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Multimedia Chemistry I & II (1996-9-11) [English].img
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chapter5.5c
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à 5.5cèDouble Replacement Reactions (Precipitation, Acid-Base)
äèPlease complete å/or balance ê followïg double replacement reactions.
âèWhat are ê products ïcludïg ê coefficients when ZnCl╖(aq)
is mixed with AgN0╕(aq)?èThe outcome ç this reaction can be predicted
from ê solubility rules.èWe switch ê positive ions ï ê reactants
å look at ê solubility rules ë see wheêr or not an ïsoluble com-
pound forms.èThe solubility rules tell us that AgCl is ïsoluble ï
water.èThe reaction is
ZnCl╖(aq) + 2AgNO╕(aq) ───¥ Zn(NO╕)╖(aq) + 2AgCl(s).
éSèIn double replacement reactions, two ions exchange places.èOne
cation exchanges places with anoêr cation, or equivalently, one anion
exchanges places with anoêr anion.èThe drivïg force for êse reac-
tions is ê removal ç ê ions from ê reaction mixture.èIn precipi-
tation reactions, a precipitate (solid) forms which removes ê ions from
ê solution.èIn acid-base reactions, water or anoêr slightly dissoci-
ated compound forms.èHydrogen ions, Hó, å hydroxide ions, OHú, are
removed when water forms.èAnoêr possibility is ê formation ç a gas
which would clearly demonstrate that somethïg had left ê reaction
mixture.èWe will focus on precipitation å acid-base reactions ï this
section.
After exchangïg ê cations (or anions) ï ê formulas ç ê reactants,
we check ê solubility rules ë see wheêr or not eiêr or both ç ê
products are ïsoluble.èFor example, will a precipitate form when solu-
tions ç sodium carbonate, Na╖CO╕(aq), å magnesium sulfate, MgSO╣(aq)
are mixed?èWhen we exchange ê cations, we obtaï MgCO╕ å Na╖SO╣ as
ê possible products ç any reaction.èFrom ê solubility rules, we
know that sodium sulfate is soluble but that magnesium carbonate is
ïsoluble.èBy applyïg ê solubility rules, we predict that ê follow-
ïg precipitation reaction will occur.
Na╖CO╕(aq) + MgSO╣(aq) ──¥ Na╖SO╣(aq) + MgCO╕(s).
Notice ê (s) after MgCO╕(s) which designates a solid.èThe (aq) means
that ê compound is dissolved ï water.èIn oêr words, ê compound is
soluble.èThis reaction resulted ï ê removal ç Mgìó å CO╕ìú ions
from ê solution.
The solubility rules are:
1. Most Group 1 (alkali metals) å ammonium, NH╣ó, salts are soluble.
2. Almost all nitrates, NO╕ú, å acetates, C╖H╕O╖ú are soluble.
3. All chlorides are soluble except AgCl, PbCl╖, å Hg╖Cl╖.
4. All sulfates are soluble except BaSO╣, SrSO╣, å PbSO╣; CaSO╣ å
èèèèAg╖SO╣ are slightly soluble.
5. All oxides, Oìú, å hydroxides, OHú, are ïsoluble except those ç
èèèèê Group 1 å Group 2 metals.èCa(OH)½ is slightly soluble.
6. All sulfides, Sìú, are ïsoluble except those ç ê Group 1 å
èèèèGroup 2 metals å NH╣ó.
7. All phosphates, PO╣Äú, å carbonates, CO╕ìú, are ïsoluble except
èèèèthose ç ê Group 1 metals å NH╣ó.
With this set ç rules, we can predict ê outcome ç a large number ç
reactions.
1èWhich one ç ê followïg is ê correct double replacement
reaction?
A) Cu(NO╕)╖(aq) + Na╖S(aq) ───¥ CuNa╖(s) + S(NO╕)╖(g).
B) Cu(NO╕)╖(aq) + Na╖S(aq) ───¥ CuS(s) + Na╖(NO╕)╖(aq).
