Ch4

Chapter 4Chapter 4

AQUEOUS REACTIONS & AQUEOUS REACTIONS & SOLUTION SOLUTION

STOICHIOMETRYSTOICHIOMETRY

CHAPTER 4CHAPTER 4

Ionic Compounds in WaterIonic Compounds in Water

Electrolyte – they conduct electricityElectrolyte – they conduct electricity They SEPARATE when they dissolveThey SEPARATE when they dissolve

NaCl NaCl Na Na++ + Cl + Cl- -

Water is POLAR, it has a charge difference from one side to another

They mostly don’t break apart, they disperseThey mostly don’t break apart, they disperse No ions, no conductivityNo ions, no conductivity Only polar compounds (have charge difference Only polar compounds (have charge difference

from one side to another) dissolvefrom one side to another) dissolve SOME FEW molecules will break apart to SOME FEW molecules will break apart to

form ions namely acids (HBr) form ions namely acids (HBr)

Molecular Compounds in WaterMolecular Compounds in Water

Strong electrolytes are boring, they split apart Strong electrolytes are boring, they split apart (disassociate) and stay disassociated (disassociate) and stay disassociated NaCl NaCl Na Na++ + Cl + Cl- -

For Weak electrolytes, only some of the For Weak electrolytes, only some of the molecules will disassociate, the rest stay molecules will disassociate, the rest stay togethertogether

The strength of the electrolyte depends on the The strength of the electrolyte depends on the amount of molecules that break disassociateamount of molecules that break disassociate

Strong & Weak ElectrolytesStrong & Weak Electrolytes


Since weak electrolytes have both the capacity to Since weak electrolytes have both the capacity to disassociate AND reassociate after separatingdisassociate AND reassociate after separating

Since there are 2 reactions (whole molecules to Since there are 2 reactions (whole molecules to ions and ions to whole molecules) we write the ions and ions to whole molecules) we write the equation to show that there are 2 reactionsequation to show that there are 2 reactions

CH3COOH (aq) CH3OO-(aq) + H+

(aq)

These reactions that occur both forwards and These reactions that occur both forwards and backwards are considered to be in backwards are considered to be in CHEMICAL EQUILIBRIUMCHEMICAL EQUILIBRIUM


These are (surprise) reactions that form a These are (surprise) reactions that form a precipitateprecipitate

If a precipitate forms, there can be no If a precipitate forms, there can be no equilibrium since the precipitate does not form equilibrium since the precipitate does not form ions and drops out of solution. The reaction ions and drops out of solution. The reaction can go forward, but can’t go backwards since can go forward, but can’t go backwards since some of the reactants have been inerted.some of the reactants have been inerted.

Precipitation ReactionsPrecipitation Reactions

Pb (NOPb (NO33))2 (aq)2 (aq) + Na + Na22 (CrO (CrO44) ) (aq)(aq)

Pb (CrOPb (CrO44) ) (s) (s) + 2 NA(NO+ 2 NA(NO33))

Pb (CrOPb (CrO44) is a solid and does not form ions, ) is a solid and does not form ions,

so there can be no reverse reaction.so there can be no reverse reaction.

See page 125 for a solubility guideSee page 125 for a solubility guide

Precipitation ReactionsPrecipitation Reactions

NONO33- All nitrates are soluble. - All nitrates are soluble. Cl- All chlorides are soluble except AgCl, HgClCl- All chlorides are soluble except AgCl, HgCl22, and , and

PbClPbCl22. . (SO(SO44)- Most sulfates are soluble. Exceptions include )- Most sulfates are soluble. Exceptions include

BaSOBaSO44, PbSO, PbSO44, and SrSO, and SrSO44. . COCO33- All carbonates are insoluble except NH- All carbonates are insoluble except NH44+ and + and

those of the those of the Group 1 elementsGroup 1 elements. . OH- All hydroxides are insoluble except those of the OH- All hydroxides are insoluble except those of the

Group 1 elements, Ba(OH)Group 1 elements, Ba(OH)22, and Sr(OH), and Sr(OH)22. Ca(OH). Ca(OH)22 is is slightly soluble. slightly soluble.

SS22- All sulfides are insoluble except those of the Group - All sulfides are insoluble except those of the Group 1 and 1 and Group 2Group 2 elements and NH elements and NH44+. +.

Solubility RulesSolubility Rules

Predicting if strong electrolytes will form a Predicting if strong electrolytes will form a precipitateprecipitate

Ag(NOAg(NO33))(aq)(aq) + NaCl + NaCl(aq)(aq) ? ?


