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Unit 3 Topics:Covalent, ionic, & acids: naming and writing
formulas*Balancing chemical equations Decomposition, composition
reactions, and combustion : predicting products %
compositionEmpirical vs. Molecular formulas: combustion train
calculation Stoichiometry conversions, limiting reagents, % Yield
AP Chemistry* You will not have formal notes for writing the
formulas for compounds. Instead, we will just do practice problems
until you get the hang of it. If you need formal notes, you can go
to my website and download the 1st year Accelerated Chemistry Notes
for Naming and Writing Formulas.
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Naming Compounds Covalent Molecules Contains only 2 nonmetals.
They are formed by sharing e between atoms. General Format:Prefix
(except mono)-name 1st element prefix-name 2nd element ending in
ide
2 Ionic Compounds Starts with metallic cation (or NH4+).Formed
when atoms transfer e from a metal to a nonmetal.General
FormatCation Name Anion Name
On a later quiz, you will have to memorize the cation and anion
symbols & charges on the Ion Sheet. For this unit, I will let
you use the Ion Sheet.
Naming Compounds
3Naming Compounds Acids Starts with H
4Balancing Equations You can only change coefficients. You can
only use whole #s.Example: C3H8 + __O2 __CO2 + __H2O
345Decomposition Reactions A reaction that breaks apart ______
______________ into simpler substances, (usually two elements or an
element and a smaller compound.)General Form:_____ ___ +
___Examples: H2O _____ + _____ KClO3 _____ + _____ Remember that
HONClBrIF elements are diatomic when alone!!Dont try to balance it
until you have correctly written the products!! one compoundAXA
XH2O2KClO2+
5Categories of Decomposition (and Composition ) Reactionsa)
carbonates metallic oxide + CO2 CaCO3 _____ + _____b) chlorates
metallic chloride + O2 NaClO3 _____ + _____c) hydroxides metallic
oxide + H2O Mg(OH)2 _____ + _____ d) oxy acids nonmetal oxide + H2O
H2SO4 _____ + _____e) binary compounds 2 elements NaCl _____ +
_____Notice that in carbonates, hydroxides, and oxy acids, the
oxygen combines with both the metal AND the nonmetal!!Every time
you try to write the formula for a new ionic compound, you must
look up the ___________ of the ions and ___________ them if they
are different!! CaOCO2NaClO2MgOH2OSO3NaCl2chargescrossH2O
6This reaction category is sometimes called Combination or
Synthesis A reaction of _____ __________________, typically a metal
and a nonmetal to form ______ ______________. It is the opposite of
decomposition. The same categories of reactions apply. Its just in
reverse!
General Form: ___ + ___ _____
Examples: Al + Cl2 _______ PbO + H2O ______
Composition Reactionstwo substancesone compound
AXAXAlCl3Pb(OH)2+ metallic + water oxide hydroxide 2 elements
binary compound
7Combustion ReactionsA reaction between O2 and a compound
containing Carbon, Hydrogen, (and sometimes Oxygen). The products
are always the same ________ + ________ This reaction is too easy!!
Dont miss it! General Form: CxHy + O2 ____ + ____Examples: C2H2 +
O2 _______ + _______C7H6O + O2 _______ + _______
CO2H2OCO2H2OCO2H2OCO2H2O
8Percent Composition (by mass)
AW stands for the atomic weight of the atom from the periodic
table.FW stands for the formula weight of the compound, i.e.--the
molar mass. AW and FW are nicknamed the W.O.T.C. (the weight on the
chart) or the Wizzle on the Chizzle.Heres another formula for %
compostion:
9Empirical Formulas
Helpful Rhyme: % to mass, mass to mole, divide by small, times
til whole. The molecular formula is a whole # multiple of the
empirical formula. When given the molecular weight of the compound,
you can compare the empirical mass to the molecular mass to see
what this whole # multiple will be. (We will practice this
calculation later.)
10Combustion Train
A weighed quantity of the substance to be analyzed is placed in
a combustion train and heated in a stream of dry O2. All the H in
the compound is converted to H2O(g) which is trapped selectively in
a previously weighed absorption tube. All the C is converted to CO2
(g) and this is absorbed selectively in a second tube. The increase
of mass of each tube tells, respectively, how much H2O and CO2 were
produced by combustion of the sample. Dehydrite [Mg(ClO4)23H2O] and
ascarite (NaOH on asbestos)
11EXAMPLE 1: A 6.49-mg sample of ascorbic acid (vitamin C) was
burned in a combustion train and 9.74 mg CO2 and 2.64 mg H2O were
formed. Determine the empirical formula of ascorbic acid. Steps to
Follow: Calculate the moles of Carbon and Hydrogen in the
compound.Calculate the moles of Oxygen (if any) in the compound.
(Sometimes other elements are present, such as Nitrogen, but you
will be given a way to find these masses as well.)The mole ratios
are the subscripts of the empirical formula. Use the Empirical
Formula Rhyme to complete the rest of the problem.Ans: C3H4O3
12EXAMPLE 2: The combustion of 62.63 grams of a compound which
contains only C,H and O yields 134.43 grams of CO2 and 13.75 grams
of H2O. What is the empirical formula of the compound? Ans: C2HO If
the compounds molecular weight is 156 g/mol, determine the
molecular formula. Ans: C8H4O4
EXAMPLE 3: The combustion of 40.10 g of a compound which
contains only C, H, Cl and O yields 58.57 g of CO2 and 14.98 g of
H2O. Another sample of the compound with a mass of 75.00 g is found
to contain 22.06 g of Cl. What is the empirical formula of the
compound? (Hint: Use the mass data to calculate the % composition
of each element in the compound.) Ans: C4H5ClO2
13Stoichiometry Conversion Factors1 mole = 22.4 L (at STP) =
6.02 x 1023 particles = Molar Mass in grams
These conversions will take up to 3 steps and no more! Always
convert to moles of the given first!
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15Limiting Reagent (or Reactant) The reactant that runs out
first limits the amount of product that can be formed.
Stoichiometry conversions can be done to determine which substance
is the limiting reagent and how much of the excess is left
over.
16% YieldThe amount of product predicted from stoichiometry
taking into account limiting reagents is called the theoretical
yield. This is the ideal amount of product that should be formed if
all goes as planned in a perfect world.The percent yield relates
the actual yield (amount of material recovered in the laboratory)
to the theoretical yield:
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