chapter 5 gui sinh vien
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Chapter 5. Some types of chemical reactions Objectives:
Describe the periodic table and some of the relationships that it summarizes
Recognize and descibe nonelectrolytes, strong and weak electrolytes.
Recognize and classify acids, bases, and salts
Assign oxidation number to elements, when they are free, in compounds, or in ions
Objectves (continue) Name and write formulas for
common binary and ternary inorganic compounds
Recognize oxidation-reduction reactions and identify which species are oxidized, reduced, oxidizing agents, and reducing agents
Recognize and describe classes of reactions
The periodic table: metals, nonmetals, and metalloids
Help predict and explain the properties of elements (function of number of protons and electrons)
Electrons in the outermost shell are called valance electrons (valance shell) chemical bonding
Atomic weight (orginated from mass number)
Periodic table Atomic number of an element is
the number of protons in the nucleus of its atoms
Elements are arranged in the periodic table in order of increasing atomic number.
The properties of the elements are periodic functions of their atomic number
Metallic character decrease
Increase
Transition metals
Noble gases
The vertical colums are referred to as groups or families
The horizontal rows are called periods
Elements in a group have similar chemical and physical properties, and those within a period have properties that change progressively across the table.
Names of some common groups The Group IA elements (except H)
are referred to as alkaline metals The Group IIA elements are called
alkaline earth metals The Group VIIA elements are called
halogens (“salt formers”) The Group VIIIA elements are
called noble (rare) gases
Some physical properties of metals and nonmetals
Metals High EC that
decreases with increasing temperature
High thermal conductivity
Metallic gray or silver luster
Almost all are solids Malleable Ductile
Nonmetals Poor electrical
conductivity (except C in graphite)
Good heat insulator No metallic luster Solids, liquids, or
gases Brittle in solid state Nonductile
Some chemical properties of metals and nonmetals
Metals Outermost shells
contain few electrons (usually 3 or fewer)
Form cations by losing electrons
Form ionic compounds with nonmetals
Solid state characterized by metallic bonding
Nonmetals Outermost shells
contain 4 or more electrons
Form anions by gaining elecrtons
Form ionic compounds with metals, and molecular (covalent) other compounds with nonmetals
Covalently bonded molecules
Metalloids (semi-metals) show some properties that are characteristic of both metals and nonmetals
Example: B, Si, Ge, As, Te Many of the metalliods, such as Si, Ge, and
Sb act as semiconductors (for electronic curcuits). Semiconductor are insulators at lower temperatures but become conductors at higher temperatures.
Aqueous solutions Solutes that are water-soluble can
be classified as either electrolytes or nonelectrolytes
Electrolytes are substances whose aqueous solutions conduct electric current.
Aqueous solution of nonelectrolytes do not conduct electricity
Dissociation refers to the process in which a solid ionic compound, such as NaCl(s), separates into its ions in solution
Ionization refers to the process in which a molecular compound separates or reacts with water to form ions in solution (HCl (g))
Three major classes of solutes are strong electrolytes
(1) strong acids, (2) strong bases, and (3) most soluble salts
These compounds are completely or nearly completely ionized (or dissociated) in dilute aqueous solutions
An acid: a substance that produces hydrogen ions, H+, in aqueous solutions
A base: a substance that produces hydroxide ions, OH-, in aqueous solutions
A salt: is a compound that contains a cation other than H+ and anion other than hydroxide ion, OH-, or oxide ion, O2-
Some strong acids and their anions
Common strong acids HCl HBr HI HNO3
HClO4
HClO3
H2SO4
Anions of these acids Cl-
Br-
I-
NO3-
ClO4- :
ClO3-:
HSO4-
SO4-
Some common weak acids and their anions
Common weak acids HF CH3COOH HCN HNO2
H2CO3
H2SO3
H3PO4
Anions of these acids F-
CH3COO-
CN-
NO2-
HCO3-
CO32-
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Reversible reactions
Reactions that occur in both directions
Examples HCl no reversible reaction H+(aq) + CH3COO-(aq)
CH3COOH(aq)
Common strong bases Group IA
LiOH NaOH KOH RbOH CsOH
Group IIA
Ca(OH)2
Sr(OH)2
Ba(OH)2
Insoluble bases & weak bases
Isoluble bases: Cu(OH)2, Zn(OH)2, Fe(OH)2 and Fe(OH)3
Weak bases: NH3 and closely related N-containing compounds, the amines,
Reactions in aqueous solutions
Formula unit equations (stoichiometric calculation)
Total ionic equations Net ionic equations (show only the
species that react: essence of a chemical reaction)
AgNO3(aq) + Cu(s) Ag(s) + Cu(NO3)2 (aq)
[ ] [ ]
Oxidation number Many reactions that involve the transfer of
electrons from one species to another are called oxidation-reduction reactions (redox reactions)
We use oxidation numbers to keep track of electron transfers.
