Announcements




Precipitation lab write-up due tomorrow
at the start of discussion
Text HW due tomorrow in discussion
Lon-capa HW #4 Type 1 due Monday,
Oct 15th at 7:00pm
Lon-capa HW #4 Type 2 due
Wednesday, Oct 17th at 7:00pm
Last Lecture…

K2SO4(aq) + Ba(NO3)2(aq)

AgNO3(aq) + KCl(aq)

NaNO3(aq) + KCl(aq)

What will happen when these are mixed
together?
Determine products



K2SO4(aq) + Ba(NO3)2(aq) 
 Products: BaSO4 + KNO3
AgNO3(aq) + KCl(aq) 
 Products: AgCl + KNO3
NaNO3(aq) + KCl(aq) 
 Products: NaCl + KNO3
Write balanced equations

K2SO4(aq) + Ba(NO3)2(aq)  BaSO4 + 2KNO3

AgNO3(aq) + KCl(aq)  AgCl + KNO3

NaNO3(aq) + KCl(aq)  NaCl + KNO3
Solubility Rules (Page 172)
1.
2.
3.
4.
5.
6.
Most nitrate salts are soluble.
Most salts of sodium, potassium, and
ammonium cations are soluble.
Most chloride salts are soluble. Exceptions:
Ag+ and Pb2+.
Most sulfate salts are soluble. Exceptions:
Ca2+, Ba2+, and Pb2+.
Most hydroxide salts are only slightly soluble.
Soluble ones are: Na+, K+, and Ca2+.
Most sulfide, carbonate, and phosphate salts
are only slightly soluble.
Precipitation Reactions



Know how to use the solubility
rules (you will be given them on
the exam).
Know how to write equations from
reactants (ionic reactants).
Understand what solutions “look”
like at a very magnified level.
Solubility rules


K2SO4(aq) + Ba(NO3)2(aq)  BaSO4 + 2KNO3
BaSO4:
Solubility Rules


Exception to rule#4
Solid




KNO3:



Nitrate salts (rule#1)
Potassium salts (rule #2)
Soluble (no solid)



Most nitrate salts are soluble.
Most salts of sodium, potassium,
and ammonium cations are
soluble.
Most chloride salts are soluble.
Exceptions: Ag+ and Pb2+.
Most sulfate salts are soluble.
Exceptions: Ca2+, Ba2+, and Pb2+.
Most hydroxide salts are only
slightly soluble. Soluble ones are:
Na+, K+, and Ca2+.
Most sulfide, carbonate, and
phosphate salts are only slightly
soluble.
Solubility rules


AgNO3(aq) + KCl(aq)  AgCl + KNO3
AgCl
Solubility Rules



Exception to rule #3
Solid
KNO3



Nitrate salts (rule#1)
Potassium salts (rule #2)
Soluble (no solid)






Most nitrate salts are soluble.
Most salts of sodium, potassium,
and ammonium cations are
soluble.
Most chloride salts are soluble.
Exceptions: Ag+ and Pb2+.
Most sulfate salts are soluble.
Exceptions: Ca2+, Ba2+, and Pb2+.
Most hydroxide salts are only
slightly soluble. Soluble ones are:
Na+, K+, and Ca2+.
Most sulfide, carbonate, and
phosphate salts are only slightly
soluble.
Clicker #1

When potassium
chloride and sodium
nitrate are mixed, what
precipitate will form?
KCl(aq) + NaNO3(aq) →
A)
B)
C)
D)
E)
KNO3
NaCl
KCl
NaNO3
No precipitate will
form.






Solubility Rules
Most nitrate salts are soluble.
Most salts of sodium, potassium,
and ammonium cations are
soluble.
Most chloride salts are soluble.
Exceptions: Ag+ and Pb2+.
Most sulfate salts are soluble.
Exceptions: Ca2+, Ba2+, and Pb2+.
Most hydroxide salts are only
slightly soluble. Soluble ones are:
Na+, K+, and Ca2+.
Most sulfide, carbonate, and
phosphate salts are only slightly
soluble.
Example


KCl(aq) + NaNO3(aq)  KNO3 + NaCl
KNO3
Solubility Rules




NaCl




Nitrate salts (rule#1)
Potassium salts (rule #2)
Soluble (no solid)
Sodium salts (rule #2)
Chloride salts (rule #3)
Soluble (no solid)
Has a reaction occurred?






