|Writing Chemical Reactions: An In-Depth Look
that when you do this section, you do not have to name the state of matter or even balance
the reaction! You just have to list the net ionic reaction (yes, this includes putting the
When doing this section, you should know your solubility rules. Knowing them is half
the battle. If an ionic compound dissociates in water, it should be listed correctly.
Those substances which are marginally soluble (Calcium hydroxide) can be written either as
two ions or as one compound).
This is an easy section if you know what you're looking for. All the reactions given
will follow these general reactions mechanisms:
- Neutralization of an acid or a base
Look for both strong and weak acids/bases.
- Equal molar amounts of potassium hydroxide and nitric acid are mixed.
Answer: OH- + H+ --> H2O
- Formation of a strong acid or base
- Dilute sulfuric acid is added to a solution of potassium fluoride
Answer: H+ + F- --> HF
- Double or Single Replacement Reacions
These are perhaps the easiest to do. Just remember your solubility rules!
- A solution of ammonium sulfide is added to a solution of magnesium iodide.
Answer: Mg2+ + S2- ---> MgS
- A solution of barium chloride is mixed with a solution of silver (I) sulfate.
Answer: Ba2+ + Cl- + Ag+ + SO42-
---> BaSO4 + AgCl
- Solid metals placed in neutral solutions
When a solid metal is placed in a neutral solution, a simple redox reaction
- A piece of zinc is placed into a solution of silver nitrate.
Answer: Zn + Ag+ ---> Zn2+ + Ag
- Solid metals placed in acidic solutions
When a solid metal is placed into an acidic solution, water and an oxide gas will
- A piece of silver is placed into dilute nitric acid.
Answer: Ag + H+ + NO3- ---> Ag+ + NO + H2O
- An organic chemistry problem (usually combustion)
When a hydrocarbon (or a similiar compound) is combusted with O2, it
goes to the CO2 and H2O. The H may be replaced with a different
element (possibly sulfur) and the C may be replaced with B (boron). Note that ALL organic
compounds on the AP test will go to carbon dioxide and water.
- Methane is burned in air.
Answer: CH4 + O2 ---> CO2 + H2O
- Pure metal/metal hydride and water
A pure metal/metal hydride and water will form a base and hydrogen gas. Remember
your OH- solubility rules!
- Lithium hydride is added to water.
Answer: LiH + H2O ---> Li+ + OH- + H2
- A metal oxide and water will form just a base
Again, remember your -OH solubility rules!
- Calcium oxide is put into water
Answer: CaO + H2O ----> Ca(OH)2
- A nonmetal oxide with water will produce just an acid
Strong acids dissociate, remember....
- Sulfutr dioxide is bubbled through water
Answer: SO2 + H2O ---> H2SO3
- The formation of a complex ion
The only way to prepare for these is to memorize all the complex ions and their
coordination number. I don't remember any, so I can't write a good example right now. :(
For this section, practice makes perfect.