1. Reactions in Aqueous Solutions
Chemistry B2A
Chapter 7
Reactions in Aqueous Solutions

2. Aqueous solution: solvent is water
Reactions in Aqueous Solutions
Ionic compounds
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.
Ions Hydrated by H2O
Hydration

9. 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).
Ionic compounds = Salts

10. All nitrates (NO3-) and acetate (CH3COO-) are soluble in water.
Ionic Compounds
All nitrates (NO3-) and acetate (CH3COO-) are soluble in water.
Most salts of Na+, K+, and NH4+ are soluble in water.
Most chlorides (Cl-) and sulfates (SO42-) are soluble in water.
(except AgCl, PbCl2, BaSO4, CaSO4, PbSO4)
Most carbonates (CO32-), phosphates (PO43-), Sulfide (S2-),
and hydroxides (OH-) are insoluble in water.
(except NaOH, KOH, Ba(OH)2, Ca(OH)2, and NH4OH)

11. 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).

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

13. 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-

14. Aqueous Solution (ionic compounds)KI
Pb(NO3)2 K+ I-
Pb2+
NO3-
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)

15. 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

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

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

18. 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)

19. 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.
produces more H+ and OH-
HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq)
NaOH(aq) + H2O(l) Na+(aq) + OH-(aq)

20. Acid-Base Reactions Neutralization
A strong acid and a strong base react together to produce a salt and water.
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.

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

22. Metal + Nonmetal : Transfer of electrons
Oxidation and Reduction reactions (redox) e-
2Na(s) + Cl2(g) NaCl(s)
Na → Na+ + e-
Cl + e- → Cl-
Metal + Nonmetal : Transfer of electrons
Oxidation and Reduction reactions (redox)

23. 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)

24. 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

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