1. Aqueous Chemistry

2. Recap To date, we have learned about:
Chemical elements and their classifications
Valence electron configurations and their effect on chemical properties and reactivity
Predicting ionic charges
Now, we will begin to learn about chemical reactions involving ionic compounds

3. Ionic Reactions
Simple chemical reactions can be classified as one of the following:
combination reactions
decomposition reactions
combustion reactions
single replacement reactions
double replacement reactions

4. Combination Reactions
In a combination reaction, multiple reactants combine to form a single product
The reaction may occur between two elements
Or between an element and a compound
Or between two compounds
3Li(s) + P(g)  Li3P(s)
Ca(s) + Cl2(g)  CaCl2(s)
MgO(s) + CO2(g)  MgCO3 (s)

5. Decomposition Reactions
2HgO(s) 2Hg(l) + O2(g) 2KClO3(s) 2KCl(s) + 3O2(g)

6. Combustion Reactions
Combustion reactions are reactions that consume O2(g) as a reactant and produce oxide compounds as products. These reactions release a lot of heat. Fires are the result of combustion reactions.
Ex. Metal Oxide formation
2Ca(s) + O2(g)  2CaO(s)
4Fe(s) + 3O2(g)  2Fe2O3 (s)
When hydrocarbons (CxHy) and carbohydrates (CxHyOx) undergo combustion, the products are always carbon dioxide and water.
C6H12O6(s) + 6O2(g)  6CO2(g) + 6H2O (L)

7. Single Replacement Reactions
In a single replacement reaction, a free element replaces a bound ion/element.
When the reaction involves metals, it can also be referred to as a transmetallation reaction.
Zn(s) + 2AgCl (aq)  ZnCl2(aq) + 2Ag(s)

8. Zn(s) + 2AgCl (aq) ZnCl2(aq) + 2Ag(s)
Single Replacement
Transmetallation reactions occur because one metal is less stable in its elemental state (0 charge) than the other.
In the reaction below, Zn displaces Ag because Zn0 is less stable than Ag0:
Zn(s) + 2AgCl (aq) ZnCl2(aq) + 2Ag(s)
Less stable metals prefer to exist as ions instead of elements, especially in aqueous solution. These unstable elements will react and become highly stable ions.
In order to know what can displace what, an activity series can be used.

9. Group Work
As shown in the table, elemental Li (s) is the least stable metal, and is the most likely to react. It will displace any metal ion. K (s) will displace any metal ion except Li. And so on.
Predict the products.
Na (s) + ZnSO4(aq)
Al (s) + KNO3 (aq)
Na2SO4(aq) + Zn (s)
No reaction

10. Single Replacement Reactions Involving Acids
When a metal reacts with a binary acid (HX), the metal replaces the hydrogen ion to yield an ionic compound and hydrogen gas.
Zn(s) + 2HCl (aq) ZnCl2(aq) + H2(g)

11. Redox Reactions
Single replacement reactions are examples of red-ox (reduction-oxidation) reactions
A reduction reaction occurs when the oxidation state (charge) of an element/ion becomes more negative the course of a reaction (i.e. the species gains electrons)
In an oxidation process, the oxidation state of an element/ion becomes more positive during a reaction (i.e the species loses electrons)

12. Redox Reactions Consider the following single replacement reaction:
Zn(s) + Cu SO4 (aq) Zn SO4 (aq) + Cu (s)
On the reactant side, we have elemental Zn. The charge on any pure element is 0
On the product side, we have a Zn2+ ion. Since the charge of Zn has gone from 0 to 2+, Zn has undergone an oxidation. Zn loses 2 electrons. Where did they go???
On the product side, we have elemental Cu, so Cu has undergone a reduction from 2+ to 0 by taking 2 electrons from Zn.
On the reactant side, we have a Cu2+ ion.

13. Oxidizing and Reducing Agents
Zn(s) + Cu SO4 (aq) Zn SO4 (aq) + Cu (s)
We have identified the reduction and oxidation processes in the reaction above
O: Zn0  Zn2+ + 2e-
R: Cu2+ + 2e-  Cu0
RED-OX REACTIONS
Because Cu2+ gets reduced, it is the oxidizing agent (it oxidizes Zn).
Because Zn gets oxidized, it is the reducing agent (it reduces Cu2+)

14. Oxidizing and Reducing Agents
Zn(s) + Cu SO4 (aq) Zn SO4 (aq) + Cu (s)

15. (C.I.R.L) Rust Formation
Reduced
4Fe(s) + 3O2(g) 2Fe2O3(s)
Oxidized

16. Double Replacement Reactions
In a double replacement result,
two salts react, and the anions exchange places
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
ZnS(s) + 2HCl(aq) ZnCl2(aq) + H2S(g)

17. Examples Balance the following double replacement reactions
A. CaBr2 (aq) + K2CO3(aq)
B. NH4Cl (aq) + MgSO4 (aq)

18. Double Replacement Reactions Yield Physical Changes
An easy way to identify a chemical reaction is if there is a change in phase.
In a Precipitation Reaction, an insoluble (solid, does not dissolve) ionic product is formed.
In the figure to the left, Na2S (aq) and Cd(NO3)2 (aq) undergo double replacement to form CdS and NaNO3 .
CdS is insoluble

19. Net Ionic Equations
It is proper practice to use NET IONIC EQUATIONS when there is a change in phase
Ex. Na2S(aq) + Cd(NO3)2(aq) NaNO3(aq) + CdS(s)
Since we know that ionic solutions dissociate in water, we can rewrite the equation above in ionic form:
2Na+(aq) + S2-(aq) + Cd2+(aq) + 2NO3-(aq) CdS(s) + 2Na+(aq) + 2NO3-(aq)
The ions in red undergo a chemical reaction, as indicated by the change in phase. The remaining ions are called SPECTATOR IONS because they are not involved in the reaction in any way.

20. Net Ionic Equations
Na+(aq) + S2-(aq) + Cd2+(aq) + NO3-(aq) CdS(s) + Na+(aq) + NO3-(aq)
The spectators ions cancel out. The remaining reactants and products comprise the net ionic equation.
In order to write a net ionic equation, you must know which ionic compounds are insoluble. The solubility rules enable this.
Cd2+(aq) + S2-(aq) CdS(s)
NET IONIC EQUATION

21. Solubility Rules All group 1 and ammonium salts are water soluble!
All nitrates, acetates, and perchlorates are soluble
With the exception of all anions mentioned in #2, Ag, Pb, and Hg(I) salts are not soluble
With the exception of those cations mentioned in #1, carbonates, sulfides, oxides, and phosphates are not soluble
With the exception of Ca, Sr, and Ba, and those cations mentioned in #1, all hydroxides are not soluble
Most sulfates are soluble EXCEPT for those of Ca, Sr, Ba, and of those cations mentioned in #3.

22. Examples
Use solubility rules to predict the products of the following double replacement reactions. Write the net ionic reaction. If there is no reaction, write ‘no reaction’:
MgBr2 (aq) + K2CO3 (aq)
NaCH3COO (aq) + CaBr2 (aq)