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CHAPTER 8
CHEMICAL EQUATIONS
SOLUTIONS TO REVIEW QUESTIONS
1. The coefficients in a balanced chemical equation represent the number of moles (or molecules or formula
units) of each of the chemical species in the reaction.
2. The physical state of a substance may be a solid, a liquid, or a gas. The symbols indicate whether a
substance is a solid, a liquid, a gas, or is in an aqueous solution. A solid is indicated by (s), a liquid by (l ),
a gas by (g) and an aqueous solution by (aq).
3. The purpose of balancing chemical equations is to conform to the Law of Conservation of Mass. Ratios of
reactants and products can then be easily determined.
4. (a)
(b)
(c)
Yes. It is necessary to conserve atoms to follow the Law of Conservation of Mass.
No. Molecules can be taken apart and rearranged to form different molecules in reactions.
Moles of molecules are not conserved (b). Moles of atoms are conserved (a).
5. These charts help to keep track of which elements are balanced in a chemical equation. The charts are
one way of keeping track of the number of atoms of each element on the reactant side of a chemical
equation and on the product side of an equation. The top row in a chart gives the number and types of
atoms on the reactant side and the bottom row gives the number and types of atoms on the product side
of a chemical equation. Using a chart may make it easier to see where coefficients are needed in a reaction
and what number that coefficient should be.
6. Chemical equations can only be balanced by changing the number of each substance reacted or produced.
If the subscripts are changed then the identity of the reactants and products is also changed. Equations
must be balanced using the actual reactants and products.
7. A combustion reaction is an exothermic process (usually burning) done in the presence of oxygen.
8. The activity series given in Table 8.2 shows the relative activity of certain metals and halogens. As you
move up the table starting with gold (Au) and ending with potassium (K) the activity increases. The same
is true as you move up from iodine (I2) to fluorine (F2). The table is useful for predicting the products of
some reactions because an element in the series will replace any element given below it. For example,
hydrogen can replace copper, silver, mercury, or gold in a chemical reaction.
9. The major types of chemical reactions are combination reactions, decomposition reactions, single
displacement reactions, and double displacement reactions.
10. Indicators that a chemical reaction has occurred are
Formation of a precipitate
Formation of a gas
A temperature change
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- Chapter 8 11. A chemical change that absorbs heat energy is said to be an endothermic reaction. The products are at a
higher energy level than the reactants. A chemical change that liberates heat energy is said to be an
exothermic reaction. The products are at a lower energy level than the reactants.
12. Although an exothermic reaction will liberate more heat than it absorbs, some heat is still necessary to get
the reaction started. The energy required to start a reaction is the activation energy.
13. Methane, carbon dioxide and water
14. Carbon dioxide levels fall in the spring as plants grow and incorporate carbon dioxide into their cells.
Carbon dioxide levels rise in the fall as plants begin to decay back into the soil releasing carbon dioxide
back into the air.
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- Chapter 8 -
SOLUTIONS TO EXERCISES
1. (a) exothermic
(b) endothermic
(c) exothermic
(d)
(e)
exothermic
endothermic
2. (a) endothermic
(b) exothermic
(c) endothermic
(d)
(e)
exothermic
exothermic
2 H2 þ O2 ! 2 H2 O
combination
(b)
3 N2 H4 ðl Þ ! 4 NH3 ðgÞ þ N2 ðgÞ
decomposition
(c)
H2 SO4 þ 2 NaOH ! 2 H2 O þ Na2 SO4
double displacement
(d)
Al2 ðCO3 Þ3 ! Al2 O3 þ 3 CO2
decomposition
(e)
2 NH4 I þ Cl2 ! 2 NH4 Cl þ I2
single displacement
3. (a)
D
H2 þ Br2 ! 2 HBr
combination
! BaSO4 ðsÞ þ H2 O2 ðaqÞ
BaO2 ðsÞ þ H2 SO4 ðaqÞ double displacement
(c)
BaðClO3 Þ2 ! BaCl2 þ 3 O2
decomposition
(d)
CrCl3 þ 3 AgNO3 ! CrðNO3 Þ3 þ 3 AgCl
double displacement
(e)
2 H2 O2 ! 2 H2 O þ O2
decomposition
4. (a)
(b)
