BACTERIAL STRUCTURE
BACTERIAL STRUCTUR
Thursday, September 17, 2009
Monday, September 14, 2009
Chemical Reactions
What is a Chemical Reaction?
Types of Chemical Reactions
Redox Reactions
Nonredox Reactions
Classifying Reactions
What is a Chemical Reaction?
A chemical reaction is a process in which the identity of at least one substance changes. A chemical equation represents the total chemical change that occurs in a chemical reaction using symbols and chemical formulas for the substances involved. Reactants are the substances that are changed and products are the substances that are produced in a chemical reaction.
The general format for writing a chemical equation is
reactant1 + reactant2 + … → product1 + product2 + …
With the exception of nuclear reactions, the Law of Conservation of Mass–matter is neither created nor destroyed during a chemical reaction– is obeyed in “ordinary” chemical reactions. For this reason a chemical equation must be balanced–the number of atoms of each element must be the same on the reactants side of the reaction arrow as on the products side. Details on balancing chemical equations are found in the units on Stoichiometry and Redox Reactions.
The general format for writing a chemical equation can be written in a short-hand version as
a A + b B + … → c C + d D + …
where the lower case letters are the stoichiometric coefficients needed to balance a specific equation.
The units on Stoichiometry, Redox Reactions, and Acid-Base Chemistry contain additional background reading, example problems, and information on the topics covered in this unit.
Types of Chemical Reactions
Chemists classify chemical reactions in various ways. Often a major classification is based on whether or not the reaction involves oxidation-reduction. A reaction may be classified as redox in which oxidation and reduction occur or nonredox in which there is no oxidation and reduction occurring.
Redox Reactions
A redox reaction can be recognized by observing whether or not the oxidation numbers of any of the elements change during the reaction.
Example Problem: Classify the reactions as either redox or nonredox.
(1) 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s)
(2) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
(3) Cl2(g) + H2O(l) → HCl(aq) + HClO(aq)
Answer: In equation (1), the iron changes oxidation numbers from 0 to +3 and oxygen changes from 0 to -2. Equation (1) represents a redox reaction. In equation (2), there is no change in oxidation numbers for the elements involved: sodium is +1, oxygen is -2, hydrogen is +1, and chlorine is -1 on both the reactants and products sides. Equation (2) represents a nonredox reaction. In equation (3), the chlorine changes from 0 to -1 in HCl and to +1 in HClO. There is no change in the oxidation numbers of hydrogen (+1 in H2O, HCl, and HClO) and oxygen (-2 in H2O and HClO). Because chlorine is oxidized and reduced, equation (3) represents a redox reaction.
The reaction described in equation (3) is interesting in that an element in one oxidation state undergoes both oxidation and reduction. Such a redox process is known as a disproportionation reaction. The element undergoing disproportionation must have at least three different oxidation states–the initial one in the reactant and one higher plus one lower in the products.
Most simple redox reactions may be classified as combination, decomposition, or single displacement reactions. In a combinations reaction two reactants react to give a single product. The general format of the chemical equation is
a A + b B + … → c C
A special case of a combination reaction in which the reactants are only elements in their naturally occurring forms and physical states at the temperature and pressure of the reaction is known as a formation reaction.
Example Problem: Identify which reactions are redox combination reactions.
(4) 6 Li2O(s) + P4O10(g) → 4 Li3PO4(s)
(5) CaO(s) + H2O(l) → Ca(OH)2(s)
(6) S(s) + 3 F2(g) → SF6(g)
(7) ZnS(s) + 2 O2(g) → ZnSO4(s)
(8) SO2(g) + Cl2(g) → SO2Cl2(g)
Answer: All of the reaction are classified as combination reactions because they involved two or more reactants producing a single product. However, redox is occurring only in equations (6), (7), and (8). In equation (6), S is oxidized from 0 to +6 and F is reduced from 0 to -1; in equation (7), S is oxidized from -2 to +6 and O is reduced from 0 to -2; and in equation (8), S is oxidized from +4 to +6 and Cl is reduced from 0 to -1.
In a decomposition reaction a single reactant breaks down to give two or more substances. The general format of the chemical equation is
a A → b B + c C + …
If the decomposition reaction involves oxidation-reduction, the reaction is often called an internal redox reaction because the oxidized and reduced elements originate in the same compound.
Example Problem: Identify which reactions are redox decomposition reactions.
(9) CuSO4⋅5H2O(s) → CuSO4(s) + 5 H2O(g)
(10) SnCl4⋅6H2O(s) → SnO2(s) + 4 HCl(g) + 4 H2O(g)
(11) NH4NO2(s) → N2(g) + 2 H2O(g)
(12) (NH4)2Cr2O7(s) → N2(g) + Cr2O3(s) + 4 H2O(g)
Answer: All of the reactions are classified as decomposition reactions because they involve a single reactant producing two or more substances. However, redox is occurring only in equations (11) and (12). In equation (11), the N in NH4+ is oxidized from -3 to 0 and the N in NO2- is reduced from +3 to 0. In equation (12), the N is oxidized from -3 to 0 and the Cr is reduced from +6 to +3.
In a single displacement reaction the atoms or ions of one reactant replace the atoms or ions in another reactant. Single displacement reactions are also known as displacement, single replacement, and replacement reactions. The general format of the chemical equation is
a A + b BC → c AC + d B
Whether or not a redox single displacement reaction occurs will depend on the relative reducing strengths of A and B.
Example Problem: Identify which reactions are redox single displacement reactions.
