Example Exercise 9.1 Atomic Mass and Avogadro’s Number

1 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Mass and Avogadro s NumberThe Atomic mass of each element is listed below the symbol of the element in the periodic table: Cu = amu, Hg = amu, S = amu, and He = amu. The mass of Avogadro s Number of atoms is the Atomic mass expressed in grams. Therefore, 1023atoms of(a)Cu = g(c)S = g(b)Hg = g(d)He = gSolutionRefer to the Atomic masses in the periodic table inside the front cover of this textbook. State the mass of Avogadro s Number of atoms for each of the following elements:(a)Copper(c)sulfur(b)Mercury(d) heliumRefer to the periodic table and state the mass for each of the following:(a)1 atom of Au(b) 1023 atoms of AuAnswers:(a) amu; (b) gPractice ExerciseWhat is the mass of an average platinum atom?

2 What is the mass of Avogadro s Number of Pt atoms?Answer:See Appendix Exercise 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Calculations ICalculate the Number of sodium atoms in mol PlanStep 1: What unit is asked for in the answer?Step 2: What given value is related to the answer?Step 3: What unit factor(s) should we apply?Since 1 mol Na = 1023atoms Na, the two unit factors are 1 mol 1023 atoms Na, and its reciprocal 1023atoms Na/1 mol Analysis Map 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H.

3 CorwinExample Exercise Calculations ICalculate the Number of formula units in mol of sodium chloride, 1022formula units NaClPractice ExerciseWhat is the Number of molecules in mol of any gas?Answer:See Appendix ExerciseWe apply the unit factor 1023atoms Na/1 mol Na to cancel moles , which appears in the answer is rounded to three digits because the given value and unit factor each have three significant 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Calculations ICalculate the Number of moles of potassium in 1021atoms PlanStep 1: What unit is asked for in the answer?

4 Step 2: What given value is related to the answer?Step 3: What unit factor(s) should we apply?Since mol K = 1023atoms K, the two unit factors are 1 mol 1023atoms K, and its reciprocal 1023atoms K/1 mol Analysis Map 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Calculations IWe apply the unit factor 1 mol 1023atoms K to cancel atoms , which appears in the answer is rounded to three digits because the given value and unit factor each have three significant the Number of moles of potassium iodide in 1025formula units of mol KIPractice ExerciseWhat is the Number of molecules in mol of iodine crystals?

5 Answer:See Appendix ExerciseContinued 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Mass CalculationsWe begin by finding the Atomic mass of each element in the periodic table. The molar mass equals the sum of the Atomic masses expressed in g/mol.(a)The Atomic mass of Ag is amu, and the molar mass of silver equals g/mol.(b)The sum of the Atomic masses for NH3is amu + 3( )amu = amu. The molar mass of ammonia equals g/mol.(c)The sum of the Atomic masses for Mg(NO3)2is amu + 2( + + + )amu = molar mass of magnesium nitrate equals the molar mass for each of the following substances:(a)silver metal, Ag(b)ammonia gas, NH3(c)magnesium nitrate, Mg(NO3)2 Calculate the molar mass for each of the following substances:(a)manganese metal, Mn(b)sulfur hexafluoride, SF6(c)strontium acetate, Sr(C2H3O2)2 Answers:(a) g/mol; (b) g/mol; (c) g/molPractice ExerciseThe molecular mass of water is amu.

6 What is the mass of Avogadro s Number of water molecules?Answer:See Appendix Exercise 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Calculations IIWhat is the mass in grams of 1022atoms of sulfur?Step 1: What unit is asked for in the answer?Step 2: What given value is related to the answer?Step 3: What unit factor(s) should we apply?By definition, 1 mol S = 1023atoms S, and the molar mass from the periodic table is g S = 1 mol S; the two pairs of unit factors are shown in Step PlanUnit Analysis Map 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H.

7 CorwinExample Exercise Calculations IIWe apply the unit factor 1 mol 1023atoms S to cancel atoms S , and g S/1 mol S to cancel mol S :SolutionWhat is the mass of 1022formula units of lead(II) sulfide, PbS? g PbSPractice ExerciseSulfur occurs naturally as S8molecules. What is the mass of Avogadro s Number of S8molecules?Answer:See Appendix ExerciseContinued 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Calculations IIHow many O2molecules are present in g of oxygen gas?Step 1: What unit is asked for in the answer?

8 Step 2: What given value is related to the answer?Step 3: What unit factor(s) should we apply?The molar mass from the periodic table is g O2 = 1 mol O2, and by definition, 1 mol O2 = 1023molecules O2. Thus, the two pairs of unit factors are shown in Step Analysis MapStrategy Plan 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise Calculations IIWe apply the unit factor 1 mol O2 g O2to cancel g O2 , and 1023molecules O2/1 mol O2to cancel moles O2. Thus,SolutionHow many formula units of lithium fluoride are found in g LiF?

9 1021formula units LiFPractice ExerciseOzone occurs naturally as O3molecules. What is the mass of Avogadro s Number of ozone molecules?Answer:See Appendix ExerciseContinued 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise of a MoleculeCalculate the mass in grams for a single molecule of carbon dioxide, CO2(given that MM = g/mol).Step 1: What unit is asked for in the answer?Step 2: What given value is related to the answer?Step 3: What unit factor(s) should we apply?By definition, 1 mol CO2 = 1023molecules. Thus, the unit factors are shown in Step PlanUnit Analysis Map 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H.

10 CorwinExample Exercise of a MoleculeWe apply the unit factor 1 mol CO2 1023molecules CO2to cancel mol the mass in grams for a single molecule of carbon monoxide, 10-23g/moleculePractice ExerciseWhat is the mass of a carbon monoxide molecule expressed in amu?Answer:See Appendix ExerciseContinued 2011 Pearson Education, Chemistry: Concepts and Critical Thinking, 6th EditionCharles H. CorwinExample Exercise of a Gas at STPC alculate the density of ammonia gas, NH3, at STP. (MM = g/mol)Step 1: What unit is asked for in the answer?Step 2: What given value is related to the answer?