D
5. There are many ways to form oxides. For example: (1) some metals plus oxygen, (2) some nonmetals
plus oxygen, (3) some metals plus water (steam), (4) combustion of hydrocarbons
6. A metal and a nonmetal can react to form a salt; the reaction of an acid and a base can form a salt.
7. (a)
2 MnO2 þ CO ! Mn2 O3 þ CO2
(b)
Cu2 OðsÞ þ CðsÞ ! 2 CuðsÞ þ COðgÞ
(c)
4 C3 H5 ðNO3 Þ3 ! 12 CO2 þ 10 H2 O þ 6 N2 þ O2
(d)
4 FeS þ 7 O2 ! 2 Fe2 O3 þ 4 SO2
(e)
2 CuðNO3 Þ2 ! 2 CuO þ 4 NO2 þ O2
(f)
3 NO2 þ H2 O ! 2 HNO3 þ NO
(g)
2 FeðsÞ þ 3 Sðl Þ ! Fe2 S3 ðsÞ
(h)
4 HCN þ 5 O2 ! 2 N2 þ 4 CO2 þ 2 H2 O
(i)
2 B5 H9 þ 12 O2 ! 5 B2 O3 þ 9 H2 O
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- Chapter 8 8. (a)
(b)
2 SO2 þ O2 ! 2 SO3
Li2 OðsÞ þ H2 Oðl Þ ! 2 LiOHðaqÞ
(c)
2 Na þ 2 H2 O ! 2 NaOH þ H2
(d)
2 AgNO3 þ Ni ! NiðNO3 Þ2 þ 2 Ag
(e)
Bi2 S3 þ 6 HC1 ! 2 BiCl3 þ 3 H2 S
D
(f) 2 PbO2 ! 2 PbO þ O2
(g) Hg2 ðC2 H3 O2 Þ2 ðaqÞ þ 2 KClðaqÞ ! Hg2 Cl2 ðsÞ þ 2 KC2 H3 O2 ðaqÞ
(h)
2 KI þ Br2 ! 2 KBr þ I2
(i)
2 K3 PO4 þ 3 BaCl2 ! 6 KCl þ Ba3 ðPO4 Þ2
9. (a)
MgðsÞ þ 2 HBrðaqÞ ! H2 ðgÞ þ MgBr2 ðaqÞ
D
(b)
CaðClO3 Þ2 ðsÞ ! CaCl2 ðsÞ þ 3 O2 ðgÞ
(c)
4 LiðsÞ þ O2 ðgÞ ! 2 Li2 OðsÞ
(d)
3 BaðBrO3 Þ2 ðaqÞ þ 2 Na3 PO4 ðaqÞ ! Ba3 ðPO4 Þ2 ðsÞ þ 6 NaBrO3 ðaqÞ
(e)
2 HC2 H3 O2 ðaqÞ þ Na2 CO3 ðaqÞ ! 2 NaC2 H3 O2 ðaqÞ þ CO2 ðgÞ þ H2 Oðl Þ
(f)
3 AgNO3 ðaqÞ þ AlI3 ðaqÞ ! 3 AgIðsÞ þ AlðNO3 Þ3 ðaqÞ
10. (a)
D
MgCO3 ðsÞ ! MgOðsÞ þ CO2 ðgÞ
(b)
CaðOHÞ2 ðsÞ þ 2 HClO3 ðaqÞ ! CaðClO3 Þ2 ðaqÞ þ 2 H2 Oðl Þ
(c)
Fe2 ðSO4 Þ3 ðaqÞ þ 6 NaOHðaqÞ ! 2 FeðOHÞ3 ðsÞ þ 3 Na2 SO4 ðaqÞ
(d)
ZnðsÞ þ 2 HC2 H3 O2 ðaqÞ ! H2 ðgÞ þ ZnðC2 H3 O2 Þ2 ðaqÞ
(e)
SO3 ðgÞ þ H2 Oðl Þ ! H2 SO4 ðaqÞ
(f)
Na2 CO3 ðaqÞ þ CoCl2 ðaqÞ ! CoCO3 ðsÞ þ 2 NaClðaqÞ
11. (a)
