Unit 4 - chapter 6
The Mole
Extra credit assignment - Must show
work!
pg. 210-214 #14 a,b,c,g ; #15 b,c,d,f,g ;
#16 b,d,f,g ; #19 a,b,c,f ; #20 d,e ; #27
a,b,e,f
Chemical composition calcs
• Find the average of : 2, 8, 6, 4, 2, 4, 5
• 4.43
• What units are used for mass measurements
• grams (or kilograms, milligrams)
• If we have a jar of pennies that has a mass of
857.2 g. The average mass of a penny is
2.73 g. How many pennies are there in the
jar?
• 857.2g / 2.73g = ~ 314 pennies
Chemical composition calcs
• If we have 12.01g of carbon and the average
mass of a carbon atom is 1.994x10-23g. How
many carbon atoms are in the sample?
• 12.01g / 1.994x10
-23g
= 6.02x1023 atoms
• In a class of chemistry students, what
percentage are female?
The Mole
BIG or
Atomic masses are
1 amu = 1.66x10-24 g
?
small
The scale of atomic masses gives a relative mass for
each atom.
The Periodic Table has atomic masses listed as the
number of grams for 1 mole of that atom.
1 Mole = 6.02x1023 things (usually atoms or molecules) this is a conversion factor!!
The Mole Diagram is provided on your Periodic Table
Molar Mass of Compound
Compounds are combinations of atoms bonded
together, so mass can be found by adding atomic
masses. Molar mass has the units g/mol.
Lets’s do some examples...
carbon dioxide
aluminum bromide
copper(II) nitrate
ammonium phosphate
Percent Composition
(the mass percent composition)
Percent = amount of the part x 100
amount of the total
Example A:
23.4 g silicon and 37.4 g of oxygen
Example B:
C2H6O
Find %mass of each element in
Review 6.1 & 6.2
• Do Section Review Questions
6.1 pg 184 #2 - 5
• Do Section Review Questions
6.2 pg 195 #1 - 6
Empirical Formula
Recall the chemical formulas like C2H6 and
Mg(NO3)2
The subscripts tell how many of each element are
in the compound.
The empirical formula is the simplest whole
number ratio for a compound.
for example CH2O
The actual formula could be C2H4O2 or C3H6O3
Empirical Formula (con’t)
The calculation is the opposite of percent composition
We need the mole ratio of the elements in the compound
from its percent composition
A scientist conducts a chemical analysis and finds 40%
carbon, 6.71% hydrogen, and 53.3% oxygen. What is
the compounds empirical formula?
Method? need to convert % into grams and then grams
into moles. Then find simple whole number mole ratio.