Reactions in Aqueous Solutions

Chapter 7Chapter 7

Aqueous Solutions

Water is the dissolving Water is the dissolving medium, or medium, or solventsolvent..

Driving Forces for Chemical Reactions

1. Formation of a precipitate (solid). 2. Formation of molecular substance (water). 3. Formation of a gas. 4. Transfer of electrons (Redox).

Types of Solution Reactions

- Precipitation reactionsPrecipitation reactionsAgNOAgNO33((aqaq) + NaCl() + NaCl(aqaq) ) AgCl( AgCl(ss) + NaNO) + NaNO33((aqaq))

- Acid-base reactionsAcid-base reactionsNaOH(NaOH(aqaq) + HCl() + HCl(aqaq) ) NaCl( NaCl(aqaq) + H) + H22O(O(ll))

ElectrolytesStrongStrong - conduct current efficiently - many ions in solution. - conduct current efficiently - many ions in solution.

NaCl, KNONaCl, KNO33, HNO, HNO33, NaOH, NaOH

Weak Weak - conduct only a small current - few ions in solution,- conduct only a small current - few ions in solution,

HCHC22HH33OO22, aq. NH, aq. NH33, tap H, tap H22OO

NonNon - no current flows - no ions in solution. - no current flows - no ions in solution.

pure Hpure H22O, sugar solution, glycerolO, sugar solution, glycerol

In what two ways can a solid ionic compound be made to conduct electricity?

•Dissolve it in water.

•Melt or fuse it.

Ions must be free to move

(mobile) in order to conduct electricity!

Dissociationionic compoundsionic compounds

metal + nonmetal (Type I & II)metal + nonmetal (Type I & II)metal + polyatomic anionmetal + polyatomic anionAmmonium compoundsAmmonium compoundsAcidsAcids

When ionic compounds dissolve in water the anions and When ionic compounds dissolve in water the anions and cations are separated from each other; this is called cations are separated from each other; this is called dissociationdissociation

We know that ionic compounds dissociate when they We know that ionic compounds dissociate when they dissolve in water because the solution conducts electricitydissolve in water because the solution conducts electricity

Dissociationpotassium chloride dissociates in water into potassium chloride dissociates in water into

potassium cations and chloride anionspotassium cations and chloride anions

KCl(aq) = KKCl(aq) = K+ + (aq) + Cl(aq) + Cl- - (aq)(aq)

copper(II) sulfate dissociates in water into copper(II) copper(II) sulfate dissociates in water into copper(II) cations and sulfate anionscations and sulfate anions

CuSOCuSO44(aq) = Cu(aq) = Cu+2+2(aq) + SO(aq) + SO442-2-(aq)(aq)

K+ Cl-K Cl

Cu+2 SO42-Cu SO4

Dissociation

potassium sulfate dissociates in water into potassium sulfate dissociates in water into potassium cations and sulfate anionspotassium cations and sulfate anions

KK22SOSO44(aq) = 2 K(aq) = 2 K+ + (aq) + SO(aq) + SO442-2-(aq)(aq)

K+

SO42-

K+

KK SO4

Ionic Compounds in Solution

In aqueous solution, soluble ionic compoundsexist in the form of ions.

K2CrO4(aq) + Ba(NO3)2(aq) ----> BaCrO4(s) + 2KNO3(aq)

Figure 7.1: The precipitation reaction that occurs when yellow potassium chormate, K2CrO4 (aq), is mixed with a colorless barium nitrate solution, Ba(NO3)2 (aq)

Solubility

1. A soluble solid readily dissolves in water-- 1. A soluble solid readily dissolves in water-- designated with (aq).designated with (aq).

2. A slightly soluble solid only dissolves to a tiny 2. A slightly soluble solid only dissolves to a tiny extent in water--designated with (s).extent in water--designated with (s).

3. An insoluble solid does not dissolve to any 3. An insoluble solid does not dissolve to any appreciable extent in water--designated with (s).appreciable extent in water--designated with (s).

Simple Rules for Solubility1.1. Most nitrate (NOMost nitrate (NO33

), acetate (C), acetate (C22HH33OO22-)-), & chlorate (ClO, & chlorate (ClO33

--) )

salts salts are solubleare soluble..

2.2. Most alkali (group 1A) salts and NHMost alkali (group 1A) salts and NH44++ are solubleare soluble..

3.3. Most ClMost Cl, Br, Br, and I, and I salts salts are soluble are soluble ((NOTNOT AgAg++, Pb, Pb2+2+, , HgHg22

2+2+))

4.4. Most sulfate salts Most sulfate salts are soluble are soluble ((NOTNOT BaSOBaSO44, PbSO, PbSO44, ,

HgSOHgSO44, CaSO, CaSO44))

5.5. Most OHMost OH salts salts are only slightly soluble are only slightly soluble (NaOH, KOH are (NaOH, KOH are soluble, Ba(OH)soluble, Ba(OH)22, Ca(OH), Ca(OH)22 are marginally soluble) are marginally soluble)

6.6. Most SMost S22, CO, CO3322, CrO, CrO44

22, PO, PO4433 salts salts are only slightly are only slightly

solublesoluble. .

