Summary Chemistry: The Central Science, ISBN: 9781442559462 Introduction to chemistry

Aqueous Reactions

You can navigate to specific sections of this handout by clicking on the links below.

Defining Aqueous Reactions: pg. 1
Precipitation Reactions: pg. 1
Acid-Base Reactions: pg. 5
Oxidation-Reduction Reactions: pg. 6
Practice Problems: pg. 10


Defining Aqueous Reactions

Aqueous reactions are reactions that take place in water. To understand them, it is
important to understand how compounds behave in water. Some compounds are
electrolytes- they dissociate into separate ions in water. However, not all electrolytes
behave the same way. Some are strong electrolytes, and dissociate completely, so no
ions are left bonded together. Others are weak electrolytes- they only partly dissociate,
and many of their ions are still bonded to each other. Other substances, nonelectrolytes,
do not dissociate at all.

There are three main types of aqueous reactions: precipitation reactions, acid-base
reactions, and oxidation-reduction (or redox) reactions.

Precipitation Reactions

Precipitation reactions produce an insoluble product- the precipitate. They contain two
aqueous reactants, one aqueous product, and one solid product.

𝑷𝑷𝑷𝑷(𝑵𝑵𝑶𝑶𝟑𝟑 )𝟐𝟐 (𝒂𝒂𝒂𝒂) + 𝟐𝟐𝟐𝟐𝑰𝑰(𝒂𝒂𝒂𝒂) → 𝑷𝑷𝑷𝑷𝑰𝑰𝟐𝟐 (𝒔𝒔) + 𝟐𝟐𝟐𝟐𝟐𝟐𝑶𝑶𝟑𝟑 (𝒂𝒂𝒂𝒂) ∗
0F




In this reaction, two soluble products, Pb(NO3)2 and KI, combine to form one soluble
product, KNO3, and one insoluble product, PbI2. This is a precipitation reaction, and PbI2
is the precipitate.


∗
In chemical equations, certain abbreviations are used to indicate the state of the substances involved. The
abbreviations are as follows: s = solid; l = liquid; g = gaseous; aq = aqueous, or soluble in water.
Provided by Aqueous Reactions
The Academic Center for Excellence 1 Updated February 2020

, Determining the Products of a Precipitation Reaction

To determine the products of a precipitation reaction, reverse the cation-anion pairs. **
For example, at the beginning of the above reaction, lead is bonded to nitrate, and
potassium is bonded to iodine. The products are these pairs reversed- lead with iodine,
and potassium with nitrate. Precipitation reactions follow this formula:

𝑨𝑨𝑨𝑨 + 𝑩𝑩𝑩𝑩 → 𝑨𝑨𝑨𝑨 + 𝑩𝑩𝑩𝑩
The products are just the cation-anion pairs reversed, or the “outies” (A and Y joined) and
the “innies” (B and X joined).

Determining Whether or Not a Reaction is a Precipitation Reaction

Once you know the products of a reaction, you can use the solubility rules to see if you
have an insoluble product, and thus, a precipitation reaction.

Solubility Rules:

Soluble: Exceptions:
All ionic compounds
containing:
1. Alkali metals (group 1A) 1. None
2. Ammonium (NH4+) 2. None
3. Nitrate (NO3-) 3. None
4. Acetate (C2H3O2-) 4. None
5. Chloride (Cl-) 5. AgCl, PbCl2, Hg2Cl2, Cul2
6. Bromide (Br-) 6. AgBr, PbBr2, Hg2Br2, CuBr2
7. Iodide (I-) 7. AgI, PbI2, Hg2I2, CuI2
8. Sulfate (SO42-) 8. 8. SrSO4, BaSO4, Hg2SO4, PbSO4, CaSO4

Insoluble: Exceptions:
Compounds containing:
1. S2- 1. When bonded to ammonium, alkali metals,
2. CO32- Ca2+, Sr2+, or Ba2+
3. PO43- 2. When bonded to ammonium or alkalis
4. OH- 3. Same as above


**
If you need help determining the formulas for these new ionic compounds from the ions, look at the
Academic Center for Excellence’s handout, “Naming Compounds.”
Provided by Aqueous Reactions
The Academic Center for Excellence 2 Updated February 2020