(13) 2 Al(s) + Fe2O3(s) → 2 Fe(s) + Al2O3(s)
(14) 2 NaI(aq) + Br2(aq) → 2 NaBr(aq) + I2(aq)
(15) Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Answer: All three reactions are redox. Both equations (13) and (14) fit the general format of the single displacement reaction by assigning A as Al, B as Fe, and C as O in equation (13) and A as Br, B as I, and C as Na in equation (14). To classify equation (15) is a little more difficult. The reaction has been represented by a net ionic equation in which the anion has been omitted. If an anion X is added to generate the overall equation, Zn(s) + CuX(aq) → ZnX(aq) + Cu(s), then assigning A as Zn, B as Cu, and C as X shows that this is also a redox single displacement reaction.
In addition to the single redox reactions described above, a redox reaction may be classified as a simple redox electron transfer reaction in which the oxidation numbers of ionic reactants are changed by the direct transfer of electrons from one ion to the other–typically in aqueous solutions. For example
2 Fe3+(aq) + Sn2+(aq) → 2 Fe2+(aq) + Sn4+(aq)
Many redox reactions do not fit into the classifications described above. For example, redox reactions involving oxygen-containing reactants in aqueous acidic or basic solutions such as
3 Cu(s) + 8 HNO3(aq, dil) → 3 Cu(NO3)2(aq) + 2 NO(g) + 4 H2O(l)
Cu(s) + 4 HNO3(aq, conc) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l)
or the combustion of oxygen with more than one element in a reactant
2 CH3OH(g) + 3 O2(g) → 2 CO2(g) + 4 H2O(l)
These types of reactions are classified as complex redox reactions.
Nonredox Reactions
There are several classifications of nonredox reactions–including combination, decomposition, single displacement, and double displacement reactions.
The general format of the chemical equation for a nonredox combination reaction is the same as for a redox combination reaction
a A + b B + … → c C
However, all reactants and the product must be compounds and no changes in oxidation numbers of the elements occur. Usually these reactions involve reactants that are acidic and basic anhydrides.
Example Problem: Identify which reactions are nonredox combination reactions.
(16) 2 Na(s) + Cl2(g) → 2 NaCl(s)
(17) SO3(g) + CaO(s) → CaSO4(s)
(18) SO2(g) + H2O(l) → H2SO3(aq)
Answer: All three equations are combination reactions, but only equations (17) and (18) are nonredox.
The general format of the chemical equation for a nonredox decomposition reaction is the same as for a redox decomposition reaction
a A → b B + c C + …
However, the reactant and all products must be compounds and no changes in oxidation numbers occur. Quite often one of the products formed will be a gas.
Example Problem: Identify which reactions are nonredox decomposition reactions.
(19) NH4HCO3(s) → NH3(g) + CO2(g) + H2O(g)
(20) NH4NO2(s) → N2(g) + 2 H2O(g)
(21) CaCO3(s) → CaO(s) + CO2(g)
Answer: All three equations are decomposition reactions, but only equations (19) and (21) are nonredox.
The general format of the chemical equation for a nonredox single displacement reaction is the same as for a redox single displacement reaction
a A + b BC → c AC + d B
However, there are no changes in the oxidation numbers of the elements during the reaction. Common nonredox single displacement reactions include ligand substitution in complexes and formation of more stable oxygen-containing compounds from less stable oxygen-containing compounds.
Example Problem: Identify which reactions are nonredox single displacement reactions.
(22) [PtCl4]2-(aq) + 2 NH3(aq) → [Pt(NH3)Cl2](s) + 2 Cl-(aq)
(23) Na2CO3(s) + SiO2(s) → Na2SiO3(l) + CO2(g)
(24) 2 AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2 Ag(s)
Answer: All three equations are single displacement reactions, but only equations (22) and (23) are nonredox.
Finally, the last classification of nonredox reactions is that of nonredox double displacement reactions. The general format of the chemical equation is
a AC + b BD → c AD + d BC
with no oxidation or reduction of A, B, C, or D occurring. These reactions are also known as double replacement, “partner” exchange, and metathesis reactions. Usually one or more of the products will be a gas, a precipitate, a weak electrolyte, or water. An important example of a nonredox double displacement reaction is the reaction of an acid with a base under aqueous conditions.
Example Problem: Identify the nonredox double displacement reactions.
(25) CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
(26) HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)
(27) AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)
Answer: All three reactions are nonredox double displacement reactions.
Classifying Reactions
Most experienced chemists can classify a given chemical reaction rather easily and quickly by “inspection” of the formulas of the reactants and products in the chemical equation. The first decision most chemists make is to determine whether or not the reaction involves redox. Based on this decision, the answers to a few more specific questions will readily lead to the reaction classification. These specific questions are based on the general formats of the chemical equations for the different classifications of the reactions described above.
To begin learning what these questions are, you might consider using the online analysis program that is available at http://www.xxx.yyy to classify the reactions given in the Example Problem. The basis of this analysis program is outlined by the flow charts given in Figures (1) and (2). Please do not memorize this flow chart–it is simply a tool to help you learn what to look for and what questions should be asked as you classify a given reaction.
Figure 1. Flow chart of questions to classify nonredox reactions. (Used by permission ...)
Figure 2. Flow chart of questions to classify redox reactions. (Used by permission...)
Example Problem: Classify each reaction.
(28) XeF6(s) → XeF4(s) + F2(g)
(29) Zn(s) + 2 AgNO3(aq) → Zn(NO3)2(aq) + Ag(s)
(30) H2SO4(aq) + Ba(OH)2 → BaSO4(s) + 2 H2O(l)
(31) XeF6(s) + RbF(s) → RbXeF7(s)
(32) 2 Cs(s) + I2(g) → 2 CsI(s)
Answer: In equation (28), Xe is reduced from +6 to +4 and some of the F is oxidized from -1 to 0. This reaction would be classified as a redox decomposition reaction. In equation (29), Zn is oxidized from 0 to +2 and Ag is reduced from +1 to 0. One of the reactants is an element and one of the products is an element. This reaction would be classified as a redox single displacement reaction. In equation (30), there is no redox occurring. Both reactants are in the form of aqueous ions, but are not complex ions. This acid-base reaction is classified as nonredox double displacement. In equation (31), there is no redox occurring. Because there is one product formed, this reaction is classified as a nonredox combination reaction. In equation (32), Cs is oxidized from 0 to +1 and I is reduced from 0 to -1. Both reactants are elements and there is only one product formed. The reaction is classified as a (redox) formation reaction.
