Comprehensive Study Guide to Gas Law Demonstrations: Pressure, Volume, and Temperature Relationships

Goal of the Demonstrations: To illustrate and observe the specific relationships between the variables of pressure, volume, and temperature as they pertain to the behavior of gases.
The Organization Sheet: A structured document used to track the progress and results of each experiment. It consists of four distinct components: * Prediction: A written entry made after the setup is explained but before the action occurs, detailing what is expected to happen. * Observations: Detailed notes recorded while watching the demonstration. * Variables: A selection of which two primary variables (Pressure, Volume, or Temperature) are being modulated or observed during the experiment. * Relationship Classification: An identification of the mathematical relationship as either direct or inverse. * Direct Relationship: As one variable increases, the other variable also increases (or vice versa). * Inverse Relationship: As one variable increases, the other variable decreases.

Direct Relationships: * Definition: A relationship where the variables move in the same direction. * Mathematical Equation: $\frac{a}{b} = k$ * Proportionality Constant ( $k$ ): In these examples, the constant is set at $10$ . * Scenario 1: If Variable $a = 10$ , then Variable $b = 1$ because $\frac{10}{1} = 10$ . * Scenario 2: If Variable $a$ increases to $20$ , then Variable $b$ must increase to $2$ to keep the constant $k$ at $10$ . * Scenario 3: If Variable $a$ increases to $30$ , then Variable $b$ must increase to $3$ to conserve the value of the constant. * Conclusion: Variables $a$ and $b$ increase proportionately to maintain the constant.
Inverse Relationships: * Definition: A relationship where one variable increases while the other decreases. * Mathematical Equation: $a \times b = k$ * Proportionality Constant ( $k$ ): Set at $10$ for the following examples. * Scenario 1: If Variable $a = 10$ , Variable $b$ must be $1$ ( $10 \times 1 = 10$ ). * Scenario 2: If Variable $a$ doubles and increases to $20$ , Variable $b$ must decrease to $0.5$ to maintain the constant ( $20 \times 0.5 = 10$ ). In other words, if Variable $a$ doubles, Variable $b$ decreases by half.

Experimental Tools and Setup: * A candle is affixed to a metal pie tin. * The tin is filled with water containing green food coloring to improve visibility of the water level. * A glass flask is provided. * Initial state: Before lighting, the water level inside the flask is identical to the level outside.
Experimental Procedure: 1. The candle is lit. 2. The flask is inverted and placed over the top of the lit candle until it rests on the bottom of the tin. 3. The candle eventually goes out.
Physical Observations: * As the candle flame dies, the green water level inside the flask rises significantly higher than the water level outside the flask. * When the experimenter attempts to pull the flask out of the water, there is a noticeable physical resistance.

Experimental Tools and Setup: * A heavy glass bell jar with thick walls. * A plastic dish base equipped with rubber circle rings to ensure a seal. * A hole in the middle of the base connected to a nozzle and a vacuum pump hose. * A balloon of standard size. * Adhesive tape used to stick the balloon to the inside top of the bell jar for visibility.
Experimental Procedure: 1. The balloon is placed inside the jar. 2. The vacuum pump is activated, pulling air out of the bell jar chamber. 3. The pump is turned off and the hose is eventually removed to let air back into the chamber.
Physical Observations: * As the air is removed from the chamber, the size of the balloon increases substantially, eventually taking the shape of the bell jar. * When air is allowed back into the chamber (re-pressurizing the environment), the balloon returns to its original size.

Experimental Tools and Setup: * An empty aluminum "Bubbly" brand can. * Approximately $3\,tablespoons$ of tap water added to the bottom of the can. * A dish containing room-temperature tap water. * A Bunsen burner to serve as a heat source. * Metal tongs to hold and manipulate the can.
Experimental Procedure: 1. The can is held over the Bunsen burner flame with a tight grip. 2. The water inside is brought to a boil. 3. Indicators of boiling: * Visual: Observation of water vapor (water in gas form) escaping from the top opening. * Audible: Periodic swishing allows the experimenter to hear the water sizzling against the hot metal walls of the can. 4. Once a significant amount of vapor is escaping, the can is inverted quickly into the dish of tap water.
Physical Observations: * Upon contact with the water, the can immediately collapses and crushes itself. * The experimenter notes that the collapse was not caused by physical strength but by environmental changes. * Resistance is felt when attempting to pull the can out of the water dish. * Resulting Contents: A significant amount of water pours out of the can once it is removed from the dish, indicating water entered the can during or after the collapse.

Experimental Tools and Setup: * A small Erlenmeyer flask. * A balloon stretched over the mouth of the flask. * Approximately $3\,tablespoons$ of water inside the flask. * A hot plate.
Experimental Procedure: 1. The flask is placed on the hot plate and the water is heated. 2. The flask is removed from the hot plate and allowed to cool.
Observation Focus: Students are required to observe the state of the balloon during both the heating and the cooling phases to determine the variables and relationship involved.

Experimental Tools and Setup: * A large syringe with a plunger and a top opening.
Experimental Procedure: 1. The plunger is pulled down to a volume of $40$ . 2. The experimenter covers the top opening to seal the system. 3. The experimenter applies maximum physical force to push the plunger into the syringe.
Physical Observations: * The experimenter manages to compress the volume from $40$ down to approximately $20$ or possibly $18$ . * At this point, it is impossible to press the plunger any further due to internal resistance. * The physical effort required was high enough to leave a visible "divot" or injury on the experimenter's finger.

Final Task: Students must complete the fourth column of the organization sheet.
Decision Criteria: For each of the five demonstrations, students must decide if the identified variables are related through multiplication or division. * If the relationship is inverse, use the multiplication model ( $P \times V = k$ ). * If the relationship is direct, use the division model ( $\frac{a}{b} = k$ ).