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9 ACIDS, BASES, AND SALTS
to yield 2 H+ per H2SO4 molecule; the second of the 2 hydrogen ions comes off
much less readily than the first. Some acids have hydrogen atoms that do not
produce H + ion in water. For example, each molecule of acetic acid produces only
one H+ ion when it dissociates in water; the other 3 H atoms stay covalently bonded
to the acetate ion:
H C C OH
H C C O + H+
Some of the most widely produced industrial chemicals are acids. Sulfuric acid
ranks first among all chemicals produced in the United States with production of
almost 40 million metric tons per year. Its greatest single use is in the production of
phosphate fertilizers, and it has applications in many other areas including petroleum
refining, alcohol synthesis, iron and steel pickling (corrosion removal), and storage
battery manufacture. Nitric acid ranks about 10th among U.S. chemicals with annual
production of 7–8 million metric tons, and hydrochloric acid is about 25th at about 3
million metric tons (annual production and rank vary from year to year).
The naming of acids is addressed in more detail in Chapter 6. Briefly, acids that
contain only H and another atom are “hydro-ic” acids, such as hydrochloric acid,
HCl. For acids that contain two different amounts of oxygen in the anion part, the
one with more oxygen is an “-ic” acid and the one with less is an “-ous” acid. This is
illustrated by nitric acid, HNO3, and nitrous acid, HNO2. An even greater amount of
oxygen is denoted by a “per-” prefix and less by the “hypo-ous” name. The guidelines discussed above are illustrated for acids formed by chlorine ranging from 0 to 4
oxygen atoms per acid molecule as follows: HCl, hydrochloric acid; HClO, hypochlorous acid; HClO2, chlorous acid; HClO3, chloric acid; HClO4, perchloric acid.
A base is a substance that contains hydroxide ion OH-, or produces it when
dissolved in water. Most of the best known inorganic bases have a formula unit
composed of a metal cation and 1 or more hydroxide ions. Typical of these are
sodium hydroxide, NaOH, and calcium hydroxide, Ca(OH)2, which dissolve in water
to yield hydroxide ion and their respective metal ions. Other bases such as ammonia,
NH3, do not contain hydroxide ion, but react with water,
NH3 + H2O → NH4+ + OH-
to produce hydroxide ion (this reaction proceeds only to a limited extent; most of the
NH3 is in solution as the NH3 molecule).
Bases are named for the cation in them plus “hydroxide.” Therefore, KOH is
A salt is an ionic compound consisting of a cation other than H+ and an anion
other than OH-. A salt is produced by a chemical reaction between an acid and a
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base. The other product of such a reaction is always water. Typical salt-producing
reactions are given below:
Ca(OH)2 + H2SO4
a salt, potassium chloride
a salt, calcium sulfate
Except for those compounds in which the cation is H+ (acids) or the anion is OH(bases), the compounds that consist of a cation and an anion are salts. Therefore, the
rules of nomenclature discussed for ionic compounds in Section 4.8 are those of
salts. The salt product of Reaction 4.9.6, above, consists of K+ cation and Cl- anion,
so the salt is called potassium chloride. The salt product of Reaction 4.9.7, above, is
made up of Ca 2+ cation and SO42- anion and is called calcium sulfate. The reaction
product of LiOH base with H2SO4 acid is composed of Li+ ions and SO42- ions. It
takes 2 singly charged Li+ ions to compensate for the 2- charge of the SO42- anion,
so the formula of the salt is Li2SO4. It is called simply lithium sulfate. It is not
necessary to call it dilithium sulfate because the charges on the ions denote the
relative numbers of ions in the formula.
The chapter summary below is presented in a programmed format to review the
main points covered in this chapter. It is used most effectively by filling in the
blanks, referring back to the chapter as necessary. The correct answers are given at
the end of the summary.
