HINTS WHEN TRYING TO PREDICT
PRODUCTS OF CHEMICAL REACTIONS
- First look for obvious precipitation reactions - two
solutions mixed together with one of the salts containing an ion that quite often is
insoluble (such as Fe, Ba, Ag, Hg, Pb).
- Then looks for other possible precipitation reactions in which one of
the above ions is present in an aqueous salt but the other solution is an acid which might
provide an anion (like sulfate or chloride) that could precipitate with the above ion.
- Next identify easy acid/base reactions - in which you have an easily
identifiable acid (nitric, sulfuric, hydrochloric) and a hydroxide salt as the base.
- Now look for easily identifiable redox reactions in which O2
is a reactant and probably an oxidizing agent and the other reagent is a hydrocarbon, a
carbohydrate, a metal, etc. The hydrocarbon and carbohydrate will react to form carbon
dioxide and water, and the metal will react to form oxides.
- Finally look for other redox reactions, such as when you have a pure
metal interacting with a ion of another metal or an acid which could dissolve it to form a
salt of the metal.
TOP TEN LIST
MOST COMMON STUDENT MISTAKES
WHEN PREDICTING AND WRITING REACTION PRODUCTS IN GENERAL CHEMISTRY
- Writing H(OH) (aq) as a product of the reaction of an acid and base.
Hopefully, you realized that this product is H2O(l).
- Writing the incorrect molecular formula for a product. For example
aluminum nitrate is often written as AlNO3, not correctly as Al(NO3)3.
To write this correctly, you need to know either that
- NO3 has a negative one charge
(predictable if you know the formula for nitric acid - HNO3 - and
realize that nitrate, the negative ion produced when a base abstracts a
proton from the neutral acid , must be NO3-,
- Al ion has a charge of 3+ in combined with
a nonmetal in a salt.
- Not writing the
simplest formula for a product. Fox example, sodium
nitrate is not Na2(NO3)2, but rather NaNO3.
- Leaving off the (aq), (s), (l), or (g) after the product. How can you
or I tell if you have a precipitation reaction if one of the products doesn't have an (s)
- Not balancing the equations.
- Not recognizing that if you have an acid as
one reactant and a salt of the form Mx(OH)y as another reactant,
then the reaction is an acid/base reaction.
- Automatically assuming that if you have a strong acid in the
reactants that the reaction has to be an acid/base reaction. This is only true if you have
a base like OH- in the reactants. Acids can also act
as oxidizing agents (for example when they dissolve pure metals) or
"precipitating agents" when they provide an anion which forms a precipitate
with a metal cation.
- Recognize the that when -OH is covalently
linked to a C, a nonmetal, IT IS NOT A BASE. In fact it might be an
acid if it is part of an oxyacid like nitric acid (HNO3), a
strong acid, or acetic acid (CH3COOH), a weak acid. C-OH is
found often in organic carbon compounds, when it is called an alcohol.
- Assuming a reaction is a redox reaction without determining the
oxidation number for each atom. (Obviously this is not necessary when the reaction is a
combustion reaction using molecular oxygen, O2.
- Not knowing the charge on ions and not putting () around certain ions when needed. For example iron
hydroxide is Fe(OH)3 not FeOH3.