1. Reactions in Aqueous Solutions
Chemistry 101
Chapter 7
Reactions in Aqueous Solutions

2. Aqueous solution: solvent is water
Reactions in Aqueous Solutions
Ionic compounds (Salt)
Aqueous solution: solvent is water

3. Reactions in Aqueous Solutions
Chemical reactions that occur in water.
In our body reactions occur in the aqueous solution.

4. Water in our body About 60% of our body.
Most of the reactions occur in aqueous solution.
Participates in many biochemical reactions.
Transports reactants and products from one place in our
body to another.
5. Eliminates the waste materials from cells and our body (urine).

5. Why does a chemical reaction occur?
Several driving forces:
Formation of a solid
Formation of water
Transfer of electrons
Formation of a gas

6. Why does a chemical reaction occur?
Several driving forces:
Formation of a solid
Formation of water
Transfer of electrons
Formation of a gas

7. Precipitation reactions
Formation of a solid
Precipitation reactions
Precipitate
KI + Pb(NO3)2  ?

8. Ionic Compounds
When an ionic compound dissolves in water, ions are produced.
Each ion is surrounded by water molecules.
Ions Hydrated by H2O
Hydration

9. Soluble solid: it completely dissolves in water (ions are formed).
Ionic Compounds
Soluble solid: it completely dissolves in water (ions are formed).
Slightly soluble solid: it partially dissolves in water.
Insoluble solid: it does not dissociate in water (almost).
Note: the terms insoluble and slightly soluble mean such a miniscule amount dissolves that you can’t see any decrease in the amount of solid present.

10. Soluble Insoluble Solubility Rules Memorize these RULES!
Preceding rules trump following rules.

11. Solubility Rules
Another way of showing the same rules.

12. Electrolytes + - Electrolyte: conducts an electric current.
Na+
Cl-
bulb
Electrolyte: conducts an electric current.
Ionization (Dissociation)
NaCl → Na+ + Cl-
strong electrolytes: molecules dissociate completely into ions (NaCl).
weak electrolytes: molecules dissociate partially into ions (CH3COOH).
nonelectrolytes: molecules do not dissociate into ions (DI water).

13. Precipitation reactions
Formation of a solid
Precipitation reactions
Precipitate
KI + Pb(NO3)2  ?

14. Aqueous Solution (ionic compounds)
aqueous solution: solvent is water
H2O
Dissociation
(Ionization)
KI(s) K+(aq) + I-(aq) KI K+ I-
H2O
Pb(NO3)2
Pb(NO3)2(s) Pb2+(aq) + 2NO3-(aq)
Pb2+
NO3-
NO3-

15. Aqueous Solution (ionic compounds)
sometimes the ions react with each other.
Positive ions will interact with negative ions. KI
Pb(NO3)2 K+ I-
Pb2+
NO3-
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
Sometimes they stick together to form a solid (precipitate).

16. total charge on left side = total charge on right side
Molecular equation:
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
Complete
Ionic equation:
2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq)  PbI2(s) + 2K+(aq) + 2NO3-(aq)
2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq)  PbI2(s) + 2K+(aq) + 2NO3-(aq)
Pb2+(aq) + 2I-(aq)  PbI2(s)
Net ionic equation:
Spectator ions
2As3+(aq) + 3s2-(aq)  As2S3(s)
total charge on left side = total charge on right side
balanced equation

17. Complete ionic equation
Example
Pb(NO3)2(aq) + Na2SO4(aq)  ?
Pb(NO3)2(aq) + Na2SO4(aq)  PbSO4(s) + NaNO3(aq)
Balance it:
Pb(NO3)2(aq) + Na2SO4(aq)  PbSO4(s) + 2 NaNO3(aq)
Pb2+(aq) + 2 NO3-(aq) + 2 Na+(aq) + SO42-(aq)  PbSO4(s) + 2 Na+(aq) + 2 NO3-(aq)
Complete ionic equation

18. Pb2+(aq) + SO42-(aq)  PbSO4(s)
Example
Pb2+(aq) + 2 NO3-(aq) + 2 Na+(aq) + SO42-(aq)  PbSO4(s) + 2 Na+(aq) + 2 NO3-(aq)
The ions that do not react are called spectator ions.
Net ionic equation:
Pb2+(aq) + SO42-(aq)  PbSO4(s)

19. Practice Molecular equation 3 KOH(aq) + Fe(NO3)3(aq)  ? Balancing
Complete ionic equation
Net ionic equation

20. Why does a chemical reaction occur?
Several driving forces:
Formation of a solid
Formation of water
Transfer of electrons
Formation of a gas

