To Verify Charles's Law by Syringe Experiment

The study of change of volume with temperature at a constant pressure for a definite amount of a gas is Charles's law. We can verify the law in several ways. In this article, we will use a syringe to prove volume is directly proportional to temperature and determine the absolute zero temperature. Two experiments are discussed below.

Experiment 1: With a syringe

In this experiment, we will verify Charles's law by studying a change of the total volume of the air in a conical flask as the flask moves through various solutions.

Objective

To verify Charles's law i.e. the volume of a fixed amount gas is directly proportional to its temperature at a constant pressure and to estimate the absolute zero temperature from volume-temperature graph.

Apparatus

Four equal beakers, a flask that can be comfortably submerged in a beaker, a rubber stopper with a syringe (100 mL to 150 mL) attached to it, a pressure sensor also attached to the rubber stopper, ice, salt, a spatula (for ice), a graduated cylinder, and a heating plate.

Nomenclature

This nomenclature is followed throughout the experiment.

1. V is the total volume of the air.
2. t is the temperature in the degree celsius of the solution in a beaker.
3. T is the temperature in the kelvin of the solution in a beaker.
4. P is the pressure under which the experiment is performed.
5. V_s is the volume reading of the syringe.
6. V_f is the volume of the flask.

Procedure

1. Prepare the four solutions as follows:
   • Ice-water: Ice, salt, and a small amount of tap water
   • Cold water: 50 % Ice and 50 % tap water
   • Warm water: Slightly heat tap water using a heating plate.
   • Hot water: Heat tap water until the temperature reaches around 40 °C to 50 °C.
2. Take a conical flask and attach its rubber stopper. A syringe and a pressure sensor should be already fixed to the rubber stopper. The rubber stopper should be tightly attached to the flask. This will isolate the air in the flask, which we will be investigating.

Note: The position of the plunger of the syringe must be in the rest (lowest) position before the rubber stopper is attached to the flask.

3. Immerse the flask in the ice-water beaker. Since the air is lighter than water, the flask will float on the water surface. So we have to hold the immersed flask inside the beaker. Wait for 4 min to 5 min, so the temperature of the ice-water and the air are in equilibrium.
4. Record the steady pressure from the display monitor, the temperature from the thermometer. The steady pressure value is important because the entire rest of the experiment will be performed at this pressure.
5. Transfer the flask to the cold water. Again wait for 4 min to 5 min. Now, the air of the flask is in contact with relatively hot water, so the air will expand. As the air expands, the pressure increases. However, we can manipulate the pressure of the air in the flask by changing the position of the plunger of the syringe.
6. After a steady-state is reached, observe the increased pressure on the monitor. Gently raise the plunger of the syringe, so the pressure on the monitor matches the pressure previously recorded.
7. Note the temperature from the thermometer and the volume from the syringe.
8. Repeat the above steps (5 to 7) for the next two beakers.
9. Remove the rubber stopper from the flask. The filled the flask completely with tap water and place the stopper back on the flask. The excess water will drain from the flask. Remove the stopper and the measure the amount of water in the flask using a graduated cylinder. This is the volume of the air in the flask before the experiment.

Precaution

1. The rubber stopper should be tightly fixed on the flask to entrap the air.
2. The temperature and the volume readings are recorded at a steady pressure.
3. Safety gloves are necessary when dealing with hot surfaces.
4. The flask should be properly immersed in the beaker, so the temperature of the air reaches the temperature of a solution.

Observation

Throughout the experiment, we measured the following parameters: the pressure of the air P, the volume reading on the syringe V_s, and the temperature of a solution t.

The pressure is made constant and its value is 0.914 atm. Also, the volume of the flask is 140 mL.

Calculation

The total volume of the air in the flask is the volume of the flask plus the volume reading from the syringe. Also, we have to convert the temperatures from the degree celsius to the kelvin.

As per Charles's law, the ratio of volume to temperature is constant.

The table below lists these ratios.

According to the above table, the ratios of volume to temperature remains constant.

The graphs of volume vs temperature are shown in the result section.

