MOLE CALCULATION ACTIVITY INTRODUCTION In this activity, you will investigate the relationship between the mass and the number of moles of a substance. Recall that the mole is a unit of measure of the atom. Similar to the way a dozen represents twelve of any item, the mole represents 6.023 x 1023 of any particle. This is particularly useful in chemistry, where chemists often asked to investigate the properties of substance and the ways in which they interact with each other. In order to do this they need to know how many molecules are in a sample of a substance. This presents two problems for chemists in that the atom is too small to visualize with the naked eye and there are way too many atoms to count, even in a very small quantity of a substance. The mole was defined to solve the problem of having to quantify large number of very small molecules. Using the mole, chemists can determine the number of molecules of a substance by comparing it to the mass of the sample. LEARNING GOALS 



Recognize that one mole equals 6.023 x 1023 particles (Avogadro’s number) Convert between mass and the number of moles of a substance using molar mass Convert between the number of particles and the mass of a substance Locate the molar mass of elements on the periodic table and calculate the molar mass of compounds INSTRUCTION In this activity, you will be asked to calculate the number of moles of a substance found in real items you can hold in your hands. As it is an inquiry based activity, there is often more than one way to answer the question. Do not be alarmed if your method is slightly different from one of your classmates. Page 1 of 11 All answers should be correct to three significant figures and should be reported using scientific notation. Once you have completed the activity, upload your work to the Dropbox for your teacher to review. SUGGESTED EQUIPMENT AND MATERIALS 




Balance Graduated cylinders Beakers Nickels Sugar 




Water Table of Densities Iron Nail Pennies Table Salt TABLE OF DENSITITES Element/Compound Density (g/cm3) Water (H2O) 1.00 Iron (Fe) 7.87 Copper (Cu) 8.93 Nickel (Ni) 8.80 Sugar (C6H12O6) 1.54 Salt (NaCl) 2.17 QUESTIONS Use Avogadro's number to solve each of the questions listed below. You may need to make a measurement before calculating the final answer. This activity is designed to have the students calculate the number of moles of an object using the equations taught in this unit. As a directed inquiry activity, students should be presented with the challenge with minimal instructions. The teacher can choose to introduce the relationship between mass, volume and density prior to the activity or use it as a hint when students pose procedural questions in class. Answers provided in this resource will not be identical for all students based on the natural variance in the mass of materials and assumptions used throughout the activity. Page 2 of 11 For example, a student that uses the density formula to calculate the mass of a penny will arrive at a slightly different mass calculation than a student that uses a balance to measure the mass because the assumption that the penny is pure copper is not true. The teacher would be advised to acknowledge the assumption and assess the work based on the rationale behind the calculations provided by the student and not the veracity of the mass. Part One: Choose ONE of the following items and determine the number of moles it contains. 1. a penny (Cu) Note:  Answers will vary based on the variance in the mass of the coins used by the student.  Although most students will use a balance, some students may use the volume of water displaced by a penny to determine its mass.  Students are to assume that the mass is 100% copper. Solution #1: Using a balance to measure the mass of a penny. Given mCu  2.35 g
M Cu  63.55 g/mol nCu
 ?
Solution The molar mass of copper is 63.55 g/mol. Calculate the number of moles (n) in one penny. mCu
nCu 
M Cu
2.35 g
g
63.55
mol
 1 mol
 2.35 g 
 63.55 g

 0.0370 mol







Therefore, there are3.70 x 10‐2 moles of copper in one penny. Page 3 of 11 Solution #2: Using the volume of water displaced by pennies to calculate the mass of a penny. Given DCu
M Cu
VCu
mCu
nCu





8.93 g/cm3
63.55 g/mol
?
?
?
Solution The molar mass of copper is 63.55 g/mol. Calculate the mass of 1 penny using the volume of water displaced by dropping 5 pennies into a graduated cylinder. Volume of 5 pennies = 1.31 mL = 1.31 cm3 m
D 
V
m  DV

g
  8.93

cm3

 11.75 g


 1.31 cm3



The mass of 5 pennies is 11.75 grams, therefore, the mass of 1 penny is 2.35 grams. Calculate the number of moles (n) in one penny. mCu
nCu 
M Cu
2.35 g
g
63.55
mol
 1 mol
 2.35 g 
 63.55 g

 0.0370 mol







Therefore, there are3.70 x 10‐2 moles of copper in one penny. 2. an iron nail (Fe) Note:  Answers will vary based on the mass of the nail used by the student.  Although most students will use a balance, some students may use the volume of water displaced by an iron nail to determine its mass.  Students are to assume that the mass is 100% iron. Page 4 of 11 Given mFe  5.95 g
M Fe  55.85 g/mol nFe
 ?
Solution nFe

mFe
M Fe
5.95 g
g
55.85
mol
 1 mol
 5.95 g 
 55.85 g

 0.106 mol







Therefore, there are 0.106 moles of iron in one nail. Part Two: Choose ONE of the following items and determine the number of moles it contains. 1. a pint of water (H2O) Note:  Students are to use an American pint of 16 fluid ounces or 473 milliliters.  Students need to convert units from milliliters to cubic centimeters.  Students can either mass the water in 1 pint or use the density formula to calculate the mass of water. Given VH2O
 1 pint
DH2O
 1.00 g/cm 3
mH2O
 ?
M H2O
 ?
nH2O
 ?
Solution Calculate the mass (m) in 1 pint of water. Convert 1 pint into cubic centimeters. 1 pint = 473 mL = 473 cm3 Page 5 of 11 Calculate the mass of water in 1 pint using the density formula. m
V
 DV
D 
m

g
 1.54

cm3

 1695.88 g


 1101 cm 3



Calculate the molar mass (M) of water. M H 2O
 2M H
 MO
g 
g 


 2 1.01
   16.00
 mol 
mol 


g
 18.02
mol
Calculate the number of moles (n) of water. mH2O
nH2O 
M H2O
473 g
g
18.02
mol
 1 mol
 473 g 
 18.02 g

