Molecules, Compounds

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Molecules, Compounds Chemical Reactions

• Overview
• Compounds
• Formulas
• Ionic compounds
• Molecular (covalent) compounds
• Molecular weight/molar mass
• Covalent Bonds
• Bonding models Lewis, VSEPR, etc.
• Molecular geometry and chemical properties
• Chemical reactions
• Balancing equations
• Molar relationships

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Chemical Representations
Representational chemical formulas,
equations CH4 2O2 ? CO2 2H2O
Chemistry
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Compounds

• Atoms are typically bound together in molecules
• Noble gases exist as individual atoms, most other
  elements found as compounds
• More stable
• Forming a bond releases energy, less stable to
  more stable
• Breaking a bond requires energy, more stable to
  less stable (misconception)

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Chemical Formulas

• AxByCz
• A, B, C elemental symbols
• x, y, z relative number of atoms in molecule
• Problem 1 How many of each atom are in the
  following molecules?
• C6H12O6 (glucose)
• NH3 (ammonia)
• NaHCO3 (baking soda)

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• Problem 1 How many of each atom are in the
  following molecules?
• C6H12O6
• b) NH3
• c) NaHCO3 (baking soda)

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• Problem 1 How many of each atom are in the
  following molecules?
• C6H12O6
• 6 carbons, 12 hydrogens, 6 oxygens
• b) NH3
• 1 nitrogen, 3 hydrogens
• c) NaHCO3 (baking soda)
• 1 sodium, 1 hydrogen, 1 carbon, 3 oxygens

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Ionic Compounds

• Ionic compounds are made up of ions held together
  by electrostatic forces ionic bonds
• Cation () anion ()
• Cation (metal) anion (nonmetal monatomic or
  polyatomic)
• Na Cl ? NaCl

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Crystal LatticeNaCl
NaCl ratio of atoms in the lattice
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Ionic Compounds

• Dissociate when they dissolve in water

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Ionic Compounds

• Monatomic ions
• Cation group number
• Li, Na, K, Rb, Cs
• Mg2, Ca2
• Al3
• Transition metals often variable
• Cu2, Cu (copper II and copper I)
• and Fe3, Fe2 (iron III and iron II)

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Ionic Compounds

• Monatomic ions
• Anion 8 group number
• add to electrons to make 8 (octet)
• O ? O2 oxide
• S ? S2 sulfide
• Cl ? Cl chloride
• P ? P3 phosphide

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Ionic Compounds

• Balance anion with cation to a neutral charge
• magnesium oxide
• Mg2 with O2

MgO
aluminum chloride Al3 with Cl
AlCl3
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Problem 2

• Write the ionic formulas for each of the
  following
• The compound that magnesium makes with chlorine
• The compound that Fe3 makes with oxygen
• Sodium fluoride
• Cesium oxide
• Copper (I) sulfide

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Problem 2

• Write the ionic formulas for each of the
  following
• The compound that magnesium makes with chlorine
• The compound that Fe3 makes with oxygen
• Sodium fluoride
• Cesium oxide
• Copper (I) sulfide

MgCl2
Fe2O3
NaF
Cs2O
Cu2S
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Polyatomic Ions

• CO32 carbonate ion
• Travels as a unit (Texans)
• Na2CO3 sodium carbonate
• Fe2(CO3)3 iron (III) carbonate

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Common Polyatomic Ions
phosphate PO43 carbonate CO32 hydroxide
OH ammonium NH4

• nitrate NO3
• nitrite NO2
• sulfate SO42
• sulfite SO32

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• Problem 3 Write the ionic formulas for each of
  the following
• Magnesium phosphate
• Ammonium carbonate
• Sodium sulfite
• Problem 4 Write the names for the following
• NaNO3
• K2SO4
• FePO4

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• Problem 3 Write the ionic formulas for each of
  the following
• Magnesium phosphate
• Mg2 with PO43
• Mg3(PO4)2
• b) Ammonium carbonate
• NH4 with CO32
• (NH4)2CO3
• c) Sodium sulfite
• Na with SO32
• Na2SO3

