Download Types of ReacUons

Types of ReacUons
Chemistry deals with matter.
One class
ification of matter has two subheadings:
heterogeneous. Almost everything we hand
le in ordinary activities falls into the lattehomogeneous and
r category, but we
must spend most of our time studying homogen
chance of coming to understand in our early studeous matter since this is the kind that we have some
categories: pure substances and solutions. The ies. Homogeneous matter can he subdivided into two
elements and compounds. There are two kind former of these can also he divided into two categories:
s of elements, at least for our prelimina
ry considerations. it
is useful to be able to quickly put the elements
metals and nonmetals. The simplest way that we encounter into one or the other of these categories:
I know of making this classification depe
nds on name and
on appearance. In the early 1800’s. chemists
separated elements. The new metals were give became systematic in the names they gave to newly
n
nam
es ending in -ium, and so one can tell
elements are metals as soon as one hears or
that many
systematic procedure.) Elements known befo reads their names. (A few mistakes were made in this
re the 1800’s do not have systematic nam
the elements that most of us have become fami
ing,
liar with, We know that some of these but they are
metals because they have what we call meta
elements are
llic luster. Elements that lack metallic
luster and that have
names ending in suffixes other than -lum (or -urn)
are non metals.
A useful classification of compounds is the follo
wing: (The definitions are reasonable for
such as the one in which we live.)
a water world
1.
Acids compounds with formulas that begin
with H
HOl, HNO
3
2. Bases- compounds with formulas that end with
-OH
NaOH, KOH
3. Metal oxides binary compounds of a meta
l and oxygen
CaO
4. Nonmetal oxides binary compounds of
a nonmetal and oxygen
2
SO
5. Salts compounds of metals that are NOT
bases or metal oxides
NaCl, MgS, 4
ZnSO
6. Other compounds (Most compounds belo
ng here) OH
, NH
4
3
These are intended to be definitions that you
categories, think of some properties that fit the can use early in the study of chemistry. For each of the
mem
some properties that you can expect a particular bers of the category. You can thus begin to think of
into one of the categories of compounds that you substance to have because the substance can be put
recognize.
-
-
-
-
-
Three of these categories need some elaboratio
n
I. AC1DS
The number of ‘frequently” encountered strong
as ions rather than as molecules) is small and acids (acids that are present in solution very largely
one should know them by name and form
HBr. HI, HNO
ula: HOl,
, 4
3
S0 and 4
2
H
,
HCIO As a first approximation. all other
.
acids may he considered
weak (present in solution largely as molecules
) unless and until the you learn otherwis
II. BASES
e.
The number of strong bases (bases that are
present in solution largely as metal ions
ions rather than as molecules) is not large and
and hydroxide
these substances should also be learned:
NaOH. KOH. 2
L1OH.
Ca(OH) 2
,
Sr(OH) 2
,
Ba(OH) All other bases should be cons
.
idered weak unless and
until one learns otherwise.
HI. SALTS
The salts that are soluble in water include all of
ammonium cations and of nitrate and acetate the salts of lithium, sodium, potassium, and
anions. All chlorides are soluble exce
pt those of
silver, lead, and mercury(l) ions. All sulfates
are
and barium. All other salts should be considere soluble except those of lead, calcium, strontium,
d only slightly soluble unless and until
otherwise.
one learns
When you are representing a reaction that occu
as ions are the strong acids, the strong bases, rs in water solution the substances that should be written
and the soluble salts.
The reactions themselves can also be put into categ
category into which a reaction fits by studying the ories. A student who is able to decide about the
natu
to be able to predict oroducts of reactions that have re of the reactants is the student who is most ikely
not been learned.
A.