H2 SO4 ðaqÞ þ 2 NaOHðaqÞ ! 2 H2 Oðl Þ þ Na2 SO4 ðaqÞ þ heat
(b)
PbðNO3 Þ2 ðaqÞ þ 2 KBrðaqÞ ! PbBr2 ðsÞ þ 2 KNO3 ðaqÞ
(c)
NH4 ClðaqÞ þ AgNO3 ðaqÞ ! AgClðsÞ þ NH4 NO3 ðaqÞ
(d)
CaCO3 ðsÞ þ 2 HC2 H3 O2 ðaqÞ ! CaðC2 H3 O2 Þ2 ðaqÞ þ H2 Oðl Þ þ CO2 ðgÞ
12. (a)
(b)
(c)
(d)
CuSO4 ðaqÞ þ 2 KOHðaqÞ ! CuðOHÞ2 ðsÞ þ K2 SO4 ðaqÞ
H3 PO4 ðaqÞ þ 3 NaOHðaqÞ ! Na3 PO4 ðaqÞ þ 3 H2 Oðl Þ þ heat
3 NaHCO3 ðsÞ þ H3 PO4 ðaqÞ ! Na3 PO4 ðaqÞ þ 3 H2 Oðl Þ þ 3 CO2 ðgÞ
2 AlCl3 ðaqÞ þ 3 PbðNO3 Þ2 ! 3 PbCl2 ðsÞ þ 2 AlðNO3 Þ3 ðaqÞ
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- Chapter 8 13. (a)
(b)
(c)
(d)
2 CaðsÞ þ 2 H2 OðlÞ ! CaðOHÞ2 ðaqÞ þ H2 ðgÞ
Br2 ðl Þ þ 2 KIðaqÞ ! I2 ðsÞ þ 2 KBrðaqÞ
CuðsÞ þ HClðaqÞ ! no reaction
2 AlðsÞ þ 3 H2 SO4 ðaqÞ ! 3 H2 ðgÞ þ Al2 ðSO4 Þ3 ðaqÞ
14. (a)
(b)
(c)
(d)
CuðsÞ þ NiCl2 ðaqÞ ! no reaction
2 RbðsÞ þ 2 H2 Oðl Þ ! H2 ðgÞ þ 2 RbOHðaqÞ
I2 ðsÞ þ CaCl2 ðaqÞ ! no reaction
3 MgðsÞ þ 2 AlðNO3 Þ3 ðaqÞ ! 2 AlðsÞ þ 3 MgðNO3 Þ2 ðaqÞ
15. (a)
(b)
(c)
(d)
SrðsÞ þ 2 H2 Oðl Þ ! H2 ðgÞ þ SrðOHÞ2 ðsÞ
BaCl2 ðaqÞ þ 2 AgNO3 ðaqÞ ! BaðNO3 Þ2 ðaqÞ þ 2 AgClðsÞ
MgðsÞ þ ZnBr2 ðaqÞ ! ZnðsÞ þ MgBr2 ðaqÞ
2 KðsÞ þ Cl2 ðgÞ ! 2 KClðsÞ
16. (a)
(b)
(c)
(d)
Li2 OðsÞ þ H2 O ! 2 LiOHðaqÞ
Na2 SO4 ðaqÞ þ PbðNO3 Þ2 ðaqÞ ! 2 NaNO3 ðaqÞ þ PbSO4 ðsÞ
ZnðsÞ þ CuSO4 ðaqÞ ! CuðsÞ þ ZnSO4 ðaqÞ
4 AlðsÞ þ 3 O2 ðgÞ ! 2 Al2 O3 ðsÞ
17. (a)
2 Ba þ O2 ! 2 BaO
(b)
(c)
(d)
(e)
18. (a)
D
2 NaHCO3 ! Na2 CO3 þ H2 O þ CO2
Ni þ CuSO4 ! NiSO4 þ Cu
MgO þ 2 HCl ! MgCl2 þ H2 O
H3 PO4 þ 3 KOH ! K3 PO4 þ 3 H2 O
C þ O2 ! CO2
D
(b)
(c)
(d)
2 AlðClO3 Þ3 ! 9 O2 þ 2 A1Cl3
CuBr2 þ Cl2 ! CuCl2 þ Br2
2 SbCl3 þ 3ðNH4 Þ2 S ! Sb2 S3 þ 6 NH4 Cl
(e)
2 NaNO3 ! 2 NaNO2 þ O2
19. (a)
(b)
(c)
D
One mole of MgBr2 reacts with two moles of AgNO3 to yield one mole of Mg(NO3)2 and two
moles of AgBr.