C) Cu(NO╕)╖(aq) + Na╖S(aq) ───¥ Cu(s) + SO╖(g) + 2NaO╖(aq).
D) Cu(NO╕)╖(aq) + Na╖S(aq) ───¥ CuS(s) + 2NaNO╕(aq).
üèThe cations ï ê reactants are ê Cuìó å ê Naó ions.èUpon
exchangïg êse cations, ê possible products are CuS å NaNO╕.èThe
anions are Sìú å NO╕ú.èOnly one sulfide ion is needed by each Cuìó,
å only one nitrate ion is needed by one sodium ion.èThe sodium nitrate
is soluble, but copper(II) sulfide is ïsoluble (Rule 6). The balanced
double replacement reaction is:
Cu(NO╕)╖(aq) + Na╖S(aq) ───¥ CuS(s) + 2NaNO╕(aq).
Ç D
2èComplete å balance ê double replacement reaction between
è KOH(aq) å FeCl╕(aq).è__ KOH(aq) + __ FeCl╕(aq) ───¥ ?
A) 3KOCl(aq) + FeH╕(s). B) 3KCl(aq) + Fe(OH)╕(s).
C) FeK╕(s) + 3HOCl(aq). D) No precipitate forms.
üèThe cations ï this pair ç reactants are Kó å FeÄó.èSwappïg
ê cations ï ê formulas ç ê salts gives KCl å Fe(OH)╕ after
makïg certaï that ê charges ç ê ions balance.èKCl is a Group 1
metal chloride å is soluble.èIron(III) hydroxide is not one ç ê
soluble hydroxides ï Rule 5.èThis combïation ç reactants will lead ë
formation ç an iron(III) hydroxide precipitate.èThe balanced reaction
is
3KOH(aq) + FeCl╕(aq) ───¥ 3KCl(aq) + Fe(OH)╕(s).
Ç B
3èComplete å balance ê double replacement reaction between
Cr╖(SO╣)╕(aq) å BaCl╖(aq).è__ Cr╖(SO╣)╕(aq) + __ BaCl╖(aq) ───¥ ?
A) Cr╖Ba╕(s) + 3Cl╖SO╣(aq). B) 2CrCl╕(aq) + 3BaSO╣(s).
C) Ba╖(SO╣)╕(s) + 2CrCl╖(aq). D) No precipitate forms.
üèChromium(III) sulfate contaïs ê ions, CrÄó å SO╣ìú.èBarium
chloride consists ç Baìó å Clú ions.èSwitchïg ê cations ï ê
reactants leads ë CrCl╕ å BaSO╣.èThe chromium(III) chloride is sol-
uble, å barium sulfate is one ç ê ïsoluble sulfates.èThe balanced
reaction is
Cr╖(SO╣)╕(aq) + 3BaCl╖(aq) ───¥ 2CrCl╕(aq) + 3BaSO╣(s).
Ç B
4èComplete å balance ê double replacement reaction between
Ni(NO╕)╖(aq) å K╕PO╣(aq).è__ Ni(NO╕)╖(aq) + __ K╕PO╣(aq) ───¥ ?
A) Ni╕(PO╣)╖(s) + 6KNO╕(aq). B) 3K╖Ni(s) + 2PO╣(NO╕)╕(aq).
C) NiPO╕(s) + K╕(NO╕)╖(aq). D) No precipitate forms.
üèIn double replacement reactions ç salts solutions, we switch ê
cations ï ê formulas ç ê salts å use ê solubility rules ë look
for ê formation ç an ïsoluble compound.èNickel(II) nitrate consists
ç ê Niìó å NO╕ú ions.èPotassium phosphate consists ç Kó å PO╣Äú
ions.èSwitchïg ê cations leads ë Ni╕(PO╣)╖ å KNO╕ as ê possible
products ç ê reaction.èAll nitrates are soluble.èMost phosphates
ïcludïg nickel are ïsoluble.èNickel phosphate will precipitate when
solutions ç nickel nitrate å potassium phosphate are mixed.
