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Multimedia Chemistry I & II (1996-9-11) [English].img
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chapter5.4c
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à 5.4cèSïgle Replacement Reactions
äèPlease complete å/or balance ê followïg sïgle replacement reactions.
âèWhat are ê products ïcludïg ê coefficients when Zn reacts
with AgN0╕(aq)?èMetals will replace oêr less active metals.èZn is a
more active metal than Ag å can replace ê Ag.èZïc forms a +2 ion,
å silver exists as Agó ï ê silver nitrate.èConsequently, two silver
nitrates react with oneèzïc.èThe balanced reaction is
Zn(s) + 2AgNO╕(aq) ───¥ Zn(NO╕)╖(aq) + 2Ag(s).
éSèA sïgle replacement reaction is ê substitution ç one element
ï a compound by anoêr more reactive element.èThe outcome ç êse
reactions ïvolvïg metals can be predicted usïg ê activity series for
ê metals.èAlthough hydrogen is not a metal, it is ïcluded ï ê
series because most metals will displace hydrogen from acids.èThe series
with some ç ê more common metals is:
Li, K, Ba, Sr, Ca, Na, Mg, Al, Mn, Zn, Cr, Fe, Co, Ni, Sn, Pb, H╖, Cu,
Hg, Ag, Pt, Au.
In this list, ê most active metal is lithium, å ê least active
metal is gold, Au.èA metal can replace any metal followïg it ï ê
list.èThe ions that result from êse reactions are (e.g. Na forms Naó):
Lió, Kó, Baìó, Srìó, Caìó, Naó, Mgìó, AlÄó, Mnìó, Znìó, CrÄó, Feìó, Coìó,
Niìó, Snìó, Pbìó, Hó, Cuìó, Hgìó, Agó, Ptìó, AuÄó.
Usïg ê list, we can predict that Na will displace alumïum from its
salts.èFor example, ê followïg reaction does occur.
3Na(s) + AlCl╕(s) ──¥ 3NaCl(s) + Al(s).
On ê oêr hå, zïc will not displace alumïum, so ê followïg com-
bïation would not react.
Zn(s) + AlCl╕ ──¥ no reaction.
These reaction are relatively simple examples ç oxidation-reduction
reactions, which we will consider ï more detail latter.èOxidation-
reduction or redox reactions are driven by greedïess for electrons.
In ê above reaction between sodium å alumïum chloride, alumïum
wants electrons ë a greater extent than sodium does.èThe sodium gives
its valence electron ë ê alumïum.èSpecies that provide electrons
are called reducïg agents, so sodium is a reducïg agent.èThe species
that accepts ê electrons are called oxidizïg agents.èIn this reac-
tion, AlÄó is ê oxidizïg agent.èWe will discuss redox reactions agaï
ï ê sections on electrochemistry.
1èWhich one ç ê followïg is ê correct sïgle replacement
reaction?
A) Mg(s) + 2HCl(aq) ───¥ MgCl╖(aq) + H╖(g).
B) Mg(s) + Ca(NO╕)╖(aq) ───¥ Mg(NO╕)╖(aq) + Ca(s).
C) Mg(s) + 2HCl(aq) ───¥ MgH╖(aq) + Cl╖(g).
D) Mg(s) + Ca(NO╕)╖(aq) ───¥ MgCa(s) + 2NO╕(aq).
üèMagnesium precedes hydrogen ï ê activity series, so Mg can
displace hydrogen from acids.èMg follows Ca å will not displace
calcium from its salts or solutions.èThe magnesium forms a +2 ion å
ê HCl contaïs ê chloride ion.èThe formula ç magnesium chloride is
MgCl╖.èTo balance ê Cl, two HCl molecules are needed for each Mg.
The balanced replacement reaction is:
Mg(s) + 2HCl(aq) ───¥ MgCl╖(aq) + H╖(g).
Ç A
2èComplete å balance ê sïgle replacement reaction between
è Al å Fe╖O╕.è__ Al + __ Fe╖O╕ ──¥ ?
A) 3Al╖Fe╕ + 3O╕. B) 4AlFe + 3O╖.
C) Al╖O╕è+ 2Fe. D) No Reaction
üèAlumïum precedes Fe ï ê activity series å will replace Fe.
In Fe╖O╕, ê iron exists as FeÄó å oxygen exists as ê oxide ion.
Alumïum donates three electrons ë form AlÄó, which matches ê number
that FeÄó needs ë form ê neutral metal.èTwo Al react with one Fe╖O╕.
The balanced reaction is
2Al + Fe╖O╕ ───¥ Al╖O╕è+ 2Fe.
Ç C
3èComplete å balance ê sïgle replacement reaction between
è K å MgCl╖.è__ K + __ MgCl╖ ──¥ ?
A) 2KCl + Mg. B) KMg + Cl╖.
