1
B. Experimentally Determining the
Empirical Formulas for Compounds
1. Calculating Percent Composition
2. Mass Percent in Chemical Compounds
What is the mass % of O in the OH radical?
What is the mass% of H in the OH radical?
2
What is the mass % of H2O in Na2SO4·4H2O?
Molar Mass of Na2SO4·4H2O
Molar Mass of Na2SO4·4H2O
Mass % of H2O in Na2SO4·4H2O
Mass % of H2O in Na2SO4·4H2O
= 33.6571¦70%
= 33.6571%
3
How do we Determine Empirical Formulas?
1.
Determine the mass of each element present in the
compound.
- if given mass % of all but one compound
100% = mass % A + mass % B + …
- if given mass percent composition, assume you
have exactly 100 grams of the compound
2.
Convert mass to number of moles present for each
atom.
3.
Find the smallest ratio of each atom to all of the other
atoms.
https://i.ytimg.com/vi/DT-uMyXWwek/movieposter.jpg
4
How do we Calculate Empirical Formulas? Cont’d
Calculated E.F.
Multip. Factor
New E.F.
Other Sub. Use
C1H1.5
2
C2H3
(0.5, 1.5, 2.5, etc)
C1H1.33
3
C3H4
(0.33, 1.33, etc)
C1H1.25
4
C4H5
(0.25, 1.25, etc)
C1H1.66
3
C3H5
(0.66, 1.66, etc)
C1H1.75
4
C4H7
(0.75, 1.75, etc)
How do we get molecular formulas from empirical formulas?
How many sticks of gum in a pack of gum?
5
Example
4. Putrescine, an incredibly foul smelling compound that is
generated during the decomposition of flesh, contains
nitrogen, hydrogen, and carbon. In some deleted footage
recently shown on Talking Dead, Rick and Carl tried to
synthesize putrescine to use it as a zombie masking
agent. In order to obtain the chemical formula of
putrescine, Rick and Carl analyzed a sample of
putrescine and found it contained 34.13|39% N and
58.50|97% C. What is the empirical formula for
putrescine?
http://images.amcnetworks.com/amc.com/wp-content/uploads/2015/10/the-walking-dead-episode-601-daryl-reedus-post-1600x600.jpg,
http://media.vanityfair.com/photos/568c0baa396977000bddd977/master/w_900,c_limit/walking-dead-kill-off-cast.jpg
6
Example 4 Work
Determine the mass of each element present in the
compound.
Convert mass to number of moles present for each atom.
7
Find the smallest ratio of each atom to all of the other
atoms.
8
Special Type of Empirical Formula Problem
- Combustion Analysis of HC or Oxygenated HC
to obtain empirical Formula
HxCy or HxCyOz + O2(g)  CO2(g) + H2O(g)
9
Example Problems
5. Menthol is composed of C, H, and O. A 0.1005 g
sample of menthol is combusted producing 0.2829
g of CO2 and 0.1159 g of H2O. What is the
empirical formula of menthol?
If the molar mass of menthol is 156 g/mol, what is
its molecular formula?
6. A 1.562 g sample of the hydrocarbon C7H16 is
burned in an excess of oxygen. What masses of
CO2 and H2O should be obtained?
10
III. Naming Chemical Compounds
A. Naming Inorganic and Simple Organic
Compounds
Organic Cmpds.
Inorganic Cmpds. 
Cmpd. formed from
primarily C and H or
C, H, N, O, and small
amounts of other
elements
All other compounds
1. Ionic Compounds (Metal + Nonmetal or
Metal + Polyatomic Ion)
Name -
Formula -
11
Rules for Names
I. Name of Cation
Most Main Group Metals
Plus Ag, Zn, and Cd
-
Most Transition Metals and Some Group 13-16 Metals
-
II. Name of the non-metal with an –ide ending or
name of the polyatomic ion
nitrogen
chlorine
oxygen
chlorate
(Memorize table pg 12 GCN)
http://www.mwsd.cc/webpages/mcallender/imageGallery/pblock21.jpg
12
Formula  Name
(first identify cation and anion with formulas)
Formula
KBr
Sr3(PO4)2
Al(IO)3
Ba3P2
Cation
Anion
Name
13
Rules for Formulas
I.
Electrically neutral
- balance charge  #’s as subscrpts
Name
lithium
oxide
aluminum
sulfate
copper(II)
chloride
calcium
periodate
ammonium
nitride
Cation
Anion
Formula
14
2.
Binary Molecular Compounds
(nonmetal + nonmetal)
Need greek prefixes
1 - mono
8
-
octa
2
-
di
9
-
nona
3
-
tri
10 -
deca
4
-
tetra
5
-
penta
6
-
hexa
7
-
hepta
https://ohkrapp.files.wordpress.com/2008/11/bill-and-ted-socrates1.jpg
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Rules for Names
1. numbers of atoms given by greek prefixes
(mono not used for first named element)
2. element farthest to the left written first (exception:
oxygen usually written last when combined with F)
3. elements in same group lowest one first
4. second element –ide ending
5. if element starts with a or o, a or o is dropped from
end of Greek prefix
16
Examples
Formula
Cation
Anion
Name
Cation
Anion
Formula
N2O
SO2
PCl5
Name
carbon
tetrachloride
diboron
tetrabromide
17
3. Binary Acids
Acid -
Binary Acid


Common Binary Acids
18
Rules for names
1. name of 2nd element add hydro as prefix and –ic as
suffix
2. add word acid at end
hydro______ic acid
Examples
Formula/Name Cation
HBr
hydrosulfuric
acid
Anion
Name/Formula
19
4. Oxoacids (or oxyacids)
- adding H to oxoanions
NO2-, NO3-, SO32-, SO42-, PO33-, PO43-, IO-, IO2-, IO3-,
IO4-, etc.
Increasing #’s of O
Ion 
___ite ___ate
Acid 
___ous
___ic
ADD ACID ENDING
Increasing #’s of O
Ion 
hypo___ite ___ite ___ate
Acid  hypo___ous
___ous
___ic
ADD ACID ENDING
per___ate
per___ic
20
Examples
Formula/Name Cation
H3PO4
HClO
perbromic acid
Anion
Name/Formula
21
5. Hydrates
CoCl26H2O
https://upload.wikimedia.org/wikipedia/commons/e/ee
/Indicating-silica-gel.png
https://upload.wikimedia.org/wikipedia/commons/e/ee/Indicating-silica-gel.png
22
C. Naming Organic Compounds
Hydrocarbon –
Types of Covalent bonds
23
Alkanes (table 3.7)
Prefix – greek and latin and others
1C
2C
3C
4C
24
Isomers 
Functional Groups
- replacing an H on an alkane, alkene, or alkyne, can
dramatically change the chemical and physical
properties of the organic molecule
Functional group –
Alcohols
Acids