Chlorides are soluble EXCEPT Ag, Hg, and Chlorides are soluble EXCEPT Ag, Hg, and Pb… soPb… so

Ag(NOAg(NO33))(aq)(aq) + NaCl + NaCl(aq)(aq) AgCl AgCl(s) (s) + Na(NO+ Na(NO33))(aq)(aq)


Acids are compounds that form positive Acids are compounds that form positive Hydrogen ions HHydrogen ions H++ when dissolved when dissolved

Bases are compounds that form negative Bases are compounds that form negative hydroxide ions OHhydroxide ions OH-- when dissolved when dissolved

As you can easily guess one HAs you can easily guess one H++ and one OH and one OH-- combine to form Hcombine to form H22OO

Acid - Base ReactionsAcid - Base Reactions

Strength of acids and bases depend on the Strength of acids and bases depend on the amount of material that disassociates amount of material that disassociates

Much disassociation makes strong acids and Much disassociation makes strong acids and basesbases

Little disassociation, weak acids and basesLittle disassociation, weak acids and bases


NEUTRALIZATIONNEUTRALIZATION When acids and bases react with each other the When acids and bases react with each other the

HH+ + and OHand OH-- ions combine ions combine A solution that is not acidic or basic is said to A solution that is not acidic or basic is said to

be neutral. Why? Wait a few slidesbe neutral. Why? Wait a few slides Acids and bases react with each other to form Acids and bases react with each other to form

water and a saltwater and a salt



02

042

24

24242

)(24242

2

222

:

22

OHSOCs

SOHOHCs

ionIonicEquat

OHSOCsSOHCsOH

OHSOCsSOHCsOH dunballance

H+ and OH- always react to form HOH or H2O

The cation (metal from the base) reacts with the anion from the acid (everything after the H) to form the salt.

Watch the subscripts on the acids and basesWatch the subscripts on the acids and bases Acids have 1,2, or even 3 HAcids have 1,2, or even 3 H++: bases 1 to many : bases 1 to many

OHOH--

When balancing the equations, you must add When balancing the equations, you must add enough acid or base to compensate and get an enough acid or base to compensate and get an electrically neutral productelectrically neutral product

And you thought the term neutralize referred And you thought the term neutralize referred to canceling out the acid and base!to canceling out the acid and base!


GAS FORMATIONGAS FORMATION Just like some reactions form solids, some Just like some reactions form solids, some

form gasesform gases If you have ever taken an antacid, or made the If you have ever taken an antacid, or made the

infamous “erupting volcano” science project in infamous “erupting volcano” science project in grade school, you have done a acid – base grade school, you have done a acid – base neutralization reaction with gas formation (so neutralization reaction with gas formation (so you can cross that off your bucket list)you can cross that off your bucket list)



The VolcanoThe Volcano

)(2)(2)(32

)(32)(3

)(3)(3

glaq

aqaq

aqaq

COOHdecomposesCOH

COHCOONaCH

NaHCOCOOHCH

Called redox reactionsCalled redox reactions Something is oxidized and something is Something is oxidized and something is

reducedreduced The element or compound whose charge goes The element or compound whose charge goes

DOWNDOWN is is REDUCEDREDUCED The one whose charge goes up is oxidizedThe one whose charge goes up is oxidized

Oxidation - Reduction ReactionsOxidation - Reduction Reactions

Atoms in elemental formAtoms in elemental form

oxidation number =0oxidation number =0 For ions For ions oxidation number = charge oxidation number = charge Metals have positive oxidation numbers, Metals have positive oxidation numbers,

nonmetals have negative numbersnonmetals have negative numbers Hydrogen can act like a metal (HCL) or a Hydrogen can act like a metal (HCL) or a

nonmetal (NaH). It’s oxidation number is +1 nonmetal (NaH). It’s oxidation number is +1 if a metal, -1 if a nonmetalif a metal, -1 if a nonmetal


Oxidation - Reduction ReactionsOxidation - Reduction ReactionsRustRust

Remember that reactions occur when elements transfer Remember that reactions occur when elements transfer electrons to fill or deplete their outer electron shellelectrons to fill or deplete their outer electron shell

66

232

232

23

32

23

32

02

0

322322

NetONetFe

OFeOFe

OFeOFeOFeOFe

O went from 0 to -2 so it was reduced

Fe went from 0 to +3 so it was oxidized

Oxidation of metals by acid or salt – replacement Oxidation of metals by acid or salt – replacement (displacement) reactions(displacement) reactionsAn ion in solution is replaced by the metalAn ion in solution is replaced by the metal


