The Gas Laws (Enquiries)

Worksheet: The Gas Laws

The gas laws (enquiries)

Aim

This set of investigations aims at helping you to derive the gas laws from analysing experimental results. This booklet should also help you to appreciate the Kelvin scale and the meaning of the Absolute Zero.

Investigation 1 (Boyle’s Law)

In this experiment you will investigate how the volume of a gas changes as the pressure is increased (for constant temperature).

Equipment

-Bourdon pressure gauge

-Glass tube

-Oil

-Air pump and valve

-Rubber tubes

-Ruler

Safety

-Glassware should be handled with care.

-If too much pressure is built in the glass tube the glass could break and project sharp bits around the lab. So, it is important that not too much pressure is applied by the pump. It is advisable to wear safety goggles.

Method

Look at the diagram above to set up the equipment
Position the zero mark of your ruler in line with the end of the glass tube
Without adding any pressure from the air pump record the (relative) volume in your table of results for this pressure
Increase the pressure by a set amount each time and record the new values of volume in your table of results
Do not increase the pressure too much to avoid the glass tube breaking

One of the control variables in this experiment is the temperature of the gas in the tube. One step in the method to ensure the temperature remains constant when you measure the volume is missing. What would you write in this missing step and where would you include it in the sequence of points 1 to 5?

______

Table of results

Complete the table of results below and add the units to the column labels. What unit could you use for the (relative) volume?

Pressure (_____) / Relative Volume (_____) 1 / Relative Volume (_____) 2 / Relative Volume (_____) 3 / Mean Relative Volume (_____)

Analysing your results

Now draw a graph of your results and use it to find the equation that links pressure to volume at constant temperature. What do you notice about the product of pressure by volume?

______

Questions

The relationship you found is called Boyle’s Law. Can you list two conditions that are necessary for this relationship to be valid? Hint: think about the set up and method of your experiment.

______

Using the Kinetic Theory of gases (in simpler words the movement of gas particles) explain how changing the two conditions you listed above would affect your results and make Boyle’s Law not applicable.

______

Which statement (below) best describes the relationship between V and p?

Volume is directly proportional to pressure
Volume is inversely proportional to pressure
Volume is inversely proportional to the square of the pressure

Explain your answer below.

______

Investigation 2 (Charles’s Law)

In this experiment you will investigate how the volume of a gas changes as its temperature is increased (for constant pressure). You will also appreciate the concept of Absolute Zero.

Equipment

-Plastic syringe and silicone oil

-Tall beaker

-Bunsen Burner, tripod and gauze

-Rubber tube and stopper

-Thermometer

-Stands and clamps

Safety

-Glassware should be handled with care.

-The beaker and water will become very hot when heated, so make sure you don’t touch the surface until the glass has cooled down. The same applies for the tripod, gauze and Bunsen Burner.

-Long hair should be tied back when operating the Bunsen Burner and safety goggles should be worn.

Method

Look at the diagram above to set up the equipment using clamps and stands to secure the syringe and thermometer
Read the volume of air in the syringe before you light the Bunsen Burner up and record this value in the table of results
Light your Bunsen Burner up and heat the water until it reaches the temperature you decided to increase it by
Record this value in your table and continue to raise the temperature by equal amounts until the water reaches boiling point

Now consider the opinions in the call outs in the previous page and answer the boy’s question (top right) before you begin the investigation. Give reasons for your answer.

______

Table of results

Complete the table of results below and add the units to the column labels. What unit could you use for the volume?

Temperature (_____) / Volume (_____)

Analysing your results

Now draw a graph of your results making sure you extend the line of best fit until it intersects the x-axis.

Questions

At what value of temperature does your line intersect the x-axis? ______

Using the Kinetic Theory of gases (in simpler words the movement of gas particles) explain the significance of your extended line of best fit. In other words, why does the volume of gas decrease as the temperature drops?

______

What would eventually happen to the gas as the temperature gets closer to the point of intersection between the line and the temperature axis? Explain your answer.

______

What would happen to the Kinetic Energy of the gas particles, if it were possible for them to reach the value of temperature at the intersection?

______

Explain why it is not possible for a gas to reach this temperature.

______

On your graph draw a line that could represent a gas which is denser than air.

The temperature at the intersection between your line and the temperature axis is called Absolute Zero and it is possible to build a temperature scale that has that point as the zero temperature. This scale is called Kelvin scale. What would the freezing temperature of water expressed in Kelvin be?

______

What is the temperature of your lab in degrees Celsius and in Kelvin?

T(oC) =______T(K) =______

What is your body temperature in degrees Celsius and in Kelvin?

T(oC) =______T(K) =______

Which statement (below) best describes the relationship between V and T at constant pressure and number of gas particles?

Volume is directly proportional to the absolute temperature
Volume is inversely proportional to the absolute temperature
Volume is directly proportional to the temperature in degrees Celsius

Explain your answer below.

______

Write an equation to express the relationship between V and T.

______

Investigation 3 (Pressure Law)

In this experiment you will investigate how the pressure of a gas changes as the temperature is increased (for constant volume).

Equipment

-Glass flask

-Large beaker

-Thermometer

-Bourdon pressure gauge

-Bunsen Burner, tripod and gauze

Safety

-Glassware should be handled with care.

-The beaker, flask and water will become very hot when heated, so make sure you don’t touch the surface until the glass has cooled down. The same applies for the tripod, gauze and Bunsen Burner.

-Long hair should be tied back when operating the Bunsen Burner and safety goggles should be worn.

Method

Look at the diagram above to set up the equipment using clamps and stands to secure the flask, gauge and thermometer
Read the pressure of air in the flask before you light the Bunsen Burner up and record this value in the table of results
Light your Bunsen Burner up and heat the water until it reaches the temperature you decided to increase it by
Record this value in your table and continue to raise the temperature by equal amounts until the water reaches boiling point

Like in Charle’s Law experiment you will need to wait for the air inside the flask to reach the same temperature as the water. How long do you think you should wait before recording the pressure? How will you ensure the temperature of the water remains the same for this time?

______

Table of results

Complete the table of results below and add the units to the column labels. What unit would you use for the temperature?

Temperature (_____) / Pressure (_____)

Analysing your results

Now draw a graph of your results making sure you extend the line of best fit until it intersects the temperature axis.

Questions

At what value of temperature does your line intersect the x-axis? ______

How does this value compare with the value obtained from Charle’s Law experiment? Give reasons as to why this has occurred.

______

Is your value close to the expected value of Absolute Zero? Suggestsome factors that might have contributed to the value you obtained.

______

Which statement (below) best describes the relationship between p and T at constant volume and number of gas particles?

Pressure is directly proportional to the absolute temperature
Pressure is inversely proportional to the absolute temperature
Pressure is directly proportional to the temperature in degrees Celsius

Explain your answer below.

______

Write an equation to express the relationship between V and T.

______

Bringing it all together (the Ideal Gas Equation)

The three relationships you found in the investigations described in this booklet could be combined to give the Ideal Gas Equation. An ideal gas is a gas whose particles are not subject to attractive forces between each others. In reality completely ideal gases do not exist, but volatile and light gases like Hydrogen, Helium, etc are a good approximation to an ideal gas.

The above equation is the Ideal Gas equation and it is valid only when the amount of gas in the system is fixed. This equation basically mean that if a fixed mass of gas starts with values of p1, V1 and T1 and then has values p2, V2 and T2, the equation can be written like this: