EM 105 Dr. Lammi EXAM II Oct. 8, 2018 Name: Please show all work and/or reasoning in the space provided or on the attached scratch page. Partial credit for incorrect answers may only be awarded if work/reasoning is shown. Remember to report the final results of your calculations with the appropriate significant figures. A Periodic Table and a page of helpful information are provided for your use. GOOD LUK!! 1. (9 pts) Please provide the correct formula or name for each of the following compounds. a. Antimony trifluoride b. NiO 3 c. N 2O 3 O 2. (13 pts) onsider N 2O 3, named in Question 1(c) above. Its atoms are arranged as follows: O-N-N-O a. Draw the best Lewis structure(s) to depict bonding in this compound, including equivalent resonance structures, if necessary. b. This compound is not very stable: at or above room temperature it readily dissociates into NO and NO 2. Please suggest an explanation for its instability based on your structure(s) in part (a). 3. (6 pts) The following questions relate to hybridization. a. Please list one key weakness of the hybridization theory. b. Please give a brief explanation of why we use the hybridization model, in spite of its weaknesses. 1
4. (13 pts) An incomplete Lewis structure for bisphenol A ( 15 16O 2), the component in some hard plastic food and beverage containers that has recently raised health concerns, is shown below. a. Add lone pairs to complete the Lewis structure. 2 Y Z b. Please estimate the bond angles X, Y, and Z. O 1 X 3 O X: Y: Z: c. Please specify the type of hybrid orbitals used by each of the three numbered atoms (O 1, 2, 3). O 1: 2: 3: d. ow many σ and how many π bonds does bisphenol A have? σ bonds: π bonds: 5. (14 pts) The following questions relate to DA (docosahexaenoic acid), 22 32O 2, one of the omega-3 fatty acids found to benefit heart health. a. Suppose that one 100.0-gram serving of tuna contains 1631 mg of DA. ow many molecules of DA does this serving of tuna contain? b. The calorie content of a food item which is a measure of the energy stored in its chemical bonds may be determined from the amount of energy given off when it is combusted. Please write and balance the chemical equation for the complete combustion of DA. (Lots of extra space here!) 2
6. (12 pts) ydrogen peroxide ( 2O 2) is often sold by chemical suppliers as a solution that is 30 % 2O 2 by mass: this means that it contains 30.0 grams of 2O 2 per 100.0 grams of water. a. Suppose that a solution containing 30.0 g of 2O 2 has a total volume of 103.5 ml. What is the molar concentration of hydrogen peroxide in this solution? b. Suppose that you wish to dilute 100.0 ml of the solution prepared in (a), to a final concentration of 0.425 M (a concentration similar to what is sold in the drugstore). To what final volume must you dilute it in order to reach this concentration? 7. (19 pts) Recently, urea (N 2) 2O 2 has begun to overtake ammonium nitrate as a cheaper source of nitrogen for N- based fertilizers. ommercially, urea is made in a two-step process: the unbalanced first step involves producing ammonium carbamate (N 2O 2N 4), as shown below: N 3 + O 2 N 2O 2N 4 a. Please write the chemical formula for ammonium nitrate. b. Please balance the equation above. c. Ammonia producers also generate large quantities of O 2 from the combustion of fossil fuels, which they can recover for use in making ammonium carbamate and urea. If a plant produces 1955 metric tons of ammonia and 1822 metric tons of O 2 per day, what is the maximum daily mass of ammonium carbamate it can produce? (Note: 1 metric ton = 1,000 kg) 3
Problem 7, continued d. Suppose that the plant actually obtains 1964 metric tons of ammonium carbamate. What is the percent yield? 8. (19 pts) In this problem, you will describe bonding in chlorite, lo 2 -. a. Please draw the best Lewis structure(s) that obey the octet rule. Include equivalent resonance structures, if necessary. Indicate the formal charge on each atom. b. Next, draw the best Lewis structure(s) that minimize formal charge, including equivalent resonance structures, if appropriate. c. Which of your final answers, (a) or (b), contain the longer l-o bonds? d. Please use either your answer for (a) OR (b) to name and sketch the molecular geometry of this ion. Also, please estimate the bond angles. e. Is lo 2 - polar or nonpolar? 4
BLANK SRAT PAGE If there is material to be graded here, make sure that it is clearly labeled and write your name on the page. 5
Useful onstants, onversion Factors and Equations onstants and onversion Factors: h = 6.626 10-34 J. s c = 2.9979 10 8 m s 1 J = 1 kg m2 s 2 N A = 6.022 10 23 Equations: dd = mm V ν = cc λ E photon = hν E K (ejected electron) = E photon - φ EE KK = 1 2 mmv2 EE = 2.178 10 18 J 1 2 1 n f n 2 E photon = E i λ matter = h mmv M iv i = M fv f 6
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