0)(2

1)(2

21)(

10)( 2 gaqaqs HFSnFHSn

Hydrogen is reduced (+1 to 0)Hydrogen is reduced (+1 to 0)

Sn is oxidized (0 to +2)Sn is oxidized (0 to +2)

The charges balanceThe charges balance


Replacement of a metal by a saltReplacement of a metal by a salt

)(21

32

)(0

)(3110 )(2)(2 aqSaq NOCuAgNOAgCu

Cu went from a 0 to a +2, so it was oxidized

Ag went from +1 to 0, so it was reduced

(NO)3 just sat back and watched (a spectator ion)

The charges ballance


Activity series of metals (p141)Activity series of metals (p141) A metal can only displace a metal that is LOWER on A metal can only displace a metal that is LOWER on

the chartthe chart If the metal is higher on the chart, there is NO reactionIf the metal is higher on the chart, there is NO reaction

)(21

32

)(0

)(3110 )(2)(2 aqSaq NOCuAgNOAgCu

Don’t memorize the series, if you need one for a test Don’t memorize the series, if you need one for a test or quiz, I’ll provide oneor quiz, I’ll provide one

Molarity (M) the ratio of moles of solute (the Molarity (M) the ratio of moles of solute (the stuff that gets dissolved) and the volume of the stuff that gets dissolved) and the volume of the solution in literssolution in liters

1 mole of HCl in 1 liter of water gives a 1M 1 mole of HCl in 1 liter of water gives a 1M solution of HClsolution of HCl

Concentration of SolutionsConcentration of Solutions


MNaClLwater

molNaClLwater

mlwater

mlwater

molNaCl

L

molM

66

1

1000*

500

3

: waterof 500mlin NaCl of moles 3


M

Lwater

mlwater

gLiOH

molLiOH

mlwater

gLiOH

9.6

1

1000*

24

1*

600

100

waterof 600mlin LiOH of 100g

mols/LM


22

22

2

BaCl 07.1208

1*

25.2

500

waterof L 2.25in BaCl of 500g

MgBaCl

molBaCl

L

gBaCl

I have two bottles of NaCl one is 233ml of I have two bottles of NaCl one is 233ml of 0.567M salt, the other 0.547ml of 4.23M salt. 0.567M salt, the other 0.547ml of 4.23M salt. I mix them together. What is the Molarity of I mix them together. What is the Molarity of the final solution?the final solution?

Sol 1: 233ml*0.567 mols/L*1L/1000ml = Sol 1: 233ml*0.567 mols/L*1L/1000ml = 0.132mol0.132mol

Sol 2: 547ml*4.23mols/L*1L/1000ml = 2.38 Sol 2: 547ml*4.23mols/L*1L/1000ml = 2.38 molmol

Sol 1 0.132mol 0.233L Sol 1 0.132mol 0.233L

Sol 2 2.38 mol 0.547 L Sol 2 2.38 mol 0.547 L

Total 2.45 molTotal 2.45 mol 0.780 L 0.780 L

Molarity= 2.45 mol/0.780L=3.14M Molarity= 2.45 mol/0.780L=3.14M

Coefficients in chemical equations are ratios of Coefficients in chemical equations are ratios of moles (pieces) of reactants and productsmoles (pieces) of reactants and products

Molarity is the amount of material (in moles) Molarity is the amount of material (in moles) in a given amount of liquidin a given amount of liquid

We can use concentration and volume to We can use concentration and volume to determine the number of moles of reactants determine the number of moles of reactants either present (in the beaker) or that are either present (in the beaker) or that are needed (what we need to add to the beaker) for needed (what we need to add to the beaker) for a reaction.a reaction.

Solution StoichiometrySolution Stoichiometry


Mass AMass A

Moles BMoles B

Moles AMoles A

Mass BMass B

Volume / Volume / Molarity AMolarity A

Volume / Volume / Molarity BMolarity B

Formula Formula WeightWeight

StoichiometryStoichiometry M=mol/LM=mol/L


How many grams of NaOH is needed to neutralize How many grams of NaOH is needed to neutralize 75ml of 2 Molar H75ml of 2 Molar H22SOSO44??

gNaOHmol

gmolNaOH

molml

L

L

molml

1240

*3.0

NaOH moles 0.30 0.15 *2 :SOH of

moleeach for needed are NaOH of moles 2

O2H SONa 2NaOH SOH

:Equation Chemical

15.01000

1*

2*75SOH Moles

42

24242

42

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