will need a bottle with cap, and a medicine dropper. For Part 2, the Rising Water Experiment, a birthday candle, food coloring, matches, a shallow dish, petroleum jelly and an Erlenmeyer flask. For the last experiment, the Invisible Giant, we will need a pair of beaker tongs, a hot plate, an empty aluminum soda can, a beaker of ice water and some ice. * Procedure
Part 1: The Cartesian Diver
First, fill the bottle to the very brim with water. Drop the medicine dropper with the bulb up and close the bottle tightly. The medicine dropper should float in the water. Squeeze the bottle gently and record your observations. Stop squeezing the bottle and again, record your observations. Part 2: Happy Birthday
First, put a small glob of petroleum jelly in the center of the shallow dish. Then, stand a birthday candle upright in the petroleum jelly. Don’t use a lot of extra petroleum jelly or the demonstration won’t work properly. Add 1 – 2 centimeters of water to the dish. Add a drop or two of food coloring. Light the birthday candle. Lastly, place the Erlenmeyer flask mouth down over the candle. Stand it up right in the dish over the candle. Record your
observations. Part 3: The Invisible Giant
Add a little bit of water to the empty soda can. Place the soda can on the hot plate and turn on the hot plate. While the water in the can is heating up, fill the dish about ¾ full of ice water. When the water in the can has reached a boil, quickly use the beaker tongs to move it from the hot plate and place it mouth down into the ice water. Record your observations. Data and Observations:
Part 1: The Cartesian Diver
In the bottle’s uncompressed state, the medicine dropper floats. When the walls of the bottle are squeezed, the medicine dropper sinks.
Part 2: Happy Birthday
When the flask is placed over a burning candle in a plate of water, the water level rises significantly when the candle burns out.
Part 3: The Invisible Giant
After heating, the soda can was place upside down into the water. The soda can implodes and was crushed instantaneously. Conclusions:
Part 1: The Cartesian Diver
1. An object floats in water when it is less dense than water. 2. Why does the dropper initially float in the water?
* The diver originally floats because the dropper contains part air and part water. Air is less dense than water, thus the medicine dropper is initially lighter or less dense than water. 3. What happens to the volume of the air trapped in the dropper when you squeeze the bottle? * When squeezed, water is forced up into the dropper bulb and compresses the air in it. 4. If the air in the dropper contract, what happens to its density? * If the air in the dropper contracts, its density increases.
5. Explain why the dropper sinks when you squeeze the bottle? * When the bottle is squeezed, the pressure increases inside the bottle. This added pressure decreases the volume of the gas in the bottle, including the gas in the medicine dropper. This demonstrates Boyle’s Law. When the volume of the gas inside the medicine dropper decreases, the space left behind is filled with water. As a result, the mass inside the medicine dropper has increased substantially, but the volume has remained the same. More mass in the same amount of volume yields a greater density. The density of the dropper increases to the point where it is now greater than the density of the water surrounding it. The Cartesian diver sinks. Part 2: Happy Birthday
1. What did you see around the mouth of the flask when you first put it into the water? How can you explain this? * Bubbles form around the mouth of the flask when it was first put into the water. Temperature increases thus, air is heated and it expands. As it expands, it comes out from under the glass container. 2. What effect did the water have on the gas inside the flask? How do you know? * The air inside the flask becomes proportionally hotter and the rapid temperature change (from high to low) when the candle goes out causes water vapor inside the glass and condenses on its sides. It is observed when the inside of the flask is moist.
3. Many people mistakenly believe that the water rises into the flask because the candle is removing oxygen from the air. This explanation is not correct because the candle replaces oxygen with carbon dioxide. What is the actual explanation for why the water rose up into the flask? * Burning candle heats the air in the glass, so the air volume increases causing positive pressure inside. As the candle goes out and the air cools inside the glass, the volume decreases lowering the pressure. Then, the outside air pressure pushes the water into the glass until the pressure inside and outside the glass have reached equilibrium.
Part 3: The Invisible Giant
1. Why did the can collapse when it was placed mouth down in the ice water? * The soda can imploded because water heated turned to water vapor (pressure increases) and when placed mouth down into the ice water, water vapor condenses back to its liquid state as it cools decreasing air pressure inside the soda can allowing greater air pressure of the outside atmosphere to crush the can. 2. Do you think the can would have collapsed if it had been placed in the water mouth up? Why or why not? * If the soda can was placed in water mouth up, water will not cool. Discussion
Part 1: The Cartesian Diver
Boyle’s Law describes the relationship between pressure and volume. Increasing pressure on a gas will decrease its volume. When the bottle is squeezed, water is forced into the dropper, decreasing the volume of air in the dropper. This makes it more massive and dense, causing it to sink. When the pressure is released the opposite effect occurs and the dropper rises.
As the pressure increases, the volume decreases;
As the pressure decreases, the volume increases.
Part 2: Happy Birthday
The “Happy Birthday” experiment is a demonstration of Charles’ Law which states that volume increases as temperature increases at constant pressure. Burning candle heats the air in the gas causing an increase in temperature and an increase in air volume as well. Air that cools rapidly under a constant pressure does so according to Charles’ law a specific version of the ideal gas law that holds the quantity of gas and the pressure constant.
Part 3: The Invisible Giant
The Invisible Giant demonstrates Gay-Lussac’s Law. When the soda can was heated with water in it, temperature increases and pressure increases at the same time. When it was cooled, water vapor condenses to liquid which will lead to rapid fall of pressure inside the can. With very little air inside the can the air pressure inside the can is much less than the air pressure outside of it. The can is crushed by the net inward forces exerted by this pressure difference. Significance to the Biological World
The real world applications for gas laws are almost too many to name and each product tends to use a few particular gas laws. Gas laws are often used to design propellants in cans because gas pressure can build up and then have a controlled release. Other types of uses can include safety devices and even transportation. Some common products are known to save lives, but they can also pose a health hazard. Airbags use Charles’ law–which states that volume is directly proportional to volume–to ignite a gasoline and air mixture that inflates an airbag in less than a second.