Chemical bonds are normally formed by the transfer or sharing of 1
, which are those in the 2
especially stable group of electrons attained by many atoms in chemical compounds
is an 3
. An ion consists of 4
. A cation has 5
and an anion has
. An ionic compound is one that contains 7
and is held together by 8
. Both F - and Mg2+
have the electron configuration 9
identical to that of the neutral
. In visualizing a neutral metal atom reacting with a
neutral nonmetal atom to produce an ionic compound, the three major energy factors
. The energy required to separate all
of the ions in a crystalline ionic compound and remove them a sufficient distance
from each other so that there is no interaction between them is called the 12
. The ion formed from Ca is 13
, the ion
formed from Cl is
, and the formula of the compound formed from these
ions is 15
. A covalent bond may be described as 16
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. In the figure,
each pair of dots between N and H represents 17
the arrow points to 18
and the circle outlines 19
. A central atom refers to 20
. A triple bond
and is represented in a structural chemical formula as 22
With increasing bond order (single
. Electronegativity refers to 25
bond strength 24
. A polar covalent bond is one in
. A coordinate covalent bond is 27
. Three major exceptions to the octet rule are 28
Resonance structures are those for which 29
Chemical formulas consist of 30
that tell the following about a compound 31
. The percentage elemental composition of a chemical compound is calculated by 32
. The empirical formula of a chemical compound is
calculated by computing the masses of each consituent element in 33
dividing each of the resulting values by 34
, dividing each value by 35
and rounding to
The prefixes for numbers 1-10 used to denote relative numbers of atoms of each kind
of atom in a chemical formula are 37
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The compound N2O5 is called 38
compound AlCl3 is called 39
contain a “tri-” because 40
. The ionic
, which does not
. Ammonium ion, NH4+, is classified as
meaning that it consists of 42
. An acid is 43
A base is 44
. A salt is 45
duced by 46
The other product of such a reaction is always 47
and is pro.
Answers to Chapter Summary
outermost shell of the atom
octet of outer electrons
an atom or group of atoms having an unequal number of electrons and protons
and, therefore, a net electrical charge
a positive charge
a negative charge
cations and anions
ionization energy, electron affinity, and lattice energy
one that joins 2 atoms through the sharing of 1 or more pairs of electrons
a pair of electrons shared in a covalent bond
an unshared pair of electrons
a stable octet of electrons around the N atom
an atom to which several other atoms are bonded
3 pair (total of 6) electrons shared in a covalent bond
or : :
the ability of a bonded atom to attract electrons to itself
the electrons involved are not shared equally
one in which only 1 of the 2 atoms contributes the two electrons in the bond
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28. molecules with an uneven number of valence electrons, molecules in which an
atom capable of forming an octet has fewer than 8 outer electrons, and
molecules in which an atom has more than 8 outer electrons
29. it is possible to draw two or more equivalent arrangements of electrons
30. atomic symbols, subscripts, and sometimes parentheses and charges
31. elements in it, relative numbers of each kind of atom, charge, if an ion
32. dividing the mass of a mole of a compound into the mass of each of the constituent elements in a mole
33. 100 g of the element
34. the atomic mass of the element
35. the smallest value
36. the smallest whole number for each element
37. 1-mono, 2-di,3-tri, 4-tetra, 5-penta, 6-hexa, 7-hepta, 8-octa, 9-nona, 10-deca
38. dinitrogen pentoxide
39. aluminum chloride
40. the charges on ions are used to deduce chemical formulas
41. polyatomic ion
42. 2 or more atoms per ion
43. a substance that dissolves in water to produce hydrogen ion, H+(aq)
44. a substance that contains hydroxide ion OH-, or produces it when dissolved in
45. an ionic compound consisting of a cation other than H+ and an anion other than
46. a chemical reaction between an acid and a base
QUESTIONS AND PROBLEMS
Section 4.1. Chemical Bonds and Compound Formation
1. Chlorofluorocarbons (Freons) are composed of molecules in which Cl and F
atoms are bonded to 1 or 2 C atoms. These compounds do not break down well in
the atmosphere until they drift high into the stratosphere, where very short wavelength ultraviolet electromagnetic radiation from the sun is present, leading to the
production of free Cl atoms that react to deplete the stratospheric ozone layer.
Recalling what has been covered so far about the energy of electromagnetic radiation as a function of wavelength, what does this say about the strength of C-Cl
and C-F bonds?
Section 4.2. Chemical Bonding and the Octet Rule
2. Illustrate the octet rule with examples of (a) a cation, (b) an anion, (c) a diatomic
elemental gas, and (d) a covalently bound chemical compound.
Section 4.3. Ionic Bonding
3. When elements with atomic numbers 6 through 9 are covalently or ionically
bound, or when Na, Mg, or A1 have formed ions, which single element do their
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outer electron configurations most closely resemble? Explain your answer in
terms of filled orbitals.