Try It Out
Classify each reaction.
(33) Na2CO3(s) + SiO2(s) → Na2SiO3(l) + CO2(g)
(34) 2 Mg(NO3)2(s) → 2 Mg(NO2)2(s) + O2(g)
(35) 3 HNO2(aq) → 2 NO(g) + NO3-(aq) + H3O+(aq)
(36) BaCO3(s) → BaO(s) + CO2(g)
(37) 2 Eu2+(aq) + 2 H+(aq) → 2 Eu3+(aq) + H2(g)
(38) [Ag(NH3)2]+(aq) + 2 CN-(aq) → [Ag(CN)2]-(aq) + 2 NH3(aq)
(39) MgO(s) + 2 HCl(aq) → MgCl2(aq) + H2O(l)
(40) CaO(s) + SO2(g) → CaSO3(s)
(41) 2 NO(g) + O2(g) → 2 NO2(g)
(42) N2(g) + 2 O2(g) → 2 NO2(g)
What is a Chemical Reaction?
Types of Chemical Reactions
Redox Reactions
Nonredox Reactions
Classifying Reactions
What is a Chemical Reaction?
A chemical reaction is a process in which the identity of at least one substance changes. A chemical equation represents the total chemical change that occurs in a chemical reaction using symbols and chemical formulas for the substances involved. Reactants are the substances that are changed and products are the substances that are produced in a chemical reaction.
The general format for writing a chemical equation is
reactant1 + reactant2 + … → product1 + product2 + …
With the exception of nuclear reactions, the Law of Conservation of Mass–matter is neither created nor destroyed during a chemical reaction– is obeyed in “ordinary” chemical reactions. For this reason a chemical equation must be balanced–the number of atoms of each element must be the same on the reactants side of the reaction arrow as on the products side. Details on balancing chemical equations are found in the units on Stoichiometry and Redox Reactions.
The general format for writing a chemical equation can be written in a short-hand version as
a A + b B + … → c C + d D + …
where the lower case letters are the stoichiometric coefficients needed to balance a specific equation.
The units on Stoichiometry, Redox Reactions, and Acid-Base Chemistry contain additional background reading, example problems, and information on the topics covered in this unit.
Types of Chemical Reactions
Chemists classify chemical reactions in various ways. Often a major classification is based on whether or not the reaction involves oxidation-reduction. A reaction may be classified as redox in which oxidation and reduction occur or nonredox in which there is no oxidation and reduction occurring.
Redox Reactions
A redox reaction can be recognized by observing whether or not the oxidation numbers of any of the elements change during the reaction.
Example Problem: Classify the reactions as either redox or nonredox.
(1) 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s)
(2) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
(3) Cl2(g) + H2O(l) → HCl(aq) + HClO(aq)
Answer: In equation (1), the iron changes oxidation numbers from 0 to +3 and oxygen changes from 0 to -2. Equation (1) represents a redox reaction. In equation (2), there is no change in oxidation numbers for the elements involved: sodium is +1, oxygen is -2, hydrogen is +1, and chlorine is -1 on both the reactants and products sides. Equation (2) represents a nonredox reaction. In equation (3), the chlorine changes from 0 to -1 in HCl and to +1 in HClO. There is no change in the oxidation numbers of hydrogen (+1 in H2O, HCl, and HClO) and oxygen (-2 in H2O and HClO). Because chlorine is oxidized and reduced, equation (3) represents a redox reaction.
The reaction described in equation (3) is interesting in that an element in one oxidation state undergoes both oxidation and reduction. Such a redox process is known as a disproportionation reaction. The element undergoing disproportionation must have at least three different oxidation states–the initial one in the reactant and one higher plus one lower in the products.
Most simple redox reactions may be classified as combination, decomposition, or single displacement reactions. In a combinations reaction two reactants react to give a single product. The general format of the chemical equation is
a A + b B + … → c C
A special case of a combination reaction in which the reactants are only elements in their naturally occurring forms and physical states at the temperature and pressure of the reaction is known as a formation reaction.
Example Problem: Identify which reactions are redox combination reactions.
(4) 6 Li2O(s) + P4O10(g) → 4 Li3PO4(s)
(5) CaO(s) + H2O(l) → Ca(OH)2(s)
(6) S(s) + 3 F2(g) → SF6(g)
(7) ZnS(s) + 2 O2(g) → ZnSO4(s)
(8) SO2(g) + Cl2(g) → SO2Cl2(g)
Answer: All of the reaction are classified as combination reactions because they involved two or more reactants producing a single product. However, redox is occurring only in equations (6), (7), and (8). In equation (6), S is oxidized from 0 to +6 and F is reduced from 0 to -1; in equation (7), S is oxidized from -2 to +6 and O is reduced from 0 to -2; and in equation (8), S is oxidized from +4 to +6 and Cl is reduced from 0 to -1.
In a decomposition reaction a single reactant breaks down to give two or more substances. The general format of the chemical equation is
a A → b B + c C + …
If the decomposition reaction involves oxidation-reduction, the reaction is often called an internal redox reaction because the oxidized and reduced elements originate in the same compound.
Example Problem: Identify which reactions are redox decomposition reactions.
(9) CuSO4⋅5H2O(s) → CuSO4(s) + 5 H2O(g)
(10) SnCl4⋅6H2O(s) → SnO2(s) + 4 HCl(g) + 4 H2O(g)
(11) NH4NO2(s) → N2(g) + 2 H2O(g)
(12) (NH4)2Cr2O7(s) → N2(g) + Cr2O3(s) + 4 H2O(g)
Answer: All of the reactions are classified as decomposition reactions because they involve a single reactant producing two or more substances. However, redox is occurring only in equations (11) and (12). In equation (11), the N in NH4+ is oxidized from -3 to 0 and the N in NO2- is reduced from +3 to 0. In equation (12), the N is oxidized from -3 to 0 and the Cr is reduced from +6 to +3.
In a single displacement reaction the atoms or ions of one reactant replace the atoms or ions in another reactant. Single displacement reactions are also known as displacement, single replacement, and replacement reactions. The general format of the chemical equation is
a A + b BC → c AC + d B
Whether or not a redox single displacement reaction occurs will depend on the relative reducing strengths of A and B.
Example Problem: Identify which reactions are redox single displacement reactions.
(13) 2 Al(s) + Fe2O3(s) → 2 Fe(s) + Al2O3(s)
(14) 2 NaI(aq) + Br2(aq) → 2 NaBr(aq) + I2(aq)
(15) Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Answer: All three reactions are redox. Both equations (13) and (14) fit the general format of the single displacement reaction by assigning A as Al, B as Fe, and C as O in equation (13) and A as Br, B as I, and C as Na in equation (14). To classify equation (15) is a little more difficult. The reaction has been represented by a net ionic equation in which the anion has been omitted. If an anion X is added to generate the overall equation, Zn(s) + CuX(aq) → ZnX(aq) + Cu(s), then assigning A as Zn, B as Cu, and C as X shows that this is also a redox single displacement reaction.
In addition to the single redox reactions described above, a redox reaction may be classified as a simple redox electron transfer reaction in which the oxidation numbers of ionic reactants are changed by the direct transfer of electrons from one ion to the other–typically in aqueous solutions. For example
2 Fe3+(aq) + Sn2+(aq) → 2 Fe2+(aq) + Sn4+(aq)
Many redox reactions do not fit into the classifications described above. For example, redox reactions involving oxygen-containing reactants in aqueous acidic or basic solutions such as
3 Cu(s) + 8 HNO3(aq, dil) → 3 Cu(NO3)2(aq) + 2 NO(g) + 4 H2O(l)
Cu(s) + 4 HNO3(aq, conc) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l)
or the combustion of oxygen with more than one element in a reactant
2 CH3OH(g) + 3 O2(g) → 2 CO2(g) + 4 H2O(l)
These types of reactions are classified as complex redox reactions.
Nonredox Reactions
There are several classifications of nonredox reactions–including combination, decomposition, single displacement, and double displacement reactions.
The general format of the chemical equation for a nonredox combination reaction is the same as for a redox combination reaction
a A + b B + … → c C
However, all reactants and the product must be compounds and no changes in oxidation numbers of the elements occur. Usually these reactions involve reactants that are acidic and basic anhydrides.
Example Problem: Identify which reactions are nonredox combination reactions.
(16) 2 Na(s) + Cl2(g) → 2 NaCl(s)
(17) SO3(g) + CaO(s) → CaSO4(s)
(18) SO2(g) + H2O(l) → H2SO3(aq)
Answer: All three equations are combination reactions, but only equations (17) and (18) are nonredox.
The general format of the chemical equation for a nonredox decomposition reaction is the same as for a redox decomposition reaction
a A → b B + c C + …
However, the reactant and all products must be compounds and no changes in oxidation numbers occur. Quite often one of the products formed will be a gas.
Example Problem: Identify which reactions are nonredox decomposition reactions.
(19) NH4HCO3(s) → NH3(g) + CO2(g) + H2O(g)
(20) NH4NO2(s) → N2(g) + 2 H2O(g)
(21) CaCO3(s) → CaO(s) + CO2(g)
Answer: All three equations are decomposition reactions, but only equations (19) and (21) are nonredox.
The general format of the chemical equation for a nonredox single displacement reaction is the same as for a redox single displacement reaction
a A + b BC → c AC + d B
However, there are no changes in the oxidation numbers of the elements during the reaction. Common nonredox single displacement reactions include ligand substitution in complexes and formation of more stable oxygen-containing compounds from less stable oxygen-containing compounds.
Example Problem: Identify which reactions are nonredox single displacement reactions.
(22) [PtCl4]2-(aq) + 2 NH3(aq) → [Pt(NH3)Cl2](s) + 2 Cl-(aq)
(23) Na2CO3(s) + SiO2(s) → Na2SiO3(l) + CO2(g)
(24) 2 AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2 Ag(s)
Answer: All three equations are single displacement reactions, but only equations (22) and (23) are nonredox.
Finally, the last classification of nonredox reactions is that of nonredox double displacement reactions. The general format of the chemical equation is
a AC + b BD → c AD + d BC
with no oxidation or reduction of A, B, C, or D occurring. These reactions are also known as double replacement, “partner” exchange, and metathesis reactions. Usually one or more of the products will be a gas, a precipitate, a weak electrolyte, or water. An important example of a nonredox double displacement reaction is the reaction of an acid with a base under aqueous conditions.
Example Problem: Identify the nonredox double displacement reactions.
(25) CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
(26) HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)
(27) AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)
Answer: All three reactions are nonredox double displacement reactions.
Classifying Reactions
Most experienced chemists can classify a given chemical reaction rather easily and quickly by “inspection” of the formulas of the reactants and products in the chemical equation. The first decision most chemists make is to determine whether or not the reaction involves redox. Based on this decision, the answers to a few more specific questions will readily lead to the reaction classification. These specific questions are based on the general formats of the chemical equations for the different classifications of the reactions described above.