One mole of N2 reacts with three moles of H2 to produce two moles of NH3.
Two moles of C3H7OH react with nine moles of O2 to form six moles of CO2 and eight moles
of H2O.
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- Chapter 8 20. (a)
(b)
(c)
Two moles of Na react with one mole of Cl2 to produce two moles of NaCl and release 822 kJ of
energy. The reaction is exothermic.
One mole of PCI5 absorbs 92.9 kJ of energy to produce one mole of PC13 and one mole of Cl2.
The reaction is endothermic.
1 mol of solid sulfur will react with 2 moles of gaseous carbon monoxide to produce 1 mol of
gaseous sulfur dioxide, 2 moles of solid carbon, and 76 kilojoules of energy in this exothermic
reaction.
21. (a)
(b)
2 HgOðsÞ þ 182 kJ ! 2 HgðlÞ þ O2 ðgÞ
2 H2 ðgÞ þ O2 ðgÞ ! 2 H2 OðlÞ þ 571:6 kJ
22. (a)
(b)
CaðsÞ þ 2 H2 Oðl Þ ! CaðOHÞ2 ðaqÞ þ H2 ðgÞ þ 635:1 kJ
2 BrF3 þ 601:6 kJ ! Br2 þ 3 F2
23. (a)
(b)
(c)
(d)
decomposition reaction, 2 AgClO3 ðsÞ ! 2 AgClðsÞ þ 3 O2 ðgÞ
single-displacement, FeðsÞ þ H2 SO4 ðaqÞ ! H2 ðgÞ þ FeSO4 ðaqÞ
combination reaction, ZnðsÞ þ Cl2 ðgÞ ! ZnCl2 ðsÞ
double-displacement, HBrðaqÞ þ KOHðaqÞ ! KBrðaqÞ þ H2 Oðl Þ
24. (a)
(b)
(c)
(d)
single-displacement, NiðsÞ þ PbðNO3 Þ2 ðaqÞ ! PbðsÞ þ NiðNO3 Þ2 ðaqÞ
combination, MgOðsÞ þ H2 Oðl Þ ! MgðOHÞ2 ðsÞ
decomposition, 2 HgOðsÞ ! 2 Hgðl Þ þ O2 ðgÞ
double-displacement, PbCl2 ðaqÞ þ ðNH4 Þ2 CO3 ðaqÞ ! PbCO3 ðsÞ þ 2 NH4 ClðaqÞ
D
25. Combinations that form a precipitate:
CaðNO3 Þ2 ðaqÞ þ ðNH4 Þ2 SO4 ðaqÞ ! CaSO4 ðsÞ þ 2 NH4 NO3 ðaqÞ
CaðNO3 Þ2 ðaqÞ þ ðNH4 Þ2 CO3 ðaqÞ ! CaCO3 ðsÞ þ 2 NH4 NO3 ðaqÞ
AgNO3 ðaqÞ þ NH4 ClðaqÞ ! AgClðsÞ þ NH4 NO3 ðaqÞ
2 AgNO3 ðaqÞ þ ðNH4 Þ2 SO4 ðaqÞ ! Ag2 SO4 ðsÞ þ 2 NH4 NO3 ðaqÞ
2 AgNO3 ðaqÞ þ ðNH4 Þ2 CO3 ðaqÞ ! Ag2 CO3 ðsÞ þ 2 NH4 NO3 ðaqÞ
26. P4 O10 þ 12 HC1O4 ! 6 Cl2 O7 þ 4 H3 PO4
10 O þ 12ð4 OÞ
6ð7 OÞ þ 4ð4 OÞ
10 O þ 48 O
42 O þ 16 O
58 O
58 O
27. In 5 Ni3(PO4)2 there are:
(a) 15 atoms of N
(b) 10 atoms of P
(c)
(d)
40 atoms of O
65 total atoms
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- Chapter 8 28. CaCO3 ðsÞ þ 2 HC2 H3 O2 ðaqÞ ! CaðC2 H3 O2 Þ2 ðaqÞ þ CO2 ðgÞ þ H2 Oðl Þ
29.