 26.2 mol







Therefore, there are 26.2 moles of water in 1 pint. 2. a dry quart of sugar (C6H12O6) Note:  Students are to use a US dry quart of 1.101 liters.  Students need to convert units from liters to cubic centimeters.  Students can use either a balance or the density formula to determine the mass of glucose. Page 6 of 11 Given VC6H12O6
 1 dry quart
DC6H12O6
 1.54 g/cm3
mC6H12O6
 ?
M C6 H12O6
 ?
nC6 H12O6
 ?
Solution Calculate the mass (m) in a dry quart of sugar. Convert 1 dry quart into cubic centimeters. 1 dry quart = 1.101 L = 1101 mL = 1101 cm3 Calculate the mass of sugar in 1 dry quart using the density formula. m
V
 DV
D 
m

Calculate the molar mass (M) of glucose. M C6 H12O 6

g
 1.54

cm3

 1695.88 g
 6M C

 1101 cm 3


 12 M H

 6M O
g 
g 
g 



 6 12.01
  12  1.01
  6  16.00

mol 
mol 
mol 



g
g
g
 72.06
 12.12
 96.00
mol
mol
mol
g
 180.18
mol
Calculate the number of moles (n) of glucose. mC6 H12O 6
nC6 H12O 6 
M C6 H12O 6


1695.88 g
g
180.18
mol




1 mol

1695.88 g   180.18
g
 9.412 mol
Therefore, there are 9 moles of glucose in 1 dry quart. Page 7 of 11 Part Three: Choose ONE of the following questions to answer. 1. How many nickel (Ni) atoms are in a nickel coin? Note:  Answers will vary based on the variance in the mass of the nickel used by the student.  Students are to assume that the mass is 100% nickel. Given VNaCl  5.05 g
DNaCl
 58.69 g/mol
NA
 6.023 x 1023 molecules/mol nNi
 ?
N Ni
 ?
Solution Calculate the number of moles (n) in 1 nickel. nNi

mNi
M Ni
5.05 g
g
58.68
mol
 1 mol
 5.05 g 
 58.68 g

 0.08606 mol







Calculate the number of moles (N) in 1 nickel. N Ni  nN A

 0.08606 mol   6.023 x 10
23
molecules 
 mol 
 5.18 x 1022 molecules
Therefore, there are 5.18 x 1022 molecules in 1 nickel. 2. How many chlorine (Cl) ions are in a teaspoon of table salt (NaCl) Note:  The volume of a tablespoon is equal to 4.92892159375 milliliters.  Students need to convert units from milliliters to cubic centimeters. Page 8 of 11 
Students can use a balance or the density formula to determine the mass of a tablespoon of salt. Given VNaCl
 1 tablespoon
DNaCl
 2.17 g/cm3
NA
M NaCl
mNaCl
nNaCl
N Cl-





6.023 x 1023 molecules/mol
?
?
?
?
Solution Calculate the mass (m) in a tablespoon of salt. Convert 1 tablespoon into cubic centimeters. 1 tablespoon = 4.92 mL = 4.92 cm3 Calculate the mass of sodium chloride in 1 tablespoon using the density formula. m
V
 DV
D 
m

g
  4.92

cm 3

 10.67 g


 2.17 cm 3



Calculate the molar mass (M) of sodium chloride. M NaCl
 M Na
 M Cl
g 
g 


  22.99
   35.45
 mol 
mol 


g
 58.44
mol
Page 9 of 11 Calculate the number of moles (n) of sodium chloride. mNaCl
nNaCl 
M NaCl



 0.1825 mol

1 mol

10.67 g   58.44
g
Calculate the number of molecules in 0.1825 moles of sodium chloride. N NaCl  nNaCl N A
 6.023 x1023 molecules 
 (0.1825 mol ) 
 1 mol


23
 1.1 x 10 molecules


10.67 g
g
58.44
mol
Calculate the number of chlorine ions. 

1 Cl- ion
23
N Cl-  
 1.1 x 10 molecules of NaCl
 molecules of NaCl 


 1.1 x 1023 Cl- ions
Therefore, there are 1 x 1023 chlorine ions in 1 tablespoon of salt. Part Four: Answer the following question. 1. How many moles are in 20 gallons of water? Note:  The volume of a gallon is equal to 3.785411784 liters.  Students need to convert units from liters to cubic centimeters.  Students can use a balance or the density formula to determine the mass of 20 gallons of water. Given  20 gallons
VH2O
DH2O
 1.00 g/cm3
M H2O
 ?
mH2O
 ?
nH2O
 ?
Page 10 of 11 Solution Calculate the mass (m) in 20 gallons of water. Convert 20 gallons into cubic centimeters. 1 gallon = 3.78411784 L 20 gallon = 75.70823568 L = 75.70823568 cm3 Calculate the mass of water in 20 gallons using the density formula. m
V
 DV
D 
m


g 
 75.70823568 cm3
 1.00

cm3 

 75.70823568 g

Calculate the molar mass (M) of water. M H 2O  2 M H
 MO
g 
g 


 2 1.01
   16.00
 mol 
mol 


g
 18.02
mol
Calculate the number of moles (n) of water. mH2O
nH2O 
M H2O


75.70823568 g
g
18.02
mol




1 mol

 75.70823568 g   18.02
g
 4 mol
Therefore, there are 4 moles in 20 gallons of water. ASSESSMENT Complete the worksheet. When you are done, upload your work to the Dropbox for review by your teacher. Page 11 of 11