To begin learning what these questions are, you might consider using the online analysis program that is available at http://www.xxx.yyy to classify the reactions given in the Example Problem. The basis of this analysis program is outlined by the flow charts given in Figures (1) and (2). Please do not memorize this flow chart–it is simply a tool to help you learn what to look for and what questions should be asked as you classify a given reaction.
Figure 1. Flow chart of questions to classify nonredox reactions. (Used by permission ...)
Figure 2. Flow chart of questions to classify redox reactions. (Used by permission...)
Example Problem: Classify each reaction.
(28) XeF6(s) → XeF4(s) + F2(g)
(29) Zn(s) + 2 AgNO3(aq) → Zn(NO3)2(aq) + Ag(s)
(30) H2SO4(aq) + Ba(OH)2 → BaSO4(s) + 2 H2O(l)
(31) XeF6(s) + RbF(s) → RbXeF7(s)
(32) 2 Cs(s) + I2(g) → 2 CsI(s)
Answer: In equation (28), Xe is reduced from +6 to +4 and some of the F is oxidized from -1 to 0. This reaction would be classified as a redox decomposition reaction. In equation (29), Zn is oxidized from 0 to +2 and Ag is reduced from +1 to 0. One of the reactants is an element and one of the products is an element. This reaction would be classified as a redox single displacement reaction. In equation (30), there is no redox occurring. Both reactants are in the form of aqueous ions, but are not complex ions. This acid-base reaction is classified as nonredox double displacement. In equation (31), there is no redox occurring. Because there is one product formed, this reaction is classified as a nonredox combination reaction. In equation (32), Cs is oxidized from 0 to +1 and I is reduced from 0 to -1. Both reactants are elements and there is only one product formed. The reaction is classified as a (redox) formation reaction.
Try It Out
Classify each reaction.
(33) Na2CO3(s) + SiO2(s) → Na2SiO3(l) + CO2(g)
(34) 2 Mg(NO3)2(s) → 2 Mg(NO2)2(s) + O2(g)
(35) 3 HNO2(aq) → 2 NO(g) + NO3-(aq) + H3O+(aq)
(36) BaCO3(s) → BaO(s) + CO2(g)
(37) 2 Eu2+(aq) + 2 H+(aq) → 2 Eu3+(aq) + H2(g)
(38) [Ag(NH3)2]+(aq) + 2 CN-(aq) → [Ag(CN)2]-(aq) + 2 NH3(aq)
(39) MgO(s) + 2 HCl(aq) → MgCl2(aq) + H2O(l)
(40) CaO(s) + SO2(g) → CaSO3(s)
(41) 2 NO(g) + O2(g) → 2 NO2(g)
(42) N2(g) + 2 O2(g) → 2 NO2(g)
Chemical Nomenclature
Chemical nomenclature is the term given to the naming of compounds. Chemists use specific rules and "conventions" to name different compounds. This section is designed to help you review some of those rules and conventions.
Oxidation and Reduction
Forming Ionic Compounds
Arrangement of Atoms
Naming Ionic Compounds
Naming Binary Molecular Compounds
Naming Inorganic Acids
Naming Compounds
Oxidation and Reduction
When forming compounds, it is important to know something about the way atoms will react with each other. One of the most important manners in which atoms and/or molecules react with each other is the oxidation/reduction reaction. Oxidation/Reduction reactions are the processes of losing and gaining electrons respectively. Just remember, "LEO the lion says GER:" Lose Electrons Oxidation, Gain Electrons Reduction. Oxidation numbers are assigned to atoms and compounds as a way to tell scientists where the electrons are in a reaction. It is often referred to as the "charge" on the atom or compound. The oxidation number is assigned according to a standard set of rules. They are as follows:
An atom of a pure element has an oxidation number of zero.
For single atoms in an ion, their oxidation number is equal to their charge.
Fluorine is always -1 in compounds.
Cl, Br, and I are always -1 in compounds except when they are combined with O or F.
H is normally +1 and O is normally -2.
The oxidation number of a compound is equal to the sum of the oxidation numbers for each atom in the compound.
Forming Ionic Compounds
Knowing the oxidation number of a compound is very important when discussing ionic compounds. Ionic compounds are combinations of positive and negative ions. They are generally formed when nonmetals and metals bond. To determine which substance is formed, we must use the charges of the ions involved. To make a neutral molecule, the positive charge of the cation (positively-charged ion) must equal the negative charge of the anion (negatively-charged ion). In order to create a neutral charged molecule, you must combine the atoms in certain proportions. Scientists use subscripts to identify how many of each atom makes up the molecule. For example, when combining magnesium and nitrogen we know that the magnesium ion has a "+2" charge and the nitrogen ion has a "-3" charge. To cancel these charges, we must have three magnesium atoms for every two nitrogen atoms:
3Mg2+ + 2N3- --> Mg3N2
Knowledge of the charges of ions is crucial to knowing the formulas of the compounds formed.