4. Ionic bonds exist because of (a)
5. In the crystal structure of NaCl, what are the number and type of ions that are
nearest neighbors to each Na+ ion?
6. What major aspect of ions in crystals is not shown in Figure 4.5?
7. What are five energy factors that should be considered in the formation of ionic
NaCl from solid Na and gaseous Cl2?
8. What are two major factors that increase the lattice energy of ions in an ionic
9. Is energy released or is it absorbed when gaseous ions come together to form an
10. What is incomplete about the statement that “the energy change from lattice
energy for NaCl is 785 kilojoules of energy released?
11. How do the sizes of anions and cations compare with their parent atoms?
12. How do the sizes of monatomic (one-atom) cations and anions compare in the
Section 4.4. Fundamentals of Covalent Bonding
13. Define covalent bond.
14. Explain the energy minimum in the diagram illustrating the H-H covalent bond
in Figure 4.9.
Section 4.5. Covalent Bonds in Compounds
15. What may be said about the liklihood of H atoms being involved in double
16. What is represented by a dashed line, –, in a chemical formula?
17. What is represented by the two dots in the formula of phosphine, PH3, below:
Section 4.6. Some other Aspects of Covalent Bonding
18. What are multiple bonds?
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Which three elements are most likely to form
19. What can be said about the nature of covalent bonds between (a) 2 atoms with
almost identical electronegativity values and (b) 2 atoms with substantially
different electronegativity values?
20. What symbols are used to show bond polarity?
21. What is the “ultimate” in polar bonds?
22. A molecule of NH3 will combine with one of BF3. Describe the kind of bond
formed in the resulting compound.
23. What is required for an atom to form a compound with more than 8 electrons in
the central atom’s outer shell?
24. What are resonance structures?
25. How many total valence electrons are in the nitrate ion, NO3 ? What are the
resonance structures of this ion?
Section 4.7. Chemical Formulas of Compounds
26. Summarize the steps involved in calculating the percentage composition of a
compound from its formula.
27. Phosgene, COCl2, is a poisonous gas that was used for warfare in World War I.
What is its percentage composition?
28. The molecular formula of acetylsalicylic acid (aspirin) is C9H8O4. What is its
29. Hydrates are compounds in which each formula unit is associated with a definite
number of water molecules. A typical hydrate is copper (II) sulfate
CuSO4•5H2O. The water of hydration can be driven off by heating, leaving the
anhydrous compound. Answer the following pertaining to CuSO4•5H2O: (a)
Mass of 1 mole of the compound, (b) mass of H2O in 1 mole of CuSO4•5H2O,
(c) percentage of H2O in CuSO4•5H2O.
30. What are the percentages of oxygen in (a) perchloric acid, (b) chloric acid, (c)
chlorous acid, and (d) hypochlorous acid (these acids were discussed in this
31. What is the simplest (empirical) formula of sodium oxalate, Na2C2O4?
32. What is the formula of dichlorine heptoxide? What is its percentage composition?
33. Chlorine dioxide, ClO2, is used as a substitute for chlorine gas in the disinfection
of drinking water. What is the percentage composition of ClO2?
34. Summarize in steps the calculation of empirical formula from the percentage
composition of a compound.
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35. If the empirical formula and the actual formula mass (molecular mass) of a
compound are known, how is the true formula calculated?
36. A chlorofluorocarbon gas is 9.93% C, 31.43% F, and 58.64% Cl. What is its
37. A 100.0 g portion of the chlorofluorocarbon gas (preceding question) was found
to occupy 25.3 L at 100°C and 1.000 atm pressure. Assuming that the gas
behaved ideally and using the ideal gas equation, how many moles of the gas are
in 100.0 of Freon? What is its molar mass? What is its molecular formula? (To
answer this question it may be necessary to refer back to a discussion of the gas
laws in Section 2.6).
38. A compound is 5.88% H and 94.12% O. What is its empirical formula?
39. The compound from the preceding problem has a molecular mass of 34.0. What
is its molecular formula?
40. A pure liquid compound with an overpowering vinegar odor is 40.0% C, 6.67%
H, and 53.3% O. Its molecular mass is 60.0. What is its empirical formula?
What is its molecular formula?
41. A compound is 29.1% Na, 40.5% S, and 30.4% O. It has a formula mass of
158.0. Fill out the table below pertaining to the compound, give its true formula,
and give its actual formula. It is an ionic compound. What is the anion?
