Announcements
To join clicker to class today ( Clickers with
LCD display joins automatically):
●
●
Turn on the Clicker ( the red LE D comes
on).
P ush “J oin” button followed by “2 0 ”
followed by the “S end” button ( switches
to flashing green LE D if successful).
•The Role of Chemistry in
the Development of Regional
Styles of Beer and Ale
•HS-109, Monday, March 3rd, 2008,
7:00 PM
•Mark Thomson, Ferris State
University
• Exam scores are now posted on the class web site.
– Average was within the normal range for this class.
– See the e-mail or the class web site for a more detailed
discussion.
– If you want to discuss your studying please see me or
another of the instructors.
• Lab next week is Pigment Synthesis. Don't forget to do
prelab. Handout will be mailed out and put on class web
site.
Review
•
Defined:
– Compound = two or more atoms arranged in a particular
geometry in particular ratios. Can be ionic.
– Molecule = a compound that is not ionic.
– Empirical formula = formula for a compound with the lowest
possible integer subscripts.
– Molecular formula = subscripts represent the actual number of
each type of atom in a single molecule.
• Naming of binary compounds.
• CO: carbon monoxide
– SO3: sulfur trioxide
• CaCl2: calcium chloride
– Mn2O3: manganese (III) oxide
• H3PO4: phosphoric acid
– HF: hydrofluoric acid
• CuSO4•2H2O: copper (II) sulfate dihydrate
• Balancing chemical reactions by inspection.
Balanced RXNs and What We can Measure
• 2H2 + O2 ––> 2H2O can be read two ways:
– 2 molecules of H2 + 1 molecule of O2 reacts to form 2
molecules of H2O
– 2 moles of H2 + 1 mole of O2 reacts to form 2 moles of
H2O, since a mole is just a group like a dozen.
– 1 mole = Avogadro's # = NA = 6.022 x 1023 things.
• Need way to get between moles in the balanced equation
and the mass we can measure in lab.
– Want to do conversion g ––> moles or moles ––> g
– Need conversion constant with units of g/mole or
mole/g.
Calculating Molar Mass
(2 mol H/mol H2O)(1.00794 g H/mol H) = 2.01588 g H/mol H2O
+(1 mol O/mol H2O)(15.9994 gO/mol O)=15.9995 g O/mol H2O
18.0153 g H2O/mol H2O
●
●
Note that you have to do the multiplication and addition in separate
steps to get the correct number of significant digits.
Subscripts apply to the elements the subscripts follow or group of
elements in parentheses that the subscripts follow
— H O means 2 H and 1 O
2
—
(NO3)2 means 2 NO3 groups
Using Avogadro's Number
and Molar Mass
23
N
=6.022
x
10
particles/mole (also number of
• A
amu/g)
MM
g
molecules
NA
Subscripts
Moles
molecules
Moles
element
Number
of
atoms
• Ex: suppose you have 24.022 g SO3 how many O
atoms? Info: 80.064 g SO3/mol SO3 or MM(SO3)= 80.064 g/mol
Avogadro's Number and Molar Mass
• NA=6.022 x 1023 particles/mole (also number of
amu/g)
MM
g
molecules
NA
Subscripts
Moles
molecules
Moles
element
Number
of
atoms
• Ex: suppose you have 24.022 g SO3 how many O
atoms? Info: 80.064 g SO3/mol SO3 or MM(SO3)= 80.064 g/
mol
– atoms O = (24.022 g SO3)(1mol SO3/80.064 g SO3) x
(3O/SO3)(6.022 x 1023 atoms/mol) = 5.420 x 1023 O
atoms
Stoichiometry/Mole Map
Stoichiometry
• Can answer questions like: How much SO3 necessary to
produce the 3.959 x 1010 kg of H2SO4 manufactured in
2000?
• Produced using this RXN: SO3(g) + H2O(l) ---> H2SO4(aq)
(balanced).
• Key info
– 80.064 g SO3/mol SO3 or M(SO3)= 80.064 g/mol
– 98.079 g H2SO4/mol H2SO4 or M (H2SO4)= 98.079 g/mol
• Route to solution (know amount of A want amount of B):
mass of A -{÷M(A)}-> moles of A -{mole ratio}-> moles B -{xM(B)}-> mass B
% Composition: useful data for
examples
• MM(H2O)= 18.0153 g H2O/mol H2O.
• MM(CO2) = 44.01 g CO2 /mol CO2
• Molecules called ethylene and propylene are
both 14.372% by mass H. The rest is carbon
(85.628%).
– MM(ethylene)= 28.054 g/mol
– MM(propylene)= 42.081 g/mol
Some extra practice problems
to try at home
A) A compound containing only C and H
was completely burned in oxygen to give
water and carbon dioxide. It yielded
0.1802 g of H2O and 0.3521 g of CO2.
What is the empirical formula for this
compound?
B) If the molar mass of the compound in A
is known to be about 58 g. What is the
molecular formula of this compound?
Answers: A) C2H5 B) C H
4 10
Percent Yield
• All the calculations we have done so far assume that
all the reactants are converted to products. Often not
true:
– Sometimes run out of a reactant (will see next week).
– Some reactions do not reach completion.
– There are often competing RXNs that take the reactants to
compounds other than the desired products. (Want: A––>B,
but get some A––>D)
– Poor experimental technique (losing half the sample down
the drain or collecting bits of filter paper with your product).
• The amount you are off by is quantified in the
Example % yield
• A common reaction of group 1 alkali metals (where
“M” represents any alkali metal) is
– 2M + 2H2O –> 2MOH (metal hydroxide) + H2
– Specific case: 2Na + 2H2O –> 2NaOH + H2
• Start with 23.0 g Na and an unlimited supply of
H2O, what is the % yield if we got 35.0 g of NaOH?
– M(Na) =22.990 g Na /mol Na
– M(NaOH)=39.997 g NaOH/mol NaOH
Other possible questions with
same info.
CaCO3 --> CaO + CO2
●How many g of CaO do I get when 80.00 g of
CO2 are produced?
Ansswer: 101.9 g CaO
– MM(CaO) =56.077 g/mol
– MM(CO2) = 44.010 g/mol
– MM(CaCO3) = 100.087 g/mol
•Concrete is made by slaking CaO with water to
make Ca(OH)2.How much Ca(OH)2 will I get
when the CaO is slaked (water added)?
– MM(Ca(OH)2) = 74.0926 g/mol
Answer: 134.6 g Ca(OH)2