Chemistry SM-1131
Week 9 Lesson 1
Dr. Jesse Reich
Assistant Professor of Chemistry
Massachusetts Maritime Academy
Fall 2008
Class Today
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Tests-returned
Chemical Reactions
Types of Chemical Reactions
Balancing Chemical Reactions
New Material: Double Displacement, acid base,
spectator ions, solubility rules, precipitation
reactions
• Take Home Quiz (described only if there is time) due
Monday!
Test
• 1-Mg(NO3)2, magnesium nitrate, Mg1N2O6
• 2-Fe(III)2(SO3)3, Iron (III) sulfite, Fe2S3O9
• 3-dinitrogen pentaoxide, diphosphorus
tetraoxide, CCl4, H2O, SF6
• 4-NH4MnO4, ammonium permanganate,
N1H4Mn1O4
• 5- H3PO4, phosphoric acid, H3P1O4
• 6- 48amu, 164amu, 400amu, 18amu, 78amu
test
• .31 mol O3, .159mol Na3PO4, .22mol
Fe(III)2(SO4)3, 1.11e5 mol H2O, 5.76e-5 mol
CaF2
• 720gO3, 4.26e3g Na3PO4, 3.52e4 g
Fe(III)2(SO4)3, 3.6e7g H2O, 0.35g CaF2
• Moles  atoms in a sec
• 27% carbon
Test Q9
15 moles O3 x 6.02e23 molecules O3 x 3 atoms
= 2.709e25
1 mole O3
1 molecule O3
unit is atoms
Test 11
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Percent Composition for C6H6 and C2H2
%C= 92.3%
%H= 7.7%
7.7H  7.7g
7.7g H x 1 g H/ mol = 7.7 mol H
92.3%  92.3g C
92.3 g C x 1mol C/ 12g C = 7.7 mol C
7.7/7.7 =1… C1H1 for both
N=6
• Molecular formula/empirical formula = N
• N=6 means that the molecule is 6 times bigger
than the empirical formula you just got.
• The empirical formula you just got was C1H1,
so the molecular formula is C6H6.
Chemical Reactions
• A chemical reaction is a rearrangement of
atoms.
• Reactants  Products
Evidence of a Chemical
Reaction
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Heat and Light
Formation of solids
Gas emitting
Changing colors
Change in temperature
Some quick vocab
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(g) means the substance is a gas
(l) means the substance is a liquid
(s) means the substance is a solid
(aq) means the substance is aqueous
Aqueous means dissolved in water.
Rules about Chemical
Equations
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Remember that law of conservation of mass?
Matter can neither be created nor destroyed.
We’ll start with skeleton equations
We’ll alter it to make a balanced equation.
Counting molecules and
atoms
• 2H2O
• 4Mg(NO3)2
• The 2 and the 4 are called coefficients, just
like 5X in math where the 5 is the coefficient.
Types of Chemical
Reactions
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There are 5 main types of reactions
Combination aka synthesis
Decomposition
Combustion
Single displacement
Double displacement
(Acid Base, gas evolution, precipitation,
oxidation and reduction aka redox)
Combination Reactions
• 2 things come together to make 1 thing.
• Carbon and Hydrogen react to form the
compound methane.
• C + H2  CH4 is the skeleton equation
• C + 2H2  CH4 is the balanced equation
Combination Reaction 2
• Mg and oxygen react at high temperature
what is formed?
• Mg + O2  MgO
• O2 is diatomic when written into reactions
(HINClBrOF)
• (How’d I know MgO, well 4 steps: symbols,
charges, switcheroo, reduce)
• To balance it…
Balancing Chemical
Reactions
• ___ Mg + ___ O2  ___MgO
• 1- for all ionic compounds correctly establish
their formula
• 2-List all elements in the rxn under the arrow
• 3-Count the number of atoms of each type on
both sides of the equation
• 4-Starting with metals change the coefficients
until both sides are balanced. DO NOT
CHANGE CHEMICAL FORMULAS.
Balancing Chemical
Reactions
• ___ Mg + ___ O2  ___MgO
___Mg___
___O___
• ___ Mg + ___ O2  ___MgO
1 Mg 1
2 O 1 NOT BALANCED
• ___ Mg + ___ O2  _2_MgO
1 Mg 2
2 O 2 NOT BALANCED
• _2_ Mg + ___ O2  _2_MgO
2 Mg 2
2 O 2 BALANCED
More examples
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N2 + 3H2  2NH3
2Al + 3F2  2AlF3
P4 + 5O2  P4O10
SO3 + H2O  H2SO4
Decomposition
• When things decompose they break down.
This reaction is where 1 molecule breaks
down into several molecules.