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• Problem 4 Write the names for the following
• a) NaNO3
• sodium nitrate
• b) K2SO4
• potassium sulfate
• c) FePO4
• iron (III) phosphate

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Covalent Compounds

• Two or more nonmetals typically bond in covalent
  bonds
• Sharing of electrons (not always equal sharing)
• Molecular formula actual atoms in molecule
  (rather than ratio)
• C6H12O6 glucose
• CH2O formaldehyde
• Molecular formula correlates to molar ratio

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Molecular Formula

• H2O 2 Hs and 1 O per molecule
• 500 H2O molecules
• How many Hs?

1000 H atoms
How many Os?
500 O atoms

• Problem 5
• How many Cl atoms are in 40 CCl4 molecules?
• How many C atoms are in 30 C6H12O6 molecules?
  How many H atoms? How many O atoms?

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Problem 5

• CCl4
• 40 molecules CCl4

160 Cl atoms
4 x 40 1 x 160 Cl atoms
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Problem 5
b) C6H12O6 30 molecules C6H12O6
180 C atoms
30 molecules C6H12O6 have 360 H atoms 30
molecules C6H12O6 have 180 O atoms
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Problem 6

• How many moles of H are in 5.0 moles of BH3?
• How many moles of Cl are in 12.0 moles of
  C2H4Cl2?

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Problem 6

• How many moles of H are in 5.0 moles of BH3?
• How many moles of Cl are in 12.0 moles of
  C2H4Cl2?
• a) 5.0 mol BH3

15.0 mol H
b) 12.0 mol C2H4Cl2
24.0 mol Cl
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Covalent Bonding

• Sharing of valence electrons
• Non-metals
• Many models
• Lewis structures number and types of bonds
• VSEPR (valence shell electron pair repulsion)
  empirical model that predicts molecular geometry
• Valence Bond model describes nature of bonds and
  predicts reactivity
• Molecular Orbital theory gold standard of
  understanding bonding, but requires high level of
  mathematics (calculus, group theory)

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Bonding

• Why do bonds form?
• A B vs. AB
• lower E higher E NO BOND
• higher E lower E BOND

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Bonding

• Why do bonds form?
• A B vs. AB
• lower E higher E NO BOND
• He Cl vs. HeCl

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Bonding

• Why do bonds form?
• A B vs. AB
• lower E higher E NO BOND
• He Cl vs. HeCl

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Bonding

• Why do bonds form?
• A B vs. AB
• higher E lower E BOND
• H Cl vs. HCl
• preferred

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Valence electrons
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Lewis dot structures

• F
• 7 valence electrons

F 8 valence electrons
N 5 valence electrons
N3 8 valence electrons
Put electrons in singly b/f pairing
N
C
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Problem 7

• How many valence electrons would you expect each
  of the following to have? Draw a Lewis structure
  for each one.
• Sr
• Se
• I (iodine)
• K
• Cs

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Problem 7

• a) Sr 2 valence electrons

b) Se 6 valence electrons
c) I 7 valence electrons
d) K 1 valence electron
e) Cs 1 valence electron
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Problem 8

• Draw Lewis dot structures for
• C
• P
• P3
• Se2

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Problem 8

• a) C 4 valence electrons

b) P 5 valence electrons
c) P3 8 valence electrons
d) Se2- 8 valence electrons
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Covalent Bonding

• Sharing of electrons
• H O

H2O
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Covalent Bonding

• Sharing of electrons
• H O H
• like Ne

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Covalent Bonding

• Sharing of electrons
• H O H
• like He

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Covalent Bonding

• Nonmetal nonmetal
• H C

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Covalent Bonding

• Nonmetal nonmetal
• H
• H C H CH4
• H

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Problem 9

• Write the Lewis structure for each atom in the
  group of atoms given. Then figure out how they
  might bond together covalently to form a stable
  compound (octet/duet).
• C, Cl, F, Cl, H (central C atom)
• N, 2 Hs, Cl (central N atom)
• P and H (use as many Hs as you need)
• 2 Cs and 6 Hs
• O, F, H (central O)

