Section 4: Aqueous Reactions - Chemistry Department -...

Section 4: Aqueous Reactions

1. Solution composition2 Electrolytes and nonelectrolytes2. Electrolytes and nonelectrolytes3. Acids, bases, and salts4 N t li ti ti4. Neutralization reactions5. Precipitation reactions6. Oxidation/reduction reactions 7 Molarity7. Molarity

1S. Ensign, aqueous reactions

Water has remarkable chemical and physical propertiesand physical properties

•High melting and boiling points

•Expands when freezes (ice floats)

•Dissolves a wide variety of substances (the•Dissolves a wide variety of substances (the universal solvent)

•Provides an ideal environment in which numerous chemical reactions can occur (aqueous reactions)

•The chemical reactions of life require and•The chemical reactions of life require, and occur in, water 2

S. Ensign, aqueous reactions

S l ti h i t f 2Solutions, solvents, and solutes

• Solution: a homogeneous mixture of 2 or more substances

• Solvent: the substance in the solution present in greatest quantity

• Solutes: other substances that are dissolved in the solvent

• Solution concentration: the amount of solute dissolved in a given quantity of solvent ordissolved in a given quantity of solvent or solution

An aqueous solution is a solutionAn aqueous solution is a solution where water is the solvent 3


Some common aqueous solutions• Solutions of sugars (glucose, fructose,

sucrose, lactose, etc)• Solutions of alcohols (methanol, ethanol, etc)• Solutions of salts (sodium chloride potassiumSolutions of salts (sodium chloride, potassium

chloride, ammonium sulfate, etc)• Solutions of acids• Solutions of acids• Solutions of bases


The solution process


The solution process

1. Break intermolecular attractions in pure l t t f i di id l l lsolute to free up individual molecules

(solute)n n solute2. Disrupt water-water intermolecular

attractions to provide room for solute to dissolve

(water)m m water3. Form new solute-water intermolecular

forcesn solute + m H2O (solute)n(water)m


Electrolytes and nonelectrolytes• Electrolytes: compounds that dissolve in water toElectrolytes: compounds that dissolve in water to

produce ions (soluble ionic compounds, acids and bases in water)– “dissociate” or “ionize” in solution

• Nonelectrolytes: compounds that dissolve in water• Nonelectrolytes: compounds that dissolve in water, and yet do not form ions in solution (soluble molecular compounds in water)p )– “dissolve” but don’t “ionize”


Sodium chloride dissolves in water to form hydrated sodium and choride ionsy

+

-


Electrolytes: acids, bases, and salts• Acids:

– Hydrogen-containing compounds that dissociate in water to produce hydrogen ion and a partner anionC d th t i [H+] i l ti– Compounds that increase [H+] in aq. solutions

• Bases:– compounds that react with (accept) hydrogen

ions, producing water– Compounds that increase [OH-] in aq. solutions

• Salts: Ionic compounds that are neither acids or bases


Acids: Hydrogen-containing compounds that dissociate in water to produce hydrogen ion (H+) and a partner anion

• Strong acids: dissociate (ionize) “completely” in solution

• Weak acids: dissolve completely but only partially ionize• Weak acids: dissolve completely, but only partially ionize in solution

• Polyprotic acids: have more than one “ionizable” proton


Bases: (1) compounds that react with (accept) hydrogen ions, producing water. (2) Compounds that increase [OH-] in

l tiaq. solutions.• Metal hydroxides

• Ammonia

• Strong bases: dissociate (ionize) “completely” in solution

• Weak bases: Ionize only partially in solution, or dissolve incompletely in solutionincompletely in solution


Strong acids and basesCommon strong acids

HCl HBr HI (but not HF)

Common strong bases

Group 1A metal hydroxides (LiOHHCl, HBr, HI (but not HF)

HClO4

HNO

Group 1A metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH). These dissociate completely at 1 M and higher

iHNO3

H2SO4 (only the first H+

ionizes completely)

concentrations

The heavier Group 2A metal hydroxides ionizes completely) p ydissociate “completely” but only at low concentrations


Salts: Compounds that dissociate (ionize) in water but are not acids or bases


Electrolytes• Strong electrolytes: salts acids and bases that dissolve• Strong electrolytes: salts, acids, and bases that dissolve

completely or nearly completely in water to form ions

W k l t l t C d th t di l i t b t• Weak electrolytes: Compounds that dissolve in water, but produce only a small concentration of ions when dissolved (partial dissociation; partial ionization)( )


