1. Chapter 4 Solutions and Chemical Reactions
Water
Importance
Life (as we know it) depends on water
Human civilization requires water for many purposes
Many important chemical reactions occur in Aqueous Solutions, where other compounds are dissolved in water
The nature of water
Bent shape and unequal sharing of electrons makes water polar
This aids water in dissolving ionic compounds (cations and anions)
Water hydrates the ions by interacting with its oppositely charged ends

2. NaCl(s) -----> Na+(aq) + Cl-(aq)
The ionic substance breaks up into independent cations and anions
Nonionic compounds can also dissolve in water if they are polar
Nonpolar substances generally don’t dissolve in water: grease, oils, skin
Electrolytes
Solutions
A solution is a homogeneous mixture the same throughout
We can vary the composition by adding more or less of the components
Solvent = usually a liquid; the most abundant component of a solution
Solute = the lesser abundant component(s) of a solution
Ethanol
NaCl(s) -----> Na+(aq) + Cl-(aq)

3. that the more ions present, the better the conductivity
B. Solutions and Electrical Conductance
A substance allowing current to flow through it is electrically conductive
Pure water does not conduct electricity
Different solutes dissolved in water help it to be conductive
Strong electrolyte = completely ionized; strongly conductive solution
Weak electrolyte = partially ionized; somewhat conductive solution
Nonelectrolyte = not ionized; nonconductive solution
Arrhenius ( ) found
that the more ions present, the
better the conductivity

4. C. Strong Electrolytes
Completely ionized when dissolved in water
Many salts (ionic compounds) are strong electrolytes
Strong Acids are strong electrolytes
Acid = substance that produces H+ when dissolved in water
Strong Acids completely ionize in solution
Hydrochloric Acid HCl(g) > H+(aq) Cl-(aq)
Nitric Acid HNO3(g) > H+(aq) NO3-(aq)
Sulfuric Acid H2SO4(l) > H+(aq) HSO4-(aq)
Strong Bases are strong electrolytes
Base = substance that produces OH- when dissolved in water
Strong bases completely ionize in solution
NaOH(s) > Na+(aq) + OH-(aq) KOH(s) > K+(aq) + OH-(aq)

5. D. Weak Electrolytes
Only partially ionized when dissolved in water
Weak Acids are weak electrolytes
Weak acid only produces a few H+ ions
Acetic acid is a weak acid
HC2H3O2(aq) > H+(aq) C2H3O2(aq)
Only 1 molecule in a 100 dissociates
Weak Bases are weak electrolytes
Weak base produces only a few OH- ions
Ammonia is a weak base
NH3(aq) + H2O(l) > NH4+(aq) + OH-(aq)
Only 1 molecule in 100 reacts
Nonelectrolytes
Does not ionize when dissolve in water
Sugar is a nonelectrolyte
C12H22O11(s) > C12H22O11(aq)

6. III. Solution Concentration
The Stoichiometry of Chemical Reactions
We must know what the reactants and products are
We must know the amounts of the reactants and products
How do we describe the amounts in a solution?
Molarity
Unit for the concentration of a solute in a solution
M = moles solute/liters of solution
1.0 M NaCl = 1 mole of NaCl dissolved in 1 L of solution
Any volume having the same concentration is also 1.0 M NaCl
500 ml (0.500 L) of 1.0 M NaCl would contain 0.5 mol NaCl
Example: Calculate M of 11.5 g NaOH in 1.5 L of total solution.

7. 5. Example: M = ? for 1.56 g HCl in a total of 26.8 ml of solution?
6. Molarity descriptions of a solution reflect composition before dissolution
1.0 M NaCl actually contains no NaCl
1.0 M NaCl is 1.0 M in Na+ and 1.0 M in Cl-
1.0 M CaCl2 is 1.0 M in Ca2+ and 2.0 M in Cl-
CaCl2(s) > Ca2+(aq) Cl-(aq)
7. Example: Give the concentration of each ion
0.5 M Co(NO3)2 = 0.5M in Co2+ and 1.0 M in NO3-
Co(NO3)2 (s) > Co2+(aq) NO3-(aq)
1M Fe(ClO4)3 = 1M Fe3+ and 3M ClO4-
8. Example: ??? moles of Cl- in 1.75L of M ZnCl2

8. 9. Example: What volume of 0.14 M NaCl contains 1.0mg NaCl?
10. Standard Solution = concentration is accurately known
Accurate masses come from an analytical balance (0.4563g)
Accurate volumes are obtained using a Volumetric Flask
Example: How much K2Cr2O7 needed for 1.00 L of M?

9. Dilution
Chemicals are often purchased or prepared as concentrated stock solutions
Dilution = adding water to stock solution to make a less concentrated one
M1V1 = M2V2 is a useful equation to calculate dilutions
Example: ??? volume of 16 M H2SO4 is needed for 1.5 L 0.10M H2SO4

10. IV. Precipitation Reactions
Definitions
When two solutions are mixed and a solid forms
Precipitate = solid that forms from a precipitation reaction
K2CrO4(aq) + Ba(NO3)2(aq) = 2K+(aq) + CrO42-(aq) + Ba2+(aq) +2NO3-(aq)
K2CrO4 and Ba(NO3)2 are both soluble (all dissolve in water)
A yellow precipitate forms when these solutions are mixed
K2CrO4(aq) + Ba(NO3)2(aq) > BaCrO4(s) + 2KNO3(aq)
AgNO3(aq) + KCl(aq) > AgCl(s) + KNO3(aq) + =
Precipitate Spectator Ions

11. B. Solubility Rules
Example: predict what will happen when you mix:
KNO3(aq) + BaCl2(aq) >
Na2SO4(aq) + Pb(NO3)2(aq) >
3KOH(aq) + Fe(NO3)2(aq) >

12. Describing Reactions in Solution
Molecular Equation shows what compounds the ions came from
Does not give clear picture of what happens in solution
K2CrO4(aq) + Ba(NO3)2(aq) > BaCrO4(s) + 2KNO3(aq)
Complete Ionic Equation represents the form of the ions in solution
All strong electrolytes are represented as their ions
2K+(aq) + CrO42-(aq) + Ba2+(aq) +2NO3-(aq) ----> BaCrO4(s) + 2K+(aq) + 2NO3-(aq)
Net Ionic Equation shows only the ions participating in the reaction
The K+ and NO3- ions occur on both sides of the complete ionic eqn.
These spectator ions can be cancelled out of each side (algebra)
Ba2+(aq) CrO42-(aq) > BaCrO4(s)
Example
3KOH(aq) + Fe(NO3)3(aq) > Fe(OH)3(s) + 3KNO3(aq)
b. 3K+(aq) + 3OH-(aq) + Fe3+(aq) + 3NO3-(aq) ----> Fe(OH)3(s) + 3K+(aq) + 3NO3-(aq)
c. Fe3+(aq) + 3OH-(aq) > Fe(OH)3(s)