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Chemistry 112 First Hour Exam Name:____________ (4 points) Please show all work for partial credit All problems are worth 12 points Please read and sign the following statement: I understand that this test is being given over the course of several days. As a result, I will not discuss the problems on this test with anyone until after Noon on Friday, September 21. Signed: ___________________ Date: ______________ 1A. How many significant figures are in each of the following numbers? .45050 ___5____ 45050 ____4___ .04505x10-3 __4_____ 1B. Below are the answers to different calculations. Express this number with the correct number of significant figures 67 x 1001 = 67067 __67000_____ 67 + 33 = 100 _100._________ decimal shows good to the 1's place (67x1001)/(67+33) = 670.67 2. Perform the following unit conversions: 87 cm to Mm 87 footAlbs to cmAkg 87 lbsAin-2 to kgAm-2 _670_________ 2 3. Calculate the Molecular mass of the following compounds N2O 2(14.01) + 16.00 = 44.02u Mg(NO2)2 24.31 + 2(14.01) + 4(16.00) = 116.33u Calcium oxide (If you don’t know the formula, make one up for partial credit) CaO 40.08 + 16.00 = 56.08 Phosphorous pentachloride (If you don’t know the formula, make one up for partial credit) PCl5 30.97 + 5(34.45) = 208.22u 4. Complete the following table: Complete Symbol # protons # electrons # neutrons 29 29 34 15 15 16 25 21 30 16 18 16 3 5. Balance the following chemical reactions: Li(s) + Cl2(g) 6LiCl(s) 2Li(s) + Cl2(g) 62LiCl(s) Mg3N2(s) + HBr(g) 6MgBr2(s) + NH3(g) Mg3N2(s) + 6HBr(g) 63MgBr2(s) + 2NH3(g) C2H2(l) + O2(g) 6 CO2(g) + H2O(g) 2C2H2(l) + 5O2(g) 6 4CO2(g) + 2H2O(g) 6A. In the blank periodic table below please indicate where the following things are found: Alkaline earth metals XXX ActinidesYYY Second period elementsZZZ 6B. Using the periodic table supplied with this test please identify the following elements (A symbol get you 1 point, a full name, correctly spelled gets you 2 points) Any Noble gas Helium to Radon_________________ A halide in the second period Neon________________ Any three transition metals _Scandium to Zinc to Lanthanum to Mercury_______ 4 7. Define the following terms: Kinetic Energy Energy associated with a moving mass = ½ MV2 Precision How close your values are to each other. Homogeneous mixture A mixture that is so uniform you cannot see and individual component Also a solution. Solute A material that is going to be dispersed in a solvent Hypothesis A guess about how a system works that will be tested. 8. A tougher question, so I saved it for last. Elemental magnesium has an atomic mass of 24.30u. There are three major isotopes of Mg: 24 Mg, 25 Mg, and 26 Mg. If 77% of elemental magnesium is the 24Mg isotope, what is the % abundance of the other 2 forms? 24.30 = .77(24) + X(25) + Y(26) 1.00=.77 + X + Y 1.00-.77-X =Y Y= .23-X Substituting into the first equation 24.30 = .77(24) + X(25) + (.23-X)(26) 24.30 = 18.48 + 25X + (.23)26 - 26X 24.30 -18.48 -(.23)26) = 25X-26X -.16 = -X 25 Mg = 16% abundance 26 Mg = 7% abundance