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Problem 9

• C Cl F H Cl

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Problem 9

• b) N Cl H

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Problem 9

• b) N Cl H
• Cl N H ClN H
• H

H
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Problem 9

• c) P 3 x H
• H P H HP H
• H

H
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Problem 9

• d) C C H
• H H
• H C C H HC C H
• H H

H H
H H
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Problem 9

• e) O F H
• F
• O H HO F

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Multiple bonds

• Some atoms form double and triple bonds
• C2H4
• C C
• H H H H

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Multiple bonds

• C2H4
• H C C H
• H H

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Multiple bonds

• C2H4
• H C C H
• H H

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Multiple bonds

• C2H4
• H C C H
• H H

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Multiple bonds

• C2H4
• H C C H HC CH
• H H

H H
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Multiple bonds

• triple bonds
• C2H2
• C C
• H H

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Multiple bonds

• C2H2
• H C C H

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Multiple bonds

• C2H2
• H C C H

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Multiple bonds

• C2H2
• H C C H

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Multiple bonds

• C2H2
• H C C H H C ? C H

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Covalent Bonds

• Atom has typically forms
• C, Si 4 valence electrons 4 bonds
• N, P 5 valence electrons 3 bonds
• O, S, Se 6 valence electrons 2 bonds
• F, Cl, Br, I 7 valence electrons 1 bond

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Problem 10

• Draw the Lewis structure for each of the atoms in
  the formula below. Then draw the Lewis structure
  for the molecule.
• HCN (central C)
• CH2O (central C)
• C2Cl2
• HNO (central N)

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Problem 10

• a)
• H C N

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Problem 10

• a)
• H C N
• H C N

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Problem 10

• a)
• H C N
• H C N HC N

C
H
N
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Problem 10

• b)
• H H C O
• H H
• H C O H C O

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Problem 10

• c)
• Cl C C Cl
• Cl C C Cl

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Problem 10

• d)
• H N O

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Problem 10

• d)
• H N O
• H N O

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Molecular Geometry (VSEPR)

• Valence Shell Electron Pair Repulsion
• Electron bonding pairs repel each other
• Adopt geometry to maximize their separation
  distance.
• Treat multiple bonds as if they were single
  electron pair.

109.5
CH4 tetrahedral
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Tetrahedral Carbon

• Anytime carbon is bonded to four other atoms, it
  has tetrahedral geometry.
• So

H3CCH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
is really
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VSEPR

• 2 electron pairs linear
• http//www.d.umn.edu/pkiprof/chemweb/VSEPR/

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VSEPR
3 electron pairs 3 bonding trigonal planar
link
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4 electron pairs
link
H

• 4 bonding tetrahedral

HCH
H
3 bonding (1 nonbonding) trigonal pyramid
? ?
2 bonding (2 nonbonding) bent or nonlinear
HOH
? ?
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Problem 11

• Given the following Lewis structures, predict the
  three dimensional molecular geometry.
• a) HNCl b) ClS

Cl
Cl


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Problem 11

• a) Trigonal pyramid

N
Cl
H
Cl
b) Bent or Nonlinear
S
Cl
Cl
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Multiple Bonds in VSEPR

• Treated like single bonds

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Trigonal planar
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Problem 12

• Given the following Lewis structures, predict the
  three dimensional molecular geometry. Draw a
  picture of the molecule.
• a) HC?N b) ONH c) HCC H

H
H
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Problem 12

• a) HC?N
• Linear

b) ONH
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Problem 12

• c) HCCH

H H
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Polar and Nonpolar Covalent Bonds

• Equal sharing of electrons
• CC C C

Ionic bonds Na Cl Complete transfer of
electrons
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Polar Covalent Bonds

• Unequal sharing of electrons
• HCl
• Different electronegativity
• Cl is more electronegative than H
• Electronegativity ability to attract electron
  density in a covalent bond

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Polar Covalent Bonds

• Unequal sharing of electrons
• HCl

Area of low electron density
Area of high electron density
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Polar Covalent Bonds
electronegativity
electronegativity
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Problem 13

• Which of the following pairs of atoms is the more
  electronegative?
• P or F
• Sr or Si
• Se or Cs

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Problem 13

• Which of the following pairs of atoms is the more
  electronegative?
• P or F
• Sr or Si
• Se or Cs

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Problem 14

• Indicate the polarity of the following bonds
  using the ? and ?- symbolism.  
• a) C?O
• b) N?P
• c) Br?F

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Problem 14

• Indicate the polarity of the following bonds
  using the ? and ?- symbolism.  