Result

1. The ratio of volume to temperature is 0.522 mL K⁻¹
2. The graph below is volume vs temperature (in K). It passes through the origin and follows the equation V = kT.



3. The graph below is also straight line with a positive slope. The x-intercept is −270 °C. Thus, the absolute zero temperature is −270 °C.

Conclusion

The experiment is successfully studied. From the calculation table, the ratio of volume to temperature remains constant under a constant pressure. Thus, the gas obeys Charles's law. Also, from the graphs, the volume of the gas is linearly proportional to its temperature at a constant pressure. This proves the Charles' law. The value of absolute zero is determined from the graph, and it is −270 °C. The value is reasonably closed to the expected value (−273.15°C).

Experiment 2: With a sealed syringe

A disposable syringe is used in the experiment. The tip of the syringe is sealed, so it acts as a piston. The sealed syringe in dip in different water baths at different temperatures. This will cause the change in the volume of the syringe. By studying volume versus temperature relation, we can verify Charles's law.

Objective

Same as in experiment 1

Apparatus

Four equal beakers, a syringe (50 mL), a syringe tip cap to sealed it, a thermometer, ice, salt, a spatula hot plate, silicone grease lubricant,

Nomenclature

The following nomenclature is followed throughout the experiment.

1. V is the volume of the air in the syringe.
2. t is the temperature in the degree celsius of a water bath.
3. T is the temperature in the kelvin of a water bath.

Procedure

1. Place the four beakers in the series and prepare the water baths as follows:
   • Ice-water: Ice, salt, and a small quantity of water
   • Cold water: 50 % ice and 50 % water
   • Warm water: Slightly heat tap water using a hot plate.
   • Hot water: Heat tap water using the hot plate until its temperature reaches around 50 °C.
2. Take the syringe and apply the lubricant to the rubber gasket of the syringe. Use safety gloves to paste a thin layer of the lubricant. A wooden split or a tongue depressor will be helpful while lubricating the surface. The proper lubrication is necessary to eliminate the friction between the surfaces.
3. Pull the plunger to a half of the syringe. Now, attach the seal cap to the tip of the syringe. This will isolate the air in the syringe from the atmosphere.
4. Give a small amount of push to the plunger downwards. If it does not revert to the original position, we may need to lubricate it properly or the seal cap may not be tightly fixed.
5. After having a satisfactory result, record the volume of the air in the syringe and room temperature through a thermometer.
6. Immerse the syringe in the coolest water bath and hold it for 3 min to 4 min. We want the air to the same temperature of the water bath.
7. Meanwhile, measure the temperature of the water bath.
8. Record the volume of the air in the syringe. The air will contract when the temperature decreases, so the volume reading will reduce.
9. Transfer the syringe in the subsequent water baths and repeat the same steps (6 to 8) to measure volume and temperature. In the subsequent water baths, the air will expand due to an increase in relative temperature.

Precaution

1. The plunger of the syringe should freely move after the lubrication. Otherwise, the volume reading will be inaccurate.
2. The seal cap must be tightly fixed before proceeding.
3. One must follow lab general safety instructions. Use safety gloves when dealing with lubricants and hot surfaces.

Observation

The experiment is conducted at a constant atmospheric pressure. The observation table is as follows:

Calculation

As Charles's law states the ratio of volume to temperature remains constant for fixed amount of gas at a constant pressure.

Result

1. The average ratio of volume to temperature is approximately 0.086 mL K⁻¹.
2. The graph of volume versus temperature (in K) is linear with a positive slope passing through the origin.



3. The x-intercept of the graph below is −249 °C. Thus, the absolute zero as per the graph is −249 °C.

Conclusion

The experiment is successfully studied. The ratio of volume to temperature is roughly constant. However, the value of the absolute zero temperature obtained from the graph is unsatisfactory. It deviates from the accepted value by 24 °C. The reason for this deviation may be an instrument error. It is not possible to get accurate readings of volume from the syringe because the least count of the instrument is limited by only two significant figures.

Associated articles

• Charles's law
• The equation of Charles's law
• Graphs of Charles's law
• Real-life examples of Charles's law
• To verify Charles's law experimentally
• Charles's law calculator