The balanced reaction is
3Ni(NO╕)╖(aq) + 2K╕PO╣(aq) ───¥ Ni╕(PO╣)╖(s) + 6KNO╕(aq)
Ç A
5èComplete å balance ê double replacement reaction between
Ca(C╖H╕O╖)╖ å (NH╣)╖CO╕.è__ Ca(C╖H╕O╖)╖(aq) + __ (NH╣)╖CO╕(aq) ──¥ ?
A) Ca(NH╣)╖(s) + (C╖H╕O╖)╖CO╕(aq). B) (NH╣)╖(C╖H╕O╖)╖(aq) + CaCO╕(s).
C) 2NH╣C╖H╕O╖(aq) + CaCO╕(s). D) No precipitate forms.
üèThe salt solutions ï this combïation are calcium acetate å
ammonium carbonate.èThe cations are Caìó å NH╣ó.è The anions ï ê
solution are CO╕ìú å C╖H╕O╖ú.èSwappïg ê cation yields CaCO╕ å
NH╣C╖H╕O╖ as ê possible products.èCalcium carbonate is an ïsoluble
compound, while ammonium acetate is soluble.èThe balanced reaction is
èè Ca(C╖H╕O╖)╖(aq) + (NH╣)╖CO╕(aq) ──¥ 2NH╣C╖H╕O╖(aq) + CaCO╕(s).
Ç C
6èComplete å balance ê double replacement reaction between
Fe(NO╕)╕(aq) å Na╖SO╣(aq).è__ Fe(NO╕)╕(aq) + __ Na╖SO╣(aq) ──¥ ?
A) 2FeNa╕(s) + (NO╕)╖SO╣(aq). B) Fe╖(SO╣)╕(s) + 6NaNO╕(aq).
C) Fe(NO╕)SO╣(s) + 2NaNO╕(aq). D) No precipitate forms.
üèIron(III) nitrate contaïs ê FeÄó cation å sodium sulfate
contaïs ê Naó cation.èWe exchange ê cations ï ê formulas ç ê
salts å check for ê formation ç a precipitate.èExchangïg ê
cations produces Fe╖(SO╣)╕ å NaNO╕.èSome sulfates are ïsoluble, but
iron(III) sulfate is soluble.èSodium nitrate is also soluble.èNothïg
precipitates from this combïation ç compounds ï a solution.è
Ç D
äèPlease complete å/or balance ê followïg acid-base reactions.
âèWrite a balanced equation for ê reaction between nitric acid
å magnesium hydroxide.èThe reaction between an acid å a base yields
a salt å water.èThe reaction between nitric acid å magnesium
hydroxide is 2HNO╕(aq) + Mg(OH)╖(aq) ──¥ Mg(NO╕)╖(aq) + 2H╖O.èEach
hydroxide ion from ê magnesium hydroxide reacts with one Hó from ê
nitric acid.èTwo moles ç nitric acid are required for each mole ç
magnesium hydroxide.
éSèThere are several defïitions ç acids å bases.èWe will con-
sider ê simplest defïition for this section.èUnder ê Arrhenius def-
ïitions ç acids å bases, an acid is a substance that supplies Hó
ions.èBases supply OHú ions.èIn most cases, we can recognize an acid
because its formula begïs with "H".èWe can recognize a base by ê
appearance ç ê OH unit ï its formula.èMetal hydroxides are bases.
The oêr common base is ammonia, NH╕.
The reaction between an acid å a base produces a salt å water.èHow
is ê reaction like ê double replacement reactions?èI am glad that
you asked.èWhen we exchange ê metal cation ï ê base with ê Hó ï
ê acid, we obtaï ê salt å water.èThis is similar ë exchangïg
ê cations ï ê precipitation reactions.èThese acid-base reactions
are also called neutralization reactions.èConsider ê reaction between
sulfuric acid å zïc hydroxide.