alkalis (1st column elements) form "+1" ions such as Na+ and Li+
alkaline earth metals (2nd column elements) form "2+" ions such as Mg2+ and Ba2+
halogens (7th column elements) form "-1" ions such as Cl- and I-
Other common ions are listed in the table below:
Positive ions (cations)
Negative ions (anions)
1+
1-
ammonium (NH4+)
acetate (C2H3O2-)
copper(I) (Cu+)
azide (N3-)
hydrogen (H+)
chlorate (ClO3-)
silver (Ag+)
cyanide (CN-)
dihydrogen phosphate (H2PO4-)
2+
hydride (H-)
cadmium (Cd2+)
bicarbonate (HCO3-)
cobalt(II) (Co2+)
hydroxide (OH-)
copper(II) (Cu2+)
nitrate (NO3-)
iron (Fe2+)
nitrite (NO2-)
lead (Pb2+)
perchlorate (ClO4-)
manganese(II) (Mn2+)
permanganate (MnO4-)
mercury(I) (Hg22+)
thiocyanate(SCN-)
mercury(II) (Hg2+)
nickel (Ni2+)
2-
tin (Sn2+)
carbonate (CO32-)
zinc (Zn2+)
chromate (CrO42-)
dichromate (Cr2O72-)
3+
hydrogen phosphate (HPO42-)
aluminum (Al3+)
oxide (O2-)
chromium(III) (Cr3+)
peroxide (O22-)
iron(III) (Fe3+)
sulfate (SO42-)
sulfide (S2-)
sulfite (SO32-)
3-
nitride (N3-)
phosphate (PO43-)
phosphide (P3-)
Naming Ionic Compounds
The outline below provides the rules for naming ionic compounds:
Positive Ions
Monatomic cations (a single atom with a positive charge) take the name of the element plus the word "ion"Examples:
Na+ = sodium ion
Zn+2 = zinc ion
If an element can form more than one (1) positive ion, the charge is indicated by the Roman numeral in parentheses followed by the word "ion"Examples:
Fe2+ = iron(II) ion
Fe3+ = iron (III) ion
Negative Ions
Monatomic anions (a single atom with a negative charge) change their ending to "-ide"Examples:
O2- = oxide ion
Cl- = chloride ion
Oxoanions (negatively charged polyatomic ions which contain O) end in "-ate". However, if there is more than one oxyanion for a specific element then the endings are:
Two less oxygen than the most common starts with "hypo-" and ends with "-ite"
One less oxygen than the most common ends with "-ite"
THE MOST COMMON OXOANION ENDS WITH "-ATE"
One more oxygen than the most common starts with "per-" and ends with "-ate"
ClO- = hypochlorite
o ClO2- = chlorite
o NO2- = nitrite
o SO32- = sulfite
Most common oxyanions with four oxygens
o SO42- = sulfate
o PO43- = phosphate
o CrO42- = chromate
Most common oxyanions with three oxygens
o NO3- = nitrate
o ClO3- = chlorate
o CO32- = carbonate
ClO4- = perchlorate
Polyatomic anions (a negatively charged ion containing more than one type of element) often add a hydrogen atom; in this case, the anion's name either adds "hydrogen-" or "bi-" to the beginningExample:CO32- becomes HCO3-"Carbonate" becomes either "Hydrogen Carbonate" or "Bicarbonate"
When combining cations and anions into an ionic compound, you always put the cation name first and then the anion name (the molecular formulas are also written in this order as well.)Examples:
Na+ + Cl- --> NaClsodium + chloride --> sodium chloride
Cu2+ + SO42- -->CuSO4copper(II) + sulfate --> copper(II) sulfate
Al3+ + 3NO3- --> Al(NO3)3aluminum + nitrate --> aluminum nitrate
Arrangement of Atoms
In naming ions, it is important to consider "isomers." Isomers are compounds with the same molecular formula, but different arrangements of atoms. Thus, it is important to include some signal within the name of the ion that identifies which arrangement you are talking about. There are three main types of classification, geometric, optical and structural isomers.
Geometric isomers refers to which side of the ion atoms lie. The prefixes used to distinguish geometric isomers are cis meaning substituents lie on the same side of the ion and trans meaning they lie on opposite sides. Below is a diagram to help you remember.
Optical isomers differ in the arrangement of four groups around a chiral carbon. These two isomers are differentiated as L and D.
Structural isomers differentiate between the placement of two chlorine atoms around a hexagonal carbon ring. These three isomers are identified as o, m, and p. Once again we have given you a few clues to help your memory.
A pop-up nomenclature calculator is available for help when naming compounds and for practice problems.
Naming Binary Molecular Compounds
Molecular compounds are formed from the covalent bonding between non-metallic elements. The nomenclature for these compounds is described in the following set of rules.
The more positive atom is written first (the atom which is the furthest to the left and to the bottom of the periodic table)
The more negative second atom has an "-ide" ending.
Each prefix indicates the number of each atom present in the compound.
Number of Atoms
Prefix
Number of Atoms
Prefix
1
mono
6
hexa
2
di
7
hepta
3
tri
8
octa
4
tetra
9
nona
5
penta
10
deca
Examples:CO2 = carbon dioxideP4S10 = tetraphosphorus decasulfide
Naming Inorganic Acids
Binary acids (H plus a nonmetal element) are acids that dissociate into hydrogen atoms and anions in water. Acids that only release one hydrogen atom are known as monoprotic. Those acids that release more than one hydrogen atom are called polyproticacids. When naming these binary acids, you merely add "hydro-" (denoting the presence of a hydrogen atom) to the beginning and "-ic acid" to the end of the anion name.Examples:HCl = hydrochloric acidHBr = hydrobromic acid
Ternary acids (also called oxoacids, are formed by hydrogen plus another element plus oxygen) are based on the name of the anion. In this case, the -ate, and -ite suffixes for the anion are replaced with -ic and -ous respectively. The new anion name is then followed by the word "acid." The chart below depicts the changes in nomenclature.
Anion name
Acid name
hypo___ite
hypo___ous acid
___ite
___ous acid
___ate
___ic acid
per___ate
per___ic acid
Example:ClO4- to HClO4 => perchlorate to perchloric acidClO- to HClO => hypochlorite to hypochlorous acid
Naming Compounds
A detailed treatise on naming organic compounds is beyond the scope of these materials, but some basics are presented. The wise chemistry student should consider memorizing the prefixes of the first ten organic compounds:
Number of Carbons
Prefix
1
meth-
2
eth-
3
prop-
4
but-
5
pent-
6
hex-
7
hept-
8
oct-
9
non-
10
dec-
There are four basic types of organic hydrocarbons, those chemicals with only carbon and hydrogen:
Single bonds (alkane): suffix is "ane", formula CnH2n+2
Double bonds (alkene): suffix is "ene", formula CnH2n
Triple bonds (alkyne): suffix is "yne", formula CnH2n-2
Cyclic compounds: use prefix "cyclo"
So, for example, an organic compound with the formula "C6H14" would be recognized as an alkane with six carbons, so its name is "hexane".
