Chem 101L-Exp.8

What color is the Hydrogen lamp to the naked eye? What appears when observed through a spectroscope?

- Color appears purple - Spectroscope tells us it contains red, green, blue and violet

How does the Hydrogen lamp produce light? How is this relevant to the purpose of this experiment?

- Electrical discharge tube-glass tube that contains metal electrodes at each end and is filled with a low-pressure gas, such as hydrogen, helium, or mercury. - A stream of fast moving electrons shoots through the gas from the cathode. - These electrons get excited to a new energy level and then return to their ground state resulting in the emission of light.

How are the terms in the Rydberg equation defined? How can they be used to determine the starting and/or ending energy levels of an electronic transition?

- For hydrogen nf=2 and then you can solve for ni - Rh = 2.18x 10^-18 J

What samples were used for observations of flame emission spectra? What property of these materials made them appropriate for this experiment? What property of these materials was observed with the naked eye? What was observed with the spectroscope? Are they the same or different? Why?

- The different salts produced different energies and different wavelengths. - With the naked eye we only observed the most intense color line noted on the spectroscope -

What instrument requires calibration in this experiment? How is it the same or different than the calibration done in Experiments 6 and 7?

- The spectroscope needs calibration form the fluorescent light, we make a calibration curve to calculate wavelength. - It's different because it's giving us a new value.

How can the components of a mixture be identified using a flame test? What observations assist in drawing conclusions about the components of the mixture? What observations are most helpful? Accurate? Can you identify the relative quantities of each component, or are you only able to identify presence or absence?

- The wavelengths that correlate with the energy states can be used along with the color you observe with your naked eye. - You cannot identify the quantities due to the lack of information, but you can identify whether it is present or not.

How is the spectroscopy done in Experiment 8 different from the measurements made in Experiment 7. In each experiment, what property of light is measured? What property of the molecule is associated with that property of the light?

- This experiment is measuring the wavelength of light where as experiment 7 is measuring the absorption of light. - The energy level of the molecule is associated with wavelength while the concentration of ion is associated with absorbency.

Can you calculate the starting or ending electronic level of an electron in a hydrogen atom based on the wavelength of light emitted? Can you calculate wavelength from knowledge of the energy levels?

- You can calculate the starting electronic level because you already know the final - You can solve for wavelength if you have the energy levels

How does the spectroscope convert the light from a particular source into a spectrum, set of bright lines, or both? Why do different light sources produce different spectra?

- diffraction device used to see the different types of wavelengths transmitted - Inside there is a transmission diffraction grating (piece of glass or plastic with fine scratches or grooves cut in its surface) - each groove scatters light but only light waves scattered in specific directions from the grooves on the grating interfere constructively, producing a strong beam - Different light sources produce different spectra because each light source comes from a different origin ( continuous- temp dependent vs emission or discrete- substance dependent)

Describe the electronic processes associated with absorption or emission of radiation. Which process is associated with an electron moving to a higher energy level?

- gain energy by absorbing light to jump to another level. - When it wants to go back to its natural state it releases a photon - Emission = Higher to lower - Absorption = Lower to higher

What are the technical challenges in this experiment? How can these challenges be overcome or minimized? What sources of error are most likely to affect the results? If source of error are present, what effect would they have on the results and/or the ability to correctly determine the components of the unknown mixture?

- the experimenter can only be so precise in their readings - the spectroscope could have lines that were etched incorrectly - the flames could be contaminated with another substance - the flame color and line colors are subjective - Makes it hard to determine what unknown you have if you think the lines are orange and teal, when actually its meant to be green and yellow

Given the Rydberg equation: Delta_E = RH (1/nf2 - 1/ni2) In the Balmer series for hydrogen, what is the initial energy level (ni) for a photon with a wavelength of 434.1 nm? REMEMBER: h = 6.626 x 10-34 J*s; c = 2.998 x 108 m/s; RH = 2.18 x 10-18 J

5

The following graph shows the calibration of a spectroscope against a series of mercury lines in the visible region of the spectrum. Based on this calibration, the wavelength of a line that appears at 5.34 on the spectroscope would have a wavelength of: y=92.497 + 39.766 R^2=0.9988

533.7 nm

When viewed through a spectroscope, calcium ions produce three distinct lines in the visible region of the spectrum, at spectroscope positions of 7.30, 7.85, and 8.45. The line corresponding to the lowest energy would have a spectroscope position of:

8.45

When observing a candle flame and a fluorescent lamp through a spectroscope, both show a continuous spectrum that appears as a rainbow on the spectroscope scale, but one of them also has bright colored lines superimposed over the rainbow. The best explanation for this behavior is: A. The candle produces only a continuous rainbow because its spectrum derives from its temperature, while the fluorescent light has both a continuous spectrum and the lines associated with the glass bulb. B. The fluorescent lamp produces only a continuous rainbow, while the candle flame has bright lines corresponding to the orange and blue parts of the flame. C. The candle produces only a continuous rainbow because its spectrum derives from its temperature, while the fluorescent light has both a continuous spectrum and the lines associated with emission from its mercury source. D. The fluorescent lamp produces only a continuous rainbow, while the candle flame has bright lines corresponding to molecular impurities that are burning in the flame.

C

Describe the Balmer series and how to recognize it through experimental observations.

The visible spectrum of light from hydrogen displays four wavelengths, 410 nm (n=3), 434 nm (n=4), 486 nm (n=5), and 656 nm (n=6), that correspond to emissions of photons by electrons in excited states transitioning to the quantum level described by the principal quantum number n=2. - There are also a number of ultraviolet Balmer lines with wavelengths shorter than 400 nm.

How the energy level of an electron related to the energy of a photon?

They are limited by orbitals.They need a specific amount of energy to jump form one orbital to the next.