CHM/150 Week 4 Boyle’s Law Lab A+ Solution

CHM/150 Week 4 Boyle’s Law Lab

Peter Jeschofnig, Ph.D. Version 42-0141-00-01

Lab Report Assistant                                                                                              

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Observations                                                                                                             

Data Table 1: Optional

Pressure (# of Books)Optional:

weight

of book

(lbs)

Volume

Trial 1

Volume

Trial 2

Volume

Trial 3

Average

Volume

1/ Volume

Total Pressure PT

P  * V

T

0

1

2

3

4

5

6

1. Find the average of each set of three volumes and record these averages in the data table.

2. Calculate the inverse 1/Vavg (mL

-1) of each volume and record these values in data table.

3. Using the graphing function of your spreadsheet prepare a graph of “Pressure (Number of

Books) Vs Volume (mL)” with “Pressure” on the y-axis and “Volume” on the x-axis.

4. Prepare a second graph showing pressure (number of books or weight) on the y-axis vs. 1/ Volume on the x axis. (Boyle’s Law states that gas Pressure x Volume = a constant (k); PV=k or V=k/P.  Therefore, volume varies inversely with pressure. Thus a graph of the gas pressure (Y axis) to the inverse of the volume (X axis) should be a straight line with a slope of ‘k’. Use the trendline function of the graphing software to have Excel put the equation of the line directly on the graph (y=mx+b). “b” is the value where the line intersects the y-axis and roughly represents the atmospheric pressure in whatever units were used on the pressure axis (books, etc)

NOTE: Remember that air pressure around us is 14.7 lbs/in2 (101kPa or 760 mmHg or 1,035 g/ cm2) at sea level (one atmospheric pressure) and the added mass to the plunger will increase it further. The line obtained for the second plot crosses the y-axis of the graph above or below the origin, which tells us that there is pressure on the gas even when there are no books on the piston.

Depending on your instructor’s requirements the graphs can be plotted in book units or converted to pressure units.

5. The local atmospheric pressure obtained through the above method must be added to all pressure readings to obtain PT (Total Pressure)

6. Finally, calculate the product of Ptotal  x Vavg  for each trial and record these values in the data table. These values represent “k” and should be relatively close together

Optional Conversion to Pressure Units: (Only if a bathroom scale is available to obtain the mass of each book): Pressure is defined as force per unit area. The SI unit for pressure is the pascal (Pa), which is defined as the force of 1 Newton acting over an area of 1 square meter. So you will need to know the force exerted by the books, plus the area of the plunger.

The downward force, F of the books can be calculated by multiplying the mass (in kg), m, of the books times the acceleration, a, due to gravity (F = ma), where a = 9.8 N/kg.

PT

The area of the piston (in units of square meters) can be calculated by measuring the diameter, and using the formula for calculating the area of a circle.

The diameter of the 60 mL syringe is 2.7 cm; r=1.35 cm; r2π = 5.73 cm2 or 5.73 x 10-4 m2

You can then calculate the pressure, in Pa, by dividing the force, F, generated by each stack of bricks by the area, A, of the piston.

Calculate the product of Ptotal x Vavg for each trial and record these values in the data table.

B.   Identify the shape of graph #2. Explain the graph.

C.   Make a general statement concerning the relationship of pressure on the volume of a confined gas.

D.  In your opinion, would the results be different if a different gas, like CO2 were used? Why? E.   What is the air pressure in book units?

F.Was the assumption of constant temperature valid for your experiment?

G.  Discuss the significance of the values obtained in the last column of the data table

(P  * Vavg)

T

H.  What are the possible sources of errors in your experiment?

I.What could one do to minimize the errors in this experiment?