Transcript Solute

Unit 7
Reactions in Aqueous Solutions
Types of Chemical Reactions
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Precipitate reaction
 Double Replacement
Acid – Base reaction
Oxidation – Reduction reaction (redox)
 Combustion reaction
 Synthesis reaction
 Decomposition reaction
 Single Replacement
Signs of a Chemical Reaction
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Color change
Change in temperature
Formation of a gas (look for bubbles)
Formation of a precipitate
(precipitate is a solid formed when mixing
2 liquids together)
Precipitate Reaction
Reactants are dissolved as ions in solution.
They are strong electrolytes.
K2CrO4 (aq) + Ba(NO3)2 (aq)  products
2 K+1(aq) + CrO4-2(aq) + Ba+2(aq) + 2 NO3-1(aq)  products
Problem is to decide what the products are!
Solubility Rules
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Soluble means that the product will dissolve
in water.
Low solubility means that is insoluble, it will
NOT dissolve in water.
The chart lists anions (negative ions) and
cations (positive ions)
Formation of a Precipitate: Happens when 2 solutions
are mixed, and a solid is formed due to a combination of
ions that is not soluble, will not dissolve in H2O.
1. Determine the ions present in each solution
2. Using the Solubility of common compounds in water chart,
determine which combination of ions has low solubility
Low solubility means will precipitate and form a solid
3. Write the balanced ionic equation for the formation of the
precipitate.
Ba(NO3)2 
Na2CrO4 
Chemical Equations – 3 types to write
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Complete Molecular chemical equations show all chemicals as
complete formulas.
K2CrO4 (aq) + Ba(NO3)2 (aq)  BaCrO4 (s) + 2 KNO3 (aq)
Complete Ionic chemical equations show all chemicals in their
actual form.
2K+1(aq)+CrO4-2(aq)+Ba+2(aq)+2NO3-1(aq)BaCrO4(s)+2K1(aq)+2NO3-1(aq)
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Net Ionic chemical equations show only the chemicals that are
directly involved in the reaction.
Ba+2 (aq) + CrO4-2 (aq)  BaCrO4 (s)
Spectator ions, those not involved, are not included.
Write all 3 types of chemical reactions
for the following combinations.
1.
Barium nitrate with sodium chromate
2.
Aluminum sulfate with strontium nitrate
3.
Cobalt (II) chloride with potassium hydroxide
4.
Magnesium chloride with sodium hydroxide
5.
Copper (II) chloride with sodium carbonate
Mixture is a substance composed of two or more
individual components. The physical properties
(such as density, melting point, boiling point) can
change.
A homogeneous mixture is uniform in composition. A
solution is a homogeneous mixture. Example:
sugar dissolved in H2O
A heterogeneous mixture is non-uniform in
composition. Example: Sand mixed with gravel
There are 3 kinds of solutions
a. Gaseous solution: All are homogeneous
mixtures. Example: the air
b. Solid solution: A solid dissolved in a solid,
Alloys. Example: woods alloy which is Pb, Sn, Cd,
and Bi, it melts at 71 oC
Turkey Timer
The spring is held down
with a blob of solid
metal. The metal alloy,
which has a low melting
point.
Metal
Alloy
When the turkey
is hot enough
(done!), the metal
melts, releasing
the spring, and
the timer pops
up.
c. Liquid solution: A solid, liquid, or gas dissolved in a liquid.
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Solvent is the liquid that does the dissolving.
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Solute is the substance being dissolved.
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Dilute solution (unsaturated) has very little solute
in a large amount of solvent. Example: Kool-aid
made with only ¼ cup of sugar.
Concentrated solution has a large amount of
solute dissolved in the solvent. Example: Kool-aid
made with the full cup of sugar.
Saturated solution has the most solute possible
dissolved in the solvent. Example: Kool-aid made
with enough sugar that some stays undissolved in
the bottom of the container.
Properties of Solutions Lab
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What happens to the boiling point when a salt is added
to H2O?
What happens to the freezing point when a salt is
added to H2O?
What happens to the temperature when a salt
dissolves in H2O?
Do all salts dissolving in H2O result in the same
temperature change direction?
What is a precipitate?
Water Softeners
Water softeners work on an ion exchange
method. Ions such as Ca+2, Mg+2, and Fe+3
make water hard. Hard water resists suds
(or forming bubbles). Hard water also
leaves deposits of these ions in pipes and
fixtures.
Water softeners are
filled with resin, small
beads which have a large
amount of surface area.
When your water
softener flushes, the
tank with a salt brine
allows the salt solutions
to flow over the resin.