• Iron(III) chloride decomposes at high
temperature into it’s elements.
• FeCl3  Fe + Cl2
• Not balanced, again HINClBrOF
Electrolysis of water
• Electrolysis is when you put a current through water. Water
turns into it’s elements. Write and balance the reaction.
• ___H2O  ___H2 + ___O2
_2H 2
_1O_2
• _2_H2O  ___H2 + ___O2
_4H_2
_2O_2
• _2_H2O  _2_H2 + ___O2
_4H_4
_2O_2
More examples of
Decomposition
• CaCO3  CaO + CO2
• 2 HgO  2 Hg + O2
• 2 KClO3  2KCl + 3O2
Combustion Reactions
• Combustion means burning and fire. What
two things does fire require? O2 and
something to burn. We normally burn
hydrocarbons (Hydro=H, Carbon = C therefore
stuff made up of H and C).
• The products are always CO2 and H2O.
• Methane and Oxygen burn write the equation.
• ___CH4+ ___O2  ___ CO2 + ___H2O
Balance a combustion
• ___CH4+ ___O2  ___ CO2 + ___H2O
__C __
__H __
__O __ (it comes from 2 places)
Balance this reaction now
Balanced Reaction
• _1_CH4+ _2_O2  _1_ CO2 + _2_H2O
1_C 1_
4_H 4_
4_O 4_ (it comes from 2 places)
Harder example
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C2H6 + O2  CO2 + H2O
2 C 1_
6 H 2_
2 O 3_
C2H6 + 3.5 O2  2 CO2 + 3 H2O
2 C 2_
6 H 6_
7 O 7_(no such thing as 0.5O2)
Double all the
coefficients
• 2C2H6 + 7 O2  4 CO2 + 6 H2O
4 C 4_
12 H 12_
14 O 14_
All combustion reactions will be just like one of
those two reaction.
Displacements
• These are the 2 hardest to tell apart when
starting.
• Single displacements typically have 1 lone
element on both sides of the reaction
• Double displacements look like the biggest
reactions out there, and you’ll see that the
two metals switch places
Single Displacement
• Magnesium metal starts making hydrogen gas
when it’s dropped in aqueous hydrochloric
acid. What’s the full reaction?
___Mg + ___HCl  ___ H2+ __ ?
Single Displacement
• ___Mg + ___HCl  ___ H2+ __ MgCl?
• NO! 4 steps when writing ionic salts ALWAYS!
So, it’s MgCl2
• ___Mg + ___HCl  ___ H2+ __ MgCl2
1 Mg 1_
1 H 2_
1 Cl 2_
___Mg + _2_HCl  ___ H2+ __ MgCl2
Single Displacement
• ___Mg + _2_HCl  ___ H2+ __ MgCl2
• Notice: Mg is elemental on the left side, and
Hydrogen is elemental on the right side.
• The single lone element was displaced by a
different lone element.
More Examples
• 3AgCl + Al  AlCl3 +3 Ag
• 2Na + H2O  H2 + 2NaOH
• Zn3N2 + 3Mg  Mg3N2 + 3Zn
Double Displacement
el double
• Silver nitrate and sodium chloride react to
form silver chloride and sodium nitrate. Write
and balance the reaction.
• KEY POINT: FIGURE OUT THE FORMULA FOR
EACH INORGANIC PIECE AND DON’T MESS
WITH THE FORMULA FOR THE REST OF THE
TIME!
El Double
• AgNO3 + NaCl  AgCl + NaNO3
• It’s already balanced.
• The Ag and Na switched places.
• That’s why it’s a double displacement.
El Double 2
• Barium nitrate and potassium sulfate reaction
to form barium sulfate and potassium nitrate.
Write and balance the equation.
Ba(NO3)2 + K2SO4  Ba(SO4) + KNO3
Ba _
K _
(NO3) _
(SO4) _
Acid Base
• These are like double displacement reactions,
except one of the compounds is going to be an
acid and the other will be an ionorganic salt
• Salt just means combination of a cation and
anion in a solid form
• Hydrochloric acid and sodium hydroxide react
together. Write the reaction.
ACID BASE
• HCl + NaOH  ____ + ____
• The “metals” swithc places. So H and Na will
switch. Na will be with Cl, and H will be with
OH
• HCl + NaOH  NaCl + H2O
Acid Base
• Phosphoric acid and sodium hydroxide are
stirred in a beaker together what products are
made?
Acid Base
• H3PO4 + NaOH  Na3PO4 + H2O = skeleton
• Balance this
Solubility
• Often times we perform a double
displacement reaction to actually collect one
of the products. We can make certain
compounds crash out of (precipitate) an
aqueous solution because of how soluble
some compounds are.