Electrolytes and nonelectrolytes

distilled water: tap water:a nonelectrolyte tap water:a weak electrolyte


Electrochemistry is a fascinating area

The chemistry going on in this simple demonstration could be the solution to much of of our future energy needsneeds


Solubility: a term that refers to how h f l t di l i imuch of a solute can dissolve in a given

amount of solvent (grams solute dissolved/100 ml solution)

• Ionic compounds• Molecular compoundsp• Acids and bases


Degrees of solubility• “soluble” in water: glucose, NaCl, NaOH,

acetic acid, MgSO4 (“soluble” means a significant amount can dissolve)

• “Insoluble” in water: CaCO3, AgCl, C6H14, I23 6 14 2(“insoluble” means a very little amount dissolves)

• “miscible” with water: ethanol, glycerol, formaldehyde (“miscible” means soluble at all y (proportions)


Solubility of salts

• Most salts are classified as “soluble”• Most salts are classified as soluble• Some salts are “insoluble” (poorly soluble)• The distinction between “soluble” and “insoluble” is• The distinction between soluble and insoluble is

based on whether a “significant amount” dissolves in water (see next slide)

• Don’t memorize which salts are soluble and insoluble at this point, but some being familiar with some general guidelines will be useful for yousome general guidelines will be useful for you


Salt Solubility (g/100 g water at 25° C

Classification

NaCl 35.9 Largely soluble

NaNO3 91.2 Largely soluble

Ca(CH3COO)2 ~33 Largely soluble( 3 )2 g y

MgSO4 ~25 Largely soluble

CaSO4 ~0.2 Largely insoluble

A Cl 0 000520 L l i l blAgCl 0.000520 Largely insoluble

CaF2 ~0.002 Largely insoluble

NH4F 45 Largely soluble

PbCl2 ~4.5 Slightly soluble

Pb(NO3)2 ~60 Largely soluble

CaCO3 0.0013 Largely insolubleCaCO3 0.0013 Largely insoluble

Na2CO3 ~230 Largely soluble

PbS2 ~2.6 x 10‐9 Largely insoluble

b( ) l l blPb(CH3COO)2 ~50 Largely soluble


Solubility of some commonly encountered salts in water• All ionic compounds with nitrate (NO -) group 1A metal ions• All ionic compounds with nitrate (NO3 ), group 1A metal ions,

and ammonium ion (NH4+) are soluble

• All binary salts of Cl-, Br-, I- are soluble, except with Ag+, Hg+, Pb2+Pb2+

• Nearly all acetate (CH3COO-) salts are soluble• Most sulfate (SO4

2-) salts are soluble (exceptions: BaSO4, ( 4 ) ( p 4,CaSO4, PbSO4, SrSO4

• Most hydroxide (OH-) salts are insoluble (ex. w/group 1A metal ions or NH + heavier group 2A hydroxides are slightly soluble)ions or NH4 , heavier group 2A hydroxides are slightly soluble)

• Most oxide (O2-) and sulfide (S2-)salts are insoluble (ex. w/group 1A metal ions or NH4

+)• Most phosphate and carbonate salts are insoluble (ex. w/group

1A metal ions or NH4+)

• Many F- salts are insoluble (ex. w/group 1A metal ions or NH4+ y ( g p 4and some others)

• Blah, blah, blah………….. That’s enough for now 21S. Ensign, aqueous reactions

Summary….• Many salts are “soluble” and hence “strong• Many salts are soluble and hence strong

electrolytes”• Most acids are weak acids and hence “weakMost acids are weak acids and hence weak

electrolytes”• Group 1A and the heavier group 2A metalGroup 1A and the heavier group 2A metal

hydroxides are strong bases and hence “strong electrolytes”

• Ammonia is a weak base and hence a “weak electrolyte”

• Soluble molecular compounds that don’t ionize in solution are nonelectrolytes


Common reactions in aqueous l isolutions

• PrecipitationPrecipitation• Neutralization

G ti• Gas generation• Metals: oxidation/reduction


Precipitation Reactions: Formation of an insoluble salt from the mixing of aqueous solutions of soluble saltsthe mixing of aqueous solutions of soluble salts

Example: Silver nitrate (AgNO3)is soluble in water Sodiumis soluble in water. Sodium chloride (NaCl) is soluble in water. Silver chloride (AgCl) iswater. Silver chloride (AgCl) is insoluble in water. •What will happen if solutions ofWhat will happen if solutions of AgNO3 and NaCl are mixed together?g

•Write a balanced chemical equation for the reaction.equation for the reaction.