The oxidation number of an element in a simple binary ionic compound is the number of electrons gained or lost by an atom of that element when it forms the compound
Some rules for assigning oxidation numbers
H2, O2 (oxidation number is zero) Ca2+ (oxidation number is +2) NaCl (the sum of the oxidation
numbers of all atoms in a compound is zero)
SO42- (polyatomic ions) (the sum is -2)
F has an oxidation number of -1 in its compound
H has an oxidation number of +1 in compounds unless it is combined with metals (NaH, CaH2) its oxidation number is -1.
Oxygen usually has an oxidation number of -2 in its compounds (some exceptions: peroxides, H2O2 (-1); superoxides, KO2 (-1/2); OF2 (+1/2))
The position of the element in the periodic table helps to assign its oxidation number:
Example
Determine the oxidation number of N in the following species:
(a) N2O4, (b) NH3, (c)HNO3, (d) NO3-,
(e) N2
Naming some inorganic compounds
Naming binary compounds: binary compounds consist of two elements
Binary ionic compounds The cation is named first and the anion
second The oxidation number of the metal is
indicated by a Roman numeral (IUPAC) An older method, still in use, uses “-
ous” and “ic” suffixes to indicate lower and higher oxidation numbers, respectively. This system can distinguish between only two different oxidation numbers for a metal.
Examples
CuCl CuCl2 FeO FeBr3
Hg2Cl2 HgCl2
Binary molecular compounds
Using prefix system for both elements
The prefixes are: mono-, di-, tri-, tetra...
Examples N2O4, Cl2O7, CS2, SF4, SF6
Binary acids
HCl(g), (aq) HF(g), (aq) H2S(g), (aq) HCN(g), (aq)
Naming ternary acids and their salts
A ternary compound consists of 3 elements
Ternary acids (oxoacids) are compounds of hydrogen, oxygen and a nonmetal. Nonmetals that have more than one oxidation number form more than one ternary acid (Ex. H2SO4, H2SO3)
Formulas of some common “-ic” acid
Group IIIA: H3BO3 (boric acid) Group IVA: H2CO3 (carbonic acid), H4SiO4
(silicic acid) Group VA: HNO3 (nitric acid), H3PO4
(phosphoric acid), H3AsO4 (arsenic acid) Group VIA: H2SO4, H2SeO4 (selenic acis),
H6TeO6 (telluric acid) Group VIIA: HClO3 (chloric acid), HBrO3,
HIO3
In case one or more acidic hydrogen atoms remain
Use the word “hydrogen” or “dihydrogen” to show the number of
Example: Name the following compounds
NaHSO4, NaHSO3, KH2PO4, K2HPO4, NaHCO3
Name the followings
Oxidation number Name
HClO4 +7 per- HClO3 +5 chloric
acid HClO2 +3 chlorous HClO +1 hypo-
Naming ternary acids and their anions
Ternary acid perXXXic acid XXXic acid XXXous acidhypoXXXous acid
Anion perXXXate XXXate XXXite hypoXXXite
Decreasing oxidation number of central atom Decreasing number of oxygen
atoms on central atom
Classifying chemical reactions
1. Oxidation-reduction reactions2. Combination reactions3. Decomposition reactions4. Displacement reactions5. Metathesis reactions
Oxidation-reduction reaction
Oxidation is an increase in oxidation number and corresponds to the loss of electrons. Reduction is a decrease in oxidation number and corresponds to a gain of electrons.
