1. Reactions in Aqueous Solutions
Chapter 8
Reactions in Aqueous Solutions

2. Will the reaction occur?
Driving forces
Forming a solid (“precipitate)
Transfer of electrons
Forming water
Forming a gas
Will the reaction occur? Yes, if one of the above driving forces happens.

3. Dissolving ions
A strong electrolyte completely separates into ions when it is mixed with water.
Example: NaCl
Complete the equation of silver nitrate dissolving in water:
AgNO3(s) 
NaCl(S)
Na+(aq) + Cl-(aq)
H2O

4. Precipitates
If you mix NaCl(aq) and AgNO3 (aq) , what possible products could form?
NaCl(aq) and AgNO3 (aq)  ?
The anions (Cl- and NO3-)change places.
NaCl(aq) and AgNO3 (aq)  NaNO3(aq) + AgCl(s)
AgCl is a precipitate, so write an “(s)”
A precipitate is an insoluble solid. Insoluble = it cannot dissolve in water.
What is the driving force in this reaction?

5. Double replacement (continued)
A double replacement reaction happens when a precipitate forms.
Reactants must be aqueous (dissolved in water)
Example: NaCl dissolved would be shown as NaCl(aq)
If something is “slightly soluble” it will also make a precipitate, so slightly soluble is almost the same as insoluble. Solubility chart on page 245 will show you when a precipitate will form.

6. Example Example: KNO3 Soluble or insoluble?
Rule #2: K+ salts are usually soluble.
Answer: Soluble (No precipitate)

7. Will this double replacement actually happen??
Practice: Will this form a reaction?
Write the formulas of the possible products (Inside and outside)
Use the solubility chart to determine if any of the products are INSOLUBLE.
If one or both products are insoluble, a chemical reaction will happen.

8. Examples:
KNO3 and BaCl2
KOH and Fe(NO3)3
Na2SO4 and Pb(NO3)2

9. Annimation: http://www. mhhe

10. Double Replacement
You should be able to write three types of chemical equations for double replacement:
1. Molecular equation
2. Complete ionic equation
3. Net ionic equation

11. Double Replacement
The molecular equation shows the complete formulas of all reactants and products
NaCl(aq) + AgNO3 (aq)  NaNO3(aq) + AgCl(s)
The complete ionic equation shows all strong electrolytes (aq) as ions.
Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)Na+(aq) + NO3-(aq + AgCl(s)

12. Double Replacement
The net ionic equation shows only the chemicals participating in the reaction.
Steps:
Remove the “spectator ions”
Spectator ions are the same on the reactant side and the product side (Na+ and NO3-)
Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)Na+(aq) + NO3-(aq + AgCl(s)
Net ionic equation:
Cl-(aq) + Ag+(aq)  AgCl(s)

13. Acid-Base Reactions and Oxidation-Reduction Reactions
8.2
Acid-Base Reactions and
Oxidation-Reduction Reactions

14. Arrhenius Acids and Bases
An Arrhenius Acid is a substance that produces H+ ions when dissolved in water.
A “strong acid” is an acid that is a strong electrolyte. It completely separates into H+ and the anion.
HCl  H+ + Cl-
Strong acids: HCl, HNO3 and H2SO4

15. Arrhenius Acids and Bases
An Arrhenius Base produces OH ions when dissolved in water.
A strong base completely separates into a metal cation and OH-
NaOH  Na+ + OH-

16. Acid-Base Reaction
Write the molecular equation, complete ionic equation and net ionic equation for the reaction of hydrochloric acid and sodium hydroxide.
Molecular equation
HCl + NaOH  H2O + NaCl
Complete ionic equation
H+ +Cl- + Na+ + OH-  H2O(l) + Na+ + Cl-
Net ionic equation
H+ +OH-  H2O(l)

17. Acid-Base Reaction
When an acid and base are mixed, the products are always water and a salt.
How do you know a reaction happened? The solution will be hot.
An acid-base reaction is the reaction of H+ and OH-

18. Oxidation Reduction
In an oxidation-reduction reaction, electrons move from one chemical to another.
Common reactions:
A metal and a nonmetal react
Reactions between nonmetals where O2 is a reactant or product.

19. Oxidation Reduction Ca(s) + Cl2(g)  CaCl2(s)
2 electrons
Ca(s) + Cl2(g)  CaCl2(s)
Which chemical is losing electrons? How many electrons?
Ca loses two electrons
Which chemical is gaining electrons? How many electrons?
Cl gains one electron

20. Oxidation Reduction This happens in two steps: Ca Ca2+ + 2e-
Cl + e-  Cl-
Draw a picture of this reaction:
Mg(s) + CuCl2(s)  Cu(s) + MgCl2(s)
Which chemical loses electrons? How many?
Which chemical gains electrons? How many?

21. 8.3 Types of reactions & “How do we know IF it will happen?”

22. Classifying reactions
Looking at a chemical equation, be able to classify it…
Based on driving force:
1. Precipitation reactions
2. Oxidation-reduction reactions
3. Acid-base reactions
Types of oxidation-reduction reactions:
1. Combustion reactions
2. Synthesis reactions
3. Decomposition reactions
4. Single Replacement

23. Double Replacement AX+BY → AY +BX
Each anion changes places with the cation.
Example: sodium sulfate + copper (II) chloride

24. Single Replacement:
A+BX → AX +B
A = a metal or group 7 element.
B = metal, group 7 element or hydrogen
X = anion
A replaces B in the BX compound.
Example:
Zn(s) +2HCl(aq)  H2(g) + ZnCl2(aq)

25. Synthesis Reactions
Synthesis– 2 or more substances combine to form one, bigger molecule.
General formula…
Example: Combustion of Ca
Ca + O2  CaO

26. Decomposition Reactions
Decomposition– one substance splits to form several smaller molecules/atoms.
General formula…
Example: Breaking water molecules.
What equation will it have? (it’s a reaction that results in Hydrogen gas, H2, and Oxygen,O2)
Usually requires energy input (heat, electricity, etc), because we are breaking bonds.

27. Combustion Reactions

28. Combustion Reactions
Combustion – a substance combines with oxygen. When they react they release energy, water vapor and carbon dioxide.
Will need to balance these
Ex: C2H5OH + O2  CO2 + H2O

29. Classifying reactions
Practice: Classify this reaction in as many ways as possible
2Ca + O2  2CaO
This is classified as a synthesis and combustion. It is also an oxidation-reduction reaction.