Na+1 cling to the resin.
The next few days, every
time you use water, the
water runs over the resin
with Na+1. The Na+1
exchanges places with
undesirable ions. When
most of the Na+1 is gone,
the water softener
flushes again.
Molarity (M) is a unit of concentration. Molarity is the
number of moles of solute dissolved per liter of
solution.
M =
# of moles
Volume in Liters
3 moles of NaCl are dissolved in 2 liters of solution.
What is the molarity?
# of moles
M =
Volume in Liters
Remember the formula for moles
Moles
=
Grams
Molar mass
3.89 grams of NiCl2 are dissolved in 300mL of water.
What is the molarity?
What mass of AgNO3 would be required to make
2.5 L of 0.10 M solution?
Freezing Point Depression
DT = (1.86oC)(
Moles of ionic solid
Kg of water
)(i)
DT = change in temperature
Kg of water: 1 Kg = 1000 mL
i = number of ions formed by one molecule of ionic solid
(example Na3PO4  3 Na+1 + PO4-3
i = 4 ions)
What will the freezing point be lowered by if 125 grams of MgCl2 is
added to 500 mL of water?
Acid – Base Reactions
Arrhenius definition:
Acid donates a H+1
Base donates a OH-1
HCl (aq)  H+1(aq) + Cl-1(aq)
NaOH (aq)  Na+1(aq) + OH-1 (aq)
When mixed together, products are
H2O and salt.
HCl (aq) + NaOH (aq)  H2O(L) + NaCl(aq)
H+1(aq)+ Cl-1(aq)+Na+1(aq)+OH+1(aq)H2O (L)+Na+1(aq)+Cl-(aq)
H+1 (aq) + OH-1 (aq)  H2O (L)
HNO3 (aq) + KOH (aq) 
Acid Rain can occur naturally.
CO2 (g) + H2O(L)  H2CO3 (aq)
Pollutants from human activities can also result in
acid rain.
2 SO2 (g) + O2 (g)  2 SO3 (g)
SO3 (g) + H2O (g)  H2SO4 (aq)
NO2 (g) + H2O (g)  H2NO3 (aq)
When acid rain percolates through the ground it will
react with CaCO3 (s) (limestone), dissolving the
limestone creating caves.
Running and dripping water with dissolved minerals
form:
stalactics: deposited minerals holding tight to
ceiling of cave
stalagmites: deposited minerals on floor of cave
Oxidation – Reduction Reactions
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All involve the transfer of eMetal + Nonmetal
Na (s) + Cl2 (g) 
NaCl (s)
Single Replacement (metal + compound)
Al (s) + Fe2O3 (s)  Al2O3 (s) + Fe(s)
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Combustion reaction: Hydrocarbon combining with
oxygen to produce water and carbon dioxide.
C2H5OH (g) +

Synthesis: Multiple atoms or molecules combining
to make one product.
H2 (g) + O2 (g)  H2O (g)
Decomposition: One reactant breaking apart to
make multiple products.
H2O (L)  H2 (g) + O2 (g)
Review
1. Ni(NO3)2  Ni+2 + 2 NO3-1
Na2CO3  2 Na+1 + CO3-2
Ni+2 + CO3-2  NiCO3
2. Ni(NO3)2 + Na2CO3  NiCO3 + 2 NaNO3
Ni+2 + 2 NO3-1 + 2 Na+1 + CO3-2  NiCO3 + 2Na+1 + 2 NO3-1
Ni+2 + CO3-2  NiCO3
3.
4.
5.
6.
7.
DT = 9.59 oC (or freeze at -9.59 oC)
4.44 M HCl
1.74 M CuSO4
8.95 g Sr(NO3)2
3.32 L of H2O
Solutions Crossword
Down
1. Miscible
15. Hydration
Across
10. Molality
23 Nonelectrolyte
24. (Change to 20 e-)
33. Solvation
36. Electrolyte
45. Henry
Precipitate Lab
Set I
Set II
Set III
Set IV
Ba(NO3)2
Na2SO4
FeCl3
NiCl2
BaCl2
Al2(SO4)3
Co(NO3)2
MgCl2
Na2CrO4
Sr(NO3)2
CoCl2
Na2SO4
K2CrO4
BaCl2
NaOH
NaOH
NaNO3
Ba(NO3)2
KOH
Ba(OH)2
KCl
AlCl3
NaNO3
MgSO4
Practice writing chemical equations.
Pick 5 reactions from the precipitate lab,
one from each set.
For each reaction chosen, write:
1. Molecular chemical equation
2. Complete ionic chemical equation
3. Net ionic chemical equation