Most nitrate salts are soluble.
Most salts of sodium, potassium,
and ammonium cations are
soluble.
Most chloride salts are soluble.
Exceptions: Ag+ and Pb2+.
Most sulfate salts are soluble.
Exceptions: Ca2+, Ba2+, and Pb2+.
Most hydroxide salts are only
slightly soluble. Soluble ones are:
Na+, K+, and Ca2+.
Most sulfide, carbonate, and
phosphate salts are only slightly
soluble.
What makes a “chemical reaction”?



Bonds in reactants have to be broken
Atoms rearrange
Bonds form to make products
3 ways to write a reaction:

Molecular equation


Complete ionic equation


How we’ve written them up to this point
shows what’s happening in the solution;
write it as appears in solution
Net ionic equation

what takes part in the chemical reaction;
Remove spectator ions (don’t do
anything; only there to balance charges!)
Reaction of AgNO3 and KCl

Molecular Equation:

AgNO3(aq) + KCl(aq)  KNO3(aq) + AgCl(s)

Complete Ionic Equation:

Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)  K+(aq) +
NO3-(aq) + AgCl(s)

Net Ionic Equation:

Ag+(aq) + Cl-(aq)  AgCl(s)
A Microscopic Look…
Reaction of K2SO4 and Ba(NO3)2

Molecular equation

K2SO4(aq) + Ba(NO3)2(aq)  BaSO4(s) + 2KNO3(aq)

Complete ionic equation

2K+(aq) + SO42-(aq) + Ba2+(aq) + 2NO3-(aq) 
BaSO4(s) + 2K+(aq) + 2NO3-(aq)

Net ionic equation

SO42-(aq) + Ba2+(aq)  BaSO4(s)
A Microscopic Look…
Mixing NaNO3 and KCl

Molecular equation:

NaNO3(aq) + KCl(aq)  NaCl(aq) + KNO3(aq)

Complete ionic equation:


Na+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) → Na+(aq) +
Cl-(aq) + K+(aq) + NO3-(aq)
all spectator ions  no net ionic equation
which means no chemical reaction occurred!
A Microscopic Look…
Clicker #2
When aqueous silver nitrate and aqueous
sodium chromate are mixed, what are the
formulas of the products?
A)
B)
C)
D)
E)
Na2NO3 and AgCrO4
NaNO3 and Ag2CrO4
NaNO3 and AgCrO4
Na2NO3 and AgCr2O7
NaNO3 and Ag2Cr2O7
Demo


Silver nitrate and sodium chromate
AgNO3(aq) + Na2CrO4(aq)  Ag2CrO4 + NaNO3



How to balance this equation?
2AgNO3(aq) + Na2CrO4(aq)  Ag2CrO4 + 2NaNO3
What happens when the two solutions are mixed
together?
Example


2AgNO3(aq) + Na2CrO4(aq)  Ag2CrO4 + 2NaNO3
Ag2CrO4
Solubility Rules


Not in rules!
NaNO3



Nitrate salts (rule#1)
Sodium salts (rule #2)
Soluble (no solid)
Since NaNO3 is soluble,
the solid must be Ag2CrO4







Most nitrate salts are soluble.
Most salts of sodium, potassium,
and ammonium cations are
soluble.
Most chloride salts are soluble.
Exceptions: Ag+ and Pb2+.
Most sulfate salts are soluble.
Exceptions: Ca2+, Ba2+, and Pb2+.
Most hydroxide salts are only
slightly soluble. Soluble ones are:
Na+, K+, and Ca2+.
Most sulfide, carbonate, and
phosphate salts are only slightly
soluble.
Reaction of AgNO3 and Na2CrO4

Molecular Equation:

