Chemical Reactions

         The number of possible reactions in inorganic chemistry is enormous.  Fortunately, many of them fall into one of the following three categories: acid base, reduction-oxidation and precipitation.  (Some reactions do not fit any of these categories.)  During this experiment you will be performing reactions from each.  Look for evidence of a reaction. Evidence that a reaction has occurred could include a color change; bubbling, a new smell, production of a solid, or heat.

 

Reduction-Oxidation (Redox)

The word “redox” is the combination of the two terms, reduction and oxidation.  Reduction is gain of electrons, and oxidation is loss of electrons.  In redox reactions, electrons are transferred.  The number of electrons gained by the substance being reduced must equal the number of electrons lost by the substance being oxidized.  The simplest type of redox reaction is when elements combine to make a compound.  The reaction:  2Mg +  O2    ®  2MgO is a redox reaction.  Two electrons are transferred from the neutral magnesium atom to the oxygen gas to form an ionic compound with the magnesium cation and the oxide anion.

 

Acid / base

The simplest type of acid /base reactions occurs when H+(aq) +  OH —(aq) ®  H2O(l).  A better definition of acid/base reaction is the transfer of a proton.  Heat is also a product of many acid / base neutralizations.  These are a few examples of acid/base reactions:

 

HCl(aq)  +  KOH(aq)  ®  KCl(aq)  +  H2O(l)

 

NH4Cl (aq)  +  KOH(aq)  ®  NH4OH(aq)  +  KCl(aq)

NH4OH(aq) is unstable and decomposes to NH3(g) + H2O(l)

 

2HNO3(aq)  +  Na2CO3(aq)  ®  H2CO3(aq)  +  2NaNO3(aq)

H2CO3(aq) is unstable and decomposes to CO2 (g) + H2O(l)

 

Precipitation

Precipitation reactions occur when two soluble ionic compounds react to form an insoluble ionic compound.  The solubility rules are used to predict which ionic compounds are soluble in water.

 

Solubility Rules:

1.  All ionic compounds containing Group I metals,  NO3- and NH4+ are soluble in water.

2.  Ionic compounds containing Cl-, Br-  and I- are soluble except for those of Ag+,  Hg22+ andPb2+. 

3.  SO42- compounds tend to be soluble.  Important exceptions are CaSO4, BaSO4,  and PbSO4.

4.  CO32- , PO43-, OH-,  CrO42- are usually insoluble.

These are a few examples of precipitation reactions:

 

NaCl(aq)  +  AgNO3(aq)  ®  NaNO3(aq)  +  AgCl(s)

 

CaCl2(aq)  +  K2SO4(aq)  ®  CaSO4(s)  +  2KCl(aq)

 

Here silver chloride and strontium sulfate are the solid precipitates that are formed.  (In reality, tiny particles of the solid are made and the solution just looks cloudy.)

 

In summary, the evidence that a chemist would use to determine if a reaction has taken place could include:

1.  The formation of a precipitate.

2.  The formation of a gas.

3.  A dramatic color change.

4.  The production of heat.

 

Spill/Disposal: C, for all procedures.

Disposal:

All chemicals reagents & products (liquid and solid) of these reactions must be disposed of in the supplied Hazardous Waste container. Use the supplied funnel to make sure all waste makes it into the container. If the solid precipitate needs to be removed from the bottom of the test tube, please rinse it out into the Hazardous Waste container using a deionized water bottle. Make sure all precipitate is removed into the HW container. Metals should also be put into the HW container. When the HW container is not in use the cap must be put back on.

 

Wash your hands thoroughly when you leave the lab.

 

 

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