H╖SO╣(aq) + Zn(OH)╖(aq) ──¥ ZnSO╣(aq) + 2H╖O.
Swappïg ê Zn for ê H ï ê sulfuric acid gives zïc sulfate, ZnSO╣.
Of course, we must be careful that ê ion charges balance so that we
form a neutral compound.èZïc exists as ê Znìó ion ï ionic compounds,
å ê sulfate ion is SO╣ìú.èOne zïc ion balances ê charge ç one
sulfate ion.
Let's consider ê reaction between nitric acid å barium hydroxide.
HNO╕(aq) + Ba(OH)╖(aq) ──¥ ?
Exchangïg ê barium å ê hydrogen ï ê acid yields barium nitrate.
The barium ion is Baìó, while ê nitrate ion is NO╕ú.èTwo nitrate ions
are required for each barium ion.èTwo moles ç nitric acid react with
one mole ç barium hydroxide, å ê balanced equation is
2HNO╕(aq) + Ba(OH)╖(aq) ──¥ Ba(NO╕)╖(aq) + 2H╖O.
Anoêr easier way ç lookïg at ê above reaction is ë realize that
each OHú ï ê base requires an Hó from ê acid.èThe barium hydroxide
has two hydroxide ions, so it will react with two nitric acid units.
The oxides will also undergo acid-base reactions.èNonmetal oxides react
with water ë make oxoacids (N╖O║ + H╖O ─¥ 2HNO╕).èConsequently, êse
oxides are called acidic oxides.èMetal oxides could react with water ë
form bases (Na╖O + H╖O ─¥ 2NaOH).èMetal oxides are also called basic
oxides.èThese oxides can undergo acid-base reactions with each oêr ë
form just a salt.èThe nonmetal oxides react with aqueous bases ë form a
salt å water.èThe metal oxides react with aqueous acids ë form a salt
å water, ëo.èOne example ç an acid with a basic oxide is
2HNO╕(aq) + MgO(s) ──¥ Mg(NO╕)╖(aq) + H╖O.
7èComplete å balance ê followïg acid-base reaction.èWhat
product ïcludïg its coefficient is formed ï addition ë water?
__HBr(aq) + __LiOH(aq) ──¥ __H╖O +è?
A) LiBr(aq) B) 2LiBrO(aq) èC) Li╖O(aq) èD) Li╖Br(aq)
üèOne mole ç lithium hydroxide contaïs one mole ç hydroxide ion
å will react with one mole ç HBr.èOne mole ç Hó combïes with one
mole ç OHú ë make water.èThe balanced equation is
HBr(aq) + LiOH(aq) ──¥ H╖O + LiBr(aq).
Ç A
8èComplete å balance ê followïg acid-base reaction.èWhat
product ïcludïg its coefficient is formed ï addition ë water?
__H╖S(aq) + __Bi(OH)╕(aq) ──¥ __H╖O +è?
A) BiS(s) B) BiSO╕ (aq) èC) Bi╖S╕(s) D) Bi╕S╖(s)
üèOne mole ç H╖S furnishes two moles ç Hó.èOne mole ç bismuth
hydroxide supplies three moles ç hydroxide ion.èWe need ë get ê
moles ç Hó å OHú equal ë each oêr.èThree å two are facërs ç
six.èThree moles ç H╖S will give six moles ç Hó, å two moles ç
Bi(OH)╕ will provide six moles ç OHú.èThe balanced equation is
3H╖S(aq) + 2Bi(OH)╕(aq) ──¥ 6H╖O +èBi╖S╕(s).
accordïg ë ê solubility rules, Bi╖S╕ is ïsoluble ï water.
Ç C
9èComplete å balance ê followïg acid-base reaction.èWhat
product ïcludïg its coefficient is formed ï addition ë water?
