TYPES OF CHEMICAL REACTIONS AND SOLUTION CHEMISTRY

I. Much of the chemistry that affects each of us occurs among substances dissolved in water.

2. Before we can understand solution reactions, we must discuss the nature of solutions in which

water is the dissolving medium, or solvent.

3. These solutions are called A 4)(j8J oS SO L UTI oAlS

Water - The Common Solvent

I. One of the most valuable properties of water is its ability to dissolve many different substances.

2. Liquid water consists of a collection of H20 molecules. The H20 molecule is 6194 " or V-

shaped with an H-O-H bond angle of about 105°.o

H 105 1-1<, -:

.0 ·• •

3. The O-H bonds in the water molecule are CoVAt.e'N T bonds formed by electron sharing

between the oxygen and hydrogen atoms. However, the electrons are not shred equally.

4. The electrons tend to spend more time close to the oxygen than to the hydrogen because oxygen

has a greater attraction for the electrons.

5. This gives the oxygen atom a slight negative charge and the hydrogen a slight positive charge.~ -I- S +

1-/ <, /' 1-1

o r -6. Because of this unequal charge distribution, water is said to be a Po LA e.. /VI 0 U= CU Llf' .

7. It is this polarity that gives water its great ability to dissolve compounds.

8. When an ionic substance dissolves in water, the "positive ends" of the water molecule are attracted

to the anions while the "negative ends" of the water are attracted to the cations.

9. The process is called HYDQ AT/O AI .

OVER

10. The hydration of its ions tends to cause a salt to "fall apart" in the water, or to dissolve. The

strong forces of attraction between the cations and the anions are replaced by strong water-ion

interactions.

I 1. When ionic substances dissolve in water, they break up into the individual cations and anions.

(aq) designates that the ions are hydrated by an unspecified number of water molecules.

12. The SOLValLiTY of ionic substances in water varies greatly. Some are very soluble while

others are barely soluble. The differences in solubilities of ionic compounds in water depend on

the relative attractions of the ions for each other and the attraction of the ions for water molecules.

13. Water also dissolves many nonionic substances.

6TI-4ArJO L

•14. Ethanol contains a polar O-H bond like those in water, which makes it very compatible with

water.

15. Pure water will not dissolve animal fat.

16. Polar and ionic substances are more soluble in water than nonpolar substances.

LIKE DIS~OL"ES Ulc(6

H-I ./ O-N

H - C - CI

H H r...:n-.11l?Q.W10lEC VLA L

ForLcc:: of A1Tf<.ACT70tJ

Strong and Weak Electrolytes

I. What happens when a substance, the Sc)LVn.:;- ,is dissolved in liquid water, the

.soL\/t=-,..J T ?

1. One useful property for characterizing a solution is its 8ECTiICAL. CoNDVoIVIT'(;.ts ability

to conduct electricity.

3. Some aqueous solutions conduct electricity very efficiently. These are said to contain

STlWtJ 6 I37-E crllOLY ~S

4. Some aqueous solutions conduct only a small amount of current. These are said to contain

Wl="1lt: 8..ECTflOl'irE..!.

5. Some aqueous solutions permit no current flow and are said to containNOtJEL.£CmOL'Y T6-J .

6. The extent to which a solution can conduct an electric current depends directly in water.

Strong Electrolytes

I. Strong electrolytes are substances are substances that are eorr1PLi=.I1:::L.t ionized when they are

dissolved in water.

2. Several classes of strong electrolytes are:SOLV~Lb SALTS

.sTrW,.J6 ACt DS

~11W1J6 tJAS6S

3. Arrhenius proposed that an Ac ID is a substance that produces W ions when it is dissolved

in water.

I~Cl~)~/020(..l)

H t (~) o~ 01- (o..~)

H~O(1)H1 (o.v) + rJ03 - (O-~JI--ttJO.B '7

1/') 0(1)/-(1 (().J) -I I-{SOC( - (o.g)I-Ia SO,", 7

OVER

, ' '

4. When He!. HNO) and H2S04 are placed in water, virtually every molecule ionizes. These

substances are strong electrolytes and are thus called' SrWiJ6 J1Cl J>.f

"); •', '

5. A strong acid is one that completely dissociates into its ions.

J.t C1 J H~rl HI,. jf,JOs, 11.;1 SOC/) I-Il10v Ile~OJAnother important ~Iass of str().ng electrolytes consists of..sVto,.;6 MSGS, ' These are

soluble ionic compounds containing the hydroxide ionOt-l -

1<' OH (S)

J.I~(l); .~

J-MO(t) '",,~

0c.. t (~) ".