Precipitation ReactionsIn all precipitation reactions, the ions of one substance In all precipitation reactions, the ions of one substance

are exchanged with the ions of another substance when are exchanged with the ions of another substance when their aqueous solutions are mixedtheir aqueous solutions are mixed

At least one of the products formed is insoluble in waterAt least one of the products formed is insoluble in water

KI(aq) + AgNOKI(aq) + AgNO33(aq) (aq) KNOKNO33(aq) + AgI(aq) + AgIss

K+

I-

Ag+

NO3-

K+

NO3-

Ag I

Describing Reactions in Solution

1.1. Molecular equation Molecular equation (reactants and products as (reactants and products as compoundscompounds))

AgNOAgNO33((aqaq) + NaCl() + NaCl(aqaq) ) AgCl( AgCl(ss) + NaNO) + NaNO33((aqaq))

2.2. Complete ionic equation Complete ionic equation (all strong (all strong electrolytes shown as electrolytes shown as ionsions))

AgAg++((aqaq) + NO) + NO33((aqaq) + Na) + Na++((aqaq) + Cl) + Cl((aqaq) )

AgCl(AgCl(ss) + Na) + Na++((aqaq) + NO) + NO33((aqaq))

Describing Reactions in Solution (continued)

3.3. Net ionic equation Net ionic equation (show only (show only components that actually react)components that actually react)

AgAg++((aqaq) + Cl) + Cl((aqaq) ) AgCl( AgCl(ss))

NaNa++ and NO and NO33 are spectator ions. are spectator ions.

Solutions of:

AgNO3

Na2SO4

If AgNO3 is mixed with Na2SO4 what ions are most abundant in the solution?

AgNO3

Na2SO4

With what ions is the solution saturated?

2AgNO3(aq) + Na2SO4(aq) 2 NaNO3 (aq) + Ag2SO4(s)

Silver Sulfate

Precipitate

2Ag+(aq)

+ 2 NO3-(aq) + 2Na+

(aq) + SO42-

(aq) 2Na+(aq) + 2 NO3

- (aq) + Ag2SO4(s)

2Ag+(aq)

+ SO42-

(aq) Ag2SO4(s)

Molecular Equation

Overall Ionic Equation

Net Ionic Equation

Acids

The nature of acids was discovered by Svante The nature of acids was discovered by Svante Arrhenius. Arrhenius.

Acids are characterized by:Acids are characterized by:

• a sour taste (lemons -- citric acid).a sour taste (lemons -- citric acid).

• producing Hproducing H+ + ions (protons) in aqueous ions (protons) in aqueous solution.solution.

• turn blue litmus red.turn blue litmus red.

Acids

Strong acids Strong acids -- dissociate completely dissociate completely (nearly (nearly 100 %)100 %) to produce H to produce H++ in solution in solution

HCl, HHCl, H22SOSO44, HNO, HNO33, HBr, HI, & HClO, HBr, HI, & HClO44

Weak acids Weak acids - dissociate to a slight extent - dissociate to a slight extent (approximately 1 %)(approximately 1 %) to give H to give H++ in solution in solution

HCHC22HH33OO22, HCOOH, HNO, HCOOH, HNO22, & H, & H22SOSO33

Figure 7.5: When gaseous HCl is dissolved in water, each molecule dissociates to produce H+

and Cl- ions

Bases

Bases are characterized by:Bases are characterized by:

• bitter taste (soap).bitter taste (soap).

• feel slippery.feel slippery.

• produce hydroxide (OHproduce hydroxide (OH--) ions in aqueous ) ions in aqueous solution.solution.

• turn red litmus blue.turn red litmus blue.

A basic solution is said to be A basic solution is said to be alkalinealkaline since they often since they often contain one of the contain one of the alkalialkali metals --Na, K, Li, etc. metals --Na, K, Li, etc.

