Transcript Lec 3

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Exam one
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today.
Review
• Naming ionic compounds and acids containing
polyatomic ions.
– CaCl2: calcium chloride
– Mn2O3: manganese (III) oxide
– Na2HPO4: sodium hydrogen phosphate
– H3PO4: phosphoric acid
• Balancing chemical Equations
– Number of each type of atom on each side must be equal.
– 2H2 + O2 –––> 2H2O (4H and 2O/side)
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 same RXN as occurred in early
atmosphere: 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
Percent Yield
• All the calculations we have done so far assume that
all the reactants are converted to products. Often not
true:
– Sometimes a limiting reagent.
– Most reactions go both backwards and forwards so 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
• Consider elements in Earth’s crust. Compounds of
Na make up about 2.5% of crust.
• A common reaction of group 1 alkali metals is
2M + 2H2O –> 2MOH (metal hydroxide) + H2
– 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