1(1' (fij;)'

.~.. ~...

Weak Electrolytes, " : '"-.", 5 .: ,~,.' :.

""" .. .'~,.

-v, " .• ~-

,,' ,t.:' Weak electrolytes are substantes thatexhibit'a small degreeo(ionizationJn water,~',,:.'" ~:'-:, ·-·-~t-· .' ':,.>"l " . '. /."'.':; .. :,t.j'.;:~'''_ '" ~'_~:_L.-.:,·,?:·i~".-_;.,·i.--"·' , -",:.:.•..: .. ~'~,

'. ;~ -: <:,' ..-;',:~:,~..

'.2.:Them';'. ~~~~~~e.:,~~aci';;.,!,,~~k b~",:::·;c';':/t ;.;9ffi~!14,,()~51)',\;;{'/:i~~;;;;illiE(4rN~;j::¢~~~\:-~~

-."

<, "

Another type of we~k el~ctrolyte is a weak base..

~1jJ;;fJH /~orB..

~7c::::~

Nonelectrolytes

~--«

't. ',.Substances that go notproduc~jon~". . :,j."'-- •.• -.- - ;--.

,~~,tJ~Ot.>

... '.\ " .'.. - <."

:". ..,-j, .

•. ' '.< ~

Composition of Solutions

1. Chemical reactions often take place when two solutions are mixed.

2. To perform stoichiometric calculations, one must know:

a. the nature of the reaction.

b. the amount of chemicals present in the solution, called CoNCl:9vJ/Z4TI ON

3. One expression of concentration is MOLA~ITf (~)

MOltS of SOlltTc-

Lln:Il.S bF SOLvT10N

A\Mv-fL

***** Determine the molarity ofa solution in which a 0.4508g sample of iron is dissolved in enough water

to make 250.0 mL of solution.

[F~J = , 0080 71 "0204 wtrrP

• dSO L=: 0,0:3 d d.-q M

4. The conventional description ofa solution's concentration may not be accurate. One must look at

what is really happening when the solute dissolves. Then determine the concentration of each ion

present.

***** Determine the concentration of the ions present in 0.250 M KZCr207/{~.O(1) 1" /? 0 ,;----~ ;J K (~1 ~ L.r J. .., (O-tp)

• .2S0 mA I(a C~ 0 11 cJmrrf. k t

I L T7~ ~Ca07

nwJz c. 500 L

L

OVER

• .JSC L

IL

** ••• Determine the mass, in grams, ofNaOH containedin 250.0 ml, of 0.400 M NaOH solution .

.,'" .

2. The solid that forms is called a p~~c..1P Irn~ .

3. To write an equation for a precipitation reaction, one must know the identities of the reactants and

the products.

4. In virtually every case, when a solid containing ions dissolves in water, the ions separate and

move around independently.

***** Look at the reaction between lead (II) nitrate and potassium chloride:

A more accurate representation is:

5. Now the chemist must PQfDIC..Tproduct ex j)t;'""2l MruTA LLY

the products. This is hard to do. Only after identifying each

is the chemist sure what reaction has taken place.

6. Some things help us predict products.

a. When ions form a solid compound, the compound must have zero net charge.

b. Most ionic materials contain only two types of ions - one type of cation and one type of an ion.

***** From our earlier example, the possible product combinations are:

/<C}J( tJOJ

Since two possibilities are the reactants in solution, the possible products are:

OVER

7. In order to predict products and determine whether a reaction takes place, one must remember the

solubility rules. The rules help one determine which ionic species will form a solid or remain in

solution .

••••• According to the solubility rules, PbCb will form a precipitate because it is insoluble in water. Our

reaction becomes:

After balancing we have: tPb~(~')+- ;)iJOJ-Cap)+ JK1~).f d dCK.7J"l -7 P60J(s) -I- J-t (~)~ ;;; AlOJ' -(tLj)

8. The key to dealing with the chemistry of an aqueous solution is first to focus on the actual

components of the solution before any reaction occurs and then to figure out how these

components will react with each other .

