NAME Answer Key Exam Numbers 24 and 38 Chemistry 111 2010 Vining 9 22 2010 Hand in only this page Questions 1 20 count for 4 points each Questions 21 and 22 are 10 points each and have partial credit 1 You dissolve some sugar in very pure water All the sugar dissolves The result is a homogeneous mixture 2 The atomic number of K is 19 3 The mass number of the only stable isotope of arsenic As is 75 4 The species 35Cl has 17 protons 18 neutrons and 18 electrons 5 An atom becomes a cation by losing electrons 6 Which ionic compound listed below does not have a correct formula CaPO4 because Ca2 and PO43 charges do not cancel should be Ca3 PO4 2 7 The elements Be and Mg are in the same periodic group and the elements C and N are in the same periodic period 8 An element has the following isotopic abundances 20 mass 45 00 g mol 78 mass 47 00 g mol 2 mass 49 00 g mol Which of the following the average molar mass of this element 46 64 g mol 9 The relationship between O2 and O3 is that they are allotropes 10 The molar mass of Mg NO3 2 is 148 3 g mol 11 What kind of compound will be formed between the elements Fe and Br ionic 12 How many F atoms are there in a 68 9 g sample of F2 68 9 mol F2 2 mol F atoms 6 022 1023 F atoms 2 18 1024 atoms 1 mol F2 1 mol F atoms 13 What is the percent mass of carbon to two significant figures in C2H6O2 12 01 g C mol C 100 39 62 07 g C2 H 6 O 2 2 mol C 14 A compound is composed of 25 93 N and 74 06 O by mass What is its empirical formula N2O5 Assume 100 g of compound so there are 25 93 g N and 74 06 g O 1 mol N 1 85 mol N 14 01 g N 1 mol O 74 06 g O 4 63 mol O 16 00 g O 25 93 g N mol O 4 63 1 5 2 50 2 mol N 1 85 2 2 15 Consider the reaction therefore empirical formula N2O5 P4 6 Cl2 4 PCl3 If 3 5 mol of P4 react how many moles of PCl3 can be formed 3 5 mol P4 4 mol PCl3 14 mol PCl3 1 mol P4 16 An experiment is performed where NaOH is slowly added to 50 0 g FeCl3 The reaction that occurs produces Fe OH 3 The plot below shows the mass of Fe OH 3 produced as a function of the mass of NaOH added Choose two correct statements Circle both on the answer sheet at point B FeCl3 is the limiting reactant at point A NaOH is the limiting reactant adding more FeCl3 will move the deflection point to the right 17 How many moles of NO2 are in 9 7 g of NO2 9 7 g NO 2 1 mol NO 2 0 21 mol NO 2 46 01 g 17 How many moles of OF2 are in 29 7 g of OF2 29 7 g NO 2 18a The formula of ammonium sulfate is 18b The name of SO2 is sulfur 19a Name AlCl3 aluminum NH4 2SO4 dioxide chloride 19a Name MgCl2 magnesium 20 Balance the following reaction chloride 1 mol OF2 0 55 mol OF2 54 00 g The formula of ammonium carbonate is The name of SO3 is sulfur trioxide 19b Name FeCl2 iron II chloride 19b Name FeCl3 iron III chloride 1 C6H12 9 O2 6 CO2 6 H2O 1 C8H18 12 O2 8 CO2 8 H2O All work must be shown for credit on this page 21 Consider the reaction 4 Cr 3 O2 2 Cr2O3 If 75 0 g of Cr are mixed with 25 0 g O2 how many grams of Cr2O3 can be formed 1 mol Cr 1 44 mol Cr 52 00 g 1 mol O 2 0 781 mol O 2 25 0 g O 2 32 00 g 1 44 mol Cr 0 781 mol O 2 so O 2 is the limiting reactant 4 3 2 mol Cr2 O3 0 521 mol Cr2 O3 0 781 mol O 2 3 mol O 2 75 0 g Cr 0 521 mol Cr2 O3 151 99 g Cr2 O3 79 1 g Cr2 O3 1 mol NH4 2CO3 22 Chemical Analysis You have a 10 56 gram sample that is a mixture of Cr2 CO3 3 and Fe2O3 You heat it and the following reaction takes place Cr2 CO3 3 s Cr2O3 s 3 CO2 g No reaction occurs to the Fe2O3 After heating the mass is found to be 8 46 g What is the mass percent of Cr2 CO3 3 in the original mixture The mass lost is all due to CO2 lost which comes from Cr2 CO3 3 Map g CO2 mol CO2 mol Cr2 CO3 3 g Cr2 CO3 3 percent Cr2 CO3 3 g CO2 lost 10 56 g 8 46 g 2 10 g CO2 1 mol Cr 1 44 mol Cr 52 00 g 1 mol CO 2 0 0477 mol CO 2 2 10 g CO 2 44 01 g 1 mol Cr2 CO3 3 0 0159 mol Cr2 CO3 3 0 0477 mol CO2 3 mol CO 2 75 0 g Cr 284 01 g Cr2 CO3 3 4 51 g Cr2 CO3 3 1 mol 4 51 g Cr2 CO3 3 Cr2 CO3 3 100 42 8 10 56 g sample 0 0159 mol Cr2 CO3 3