+
CH4 + 2 O2
Δ
+
Δ
CO2 + 2 H2O
+
+
C
O
H
30. (a)
C(s) þ O2(g) ! CO2(g)
(b)
! 2 CO(g)
CO2(g) þ C(s) (c)
Fe2O3(s) þ 3 CO(g) ! 2 Fe(l) þ 3 CO2(g)
D
D
Fe3O4(s) þ 4 CO(g) ! 3 Fe(l) þ 4 CO2(g)
31. 2 B þ 3 G2 ! 2 BG3
32. The metals that should be chosen are (b) zinc, (c) aluminum, and (e) calcium. These metals are more
active than nickel, therefore will react in a solution of nickel(II) chloride; (a) copper and (d) lead are less
active and will not react with nickel(II) chloride solution (see Table 8.2).
Equations
Zn þ NiCl2 ! Ni þ ZnCl2
2 Al þ 3 NiCl2 ! 3 Ni þ 2 AlCl3
Ca þ NiCl2 ! Ni þ CaCl2
33. Ti þ NiðNO3 Þ2 ! Reaction occurs
! Reaction occurs
Ti þ PbðNO3 Þ2 ! no reaction
Ti þ MgðNO3 Þ2 Ti is above Ni and Pb in the activity series since both react. Ti is below Mg in the series since it will not
replace Mg. From the printed activity series in the chapter Ni lies above Pb so the order is:
Mg
Ti
Ni
Pb
34. (a)
(b)
(c)
(d)
4 Cs þ O2 ! 2 Cs2 O
2 Al þ 3 S ! Al2 S3
SO3 þ H2 O ! H2 SO4
Na2 O þ H2 O ! 2 NaOH
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- Chapter 8 -
35. (a)
(b)
(c)
(d)
2 H2(g) þ O2(g) ! 2 H2O(g)
! 3 H2(g) þ CO(g)
CH4(g) þ H2O(g) CO(g) þ H2O(g) ! H2(g) þ CO2(g)
! 2 H2O(g) þ CO2(g)
CH4(g) þ 2 O2(g) One molecule of carbon dioxide is produced from one molecule of methane regardless of whether
it is converted into hydrogen gas or burned in oxygen. If the goal is to reduce carbon dioxide
emission, there is no advantage in using hydrogen synthesized from methane as a fuel.
! 2 KNO3(aq) þ PbCrO4(s)
36. (a) Pb(NO3)2(aq) þ K2CrO4(aq) (b) CdCl2(aq) þ Li2S(aq) ! CdS(s) þ 2 LiCl(aq)
(c) Pb(C2H3O2)2(aq) þ H2CO3(aq) ! PbCO3(s) þ 2 HC2H3O2(aq)
(d) Hg(NO3)2(aq) þ Na2S(aq) ! HgS(s) þ 2 NaNO3(aq)
(e) 4 Ti(s) þ 3 O2(g) ! 2 Ti2O3(s)
(f) 4 Fe(s) þ 3 O2(g) ! 2 Fe2O3(s)
37. (a)
D
2 ZnO ! 2 Zn þ O2
D
D
(b)
SnO2 ! Sn þ O2 or 2 SnO2 ! 2 SnO þ O2
(c)
Na2 CO3 ! Na2 O þ CO2
(d)
MgðClO3 Þ2 ! MgCl2 þ 3 O2
38. (a)
(b)
(c)
(d)
Lead(II) chromate
Cadmium sulfide
Lead(II) carbonate
Mercury(II) sulfide
Titanium(III) oxide
Iron(III) oxide
D
D
MgðsÞ þ 2 HClðaqÞ ! H2 ðgÞ þ MgCl2 ðaqÞ
2 NaBrðaqÞ þ Cl2 ðgÞ ! 2 NaClðaqÞ þ Br2 ðl Þ
3 ZnðsÞ þ 2 FeðNO3 Þ3 ðaqÞ ! 2 FeðsÞ þ 3 ZnðNO3 Þ2 ðaqÞ
2 AlðsÞ þ 3 CuðNO3 Þ2 ðaqÞ ! 3 CuðsÞ þ 2 AlðNO3 Þ3 ðaqÞ
