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Lecture 5
Chapter 3 Stoichiometry (continued)
Reading: section 57
Homework 3: 12, 14, 16, 18, 20, 22b, 22d, 24b, 24d, 34, 38,
44, 48, 52, 54, 58, 62, 64, 72, 74.
Due: Thursday Oct. 11, 8PM
The Mole
Problem 1:
How many moles of copper are in 2.50g Cu?
Problem 2:
What’s the mass in grams of one atom of copper?
Problem 3:
What mass of Ca
3
(PO
4
)
2
should be weighed out for an
experiment that requires 0.836 moles of Ca
2+
?
Problem 4
: How many H atoms are there in 2.50 g of C
2
H
6
O?
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Empirical formulas from analyses (procedure):
1: Express composition in grams. If percent composition is given,
assume a 100g sample.
2: Determine the number of moles of each element.
3: Divide by the smallest number of moles to obtain the mole ratio
which is also the atom ratio.
4: Multiply by a factor to get a whole numbers.
5. Write the formula.
Empirical formulas from analyses (examples):
Problem1:
What is the empirical formula of a compound which
contains 69.6% Mn and 30.4% O?
Problem2:
Analysis of an unknown compound gave 39.72% C, 1.67%
H, 58.61% Cl. The molecular weight was found to be 181.4. Determine
the molecular formula.
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 Fall '07
 Wyzlouzil
 Mole, Stoichiometry, 30.4%, 1.67%, 3.0 g, 2.50g

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