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Writing Chemical Reactions: An In-Depth Look

Remember 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 correct charge).

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:

  1. Neutralization of an acid or a base
    Look for both strong and weak acids/bases.
    1. Equal molar amounts of potassium hydroxide and nitric acid are mixed.
      Answer: OH- + H+ --> H2O
  2. Formation of a strong acid or base
    1. Dilute sulfuric acid is added to a solution of potassium fluoride
      Answer: H+ + F- --> HF
  3. Double or Single Replacement Reacions
    These are perhaps the easiest to do. Just remember your solubility rules!
    1. A solution of ammonium sulfide is added to a solution of magnesium iodide.
      Answer: Mg2+ + S2- ---> MgS
    2. A solution of barium chloride is mixed with a solution of silver (I) sulfate.
      Answer: Ba2+ + Cl- + Ag+ + SO42- ---> BaSO4 + AgCl
  4. Solid metals placed in neutral solutions
    When a solid metal is placed in a neutral solution, a simple redox reaction usually occurs.
    1. A piece of zinc is placed into a solution of silver nitrate.
      Answer: Zn + Ag+ ---> Zn2+ + Ag
  5. Solid metals placed in acidic solutions
    When a solid metal is placed into an acidic solution, water and an oxide gas will form
    1. A piece of silver is placed into dilute nitric acid.
      Answer: Ag + H+ + NO3- ---> Ag+ + NO + H2O
  6. 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.
    1. Methane is burned in air.
      Answer: CH4 + O2 ---> CO2 + H2O
  7. 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!
    1. Lithium hydride is added to water.
      Answer: LiH + H2O ---> Li+ + OH- + H2
  8. A metal oxide and water will form just a base
    Again, remember your -OH solubility rules!
    1. Calcium oxide is put into water
      Answer: CaO + H2O ----> Ca(OH)2
  9. A nonmetal oxide with water will produce just an acid
    Strong acids dissociate, remember....
    1. Sulfutr dioxide is bubbled through water
      Answer: SO2 + H2O ---> H2SO3
  10. 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.


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