C) KCl╖ + Mg. D) No Reaction
üèPotassium is a more active metal than magnesium å will replace
Mg.èMagnesium chloride consists ç Mgìó å Clú ions.èSïce each K
provides one electron, two potassium aëms must react for each MgCl╖.
The balanced reaction is
2K + MgCl╖ ───¥ 2KCl + Mg.
Ç A
4èComplete å balance ê sïgle replacement reaction between
è Zn å CuSO╣.è__ Zn + __ CuSO╣ ───¥ ?
A) ZnSO╣ + Cu. B) ZnO + CuO + SO╖.
C) ZnSO╕ + CuO. D) No Reaction
üèIn a sïgle replacement reaction ïvolvïg metals å metal
cations, one metal simply replaces ê oêr ï ê ionic compound.
Zïc is a more active metal than copper å will replace ê copper ï
ê copper(II) sulfate.èSïce Zn donates two electrons ï êse reac-
tions, only one Zn is required for each Cu ï CuSO╣.èThe balanced reac-
tion is
Zn + CuSO╣ ───¥ ZnSO╣ + Cu.
Ç A
5èComplete å balance ê sïgle replacement reaction between
è Fe å NaBr.è__ Fe + __ NaBr ───¥ ?
A) FeBr╖ + 2Na. B) FeBr╕ + 3Na.
C) FeNa╖ + Br╖. D) No Reaction
üèSodium is a more active metal than iron, so iron can NOT replace
sodium from its salts.èNo reaction occurs between êse substances.
Ç D
6èComplete å balance ê sïgle replacement reaction between
è K å AlBr╕.è__ K + __ AlBr╕ ───¥ ?
A) Al + KBr + Br╖. B) Al + 3KBr.
C) 2K╕Al + 3Br╖. D) No Reaction
üèPotassium is a more active metal than alumïum å will replace
Al.èAlumïum bromide consists ç AlÄó å Brú ions.èSïce each K
provides one electron, three potassium aëms must react for each AlBr╕.
The balanced reaction is
3K + AlBr╕ ───¥ Al + 3KBr.
Ç B
7èComplete å balance ê sïgle replacement reaction between
è Sn å HCl.è__ Sn + __ HCl ───¥ ?
A) 2SnCl + H╖(g). B) SnCl╖ + H╖(g).
C) SnH╖ + Cl╖(g). D) No Reaction.
üèTï, Sn, precedes H╖ ï ê activity series, so tï will react
with acids ë release hydrogen.èIn this reaction, ê tï forms Snìó.
With oêr acids, SnÅó can form but we are not ready ë discuss those
reactions.èSïce hydrochloric acid contaïs ê Hó ion, each tï will
react with two HCl units.èThe balanced reaction is
Sn + 2HCl ───¥ SnCl╖ + H╖(g).
Ç B
8èComplete å balance ê sïgle replacement reaction between
è Cu å AgNO╕.è__ Cu + __ AgNO╕ ───¥ ?
A) Cu(NO╖)╖ + 2AgO. B) CuO + AgNO╖.
C) Cu(NO╕)╖ + 2Ag. D) No Reaction
üèIn a sïgle replacement reaction ïvolvïg metals å metal
cations, one metal simply replaces ê oêr ï ê ionic compound.
Copper is a more active metal than silver å will replace ê silver ï
ê silver nitrate.èSïce Cu donates two electrons ï êse reactions,
one Cu requires two AgNO╕ ë make ê electron transfer balance.
The balanced reaction is
Cu + 2AgNO╕ ───¥ Cu(NO╕)╖ + 2Ag.
Ç C
9èComplete å balance ê sïgle replacement reaction between
è Cu å HCl.è__ Cu + __ HCl ───¥ ?
A) 2CuCl + H╖(g). B) CuCl╖ + H╖(g).
C) CuH╖ + Cl╖(g). D) No Reaction
üèH╖ donates electrons more readily than Cu does.èConsequently, Cu
will not replace Hó, which would form H╖, from nonoxidizïg acids like
HCl.èNo reaction occurs between Cu å HCl.
Ç D
10èComplete å balance ê sïgle replacement reaction between
è H╖(g) å AuCl╕.è__ H╖(g) + __ AuCl╕ ───¥ ?
A) 2AuH + 3Cl╖. B) AuH + 3HCl.
C) 2Au + 6HCl. D) No Reaction
üèHydrogen comes before gold, Au, ï ê activity series.èGold
will be replaced by hydrogen.èThe gold(III) chloride consists ç AuÄó
å Clú ions.èHydrogen provides two electrons, while gold needs three.
Two å three are facërs ç six, so two gold ions will accept six elec-
trons from three hydrogen molecules.èThe chloride ion just goes along
for ê ride.èThe balanced reaction is
3H╖(g) + 2AuCl╕ ───¥ 2Au + 6HCl.
Ç C