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# 2nd_lab - UOIT Chem 1800 W10 Exp 2-7.9 Experiment 2 Atomic...

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UOIT Chem. 1800, W10: Exp. 2-7.9 59 Experiment 2 - Atomic Spectroscopy Name: ____________________________ Student Number ____________________________ Day ____________________________ Time: ____________________________ TA Name ____________________________

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UOIT Chem. 1800, W10: Exp. 2-7.9 60 Results, Discussion and Questions 1. For each line in the hydrogen spectrum deduce n 2 (the upper state) and n 1 (the lower state). This question requires no math; just some deduction! Hint: the lines are in the visible regions; to which series must they belong (consult your textbook)? 2. Spectroscopists define a quantity called the “wavenumber” (= 1 / ± ) and give it the symbol ± ² . The units are cm -1 . Photon energies are linearly dependent on ± ² : (2.5) Eh hc hc === ν λ The Rydberg equation can be re-written as: (2.6) =− ± ² ³ ´ µ R nn 11 1 2 2 2 For each line of the hydrogen spectrum calculate the Rydberg constant in wavenumbers (in cm -1 ) using equation (2.6). You must first convert the wavelength of each transition from nanometres to centimetres. Show a sample calculation. 3. Re-arrange equation (2.6) into the form of a line (Hint: (1 / n 1 2 ) is constant. Put x = (1 / n 2 2 ) and re-arrange the equation to the form y = mx + b) . Plot ± ² (y-axis) versus 1/n 2 2 (x-axis) and find the line of best fit (i.e., the regression line). From the equation for the line of best fit, calculate the Rydberg constant (this is likely how Rydberg would have determined this value). Compare the different values you calculate with the literature value for the Rydberg constant. Show a sample calculation.
UOIT Chem. 1800, W10: Exp. 2-7.9 61 Wavelength / nm n 1 n 2 Rydberg Constant / cm -1 Percentage Error Rydberg Constant from Graph 4. If you could record the absorption spectrum of hydrogen gas, what would it look like? Justify your answer. 5. In Part III what is your unknown cation? Justify your answer. 6. When you observe the spectra of the metal salts, how do you know the emission comes from the cation and not the anion? Suggest an experiment to verify this. 7. What is the vapour (or gas) present in fluorescent lights? What experimental evidence do you have?

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UOIT Chem. 1800, W10: Exp. 2-7.9 62 DATA SHEET Part I: Calibration of Spectroscope Colour of Line Wavelength / nm Scale position yellow 579.0 green 546.1 blue 435.8 violet 404.7 Part II: Hydrogen Spectrum Colour Scale Reading Wavelength / nm (from graph)
UOIT Chem. 1800, W10: Exp. 2-7.9 63 Part III: Spectra of Cations Solution Flame Colour Scale Positions Wavelengths / nm (from graph) KCl LiCl CaCl 2 NaCl unknown Part IV: Fluorescent and Incandescent lamps Describe what you see for: I) Fluorescent lamp ii) Incandescent lamp

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UOIT Chem. 1800U, W10; Exp. 3 - 7.9 64 3. MEASUREMENT OF THE IDEAL GAS CONSTANT, ‘R’ Objectives 1) To apply Dalton’s Law of Partial Pressures to a mixture of gases (water vapour and hydrogen); 2) To measure the ideal gas constant and compare the measured value with the accepted value (8.314 L kPa mol -1 K -1 . Introduction The behaviour of gases as the pressure, volume, temperature and amount of gas (i.e., the number of moles of gas) are changed was one of the earliest things to be studied systematically in science. Over 300 years ago Boyle observed that (to a very good approximation) the volume of a
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2nd_lab - UOIT Chem 1800 W10 Exp 2-7.9 Experiment 2 Atomic...

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