Precipitation Reactions: Formation of an insoluble salt from the mixing of aqueous solutions of soluble saltsthe mixing of aqueous solutions of soluble saltsExample: Silver nitrate (AgNO3) is soluble in water. Sodium chloride (NaCl) is soluble in water. Silver chloride (AgCl) is insoluble in water.

•What will happen if solutions of AgNO3 and NaCl are mixed together?

•Write a balanced chemical equation for the reaction.


More solution chemistry terms•Molecular equation: shows the complete chemical formulas of reactants and products, not necessarily as they actually exist in solution

•Complete ionic equation: all soluble salts are shown as ions- i.e. in the form they actually exist in solutions

•Net ionic equation: includes only ions and molecules that are directly involved in a chemical reaction occurring in solution

•Spectator ions: ions in solution that are not involved in a chemical reaction, and appear in identical forms on both sides of the chemical equationequation


Write molecular, complete ionic, and net ionic equations for the formation of a precipitate of PbI after mixing solutions of precipitate of PbI2 after mixing solutions of Pb(NO3)2 and KI

Lead (II) iodide precipitates when potassium iodide is mixed with lead (II) nitrate.Author PRHaneylicensed under the Creative Commonslicensed under the Creative CommonsAttribution-Share Alike 3.0 Unported license.


Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte y ( ) y

is formed

• A reactant may be soluble or insoluble to begin with

• Sometimes a product is a gas, or reacts further to produce a gasproduce a gas

• Reactions can be represented by molecular complete• Reactions can be represented by molecular, complete ionic, or net ionic equations


Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• Reactions can be represented by molecular, complete ionic, or

net ionic equationsH d hl i id di h d id– Hydrochloric acid + sodium hydroxide

– Sulfuric acid + potassium hydroxide


Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• A reactant may be insoluble to begin with

– Insoluble hydroxide plus strong acid:

– Insoluble metal oxide + strong acid:


Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• Sometimes a product is a gas, or the product reacts further to

produce a gas– Strong acid + sodium sulfide or sodium cyanideStrong acid + sodium sulfide or sodium cyanide

– Strong acid + carbonate or sulfite salt


Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• Sometimes a product is a gas, or the product reacts further to

produce a gas– Alka seltzerAlka seltzer

– Baking powder


Common reactions in aqueous l isolutions

• PrecipitationPrecipitation• Neutralization

G ti• Gas generation• Oxidation/reduction


Oxidation/reduction reactions: chemical ti h l t t f dreactions where electrons are transferred

from one reactant to another


Oxidation/reduction reactions: chemical reactions where electrons are transferred from one reactant to another

Na: 1s2 2s22p6 3s1 Cl: 1s2 2s22p6 3s23p5

1

n = 2

n = 3

11p+ 1

n = 2

n = 3

17 p+n = 111p+ n = 117 p+


Oxidation/reduction reactions: chemical reactions where electrons are transferred from one reactant to another

Na+: 1s2 2s22p6 Cl-: 1s2 2s22p6 3s23p6

+ -

1

n = 211p+ 1

n = 2

n = 3

17 p+n = 111p+ n = 117 p+


Oxidation/reduction reactions• Oxidation: lose electrons

– Metals lose electrons to obtain a Noble gas e- configuration g g(Li Li+ + e-)

• Reduction: gain electrons– nonmetals often gain electrons to obtain a Noble gas

electron configuration (Cl2 + 2e- 2Cl-)Some cations will gain electrons to form a stable “reduced”– Some cations will gain electrons to form a stable reduced product (2H+ + 2e- H2)

• An oxidation reaction must be linked to a reductionAn oxidation reaction must be linked to a reduction reaction

• “Oxidation numbers” assigned to atoms and ions in gcompounds are used to keep track of electrons gained or lost during oxidation/reduction reactions 37


Oxidation numbers• An atom in its elemental state has an oxidation number of

zero, meaning it has neither gained nor lost electrons– Oxidation numbers of H, N, O, C, and S in H2, N2, O2, C(graphite), and S8

are all zero

• For monatomic ions, the oxidation number is the same as the ion charge

Monatomic metal cation Oxidation number

Monatomicnonmetal anion Oxidation number

Li+ Na+ K+ Cu+ “plus one” (+1) F- Cl- Br- I- “minus one” ( 1)Li+ Na+, K+, Cu+ plus one (+1) F- Cl-, Br-, I- minus one (-1)