Examples:N2O4 = dinitrogen tetraoxideS2F10 = disulfur decafluoride
Practice Problems
Find the formulas of the following molecules:
1.
aluminum fluoride
8.
ammonium dichromate
2.
carbon tetrachloride
9.
magnesium acetate
3.
strontium nitrate
10.
zinc hydroxide
4.
sodium bisulfate
11.
nitric acid
5.
iron(III) oxide
12.
hypochlorous acid
6.
mercury(II) nitrate
13.
phosphoric acid
7.
sodium sulfite
14.
aluminum nitrate
A solution set is available for viewing.
Write the names of the following molecules:
1.
CaCO3
8.
Mg3(PO4)2
2.
SCl2
9.
Ba(NO2)2
3.
Li2CrO4
10.
Hg2Cl2
4.
NaSCN
11.
NaHCO3
5.
KClO3
12.
H2S
6.
Ca(C2H3O2)2
13.
H2SO3
7.
K2Cr2O7
14.
SO3
Chemical nomenclature is the term given to the naming of compounds. Chemists use specific rules and "conventions" to name different compounds. This section is designed to help you review some of those rules and conventions.
Oxidation and Reduction
Forming Ionic Compounds
Arrangement of Atoms
Naming Ionic Compounds
Naming Binary Molecular Compounds
Naming Inorganic Acids
Naming Compounds
Oxidation and Reduction
When forming compounds, it is important to know something about the way atoms will react with each other. One of the most important manners in which atoms and/or molecules react with each other is the oxidation/reduction reaction. Oxidation/Reduction reactions are the processes of losing and gaining electrons respectively. Just remember, "LEO the lion says GER:" Lose Electrons Oxidation, Gain Electrons Reduction. Oxidation numbers are assigned to atoms and compounds as a way to tell scientists where the electrons are in a reaction. It is often referred to as the "charge" on the atom or compound. The oxidation number is assigned according to a standard set of rules. They are as follows:
An atom of a pure element has an oxidation number of zero.
For single atoms in an ion, their oxidation number is equal to their charge.
Fluorine is always -1 in compounds.
Cl, Br, and I are always -1 in compounds except when they are combined with O or F.
H is normally +1 and O is normally -2.
The oxidation number of a compound is equal to the sum of the oxidation numbers for each atom in the compound.
Forming Ionic Compounds
Knowing the oxidation number of a compound is very important when discussing ionic compounds. Ionic compounds are combinations of positive and negative ions. They are generally formed when nonmetals and metals bond. To determine which substance is formed, we must use the charges of the ions involved. To make a neutral molecule, the positive charge of the cation (positively-charged ion) must equal the negative charge of the anion (negatively-charged ion). In order to create a neutral charged molecule, you must combine the atoms in certain proportions. Scientists use subscripts to identify how many of each atom makes up the molecule. For example, when combining magnesium and nitrogen we know that the magnesium ion has a "+2" charge and the nitrogen ion has a "-3" charge. To cancel these charges, we must have three magnesium atoms for every two nitrogen atoms:
3Mg2+ + 2N3- --> Mg3N2
Knowledge of the charges of ions is crucial to knowing the formulas of the compounds formed.
alkalis (1st column elements) form "+1" ions such as Na+ and Li+
alkaline earth metals (2nd column elements) form "2+" ions such as Mg2+ and Ba2+
halogens (7th column elements) form "-1" ions such as Cl- and I-
Other common ions are listed in the table below:
Positive ions (cations)
Negative ions (anions)
1+
1-
ammonium (NH4+)
acetate (C2H3O2-)
copper(I) (Cu+)
azide (N3-)
hydrogen (H+)
chlorate (ClO3-)
silver (Ag+)
cyanide (CN-)
dihydrogen phosphate (H2PO4-)
2+
hydride (H-)
cadmium (Cd2+)
bicarbonate (HCO3-)
cobalt(II) (Co2+)
hydroxide (OH-)
copper(II) (Cu2+)
nitrate (NO3-)
iron (Fe2+)
nitrite (NO2-)
lead (Pb2+)
perchlorate (ClO4-)
manganese(II) (Mn2+)
permanganate (MnO4-)
mercury(I) (Hg22+)
thiocyanate(SCN-)
mercury(II) (Hg2+)
nickel (Ni2+)
2-
tin (Sn2+)
carbonate (CO32-)
zinc (Zn2+)
chromate (CrO42-)
dichromate (Cr2O72-)
3+
hydrogen phosphate (HPO42-)
aluminum (Al3+)
oxide (O2-)
chromium(III) (Cr3+)
peroxide (O22-)
iron(III) (Fe3+)
sulfate (SO42-)
sulfide (S2-)
sulfite (SO32-)
3-
nitride (N3-)
phosphate (PO43-)
phosphide (P3-)
Naming Ionic Compounds
The outline below provides the rules for naming ionic compounds:
Positive Ions
Monatomic cations (a single atom with a positive charge) take the name of the element plus the word "ion"Examples:
Na+ = sodium ion
Zn+2 = zinc ion
If an element can form more than one (1) positive ion, the charge is indicated by the Roman numeral in parentheses followed by the word "ion"Examples:
Fe2+ = iron(II) ion
Fe3+ = iron (III) ion
Negative Ions
Monatomic anions (a single atom with a negative charge) change their ending to "-ide"Examples:
O2- = oxide ion
Cl- = chloride ion
Oxoanions (negatively charged polyatomic ions which contain O) end in "-ate". However, if there is more than one oxyanion for a specific element then the endings are:
Two less oxygen than the most common starts with "hypo-" and ends with "-ite"
One less oxygen than the most common ends with "-ite"
THE MOST COMMON OXOANION ENDS WITH "-ATE"
One more oxygen than the most common starts with "per-" and ends with "-ate"
ClO- = hypochlorite
o ClO2- = chlorite
o NO2- = nitrite
o SO32- = sulfite
Most common oxyanions with four oxygens
o SO42- = sulfate
o PO43- = phosphate
o CrO42- = chromate
Most common oxyanions with three oxygens
o NO3- = nitrate
o ClO3- = chlorate
o CO32- = carbonate
ClO4- = perchlorate
Polyatomic anions (a negatively charged ion containing more than one type of element) often add a hydrogen atom; in this case, the anion's name either adds "hydrogen-" or "bi-" to the beginningExample:CO32- becomes HCO3-"Carbonate" becomes either "Hydrogen Carbonate" or "Bicarbonate"
When combining cations and anions into an ionic compound, you always put the cation name first and then the anion name (the molecular formulas are also written in this order as well.)Examples:
Na+ + Cl- --> NaClsodium + chloride --> sodium chloride
Cu2+ + SO42- -->CuSO4copper(II) + sulfate --> copper(II) sulfate
Al3+ + 3NO3- --> Al(NO3)3aluminum + nitrate --> aluminum nitrate
Arrangement of Atoms
In naming ions, it is important to consider "isomers." Isomers are compounds with the same molecular formula, but different arrangements of atoms. Thus, it is important to include some signal within the name of the ion that identifies which arrangement you are talking about. There are three main types of classification, geometric, optical and structural isomers.