• We’ll take two soluble compounds, they will
react, and they will typically make one soluble
product and one insoluble product.
Na2SO4 and BaCl2
• Na2SO4 + BaCl2  NaCl + Ba(SO4) skeleton
• Balance this (if you make a compound Na2Cl2
you are wrong and bad! We don’t mess with
formulas after they are set. We just change
coefficients).
Solubility Rules
• You did that reaction in lab! The BaSO4 was a
powder that crashed out of solution and you
filtered it off! Why did it crash out? Because
of solubility rules.
Solubility Rules
• Any compound with Li, Na, K, or NH4 will always be
soluble
• Any compound with NO3 or C2H3O2 will always be
soluble
• Compounds with Cl, Br, I will be soluble except with
Ag, Hg or Pb
• Compounds with SO4 will be soluble except with Sr,
Ba, Pb, or Ca
• Compounds with CO3 and PO4 are insoluble unless
with Li, Na, K or NH4
Barium
• Ok, so let’s take our barium and sulfate
reaction and try to figure out which are
soluble pieces and which are not.
Solubility Rules with
Sulfate lab
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Na2SO4(?) + BaCl2(?)  NaCl(?) + Ba(SO4)(?)
Compounds with Na are ?
Compounds with Cl are?
Compounds with Na are?
Compounds with Sulfate are? Except with?
Solubility
• Na2SO4(aq) + BaCl2(aq)  NaCl(aq) + Ba(SO4)(s)
Dissolving
• So, what happens when an inorganic
compounds dissolves (this is totally different
than a molecular compound dissolving)?
• Water molecules act as crowbars that split
molecules into pieces. The two pieces formed
are the cations and the anions.
• When you see table salt it’s the compound
NaCl. When you dissolve it in water it’s
actually Na+ and Cl-.
Try some more
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Ag(NO3) Ag+ and NO3Na2(SO4) 2Na+ and SO4-2
H3PO4  3H+ and PO43Na(OH)  Na + and OHLi3(PO4)  3Li+ and PO43-
Molecular Compounds
• Molecular compounds don’t do that.
• C6H6O6(s)  C6H6O6(aq) no change occurs.
Spectator
• Spectator ions- reactions have components
that aren’t that important to the overall
effect. We can tell they aren’t that important
because they appear on both sides of the
chemical equation. They aren’t really
participating, they are just hanging out. We
call them spectator ions.
Net Ionic Equations
• Net just means overall, so we’re trying to
figure out what’s the overall reaction.
• Aluminum chloride and sodium phosphate
undergo a double displacement reaction.
What precipitates and what’s the net ionic
equation?
• AlCl3 + Na3PO4  AlPO4 + NaCl = skeleton
• AlCl3 + Na3PO4  AlPO4 + 3NaCl = balanced
• AlCl3(aq) + Na3PO4(aq)  AlPO4(s) + 3NaCl(aq) total eq
Total Ionic
• AlCl3(aq) + Na3PO4(aq)  AlPO4(s) + 3NaCl(aq)
total eq
Al+3(aq) + 3Cl-(aq) + 3Na+(aq) + PO43-(aq)  AlPO4(s) + 3Na+(aq) + 3Cl-(aq)
• That’s the total ionic equation
• Note the (s) thing is not in pieces. That’s
because only things that are (aq) are going to
break up like that.
• To get the net ionic we have to cancel out the
spectator ions from both sides.
Net
Al+3(aq) + 3Cl-(aq) + 3Na+(aq) + PO43-(aq)  AlPO4(s) + 3Na+(aq) + 3Cl-(aq)
3Cl-(aq) + 3Na+(aq) appear on both sides of the equation. We’re
going to cancel them out. If we do that it leaves us with the
“Net Ionic Equation.”
• Al+3(aq) + PO43-(aq)  AlPO4(s) is the net
equation.
So steps?
• 1-Inorganic formula writing for each inorganic
compound
• 2-skeleton equation
• 3-balanced equation
• 4-total equation (add solubilities)
• 5-Total ionic equation
• 6-Cancel out spectator ions
• 7-Net ionic equations
Chapter 7 Take Home
Quiz 8pts
• 1-Berylium chloride and aluminum react together. What is
the reaction type? Balance the chemical reaction.
• 2-Magnesium chloride and sodium phosphate undergo a
double displacement reaction. Go through all the steps to
show the net ionic equation.
• 3- When you cook with a propane grill you burn propane.
Write the combustion rxn.
• 4- Sulfuric acid and magnesium hydroxide are spilled in a
warehouse. What reaction type is this. Do all the steps to
show the net ionic reaction.