21. Acids and Bases
Acids: sour
Bases: bitter or salty

22. Acids and Bases Arrhenius definition:
Acid: produces H3O+ (H+) in water.
CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)
H3O+ (Hydronium ion):
H+(aq) + H2O(l) H3O+(aq)
Base: produces OH- in water.
H2O
NaOH(s) Na+(aq) + OH-(aq)
NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

23. Weak acid and base: it is partially ionized in aqueous solution.
Acids and Bases
Weak acid and base: it is partially ionized in aqueous solution.
produces less H+ and OH-
CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)
NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
Strong acid and base: it is completely ionized in aqueous solution.
HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq)
NaOH(aq) + H2O(l) Na+(aq) + OH-(aq)
produces more H+ and OH-

24. Acid-Base Reactions Neutralization
Strong acid + Strong base → Salt + H2O
NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)
Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) +  Na+(aq) + Cl-(aq) + H2O(l)
H+(aq) + OH-(aq) H2O(l)
The only chemical change is the formation of water.

25. Why does a chemical reaction occur?
Several driving forces:
Formation of a solid
Formation of water
Transfer of electrons
Formation of a gas

26. e- 2Na(s) + Cl2(g) 2NaCl(s) Na → Na+ + e- Cl + e- → Cl-
Oxidation and Reduction reactions (redox) e-
2Na(s) + Cl2(g) NaCl(s)
Na → Na+ + e-
Cl + e- → Cl-

27. oxidation: it is the loss of electrons.
Oxidation and Reduction reactions (redox)
oxidation: it is the loss of electrons.
reduction: it is the gain of electrons.
Na → Na+ + e-
Cl + e- → Cl-
Remember – LEO says GER.
Loss of Electrons is Oxidation
Gain of Electrons is Reduction.

28. Metal + Nonmetal : Transfer of electrons
Oxidation and Reduction reactions (redox)
Metal + Nonmetal : Transfer of electrons
Oxidation and Reduction reactions (redox)
Oxidation and reduction always occur together.
(The lost e- must go somewhere!)

29. oxidation: it is the loss of electrons.
Oxidation and Reduction reactions (redox)
oxidation: it is the loss of electrons.
reduction: it is the gain of electrons.
Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)
redox reaction
Zn(s)  Zn2+(aq) + 2e- Zn is oxidized (reducing agent)
Cu2+(aq) + 2e-  Cu(s) Cu2+ is reduced (oxidizing agent)

30. oxidation: is the gain of oxygen / loss of hydrogen.
Oxidation and Reduction reactions (redox)
oxidation: is the gain of oxygen / loss of hydrogen.
reduction: is the loss of oxygen / gain of hydrogen.
CH4(s) + 2O2(g)  CO2(g) + 2H2O(g)
redox reaction
C gains O and loses H
is oxidized
(reducing agent)
O gains H
Is reduced
(oxidizing agent)
single replacement reaction and combustion reactions  redox reactions
double replacement reactions  non redox

31. 2 Al(s) + Fe2O3(s)  2 Fe(s) + Al2O3(s)
Oxidation and Reduction reactions (redox)
Example 2:
2 Al(s) + Fe2O3(s)  2 Fe(s) + Al2O3(s)
Called the Thermite reaction.
Let’s just say it’s vigorous!
is oxidized
is reduced

32. Cu(s) + 2 Ag+(aq)  2 Ag(s) + Cu2+(aq)
Oxidation and Reduction reactions (redox)
Example 3:
Cu(s) + 2 Ag+(aq)  2 Ag(s) + Cu2+(aq)
is oxidized
is reduced

33. Zn(s) + 2 HCl(aq)  H2(g) + ZnCl2(aq)
Oxidation and Reduction reactions (redox)
Example 4:
Zn(s) + 2 HCl(aq)  H2(g) + ZnCl2(aq)
Zn(s) + 2 H+(aq)  H2(g) + Zn2+(aq)
is oxidized
is reduced
Note: this reaction also shows the fourth driving force of a reaction, namely, the formation of a gas.

34. Practice: 2 Mg(s) + O2(g)  2 MgO(s)
Oxidation and Reduction reactions (redox)
Practice:
2 Mg(s) + O2(g)  2 MgO(s)

35. Classification of chemical reactions
Precipitation
Reactions
Oxidation-Reduction
Acid-Base
Combustions
Synthesis (combination)
(Reactants are elements.)
Decomposition (Analysis)
(Products are elements.)