39. (a) 2 ðNH4 Þ3 PO4 ðaqÞ þ 3 BaðNO3 Þ2 ðaqÞ ! Ba3 ðPO4 Þ2 ðsÞ þ 6 NH4 NO3 ðaqÞ
(b) Na2 SðaqÞ þ PbðC2 H3 O2 Þ2 ðaqÞ ! PbSðsÞ þ 2 NaC2 H3 O2 ðaqÞ
(c) CuSO4 ðaqÞ þ CaðClO3 Þ2 ðaqÞ ! CaSO4 ðsÞ þ CuðClO3 Þ2 ðaqÞ
(d) BaðOHÞ2 ðaqÞ þ H2 C2 O4 ðaqÞ ! BaC2 O2 ðaqÞ þ 2 H2 Oðl Þ
(e) H3 PO4 ðaqÞ þ 3 KOHðaqÞ ! K3 PO4 ðaqÞ þ 3 H2 Oðl Þ
(f) H2 SO4 ðaqÞ þ Na2 CO3 ðaqÞ ! Na2 SO4 ðaqÞ þ H2 Oðl Þ þ CO2 ðgÞ
40. (a) K2 SO4 ðaqÞ þ BaðC2 H3 OÞ2 ðaqÞ ! 2 KC2 H3 O2 ðaqÞ þ BaSO4 ðsÞ
(b) H2 SO4 ðaqÞ þ 2 LiOHðaqÞ ! Li 2 SO4 ðaqÞ þ 2 H2 Oðl Þ
(c) ðNH4 Þ3 PO4 ðaqÞ þ NaBrðaqÞ ! no reaction
(d) CaI2 ðaqÞ þ 2 AgNO3 ðaqÞ ! CaðNO3 Þ2 ðaqÞ þ 2 AgIðsÞ
(e) 2 HNO3 ðaqÞ þ SrðOHÞ2 ðaqÞ ! SrðNO3 Þ2 ðaqÞ þ 2 H2 Oðl Þ
(f) CsNO3 ðaqÞ þ CaðOHÞ2 ðaqÞ ! No reaction
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- Chapter 8 41. (a)
(b)
CH4 þ 2 O2 ! CO2 þ 2 H2 O
2 H2 þ O2 ! 2 H2 O
42. (a)
(b)
(c)
CH4 þ 2 O2 ! CO2 þ 2 H2 O
2 C3 H6 þ 9 O2 ! 6 CO2 þ 6 H2 O
C6 H5 CH3 þ 9 O2 ! 7 CO2 þ 4 H2 O
43. 1. combustion of fossil fuels
2. destruction of the rain forests by burning
3. increased population
44. Carbon dioxide, methane, and water are all considered to be greenhouse gases. They each act to trap the
heat near the surface of the earth in the same manner in which a greenhouse is warmed.
45. The effects of global warming can be reduced by:
1. developing new energy sources (not dependant on fossil fuels)
2. conservation of energy resources
3. recycling
4. decreased destruction of the rain forests and other forests
46. About half the carbon dioxide released into the atmosphere remains in the air. The rest is absorbed by
plants and used in photosynthesis or is dissolved in the oceans.
47. In the Northern Hemisphere, the concentration of CO2 peaks once in May, dropping as plants use the CO2
to produce growth, until October when the second peak occurs as a result of the fallen leaves decaying.
48. (a)
Ag+,
Co2+, Ba2+,
Zn2+,
Sn2+,
+Cl–
AgCl(s)
Co2+, Ba2+, Zn2+, Sn2+,
–
+SO24
BaSO4(s)
Co2+, Zn2+, Sn2+,
+F –
ZnF2(s)
Co2+, Sn2+,
+I–
SnI2(s)
Co2+
(b) All the anionic salts are sodium salts because you need to use soluble reagents and all sodium salts are
soluble.
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