••••• Using the solubility rules, predict what will happen when each ofthe following pairs of solutions are

mixed:

a. BaCh (aq) and Na2S04 (aq) FfI. U~ 130..SO€{

b. AgNOJ (aq) and Na3P04 (aq) PPT, OF ~ 3 ra,c. NaOH (aq) and Fe(N03)3 (aq) PPT OF Fe (OU)3

Describing Reactions in Solution

gives the overall reaction stoichiometry but not

necessarily the actual forms of the reactants and products in solution.

* •••• From our previous example:

Pi:, (l\lo1L (~) -+ cJ k'Ci CO}

2. The eo M ()LI:::/E ..:miJ IL f:2V,4DOtdpresents as ions all reactants and products that are

strong electrolytes.

3. The ,.JET rON IL lFqVAT10J includes only those solution components undergoing a

change. Spectator ions are not included.

--=7

Stoichiometry of Precipitation Reactions

I. The same stoichiometric principles apply.

2. It is sometimes difficult to tell immediately what reaction will occur when two solutions are

mixed.

3. To obtain the moles of reactants we must use the volume of the solution and its molarity .

•• *•• What volume of O. 100M Na3P04 is required to precipitate all the lead(lI) ions from 150.0mL of

0.250 M Pb(NOJ)2 ?

,J,JaJIt1 (~) 4 3 Pb (I\lO$)J (~) -'7 Pb3 (PO'1)J (S) + & Ala AlOa (~)

tL

OVER

***** What mass of barium sulfate is produced when 100.0 mL of a 0.100 M solution of barium chloride is

mixed with 100.0 mL of a 0.100 M solution of iron (Ill) sulfate?

3 6C\ a~ (~) 4 Fe,J (£0« \ (~n) -"7 3 &. SOIJ en-i, roo L • WO r>tvJl &dz.. 3/'Ylv-f &S()«

.IOC) L .leJOt>t~ /;1. (soJ.)IL

***** A 100.0 mL aliquot of 0.200 M aqueous potassium hydroxide is mixed with 100.0 mL of 0.200 M

aqueous magnesium nitrate.

a. Write a balanced chemical equation for any reaction that occurs.

b. What precipitate forms?

c. What mass of precipitate is produced?

I LKoHfl'1 (, ~\CJ.,oooL /<OH

j 30HJ J = I

I. II d-

L/I'\\ ,T1,JG Rf::'""A(TAtJ T ) .so au. OF TJ.I~ C/-I IS uJI:="1)1(0H .IS T1-J£

s ~EC-rn 'TOe. .l'btJ .s ALE \(-t- 4",10 NO?;

[~+J 1000 L • Z.b(,)l11.~ ~o~ IM~ k t- t tKr1/z . z: O. /00

II... I~\i.,..l~OH • JOOOL L

d. Calculate the concentration of each ion remaining in solution after precipitation is complete.

fj ,l~~,..d 01-1- (~) -7 (rlJ (Olf)) (S)

/L

ACID BASE REACTIONS

I. The Arrhenius definition of an acid and a base is that an acid produces H r ions and a base

produces () H - ions.

2. A more generalized, and useful, definition was provided by Johannes Bronsted and Thomas Lowry. The

Bronsted-Lowry definition of an acid is that it is a substance that is a . Pfb:;ro IV oOAIOI(

A base is a P{(OTO r.J 4Cf!A?P701(.

3. Predicting the results of an acid-base reaction can be difficult.

4. When aqueous hydrogen chloride mixes with aqueous sodium hydroxide, the combined solution

contains: Ht J CJ -, A.1Cl;, 0 H -

OVER

'. 5. This is because HCl is a strong acid and NaOH is a strong base. Both will dissociate completely;

6. The recombination produces ~~ cJ ,which ;s soluble so it remains ,Ja. -r and CJ ~ These.

speciesare spectator ions. , •7. Thett-t-: and theOH -cannot coexist in solution ~ecause w~teris a no~electr~lyte.

:i.-" - .. '

;""'7 Iid-O (l)',"t·, •. ,..... '.