? ?
? ?
? ?
b) N?P
a) C?O
c) Br?F
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Molecular Polarity

• Polar bonds that cancel ? nonpolar molecule
• OCO

Overall molecule nonpolar
Polar bonds that do NOT cancel ? polar molecule
Polar molecules dissolve other polar molecules
(some ionic compounds Nonpolar molecules dissolve
other nonpolar molecules
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Chemical Reactions

• Chemical reactions occur when bonds break and
  reform in different arrangements
• Can absorb or release heat
• Overall energy needs to be downhill (more
  stable products)

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Chemical Equations (Reactions)
No coefficient assume it is 1
Designates the total number of H2 molecules that
react

• N2 3H2 ? 2NH3

Ratio of NH is 13 in product molecule
product(s)
reactants
Total molecules of product formed 2
Designates the atoms of N in each molecule
Designates the atoms of H in each molecule
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Chemical Equations

• CH4 O2 ? CO2 H2O

reactants
products
Number and type of atoms on each side must be
equal (balance)
CH4 O2 ? CO2 H2O 1 C 4 H 2 O
1 C 2 H 3 O
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Chemical Equations

• CH4 O2 ? CO2 H2O

reactants
products
Number and type of atoms on each side must be
equal (balance)
CH4 O2 ? CO2 2H2O 1 C 4 H 2 O
1 C 4 H 4 O
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Chemical Equations

• CH4 O2 ? CO2 H2O

reactants
products
Number and type of atoms on each side must be
equal (balance)
CH4 2O2 ? CO2 2H2O 1 C 4 H 4 O
1 C 4 H 4 O
balanced
Can only change coefficients Cannot change
molecular formula
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Chemical Equations as Conversion Factors

• 2Fe O2 ? 2FeO
• If we start with 2.0 mol of Fe, how many moles of
  O2 do we need, and how many moles of FeO are
  produced?
• If we start with 4.0 mol of Fe, how many moles of
  O2 do we need, and how many moles of FeO are
  produced?
• 4.0 mol Fe

2.0 mol O2
4.0 mol Fe
4.0 mol FeO
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The Mole

• Chemists use moles as a way to count atoms
• Molar ratio corresponds to ratio of atoms and
  molecules in balanced equation
• Mole (and thus molecules) linked to laboratory by
  mass in grams and molar mass (molecular weight)

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Gram to Mole Conversions

• Grams ? molar mass moles
• Moles x molar mass grams
• How many moles in 35.5 g of PCl3?
• 35.5 g

Ratio method
0.260 mol
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Gram to Mole Conversions

• Grams ? molar mass moles
• Moles x molar mass grams
• How many grams is 6.50 mol of PCl3?
• 6.50 mol

892.6 g
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Problem 15

• Calculate the number of moles in 24.4 g of H2.
• If the H2 reacts with oxygen to make hydrogen
  peroxideH2 O2 ? H2O2
• How many moles of H2O2 will form?
• c) How many g of H2O2?

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Problem 15 a) number of moles in 24.4 g of H2.
24.4 2.02 (x) x 12.1 mol
24.4 g
12.1 mol H2
b) H2 O2 ? H2O2 How many moles of H2O2
will form? 11 ratio 12.1 mol H2O2
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Problem 15 c)
How many g of H2O2? 12.08 mol H2O2 (2(1.01 g/mol)
2(16.00 g/mol))
34.02 g/mol
12.08 mol H2O2 (34.02 g/mol) 411 g H2O2