Oxidation and reduction occur simultaneously. (In brief, the reaction is called redox reaction)
Ex: Fe(s) + O2(g) Fe2O3(s)
Oxidizing and reducing agents
Oxidizing1. Oxidize other
substances2. Contain atoms that
are reduced3. Gain electrons
Reducing1. Reduce other
substances2. Contain atoms that
are oxidized3. Lose electrons
ExampleFe(s) + Cl2 FeCl3
Redox reaction
Disproportionation reaction is a redox reaction in which the same element is oxidized and reduced
ExampleCl2 + H2O HCl + HClO
Combination reactions
Reactions in which two or more substances combine to form a compound are called combination reactions
Example Mg + F2 MgF2
Combination reactions Element + Element CompoundNa(s) + Cl2(g) NaCl(s) (metal + nonmetal)
P4 + Cl2 PCl3 (nonmetal + nonmetal) Compound + Element CompoundPCl3(l) + Cl2(g) PCl5(s) Compound + Compound CompoundCaO(s) + H2O (l) Ca(OH)2 (aq)
Decomposition reactions
Decomposition reactions are those in which a compound decomposes to produce (1) two elements, (2) one or more element and one or more compounds, (3) two or more compounds
Example CaCO3(s) CaO(s) + CO2(g)
Decomposition reaction
Compound Element + Element Compound Compound +
Element Compound Compound +
Compound
Displacement reactions
Reactions in which one element displaces another from a compound are called displacement reactions
ExampleZn(s) + CuSO4(aq) Cu(s) +
ZnSO4(aq)
Displacement reaction [More active metal + salt of less active metal]
[Less active metal + salt of more active metal] [Active metal + nonoxidizing acid] [Hydrogen +
salt of acid]H2SO4 (should be in very dilute solution) [Active nonmetal + salt of less active nonmetal]
[Less active nonmetal + salt of more active nonmetal]Each halogen will displace less active (heavier) halogens
F2>Cl2>Br2>I2
Metathesis reactions
In many reactions between two compounds in aqueous solution, the positive and negative ions appear to “change partners” to form two new compounds, with no change in oxidation number. Such reactions are called metathesis reactions
Example AgNO3(aq)+NaCl(aq) AgCl(s)+NaNO3(aq)
Metathesis reactions
Acid-base (neutralization) reactions: formation of nonelectrolyte
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
Precipitation reactions
Exercise Assign oxidation numbers to the
element specified in each group of ions
(a) P in PCl5, P4O6, P4O10, HPO3, H3PO3, POCl3, H4P2O7, Mg3(PO4)2
(b) Mn in MnO, MnO2, Mn(OH)2, K2MnO4, KMnO4, Mn2O7.
(c) O in OF2, Na2O, Na2O2, KO2
Exercise Write each of the following formula unit equations
as net ionic equation if the two differ? For the redox reactions, identify the oxidizing agent, the reducing agent, the species oxidized and the species reduced
(a) AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + Ag(s)
(b) KClO3(s) KCl(s) + KClO4
(c) AgNO3(aq) + K3PO4(aq) Ag3PO4(s) + KNO3(aq)
heat
Exercise
Balancing and Classifying reactions(a) Zn(s) + AgNO3(aq) Zn(NO3)2(aq) + Ag(s)
(b) Ca(OH)2(s) CaO(s) + H2O(g)
(c) HI(g) H2(g) + I2(g)
(d) Cu(NO3)2(aq) + Na2S(aq) CuS(s) + NaNO3(aq)
(e) SO2(g) + H2O(l) H2SO3(aq)
(f) H2SO3(aq) + KOH(aq) K2SO3(aq) + H2O(l)
heat
heat
Write the chemical formula or name of the following compounds