Mg2+, Ca2+, Sr2+, Fe2+ “plus two” (+2) O2-, S2- Se2-, Te2- “minus two” (-2)

Al3+, Fe3+, Cr3+, Ni3+ “plus three” (+3) N3-, P3- “minus three” (-3)

• Note H, a nonmetal, can have an oxidation number of +1 in the hydrogen ion (H+) or -1 in the hydride ion (H-)

• The oxidation numbers of atoms in molecular compounds and polyatomic ions are assigned by rules we will discuss later 38


Metals lose electrons to obtain a Noble gas e- configuration (Li Li+ + e-)

Nonmetals gain electrons to obtain a Noble gas electron configuration (Cl2 + 2e- 2Cl-)

Some cations will gain electrons to form a stable “reduced” product (2H+ + 2e- H )

Alkali metal plus halogen gas:

Some cations will gain electrons to form a stable reduced” product (2H+ + 2e- H2)

Alkali metal plus water:

Metal plus strong acid:


Solution concentration• The amount of solute dissolved in a given

quantity of solvent or solution

1 00 L1.00 L

50 particles/liter25 particles/liter10 particles/liter40


MolarityMolarity

Molarit M Moles soluteMolarity = M = Volume of solution (liters)

molsL

# of particlesDefined volumeL Defined volume

[sol te][solute]


(1) Add proper mass f l t t

(2) Mix to (3) Add more (4) Solution ofof solute to prepare defined volume of solution, add some water

dissolve solute(3) Add more water to reach final desired volume

(4) Solution of defined molarity


Preparing a 1 M solution of sodium chloride1711 17Cl

35.45

11Na

22.99

FWNaCl = 58.44 amu = 58.44 g/mol


Preparing a 1 M solution of sodium chlorideFWNaCl = 58.44 g/molNaCl

58.44 gNaCl

1 mol/LNaCl

1.00 L

NaCl


Interconversion of mass, mols, and b f ti lnumber of particles

Molar Avogadro’sbmass moles moleculesmass number

Interconversion of mass, mols, and concentration of particlesconcentration of particles

Molar mass

Volume of solution molsmass moles molaritymass solution mols

L


Potassium permanganate (KMnO4), a common lab chemical, is a purple-black solid that dissolves in water to give a is a purple black solid that dissolves in water to give a deep purple solution. If you dissolve 0.435 g of KMnO4 in enough water to give 250 ml of solution, what is [KMnO4] i l /L?

FW O = 158 0 g/mol

in mols/L?

FWKMnO4= 158.0 g/mol


If you dissolve 0.435 g of KMnO4 in enough water to give 250 ml of solution, what is [KMnO4] in mols/L?g [ 4]

mass moles molarity

Molar mass

Volume of solution y

FWKMnO4= 158.0 g/mol V = 0.25 l


Molarity as a conversion factorMolarity as a conversion factor

Molar Volume of

mass moles molarity

Molar mass

Volume of solution

Molar mass

Molarity of solutionmass moles volumemass solution

gmol

moll


How many mols of HCl are present in 250 ml of 12 M HCl?

Molar Molarity of

mass moles volumemass solutiong

molmol

l


You need 5.0 mols of HCl. What volume of 12 M HCl would provide these 5.0 mols?

mass moles volume

Molar mass

Molarity of solution

g molgmol l


For a certain experiment, you need 250 mlp , yof 1.50 M sodium carbonate (Na2CO3). How do you prepare this solution?y p p

Molar mass

Molarity of solutionmass moles volumemass solution

mass moles molarity

Molar mass

Volume of solution y


For a certain experiment, you need 250 ml of 1.50 M sodium carbonate (Na2CO3). How do you prepare this solution?

Molar Molarity of

mass moles volume

Molar mass

Molarity of solution


Changing solution concentration byconcentration by

dilution

20 particles/100 ml 20 particles/200 ml53


DilutionWhat is the concentration of an NaOH solution prepared by diluting 0.25 L of 6.0 M NaOH to a final volume of 1.25 L by addition of water?

⎟⎞

⎜⎛

⎟⎟⎞

⎜⎜⎛

⎟⎞

⎜⎛ L 0.25NaOH mol 6.0

⎟⎠

⎜⎝⋅⎟⎟⎠

⎜⎜⎝⋅⎟⎠

⎜⎝ L 1.25L 1.0

·V ÷VM1 M2

·V1 moles÷V2


Wh t l f 6 0 M N OH d tDilution

What volumes of 6.0 M NaOH and water are required to prepare 0.50 liters of 1 M NaOH?