Reactions involving no changes in oxidation states
Metathetical reactions
I.
reactions can be expected
These reactions start with two reactants and produce two products. Such
salt, and water (for
base,
acid,
unds:
compo
of
types
these
from
come
ts
when the two reactan
positive parts of
the
ging
exchan
ed
by
predict
convenience wrftten as HOH). The products can be
unds.
compo
of
types
same
the
from
are
ts
produc
the two reactants. The
HOt
+
NaOH
—
NaCI
+
HOH
of the substances should be
One then uses the information previously presented to decide which
is a soluble salt, and so all
Nritten as ions: HOt is a strong acid. NaOH is a strong base. and NaCI
are not appropriately
change
not
do
that
nces
substa
three should he written as ions. Since
becomes
above
n
reactio
the
n
equatio
al
chemic
or
n
a
reactio
al
chemic
in
a
represented
H+OH- HOH
Some combination reactions related to metathetical reactions
II,
reactants indicated with
These reactions produce a single product predictable from the types of the
each of the examples below.
a)
a base, the metal in the same oxidation state as in the oxide
Metal oxide + water
CeO(s) + HOH Ca(OH)—
Then revised to
2 + 0H
OaO(s) + HOH — Ca
in the oxide
Nonmetal oxide + water an acid, the nonmetal in the same oxidation slate as
S0 (no strong acid or strong base or soluble salt, so no ions)
2
H
2 +HOH —* 3
SO
b)
where it has the
Metal oxide + nonmetal oxide -+ salt, with the nonmetal appearing in a radical
same oxidation state as in the oxide
3 (no strong acid or strong base or soluble salt, so no ions>
2 —* OaSO
CaO + SO
c)
Ill.
in the
Some decomposition reactions (the reverse of the combination reactions
of
each
in
ts
produc
two
are
there
and
t
reactan
category just above) There is one
these reactions.
a)
Base — metal oxide + water
) — CaO(s) + HOH
s)
Ca(OH
(
2
b)
Acid containing oxygen — nonmetal oxide
r42003 - 002 ÷ HOH
0)
+
water
Salt containing oxygen —. metal oxide ÷ nonmetal oxide
(s) — CaD(s) + 002
3
OaCO
Hydrolysis reactions
IV.
ns. In addition to
The reactions of salts with water can usually be handled as metathetical reactio
halides, react
tallic
nonme
larly
particu
,
6
ry
above)
(catego
unds
compo
other
of
the
salts, some
the more (or
with
water
the
from
H
ing
the
combin
with water. If the water is written as HOH,
for one of the
a
formul
the
gives
und
usually
compo
other
the
from
t
elemen
e
negativ
most) electro
a for this second
products. The other product contains the remaining elements. The formul ties.
proper
acidic
its
clear
make
to
order
in
ged
rearran
be
to
needs
comDound usually
PC[
±
HOH
-
HOt
+
HQ
3
P
2
H
P0 or, more accurately, to )
3
[H
3 (rearranged to ]
P(OH)
V.
Reactions of coordination compounds and ions
The number of different reactions falling into this catego
chemistry courses is rarely large. The ligands most freque ry that are considered in general
ntly considered, attached to a central
atom that is usually a metal ion, are the ammonia molecu
le and the hydroxide ion. Writing the
reactions that form the coordination ions requires:
1.
recognition of the possibility of the formation of
the coordination ion when an
ample source of the ligands is available
2.
knowledge of the metal ions likely to form coordination
ions, of what the common
ligands are, and of the likely number of the ligands
to be attached to the central
ion.
It may be useful to keep in mind that the number of ligand
sometimes twice the oxidation number of the central metal. s attached to a central metal ion is
Ag(NH,) 4
,
t
2
Zn(OH)
2
The breakup of these coordination ions is frequently achiev
ed by adding an acid. The products
are the metal ion and the species formed when hydrogen
ions from the acid react with the ligand
4 from NH
(NH
3 and HOH from 0H).
Al(OH) + H
4
t -+ Al
3t + HOH
VI.
Reactions based on nonwater definitions of acids
and bases
Both Brönsted and Lewis definitions of acids and base
s can be illustrated by the writing of
equations. Recognizing that an acid and a base are the
definitions and knowing how they react is the best approach reactants according to one of the
BrOnsted reactions involve the transfer of a proton. Lewis for the writing of such reactions.
reactions involve the formation of a
coordinate covalent bond.
