CHE 111 - Module 3

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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

CHAPTER 3

LECTURE NOTES

STOICHIOMETRY
• 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

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

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

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

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
• Molecular Formulas C2H6O
• Condensed Formulas C2H5OH

H H

• Structural Formulas H-C-C-O-H

H H

• Molecular Models (classroom models)
Molecular Models
• Cache program - models - organic models - ethanol
• CD-ROM screen 3.4
• Model of ice
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 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

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
• Table 3.1 - page 89
• CD-ROM Screen 3.6
• Hand out
• Flash Cards
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-

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Common Polyatomic Ions

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Oxoanions

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.

Ex.

NO3- is called nitrate ion

NO2- is called nitrite ion

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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

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Naming Oxoanions

Ex.

ClO4- is called perchlorate

ClO3- is called chlorate

ClO2- is called chlorite

ClO- is called hypochlorite

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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.

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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

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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.

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Naming Molecular Compounds
• 1 mono
• 2 di
• 3 tri
• 4 tetra
• 5 penta
• 6 hexa
• 7 hepta
• 8 octa
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
• 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
• 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
• 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
• 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
• 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