2AgNO3(aq) + Na2CrO4(aq)  Ag2CrO4(s) + 2NaNO3(aq)

Complete Ionic Equation:

2Ag+(aq) + 2NO3-(aq) + 2Na+(aq) + CrO4-(aq) 
2Na+(aq) + 2NO3-(aq) + Ag2CrO4(s)

Net Ionic Equation:

2Ag+(aq) + CrO42-(aq)  Ag2CrO4(s)
A Microscopic Look…
Mixing Acids and Bases




Sodium hydroxide and hydrochloric acid
NaOH(aq) + HCl(aq)  NaCl + H2O
What happens when the two solutions are mixed
together?
No solid formed! So does that mean that no reaction
occurred?
Mixing Acids and Bases

Molecular equation:

NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)

Complete ionic equation:

Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) → Na+(aq) +
Cl-(aq) + H2O(l)

Net ionic equation:

OH-(aq) + H+(aq) → H2O(l)
Clicker #3

Is the resulting net ionic equation a chemical reaction?
H+(aq) + OH–(aq) → H2O(l)
A) Yes. There is a new compound formed from H+ and
OH–.
B) Yes. Whenever two compounds are mixed, a
chemical reaction always occurs.
C) No. A precipitate (solid) must be formed to be
considered a chemical reaction.
D) No. There was no color change so a chemical
reaction did not occur.
What makes a “chemical reaction”?



Bonds in reactants have to be broken
Atoms rearrange
Bonds form to make products
A Microscopic Look…
Clicker #4

Will the resulting solution conduct electricity?
A) No. There is no precipitate formed and a
solid is required to conduct electricity.
B) No. The resulting solution is pure water
which does not conduct electricity.
C) Yes. The resulting solution is pure water
which conducts electricity.
D) Yes. The resulting solution contains ions
which conduct electricity.
Acids and Bases

Molecular equation:

Ba(OH)2(aq) + H2SO4(aq)  BaSO4(aq) + 2H2O(l)

Complete ionic equation:



Ba2+(aq) + 2OH-(aq) + 2H+(aq) + SO42-(aq) →
BaSO4(s) + H2O(l)
Net ionic equation:
Ba2+(aq) + 2OH-(aq) + 2H+(aq) + SO42-(aq) →
BaSO4(s) + H2O(l)
A Microscopic Look…
Clicker #5

Will the resulting solution conduct electricity?
A) No. There is no precipitate formed and a
solid is required to conduct electricity.
B) No. The resulting solution is pure water
which does not conduct electricity.
C) Yes. The resulting solution is pure water
which conducts electricity.
D) Yes. The resulting solution contains ions
which conduct electricity.
Concentration and Molarity



What does concentration tell us?
 Quantity per volume (ratio!)
Density: mass of substance per volume of solid or
liquid (or solution)
Molarity: number of moles of species per volume of
aqueous solution
Clicker #6

Which of the three solutions is the most
concentrated?
A)
B)
C)
D)
Solution #1
Solution #2
Solution #3
The concentrations are the same.
Concentration and Molarity



Which liquid is the most concentrated (has the most
food coloring)?
They are all the same!
While the volumes are different, the RATIO of food
coloring per volume is still the same
Concentration and Molarity

How could we change the concentration then?

Add more food coloring – higher concentration

Remove water by evaporation – higher concentration

Add more water – lower concentration
Concentration and Molarity


Think about what concentration means before getting
lost in the math
Solutions are always homogeneous!
Concentration and Molarity

Start with 12 “particles” in 6.0L water
12/6.0
6/3.0L
2/1.0
=2
=2
=2
2/6.0
= 1/3
Molarity

Concentration of solution – molarity

Molarity = (moles of solute) / (liters of solution)

has units of moles per liter (moles/L)

Solute is whatever is being dissolved into solution
Announcements




Precipitation lab write-up due tomorrow
at the start of discussion
Text HW due tomorrow in discussion
Lon-capa HW #4 Type 1 due Monday,
Oct 15th at 7:00pm
Lon-capa HW #4 Type 2 due
Wednesday, Oct 17th at 7:00pm