CHMY 141 Heat of Reactions Helium Curve Lab Report Please download both this pdf and the Excel Worksheet. In part I, you can measure the distance from eit

CHMY 141 Heat of Reactions Helium Curve Lab Report Please download both this pdf and the Excel Worksheet.

In part I, you can measure the distance from either the left or right side of the image (but make sure to record your distance with the correct wavelength–red light has the longest wavelength and blue/violet light has the shortest wavelength).

Please download both this pdf and the Excel Worksheet.

In part I, you can measure the distance from either the left or right side of the image (but make sure to record your distance with the correct wavelength–red light has the longest wavelength and blue/violet light has the shortest wavelength).

Please download both this pdf and the Excel Worksheet.

In part I, you can measure the distance from either the left or right side of the image (but make sure to record your distance with the correct wavelength–red light has the longest wavelength and blue/violet light has the shortest wavelength).

Please download both this pdf and the Excel Worksheet.

In part I, you can measure the distance from either the left or right side of the image (but make sure to record your distance with the correct wavelength–red light has the longest wavelength and blue/violet light has the shortest wavelength).

Please download both this pdf and the Excel Worksheet.

In part I, you can measure the distance from either the left or right side of the image (but make sure to record your distance with the correct wavelength–red light has the longest wavelength and blue/violet light has the shortest wavelength). Helium
Measured Distance
(mm)
Actual Wavelength
(nm)
447.1
471.3
492.2
501.5
587.5
667.8
Calibration Curve:
Slope
Intercept
#DIV/0!
#DIV/0!
Create your calibration graph below. Your slope and intercept should match the values shown above.
Select data, insert x,y scatter chart, select data points, right click choose add trendline, add equation of
Hydrogen
Measured Distance Calculated Wavelength
(mm)
(nm)
se add trendline, add equation of the line
D E (J)
n initial
n final
2
2
2
2
Rydberg
Constant
Color
Wavelength (nm)
Voltage (V)
IR 940
IR 880
Red 640
Yellow 602
Green 568
Green 502
Blue 470
940
880
640
602
568
502
470
1.08
1.161
1.559
1.708
1.8
2.164
2.328
Frequency (Hz)
Create a graph below. The slope of this graph must be Plank’s Constant.
Energy (J)
Part I: Determining the Rhydberg Constant
1. In the table below, record the color of each emission line for helium.
Wavelength (nm)
Color
447.1
471.3
492.2
501.5
587.5
667.8
Please enter your answers in
this column
2. Which color has the longest wavelength?
3. Which color has the shortest wavelength?
4. Which color has the highest energy?
5. Which color has the lowest energy?
6. Write a statement relating wavelenght and energy.
7. What was the percent error for your average calculated
Rydberg constant?
8. What was the percent error for the Rydberg constant
calculated using the slope?
9. Which method do you believe is better to calculate the
Rydberg constant. Justify your answer by explaining why you
chose this method.
Part II: Determining Plank’s Constant
1. What generalization can you make regarding wavelength and energy?
2. What generalization can you make regarding frequency and energy?
gth and energy?
y and energy?
Laboratory
3
Atomic Spectroscopy
& The Energy of Light
Objectives
• Use spectroscopic techniques to explore the spectra of excited gases
• Use a known spectrum to calibrate a wavelength scale
• Use a hydrogen spectrum to determine energies of Balmer series electron transitions
• Calculate the Rydberg constant based on spectral measurements
•
•
Use LED activation voltages to find the value of h, Planck’s constant
Calculate the value of h using two different methods
Equipment and Materials
• Ruler
Introduction
The relationship between energy, color, wavelength, and frequency of visible light can be
examined using a handheld spectroscope. In this lab, you will perform two exercises to
investigate these relationships.
In the first, you use the visible emission spectrum of atomic helium to generate a calibration
curve. This calibration curve will allow you to determine wavelength by measuring the distance of
the emission lines in the spectral images. This will be used to determine the wavelength of spectral
lines in an atomic hydrogen spectrum. As early scientists have done, you can then determine the
energy of electron transitions in the hydrogen atom, and calculate the numerical value of the Rydberg
constant.
In the second exercise, you will look closer at the relationship between the color and energy of light
using data from different colored LEDs. From this, you will be able to determine the value of Planck’s
constant using the relationship E = hν.
PART I. ATOMIC SPECTRA
Observation
1. A spectroscope is a device that disperses and separates light based on wavelength. These devices can be easily
created using a compact disc (CD). For fun, check out https://www.youtube.com/watch?v=gqLojYvNu6c to build
your own. We have used a similar device to collect the spectra below for helium.
1
Chemistry 141 Experimental Chemistry
Data Collection
1. To the nearest millimeter, record the distance from the edge of the image to the center of each
major line in the spectrum using a ruler. You should see 6 major lines. Record the wavelength and the
distance measurement (mm) in the provided excel workbook. The wavelengths (nm) of the major lines
are: 447.1, 471.3, 492.2, 501.5, 587.5, 667.8 nm.
2. Now measure the four major lines in the hydrogen spectrum in the same manner as you did for the
helium tube. Record your data in the excel workbook.
Data Analysis
1. Calibrate your scale by plotting the measurement of the helium lines in mm on the x-axis and each
line’s wavelength, in nm, on the y-axis. Find the equation of the line using a linear model. Display both
the equation and R2 value on your graph.
2. Using the equation of your line and the measured values (in mm) for the hydrogen spectrum lines,
calculate the values for your hydrogen spectrum wavelengths. Do this calculation in the excel
workbook in the column labeled “Calculated Wavelength (nm)”.
3. Calculate the energy associated with each of the four transitions observed for hydrogen using your
calculated wavelengths. This value corresponds to the ΔE for an electron transition from a higher nlevel to the n=2 level.
2
Atomic Spectroscopy & The Energy of Light
Laboratory 3
3. Enter the starting n-level for each transition in the excel worksheet (the ending n-level is
always 2). You may find the figure below helpful in determining the correct starting n-level.
n
Energy
∞
6
5
4
3
2
Balmer series
4. Using the Rydberg equation, the value for ΔE calculated above, and your values for
the starting and ending n-levels, calculate a value for the Rydberg constant (in Joules)
for each of your spectral lines.
5. Now, calculate the average Rydberg constant from these four values.
6. Determine a %error for your value of the Rydberg constant using this method. The
value of the Rydberg constant is 2.18 × 10-18.
7. Use the Rydberg equation as listed below to graph your data, and determine the value
of the Rydberg constant from the slope of the line.
8. Report the %error for this technique in the excel worksheet.
DE = -2.18 # 10 -18 J c
1
1
m
nf 2 ni 2
3
Chemistry 141 Experimental Chemistry
PART II. DETERMINING PLANK’S CONSTANT
1. Light emitting diodes (LEDs) require a minimum amount of energy to produce light. In this
experiment, we supply increasing amounts of electrical energy to individual LEDs until the LED
produces light. The voltage needed for each LED has been recorded on in the excel workbook (Click
on the worksheet named “Plank’s Constant Determination”).
2. Next, you will create a graph in which the slope is equal to Plank’s constant. Try to do this on
your own using the equation E = hν. (Hint: You must calculate frequency, ν, in units of m-1, and
you must determine E in units of J; 1 V = 1.62021 x 10-19 J.) Show both the equation for your
straight line fit, and your R2 value.
Data Analysis
1. Calculate the percent error for Plank’s constant using the actual value (6.626 x 10-34 Js) and
record this in the excel worksheet.
4

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