Grams of element
Element in 100 g compound
Mol element in
100 g compound mol element with fewest moles
42. An ionic compound is 41.7% Mg, 54.9% O, and 3.4% H. What is its empirical
formula? Considering the ions in Table 3.6, what is the actual formula?
43. Ethylenediamine is 40.0% C, 13.4% H, and 46.6% N; its formula mass is 60.1.
What are its empirical and molecular formulas?
44. The empirical formula of butane is C2H5 and its molecular mass is 58.14. What
is the molecular formula?
45. Suppose that you were asked to give the Lewis formula of formic acid, H2CO2,
where the atomic number of H is 1, that of C is 6, and that of O is 8. The total
number of valence (outer shell) electrons that would have to be placed correctly
in the structure is
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46. Given the Lewis symbols of hypothetical elements X and Z,
The compound most likely formed by these two elements would be
Covalently bound compound formula X2Z 3.
Covalently bound compound formula XZ.
Ionic compound formula X2Z.
Ionic compound XZ 2.
Ionic compound XZ.
47. Of the following, the statement that is untrue regarding ionic NaCl and its
formation from gaseous Na and Cl atoms is
A. Energy called electron repulsion is consumed in putting an electron on a Cl
atom to produce a Cl- ion.
B. Energy called ionization energy is required to remove an electron from a Na
atom to produce a Na+ ion.
C. A relatively large amount of energy (lattice energy) is released when the Na+
and Cl- ions come together to form crystalline NaCl.
D. A particular Cl- ion in the crystal of NaCl has 6 Na+ ions as its nearest
E. Every ion in the crystal of NaCl is closest to ions of opposite charge,
resulting in forces of attraction that account for the stability of ionic bonds.
48. Consider the single, double, and triple bonds connecting the 2 carbon atoms in
the 3 compounds C2H6, C 2H4, and C2H2. Of the following pertaining to these
bonds, the untrue statement is
A. The C=C bond is shorter than the C–C bond.
B. The C≡C bond is stronger than the C=C bond.
C. Because it must accomodate a total of 6 electrons rather than 2, the C≡C
bond is longer than the C–C bond.
D. As bond multiplicity increases, the bond strength increases and the bond
E. The bonds can act like springs in that the atoms connected by the bonds
vibrate when exposed to the right wavelength of infrared radiation.
49. Remember that O and S atoms all have the same number of valence electrons.
Considering the structures (Lewis formulas),
the true statement is
A. Only one of these structures can be correct.
B. Both of these structures are incorrect.
C. The structure on the left shows the incorrect number of outer shell electrons
for the O atom on the left.
D. The structures are equivalent resonance structures.
E. The text showed the sulfur atom on one end, not in the middle.
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Manahan, Stanley E. "CHEMICAL REACTIONS, EQUATIONS, AND STOICHIOMETRY"
Fundamentals of Environmental Chemistry
Boca Raton: CRC Press LLC,2001
5 CHEMICAL REACTIONS, EQUATIONS,
5.1 THE SENTENCES OF CHEMISTRY
As noted earlier, chemistry is a language. Success in the study of chemistry
depends upon how well chemical language is learned. This chapter presents the last
of the most basic parts of the chemical language. When it has been learned, the
reader will have the essential tools needed to speak and write chemistry and to apply
it in environmental and other areas.
Recall that the discussion of chemical language began by learning about the
elements, the atoms composing the elements, and the symbols used to designate
these elements and their atoms. Atoms of the elements bond together in various
combinations to produce chemical compounds. These are designated by chemical
formulas consisting of symbols for the kinds of atoms in the compound and
subscripts indicating the relative numbers of atoms of each kind in the compound. In
chemical language, the symbols of the elements are the letters of the chemical
alphabet and the formulas are the words of chemistry.
Chemical Reactions and Equations: The Sentences of the Chemical
The formation of chemical compounds, their decomposition, and their
interactions with one another fall under the category of chemical reactions.
Chemical reactions are involved in the annual production of millions of kilograms of
industrial chemicals, bacterially mediated degradation of water pollutants, the
chemical analysis of the kinds and quantities of components of a sample, and
practically any other operation involving chemicals. To a very large extent,
chemistry is the study of chemical reactions expressed on paper as chemical
equations. A chemical equation is a sentence of chemistry, made up of words
consisting of chemical formulas. A sentence should be put together according to
rules understood by all those literate in the language. The rules of the chemical
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