Geometric isomers refers to which side of the ion atoms lie. The prefixes used to distinguish geometric isomers are cis meaning substituents lie on the same side of the ion and trans meaning they lie on opposite sides. Below is a diagram to help you remember.
Optical isomers differ in the arrangement of four groups around a chiral carbon. These two isomers are differentiated as L and D.
Structural isomers differentiate between the placement of two chlorine atoms around a hexagonal carbon ring. These three isomers are identified as o, m, and p. Once again we have given you a few clues to help your memory.
A pop-up nomenclature calculator is available for help when naming compounds and for practice problems.
Naming Binary Molecular Compounds
Molecular compounds are formed from the covalent bonding between non-metallic elements. The nomenclature for these compounds is described in the following set of rules.
The more positive atom is written first (the atom which is the furthest to the left and to the bottom of the periodic table)
The more negative second atom has an "-ide" ending.
Each prefix indicates the number of each atom present in the compound.
Number of Atoms
Prefix
Number of Atoms
Prefix
1
mono
6
hexa
2
di
7
hepta
3
tri
8
octa
4
tetra
9
nona
5
penta
10
deca
Examples:CO2 = carbon dioxideP4S10 = tetraphosphorus decasulfide
Naming Inorganic Acids
Binary acids (H plus a nonmetal element) are acids that dissociate into hydrogen atoms and anions in water. Acids that only release one hydrogen atom are known as monoprotic. Those acids that release more than one hydrogen atom are called polyproticacids. When naming these binary acids, you merely add "hydro-" (denoting the presence of a hydrogen atom) to the beginning and "-ic acid" to the end of the anion name.Examples:HCl = hydrochloric acidHBr = hydrobromic acid
Ternary acids (also called oxoacids, are formed by hydrogen plus another element plus oxygen) are based on the name of the anion. In this case, the -ate, and -ite suffixes for the anion are replaced with -ic and -ous respectively. The new anion name is then followed by the word "acid." The chart below depicts the changes in nomenclature.
Anion name
Acid name
hypo___ite
hypo___ous acid
___ite
___ous acid
___ate
___ic acid
per___ate
per___ic acid
Example:ClO4- to HClO4 => perchlorate to perchloric acidClO- to HClO => hypochlorite to hypochlorous acid
Naming Compounds
A detailed treatise on naming organic compounds is beyond the scope of these materials, but some basics are presented. The wise chemistry student should consider memorizing the prefixes of the first ten organic compounds:
Number of Carbons
Prefix
1
meth-
2
eth-
3
prop-
4
but-
5
pent-
6
hex-
7
hept-
8
oct-
9
non-
10
dec-
There are four basic types of organic hydrocarbons, those chemicals with only carbon and hydrogen:
Single bonds (alkane): suffix is "ane", formula CnH2n+2
Double bonds (alkene): suffix is "ene", formula CnH2n
Triple bonds (alkyne): suffix is "yne", formula CnH2n-2
Cyclic compounds: use prefix "cyclo"
So, for example, an organic compound with the formula "C6H14" would be recognized as an alkane with six carbons, so its name is "hexane".
Examples:N2O4 = dinitrogen tetraoxideS2F10 = disulfur decafluoride
Practice Problems
Find the formulas of the following molecules:
1.
aluminum fluoride
8.
ammonium dichromate
2.
carbon tetrachloride
9.
magnesium acetate
3.
strontium nitrate
10.
zinc hydroxide
4.
sodium bisulfate
11.
nitric acid
5.
iron(III) oxide
12.
hypochlorous acid
6.
mercury(II) nitrate
13.
phosphoric acid
7.
sodium sulfite
14.
aluminum nitrate
A solution set is available for viewing.
Write the names of the following molecules:
1.
CaCO3
8.
Mg3(PO4)2
2.
SCl2
9.
Ba(NO2)2
3.
Li2CrO4
10.
Hg2Cl2
4.
NaSCN
11.
NaHCO3
5.
KClO3
12.
H2S
6.
Ca(C2H3O2)2
13.
H2SO3
7.
K2Cr2O7
14.
SO3
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