Chemistry:  chapter 3 pages 80 – 85 &  chapter 7 pages 221 – 233

Moles, Moles Relationships and Mole Conversions

I.  Mass

      A.  masses listed on the periodic table are relative, average atomic masses

            1.  weighted average of isotopes determined by the abundance of each isotope and it's mass

            2.  based on a standard:  1 atom of carbon = 12 amu

            3.  all masses are compared to carbon–12 as a reference

      B.  on the atomic level measured in atomic mass units  ( amu  or  u )

      C.  on the macroscopic level

            1.  the atomic mass unit is too small to measure in the macroscopic world  (1 amu = 1.66 x 10–24 g)

2.      there must be some conversion number that will relate the atomic level (amu) to the

macroscopic level (grams)

            3.  this number is called a mole (also called Avogadro's number) and it is equal to 6.02 x 1023

            4.  therefore: 

                  a.  1 mole of carbon atoms = 6.02 x 1023 atoms;   AND

                  b.  1 mole of carbon atoms = 12 grams

;   AND

                  c.  6.02 x 1023 carbon atoms = 12 grams

      D.  determining the molar mass  (mole mass  or  molecular mass  or  formula mass)

            1.  determine what the elements are

            2.  determine how many of each element there are

            3.  determine the mass of each element

            4.  multiply the number of each element by its mass and add the numbers

II.  Percent Composition by Mass

      A.  

      B.  to find the percent composition by mass of the elements in a compound, you need to know :

            1.  how much mass does the element (part) contribute to the compound’s molar mass (whole) 

            2.  the compound’s molar mass (whole)

III.  Method for solving problems:

      A.  factor-label or unit analysis or dimensional analysis

  1. use the given information and a conversion factor to find the unknown

IV.  Mole Conversions

  1. based on the relationship

mass in grams of the substance

(molar mass)

ä                                                                                           ã

 å                                                        æ

1 mole              ß                                à        6.02 x 1023 "things"

(“things” can be molecules, formula units, etc.)

 

      B.  grams to moles

 

      C.  moles to grams

 

      D.  "things" to moles

 

      E.  moles to "things"

 

      F.  "things" to grams  

 

      G.  grams to "things"

 

V.  Molarity

      A.  the concentration of a solution

      B.  shown by M

      C.              or        

VI.  Empirical Formula

      A.  the simplest (lowest) whole number mole ratio between elements in the compound

      B.  find moles of each element  (convert grams to moles)

      C.  divide the moles of each element by the smallest moles

      D.  multiply, if needed, to get whole number and use as subscripts

VII.  Molecular Formula

      A.  whole number multiple of the empirical formula

B.     the molecular formula mass is the same ratio larger than the empirical formula mass as the

molecular formula is larger than the empirical formula

      C.  find the empirical formula

      D.  find the empirical formula mass

      E.  find the molecular formula mass

F.      compare the molecular formula mass with the empirical formula mass to determine how much

larger the molecular mass is than the empirical formula mass

      G.  multiply subscripts of empirical formula by how much larger the molecular formula is

VIII.  Hydrate

      A.  a compound with water molecules bonded to it

      B.  the compound is an anhydrous salt  (anhydrous means without water)

      C.  it is represented as:  y  salt formula . x  H2O 

      D.  to find the formula of a hydrate:

            1.  determine the moles of anhydrous salt  (convert grams to moles)

            2.  determine the moles of water present  (convert grams to moles)

            3.  divide the moles of the salt and the water by the smallest moles (this should always be the salt

moles),  this is x  and y

            4.  y is usually 1