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1. What produces the characteristic colors in flame spectra? (1 points)
Feedback: Characteristic colors are produced when electrons in atoms are excited by the heat of the flame and then emit specific photons when returning to their ground state.
2. What is the characteristic flame color of sodium? (1 points)
Feedback: Sodium produces a very intense and characteristic yellow-orange color, visible even in small concentrations. This is due to specific electronic transitions in sodium atoms.
3. Which element produces an intense green flame? (1 points)
Feedback: Barium produces a very characteristic intense green flame. This flame test is useful for identifying the presence of barium compounds in unknown samples.
4. Match each element with its characteristic flame color: (5 points)
Feedback: Each element has a characteristic color: Li (crimson red), K (violet), Ca (orange), Cu (blue-green), Sr (intense red). These colors are unique for each element.
5. Indicate the approximate wavelength (in nm) of these spectral lines: (4 points)
Feedback: Characteristic wavelengths are: Na (589 nm), H-alpha (656 nm), Hg green (546 nm), H-gamma (434 nm). These lines are fundamental in spectroscopy.
6. What instrument is used to observe and analyze emission spectra? (1 points)
Feedback: The spectroscope is the instrument that separates light into its spectral components, allowing observation of characteristic emission lines of each element.
7. What is the main advantage of using a platinum wire in flame tests? (1 points)
Feedback: Platinum is inert and doesn't produce its own colors in the flame, so it doesn't interfere with observation of characteristic colors of the elements being analyzed.
8. Why is it necessary to clean the wire between each flame test? (1 points)
Feedback: Cleaning the wire is crucial to prevent remains from the previous sample from contaminating the next test and producing mixed or erroneous colors.
9. Order the flame test procedure steps (1-6): (6 points)
Feedback: The correct procedure ensures precise results: prior cleaning, verification, sample application, flame observation, result recording, and final cleaning.
10. What type of electronic transition produces emission lines? (1 points)
Feedback: Emission lines are produced when electrons move from higher to lower energy levels, emitting photons with specific energies that correspond to determined colors.
11. What is the relationship between the energy of the emitted photon and its frequency? (1 points)
Feedback: Planck's equation E = hf relates photon energy to its frequency. This fundamental relationship explains why each electronic transition produces a specific frequency (and color).
12. What can interfere with flame color observation? (1 points)
Feedback: Sodium, even in very small amounts, produces an intense yellow color that can mask other weaker colors, interfering with identification of other elements.
13. What is the basis for qualitative identification by flame spectra? (1 points)
Feedback: Each element has a unique pattern of spectral lines, like an optical 'fingerprint', that allows its unequivocal identification even in complex mixtures.
14. What element is responsible for colors in fireworks? (1 points)
Feedback: Fireworks use salts of different metals: strontium for red, barium for green, sodium for yellow, copper for blue-green, etc. It's a practical application of emission spectra.
15. What is the main limitation of flame tests for chemical analysis? (1 points)
Feedback: Flame tests mainly identify alkali and alkaline earth metallic elements. Non-metals and many transition metals don't produce observable characteristic colors.
16. What advantage does emission spectroscopy have over simple visual flame observation? (1 points)
Feedback: Emission spectroscopy can detect lines that the human eye doesn't perceive, allows quantitative concentration measurements, and provides greater precision in elemental identification.
17. What astronomical application do emission spectra have? (1 points)
Feedback: Astronomers use spectroscopy to determine what elements are present in stars and other celestial objects, analyzing emission and absorption lines in their light.