Bases

Strong bases Strong bases - react completely with water to - react completely with water to give OHgive OH ions. ions.

sodium hydroxidesodium hydroxide

Weak bases Weak bases - react only slightly with water to - react only slightly with water to give OHgive OH ions. ions.

ammoniaammonia

Acid-Base Reactions

Acid + Base ----> Salt + water

Molecular EquationHCl(aq) + NaOH(aq) ----> NaCl(aq) + HOH(l)

Complete Ionic EquationH+

(aq) + Cl-(aq) + Na+

(aq) + OH-(aq) -----> Na+

(aq) + Cl-(aq)

+ HOH(l)Net Ionic EquationH+

(aq) + OH-(aq) -----> HOH(l)

Acid-Base Neutralization

The net ionic equation for the neutralization of any strong acid and base will always be:

HH++(aq) (aq) + OH+ OH--

(aq)(aq) -----> HOH -----> HOH(l)(l)

Salts

Salts are Salts are ionic compoundsionic compounds consisting of: consisting of:

a. metal & nonmetal -- a. metal & nonmetal -- KClKCl

b. metal & polyatomic ion -- b. metal & polyatomic ion -- CuSOCuSO44

c. polyatomic ion & nonmetal -- c. polyatomic ion & nonmetal -- NHNH44ClCl

d. two polyatomic ions -- d. two polyatomic ions -- (NH(NH44))22SOSO44

Oxidation-Reduction Reactions(Redox Reactions)

Redox reaction -- Redox reaction -- involves the transfer of involves the transfer of electronselectrons

• loss and gain of electrons must be loss and gain of electrons must be exactlyexactly equal. equal.

• loss and gain of electrons must be loss and gain of electrons must be simultaneous.simultaneous.

Oxidation

• loss of electrons loss of electrons

• metal atoms -- Na, Ca, & Kmetal atoms -- Na, Ca, & K

• NaNaoo ---> Na ---> Na1+ 1+ + 1e+ 1e--

• CaCao o ---> Ca---> Ca2+ 2+ + 2e+ 2e--

• nonmetal ions -- Clnonmetal ions -- Cl--, S, S2-2-, & O, & O2-2-

• ClCl1-1- ---> Cl ---> Clo o ++ 1e-1e-

• SS2-2- ---> S ---> So o + 2+ 2 e-e-

Reduction

• gain of electrons.gain of electrons.

• nonmetal atoms.nonmetal atoms.

• OOoo + 2e + 2e-- ---> O ---> O2-2-

• FFoo + 1e + 1e-- ---> F ---> F1-1-

• metal ions.metal ions.

• KK1+ 1+ + 1e+ 1e- - ---> K---> Koo

• BaBa2+2+ + 2e + 2e-- ---> Ba ---> Baoo

Figure 7.7: When powdered aluminum and iodine (shown in the foreground) are mixed (and a little water added), they react

vigorously

Oxidation & Reduction Half-Reactions

• Always add electrons (negative) to the Always add electrons (negative) to the more positive side of the equation.more positive side of the equation.

• The charge on both sides of an equation The charge on both sides of an equation must be equal.must be equal.

• Oxidation -- NaOxidation -- Naoo ----> Na ----> Na1+ 1+ + 1 e-+ 1 e-

• Reduction -- ClReduction -- Cl2 2 + 2 e+ 2 e- - ----> 2 Cl----> 2 Cl- -

OIL RIG

Oxidation Is Loss.

Reduction Is Gain.

Redox Reactions

• Metal-nonmetal reactions are Metal-nonmetal reactions are alwaysalways redox reactions.redox reactions.

• Any reaction that has a free element (such Any reaction that has a free element (such as Oas O22) as a reactant or product are redox.) as a reactant or product are redox.

• All single replacement reactions are redox.All single replacement reactions are redox.

• All combustion reactions are redox.All combustion reactions are redox.

Synthesis I (Composition)

A + X ----> AX A + X ----> AX ALWAYS REDOXALWAYS REDOX

Element + Element -----> Binary CompoundElement + Element -----> Binary Compound

FeFe(s)(s) + S + S(s)(s) ----> FeS ----> FeS(s)(s)

4 Al4 Al(s)(s) + 3 O + 3 O2(g)2(g) ----> 2 Al ----> 2 Al22OO3(s)3(s)

Synthesis II (Composition)

A + X ----> AX A + X ----> AX NOT REDOXNOT REDOX

Compound + Compound ----> Compound (3 Compound + Compound ----> Compound (3 or more or more elements)elements)

Ammonia + Acid ----> Ammonium SaltAmmonia + Acid ----> Ammonium Salt

NHNH3(g)3(g) + HCl + HCl(g)(g) ----> NH ----> NH44ClCl(s)(s)

2 NH2 NH3(aq)3(aq) + H + H22SOSO4(aq)4(aq) ----> (NH ----> (NH44))22SOSO4(aq)4(aq)

Synthesis II (Composition)ContinuedWater + An OxideWater + An Oxide

Rule # 1 --Rule # 1 --Water + Water + Metal OxideMetal Oxide ----> Metal ----> Metal Hydroxide (Base)Hydroxide (Base)

HOHHOH(l)(l) + CaO + CaO(s)(s) ----> Ca(OH) ----> Ca(OH)2(s)2(s)

HOHHOH(l)(l) + Na + Na22OO(s)(s) ----> 2 NaOH ----> 2 NaOH(aq)(aq)

Rule # 2 --Water + Nonmetal Oxide ----> Acid

HOH(l) + SO3(g) ----> H2SO4(aq)

HOH(l) + N2O5(g) ----> 2 HNO3(aq)

Single Replacement I

A + BX ----> AX + B ALWAYS REDOX

Element + Compound ----> Different Element + Different

Compound

Metal Reactivities:

K > Na > Ca > Mg > Al > Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H > Sb > Cu > Hg > Ag > Pt > Au

Single Replacement I(Continued)A is a metal.