8.
Reactions involving changes in oxidation states
1.
Some combination reactions
Two elements react to form a binary compound of
electropositive element is written first and valence relatio the two. The symbol for the more
ns are used to obtain the formula.
II.
Reactions between an oxidizer and a reducer
Products from such reactions can usually be predicted from
oxidizers and reducers. A useful list of such reagents follow knowledge about a limited number of
s.
Important oxidizers
Mn0 in acid solution
4
2 in add solution
Mn0
Mn04 in neutral or basic solution
C
1
7
0
2
n
r acid solution
H NO
, concentrated
3
3 dilute
HNO
S0 hot, concentrated
2
H
4
Metal-ic ions
Free halogens
Mn
2
2t
Mn
2
Mn0
Cr3t.
NO
2
NO
2
SO
metal-ous ions
halide ions
NaOH
or
4
HCIO
mportant reducers
Formed in the reaction
Formed in the reaction
Halide ions
Free metals
Sulfite ions (or S02)
Nitrite ions
Free halogens, dil. basic soin.
Free halogens, conc,basic soin.
Metal-ous ions
Free halogen
Metal ions
Sulfate ions
Nitrate ions
Hypohalite ions
Halate ions
Metal-ic ions
To predict products of a reaction that fits into this category, a student looks at the reagents given
in the question to see if there are available both an oxidizer and a reducer. This step may involve
recognizing the ions that are pairs of the compounds listed as the reagents. Then one can write
the appropriate products from the oxidizer and the reducer present. One keeps in mind the acid
or the base present if an acid or a base is listed as a reactant. In acidic solutions, any metal ions
formed can combine with the anion of the acid to form salts. Keeping in mind the solubilities of
the salts, one can then predict whether the products include a precipitated salt or whether ions
are the appropriate products. In basic solutions, any anions present can combine with the cation
or the base present to form salts. Again, the solubility considerations indicate whether formulas of
salts or of ions should be written as products. (In case the requirement is that molecular
equations equations with no ions are to be written, the preceding sentences indicate how the
molecular formulas can be developed.)
-
3.
-
Displacement reactions
The reactants are an element and a compound. A more reactive element (in the free state) can
displace a less reactive element with similar properties from a compound. The products are the
ess reactive element and a compound containing the more reactive element. For example, zinc
metal reacts with tin(Il) sulfate to form zinc sulfate and metallic tin, and free chlorine reacts with
sodium bromide to form sodium chloride and free bromine. A list of reduction potentials can be
consulted to determine which of the elements present is the more reactive.
C. Organic reactions
Predicting the products of the limited number of organic reactions appropriate for the Advanced
Placement Chemistry Examination requires knowing the formula that is characteristic for each of the
2 is such a formula for the
very important homologous series of organic compounds. For example, CH+
alkanes. Such formulas for the other major hydrocarbon series and for alcohols, acids, ethers, esters
and amines (probably the reactants to be expected) and the structural formulas for a typical compound
or two from each series are the facts that students should have to be able to write these reactions. The
more common types of reactions inciude the following.
Oxidation
I.
Complete oxidation of any organic compound containing no elements but carbon, hydrogen, and
oxygen yields carbon dioxide and water. Partial oxidation products depend on the reactant and
so are not generally predictable.
Addition
I!.
These reactions, which form only one product, are the characteristic reactions of the hydrocarbon
series whose members have double or triple bonds.
Substitution
Ill.
These reactions give two products. Any hydrocarbon can show this type of reaction. It is the
characteristic reaction for the hydrocarbon series that have no multiple bonds. A hydrogen atom
eaves the organic compound and is bonded to an atom or atoms from the inorganic reactant.
The place of the hydrogen, in the organic compound, is taken by an atom, or radical, from the
inorganic reactant.
Esterfication
IV.
acid reacts with an alcohol to form an ester and water.
organic
An
SaponificatIon.
V.
An ester reacts with a strong base to form a salt, which may be a soap, and an alcohol.