⎟⎞

⎜⎛

⎟⎞

⎜⎛

⎟⎟⎞

⎜⎜⎛ L 1.0NaOH mol 1.0L 0.50

⎟⎠

⎜⎝⋅⎟⎠

⎜⎝⋅⎟⎟⎠

⎜⎜⎝ NaOH mol 6.0L 1.0

V1 V2·M1 moles ÷M2


DilutionV V·V1M1 M2moles÷V1

÷V2

· V2

V V·M1 l ÷M2

M x V = moles

V1 V21 moles

÷M1 ·M2

M2

M1 x V1 = moles

M2 x V2 = moles2 2

moles = moles

So:

M1 x V1 = M2 x V2 56S. Ensign, aqueous reactions

Review some solution termsM l l ti h th l t h i l f l•Molecular equation: shows the complete chemical formulas

of reactants and products, not necessarily as they actually exist in solutionexist in solution

•Complete ionic equation: all soluble salts are shown as ions i e in the form they actually exist in solutionsions- i.e. in the form they actually exist in solutions

•Net ionic equation: includes only ions and molecules that di l i l d i h i l i i iare directly involved in a chemical reaction occurring in

solution

•Spectator ions: ions in solution that are not involved in a chemical reaction, and appear in identical forms on both id f th h i l tisides of the chemical equation


What concentrations of species are present in solutions of strong electrolytes?in solutions of strong electrolytes?

• Molecular equation: shows the complete chemical formulas of reactants and products, not necessarily as they actually

0.025 M NaCl0 025 M Na SO necessarily as they actually

exist in solution• Complete ionic equation: all

soluble salts are shown as ions- i.e. in the form they

0.025 M Na2SO4

ions i.e. in the form they actually exist in solutions

• Net ionic equation: includes only ions and molecules that are directly involved in a ychemical reaction occurring in solution

• Spectator ions: ions in solution that are not involved in a h i l ti dchemical reaction, and appear

in identical forms on both sides of the chemical equation


Useful problem solving strategies for chemical reactions occurring in aqueous solutionsInterconverting moles, molarity, and volume:g , y,

M V·Vmoles

÷V

÷M

· M

Dilution problems:·V1M1 M2moles÷V1

÷V2

· V21

V1 V2·M1 moles÷M1 ·M2

÷M2

massa molesa Ma or VaMolar massa

Ma or Va

Interconverting mass, moles, and volume in aqueous chemical reactions:

Stoichiometric relationship in a reaction


massb molesb Mb or VbMolar massb Mb or Vb

Problem solving strategy for chemical ti i i l tireactions occurring in aqueous solutions

Molar mass Ma or Vamassa molesa Ma or VaMolar massa a a

Stoichiometric relationship in arelationship in a reaction

massb molesb Mb or VbMolar massb Mb or Vbmassb molesb Mb or Vb


Sodium bicarbonate (NaHCO3) is often used to neutralize spills of acids such as sulfuricto neutralize spills of acids such as sulfuric acid (H2SO4).

2NaHCO3(s) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) + 2CO2(g)

What mass of NaHCO3 would be required to

M V

3 qneutralize 25 ml of 6.0 M H2SO4?

massa molesa Ma or VaMolar massa

Ma or Va

Stoichiometric Start here…

relationship in a reaction

l M VMolar massb Mb or Vbmassb molesb Mb or Vbb b b

End here61


2NaHCO3(s) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) + 2CO2(g)

What mass of NaHCO3 would be required to neutralize 25 ml of 3 q6.0 M H2SO4? massa molesa Ma or Va

Molar massaMa or Va

Stoichiometric relationship in a

Start here…

preaction


End here


What volume of 0.105 M HClO4 would be required to neutralize 50.0 ml of 0.0875 M

mass moles M or VMolar massaMa or Va

NaOH?

massa molesa Ma or Va

Stoichiometric relationship in a

Start here…

reaction


End here


What volume of 0.105 M HClO4 would be required to neutralize 50.0 ml of 0.0875 M NaOH?


What volume of 0.158 M HCl would be required to neutralize 2.87 g of Mg(OH)2?


What is the total concentration of all solute species present in a solution prepared by mixing 50.0 ml of 0.20 M KClO3 with 25.0 ml of 0 20 M Na SO ??ml of 0.20 M Na2SO4??


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