A is more reactive than B A + BX ----> AX + B

Cu(s) + 2 AgNO3(aq) ---->Cu(NO3)2(aq) + 2 Ag(s)

Zn(s) + 2 HCl(aq) ----> ZnCl2(aq) + H2(g)

Rule # 3 -- Active Metal + Water ----> Metal Hydroxide + Hydrogen

Ca(s) + 2 HOH(l) ----> Ca(OH)2(s) + H2(g)

Single Replacement I(Continued)

A is a metal.

A is less reactive than B

A + BX ----> No Reaction (NR)

Cu(s) + HCl(aq) ----> NR

Single Replacement II

Y + BX ----> BY + X ALWAYS REDOX

Element + Compound ----> Different Element + Different

Compound

Nonmetal Reactivities:

F > O > Cl > Br > I

Single Replacement II(Continued)

Y is a nonmetal.Y is more reactive than X Y + BX ----> BY + X

Cl2(g) + 2 KBr(aq) ----> 2 KCl(aq) + Br2(aq)

Y is less reactive than X Y + BX ----> No Reaction

Cl2(g) + KF(aq) ----> NR

Single Replacement(Continued)

Remember!!Remember!!Metals replace metals.Metals replace metals.

MgMg(s) (s) + 2 Ag(NO+ 2 Ag(NO33))2(aq) 2(aq) ----> 2 Ag----> 2 Ag(s)(s) + Mg(NO + Mg(NO33))2(aq) 2(aq)

Nonmetals replace nonmetals.Nonmetals replace nonmetals.

ClCl2(g)2(g) + 2 KBr + 2 KBr(aq) (aq) ----> Br----> Br2(aq) 2(aq) + 2 KCl+ 2 KCl(aq)(aq)

Figure 7.6: The thermite reaction

gives off so much heat that the iron formed

is molten

Decomposition I

AX ----> A + X ALWAYS REDOX

AX is a binary compound.

Binary Compound ----> Element + Element

elect

2 NaCl(l) ----> 2 Na(l) + Cl2(g)

elect

2 HOH(l) ----> 2 H2(g) + O2(g)

Decomposition II

AX -----> A + X MAY OR MAY NOT BE REDOX

AX is a ternary compound.

Rule # 4 -- Metal Chlorates ----> Metal Chlorides + Oxygen

2 KClO3(s) ----> 2 KCl (s) + 3 O2(g) REDOX

Decomposition II(Continued)

Rule # 5 -- Metal Carbonates ----> Metal Oxides + Carbon

Dioxide

CuCO3(s) ----> CuO (s) + CO2(g) NOT REDOX

Decomposition II(Continued)

Rule # 6 -- Metal Hydroxides ----> Metal Oxides + Water

Ca(OH)2(s) ----> CaO (s) + HOH(g) NOT REDOX

Decomposition II(Continued)

Rule # 7 -- Acid ----> Nonmetal Oxide + Water

H2SO4(aq) ----> SO3(g) + HOH(g) NOT REDOX

Double Displacement (Double Replacement)

AX + BY ----> AY + BX NEVER REDOX

Compound + Compound ----> 2 New Compounds

Acid-Base & Precipitation Reactions (Chapter 7)

HH22SOSO4(aq)4(aq) + 2 NaOH + 2 NaOH(aq) (aq) ----> Na----> Na22SOSO4(aq) 4(aq) + 2 HOH+ 2 HOH(l)(l)

NaClNaCl(aq) (aq) + AgNO+ AgNO3(aq)3(aq) ----> NaNO ----> NaNO3(aq)3(aq) + AgCl + AgCl(s)(s)

Combustion

AX + OAX + O2 2 ALWAYS REDOXALWAYS REDOX

AX is a hydrocarbon.AX is a hydrocarbon.

CCxxHHyy + O + O2(g)2(g) ----> CO ----> CO2(g)2(g) + HOH + HOH(g)(g)

CHCH4(g)4(g) + 2 O + 2 O2(g)2(g) ----> CO ----> CO2(g)2(g) + 2 HOH + 2 HOH(g)(g)

2 C2 C66HH6(l) 6(l) + 15 O+ 15 O2(g) 2(g) ----> 12 CO----> 12 CO2(g) 2(g) + 6 HOH+ 6 HOH(g)(g)