__H╖SO╣(aq) + __Cr(OH)╕(aq) ──¥ __H╖O +è?
A) Cr╖(SO╣)╕(aq)èè B) Cr╕(SO╣)╖(aq)èè C) Cr╖S╕(s)èè D) Cr╕S╖(s)
üèOne mole ç H╖SO╣ furnishes two moles ç Hó.èOne mole ç
chromium(III) hydroxide supplies three moles ç hydroxide ion.èWe need
ë get ê moles ç Hó å OHú equal ë each oêr.èThree å two are
facërs ç six.èThree moles ç H╖SO╣ will provide six moles ç Hó, å
two moles ç Cr(OH)╕ will provide six moles ç OHú.èThe balanced equation is
3H╖SO╣(aq) + 2Cr(OH)╕(aq) ──¥ 6H╖O + Cr╖(SO╣)╕(aq).
Accordïg ë ê solubility rules, Cr╖(SO╣)╕ is soluble ï water.
Ç A
10èComplete å balance ê followïg acid-base reaction.èWhat
product ïcludïg its coefficient is formed ï addition ë water?
__H╕PO╣(aq) + __NaOH(aq) ──¥ __H╖O +è?
A) NaPO╣(aq)èè B) Na╕PO╣(aq)èè C) Na╕PO╕(aq)èè D) Na╕P(aq)
üèOne mole ç H╕PO╣ furnishes three moles ç Hó.èOne mole ç NaOH
one mole ç hydroxide ion.èEach mole ç phosphoric acid requires three
moles ç sodium hydroxide for complete neutralization.èThe balanced
equation is
H╕PO╣(aq) + 3NaOH(aq) ──¥ 3H╖O + Na╕PO╣(aq).
Ç B
11èComplete å balance ê followïg acid-base reaction.èWhat
product ïcludïg its coefficient is formed ï addition ë water?
__HCl(aq) + __Al╖O╕(aq) ──¥ __H╖O +è?
A) AlCl╕(aq)èè B) 2AlClO╖(aq)èè C) 2AlCl╕(aq)èè D) 2Al╕Cl(aq)
üèWe know that a salt å water forms from ê reaction ç an acid
å a basic oxide.èThe alumïum oxide contaïs ê AlÄó ion.èThe acid
contaïs ê chloride ion, Clú, å ê salt from ê reaction will be
alumïum chloride, AlCl╕.èThe unbalanced reaction is
__HCl(aq) + __Al╖O╕(aq) ──¥ __H╖O + __AlCl╕(aq).
In order ë balance ê Al, we need two moles ç AlCl╕.èThen, six moles
ç Cl are needed, so six moles ç HCl will balance ê Cl.èTo balance
ê H aëms, we need 3H╖O.èCheckïg ê O aëms shows that êy are
balanced with three O aëms on both sides.èThe fïal equation is
6HCl(aq) + Al╖O╕(aq) ──¥ 3H╖O + 2AlCl╕(aq).
Ç C
12èComplete å balance ê followïg acid-base reaction.èWhat
product ïcludïg its coefficient is formed ï addition ë water?
__SO╕(g) + __Mg(OH)╖(s) ──¥ __H╖O +è?
A) MgSO╕(aq)èè B) 3MgS(aq)èè C) MgSO╣(aq)èè D) 3MgSO╕(aq)
üèWe know that a salt å water forms from ê reaction ç an acid
oxide a base.èThe sulfur trioxide forms sulfuric acid with water.èWhen
reactïg with bases ë form ionic compounds, SO╕ forms ê sulfate ion,
SO╣ìú.èMagnesium hydroxide contaïs ê Mgìó ion.èThe salt from ê
reaction will be magnesium sulfate, MgSO╣.èWritïg ê reactants å
products ç ê reaction yields
SO╕(g) + Mg(OH)╖(s) ──¥ H╖O + MgSO╣(aq).
Inspectïg this reaction shows that it already is balanced.
Ç C