2-Test-practice-d

# 2-Test-practice-d - Exam#2 Practice Name Read the...

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1 Exam #2 - Practice Name ___________________ Read the instructions carefully and follow them. Show your calculations to receive maximum credit. Significant figures should be correct. You have until 8:50 am to complete this exam. NOTE: All Lewis structures should include lone pairs and any non-zero formal charges. Table 1. Potentially useful equations. Table 2. Fundamental physical constants h = 6.63 x 10 -34 J s c = 3.00 x 10 8 m s -1 k = 8.99 x 10 9 J m C -2 m e = 9.11 x 10 -31 kg e = -1.60 x 10 -19 C Avogadro’s number = 6.02 x 10 23 mol -1 Table 3. Prominent infra-red absorption peaks. Group Wavenumber (cm -1 ) Description O-H 3700-3200 Very broad N-H 3500-3300 C-H 3300-2700 C=O 1900-1640 Very sharp E = " 2 k 2 e 4 # 2 m n 2 h 2 E = hv = h " c # r = n 2 h 2 4 ke 2 " 2 m " ( m # v ) # " x \$ h 4 % " = h m # v PE = M " k " q 1 " q 2 r

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2 1) Metal cations form ionic compounds with nitrates (NO 3 - ) and carbonates (CO 3 2- ). a) Draw Lewis structures of the nitrate and carbonate anions, assigning formal charges and drawing any resonance structures that do not involve open-shell atoms. b) If a mixture of magnesium nitrate and magnesium carbonate is added to water, one compound remains undissolved at the bottom of the flask. i) What are the empirical formulas for magnesium nitrate and magnesium carbonate? ii) Which is the undissolved compound? Why? iii) The mixture is 30% by weight of magnesium nitrate and 5.0 g of the mixture is added to water. Assuming that the compound you chose in part ii is completely insoluble, what is the weight of material left undissolved at the bottom of the flask?
3 2) Examine the set of compounds below and complete the tables: NaOCH 2 CH 3 HOCH 2 CH 3 ICH 2 CH 2 CH 3 FCH 2 CH 3 H 2 NCH 2 CH 2 CH 3 Mg(OCH 2 CH 3 ) 2 a) Rank the compounds in order of their boiling points. Compound with the highest boiling point Compound with the lowest boiling point b) Which compounds are ionic? c) Rank the compounds that only contain covalent bonds in the order of their dipole moments. Compound with the highest dipole moment Compound with the lowest dipole moment

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4 3) C, Si, and Ge all form bonded networks with the same solid structure but with the different properties given below: Table 4: Properties of the network compounds of group 4 elements. Absorbs all light with energy above (J) Density (g/cm 3 ) Melting point (C°) Bond length (Å) C (diamond) 8.83 x 10 -19 3.53 4000 1.50 Si 1.80 x 10 -19 2.32 1683 K 2.35 Ge 1.05 x 10 -19 5.32 1210 K 2.45 a) What wavelength of light (in nm) has 8.83 x 10 -19 J of energy? b) Will diamond absorb light of greater or smaller wavelengths than your answer above? c) Sketch the UV-visible absorption spectrum of diamond: 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 Absorbance (%) Wavelength (nm)
5 d) What will the color of Ge be?

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