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CHE 111 - Module 3. CHAPTER 3 LECTURE NOTES. STOICHIOMETRY. Stoichiometry is the study of the quantitative relationships between the amounts of reactants and products in chemical reactions.

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CHE 111 - Module 3

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che 111 module 3

CHE 111 - Module 3



  • Stoichiometry is the study of the quantitative relationships between the amounts of reactants and products in chemical reactions.
  • We use BALANCED equations to understand stoichiometric relationships of the elements and compounds within a chemical reaction.
the balanced equation
The Balanced Equation

2Al(s) + 3Br2(l) Al2Br6(s)

2mol of Al : 3mol of Br2 : 1mol of Al2Br6

Therefore the ratio of Al to Br2 to Al2Br6

is 2:3:1 for the chemical reaction to occur.

a closer look at the equation
A Closer Look at the Equation

2Al(s) + 3Br2(l) Al2Br6(s)

  • The chemicals on the left are the reactants and the right are the products.
  • The coefficient in front of the chemical denotes the stoichiometric relationship.
numerical subscripts
Numerical Subscripts

2Al(s) + 3Br2(l) Al2Br6(s)

  • The numerical subscriptrepresents the number of atoms present in the molecule
    • ex. Br2 means that an atom of Br is bonded to another atom of Br
    • Therefore: Br-Br = Br2
denoting the phase of matter
Denoting the Phase of Matter

2Al(s) + 3Br2(l) Al2Br6(s)

The subscript letters in parenthesis denote the phase of matter that the chemical is in.

formulas and models of ethanol
Formulas and Models of Ethanol
  • Molecular Formulas C2H6O
  • Condensed Formulas C2H5OH


  • Structural Formulas H-C-C-O-H


  • Molecular Models (classroom models)
molecular models
Molecular Models
  • Cache program - models - organic models - ethanol
  • CD-ROM screen 3.4
  • Model of ice
ions and ionic compounds
Ions and Ionic Compounds
  • Ions are atoms or groups of atoms that have lost or gained electrons resulting in an overall positive or negative charges.
  • Ionic compounds are compounds formed by the combination of (+) and (-) ions. (+) ions are called cations

(-) ions are called anions

formation of ions
Formation of Ions

Formation of a cation by a loss of electrons

Li atom  Li+ + 1 e- released

(3p and 3e-)  (3p and 2e-)

Formation of an anion by gaining electrons

F atom + 1 e- added  F

(9p and 9e-)  (9p and 10e-)

ions and the periodic table
Ions and the Periodic Table

Metals of group 1A, 2A & 3A form

+1, +2, and +3 ions; and non-metals

of group 5A, 6A, and 7A form -3, -2,

and -1 respectively.

polyatomic ions
Polyatomic Ions
  • Table 3.1 - page 89
  • CD-ROM Screen 3.6
  • Hand out
  • Flash Cards
common polyatomic ions
carbonate ion CO3-2

sulfate ion SO4-2

sulfite ion SO3-2

hydroxide OH-

phosphate PO4-3

permanganate MnO4-

chromate CrO4-2

dichromate Cr2O7-2

ammonium NH4+

oxalate C2O4-2

bicarbonate HCO3-

cyanide ion CN-

acetate C2H3O2-

peroxide O2-2

thiosulfate S2O3-2

bisulfite HSO3-


Common Polyatomic Ions



A polyatomic anion containing oxygen is called an oxoanion and is named as follows:

  • Greater # of O atoms has the suffix -ate.
  • Lesser # of O atoms has the suffix -ite.


NO3- is called nitrate ion

NO2- is called nitrite ion

naming oxoanions


Naming Oxoanions

More than 2 ions in an oxoanion grouping

are named as follows:

  • Largest # of O atoms has a prefix of per- and a suffix of -ate
  • Next larger # of O atoms has a suffix -ate
  • Smaller # of O atoms has a suffix -ite
  • Smallest # of O atoms has a prefix of hypo- and a suffix of -ite
naming oxoanions16


Naming Oxoanions


ClO4- is called perchlorate

ClO3- is called chlorate

ClO2- is called chlorite

ClO- is called hypochlorite

ionic compounds


Ionic Compounds

Ca+2 + 2Cl- CaCl2

Each ion comes together based on charge to form an overall neutral ionic compound.

3Ca+2 + 2PO4-3 Ca3(PO4)2

The cation and the polyatomic ion come together based on charge to form an overall neutral ionic compound.

naming ionic compounds


Naming Ionic Compounds
  • Naming Positive Ions – Cations
  • Cations are named first in the compound and as follows:
    • Monatomic cations are mostly metals and are named directly as they are on the periodic table.
    • Transition metals are named according to their ionic charge
    • Polyatomic cation, NH4+ is named ammonium directly
naming ionic compounds19


Naming Ionic Compounds
  • Naming Negative Ions – Anions
  • Anions are named lastly and have specific naming rules as follows:
    • Monatomic ions are named with an –ide after its atomic name
    • Polyatomic ions are named as memorized dropping the word ion.
naming molecular compounds


Naming Molecular Compounds
  • 1 mono
  • 2 di
  • 3 tri
  • 4 tetra
  • 5 penta
  • 6 hexa
  • 7 hepta
  • 8 octa
formula molecular weights
Formula & Molecular Weights
  • Review of spectra lab - MW calculations
  • CD-ROM Screen 3.14
  • Definition: The total mass of the formula unit or molecule with consideration to the mass of each component element that makes up the overall unit.
calculating formula mw
Calculating Formula & MW
  • Remember we said that:

1 mole C = 12.011g C = 6.02x1023 atoms C

  • If we add up the number atoms present of each element in a molecule or formula unit and multiply each by its atomic weight on the periodic table,
  • Then the resultant sum of each element added together will give you the formula or molecular weight.
example of mw calculation
Example of MW Calculation
  • Determine the MW of H20
    • 1 O @ 15.999g/mole
    • 2 H @ 1.008g/mole
      • Therefore 2 x 1.008 = 2.016g/mole
      • and 1 x 15.999 = 15.999g/mole

Total molar mass = 18.015g/mole

Determine the MW of ethanol: C2H5OH

converting mass to moles
Converting Mass to Moles
  • Question: How many moles of H2O are in 42.0g of water?
  • Answer: First you determine the MW of water as we did on the previous slide, then you convert

42.0g H2O x 1 mole H2O =

18.016g H2O

percent composition
Percent Composition
  • Calculate the percent composition of NH3
    • First determine the atomic weights of each N and H from the periodic table
    • Then calculate the MW of the ammonia molecule
    • Take the mass of each element and divide by the MW and multiply 100%
  • CD-ROM Screens 3.14 and 3.16
hydrated compounds
Hydrated Compounds
  • Definition: Ionic compound that has water molecules incorporated within its crystal structure
  • Ex. CuCl2•2H2O
    • Where we name this compound copper(II) chloride dihydrate
    • When calculating MW, we calculate the two waters into the overall mass of the compound