-: ". :::i>::" "::'. <'•• :'-1.:, •... .: "J"

weak acid, with anaqueousshlutionofp()taSsiumhyd~?"ld~, the species

, '

'.' HC~H3061 )'.,,' ,c'

9. BecaJ~e the OH' has such 'a strong'~ffinjtY'f~rprot~~~~;ifcan strip them';~m the 'H~2H302:'- - " -; ',"'- -,- .

: oi+':~{~~}.'H ~~14 (J:,~;'••~. ,\,I.'i.,~.;.9.r..;e~.,~;f~/f{'((~)\~••-:••'.-. "";' .. ~~'_j_' .~__ "-~>. ~._ .• _ -<_t-;-)~'-~

'..::\Y;,'; .;::.i." _ .' ':~';;':"';,-",.' ,)21f?::.; , ;.::;1:~;:;{;.>:·>;i:;':;·}_.{.:.{,._ <.~-\':; , .10. The hydroxide ion is such a strongb~se that for purp~se_spfstoi~hiometriccalculations.it

". assumed to reactc~mple~~I; ~ithany~eaka~id i(e~~o·u~ter,s:',->;t.•.•·..-_.->-.,- «; ·'··:·":~i.·.· ., .

. 11.A~ acid-b~e' reacti~n is ~ft~ncalled atJaffrcAu-;';'ne';J "'Rtmt:noA/ ". ~henjust enough base

is added with theacidina~olution, we say the ~cid~as:heellneutralized. • .

j

". .-

..•...'.•..'

,. ' ..-

••••• What volum~ofO.250M KOH wiUreact com~Iet~IYwith25.00mLofd.260M HCI1

~~O(lJ.~--.

OH~t~)

to,J.5 L ·Me.( ...·.1·. ,·JCOwv-R 1-/-1: .. .':~'.":' f· IL ..H{j _.'

... :.:

~~ O~~ ~...6.0~5~.Hlt H:~~;-.I "~ . c"

~.s,

. f;-;;''-- -~.' -',1 .

0.0; s..~~ ..oH~~.:JS'O )~~OH~

.' .' ,.~

**ut Hydrochloric acid (75.0 mL of 0.250 M) is added to 225.0 mL Of 0.550 M Ba(OH)2 solution. What

is the concentration of the excess H+ or OH' left in the solution?

IV\,.{ O~- ,~O)S L iS4(OH)z.=

I

-mE MOLE RAnO 01- H~ TO

1+ t- WiLL R.Vt.J OUT t= IIl.ST

O.OI81~ wv-l H-+ eEY-\CU Win)

o, 0 d «(15\' $SO ","/ & (OU),I L

oH - .D\-I THE t2~Cn"tJ .t:5 I: I So nit?

lH-tJ=OO.o/~7S mrl.. 01-1- TO mo~1X.-t o,olf7Jh1,.1 /-{(J

-rurAL \/'0 LV mt::- = ?S.OML+

[OI1-J -=- · OO"MJ, .300 L :=

c} ~ S,D m L = 300, 0 M L

0.0 ..l00 M

Acid Base Titrations

I. VOLVME17lIC. ANt\L'( S Uby doing a titration.

is a technique for determining the amount of a certain substance

2. A TIT/2.ClTIo;J

concentration, TlillArJ rII tJA l'f TE"

involves delivery ofa measured volume ofa solution of known

• into a solution containing the substance being analyzed.

3. The titrant contains a substance that reacts in a known manner with the analyte.

4. The point in the titration where enough titrant has been added to react exactly with the analyte is calledthe ~QVIV tllt?i\lC£ POII>J.T or $TV ICl-jl 0 MI:mlIC POI AiT .

OVER

, "

5. This point is often marked by an ,.I7IJbICQTO.e.. ' ,a substance added at the beginning of the

titration that changes color at (or near) the equivalence point.

6. The point where the indicator actually changes color is caIled the, E].JC PoIAIr

, titration;

of the

7~ When the analyte is abase or an acid, the required titrant is a strong acid or strong base, respectively.

This procedure is called an' Rei 0 --tailS F T1rll4 nop

I:' 2 Na (s) +C12(g)'-+2NaCI (s)-:

~: ~:'". ~.".

2, Bothreactants haven? charge, they areneutral, NaCI is an ioniccompoundcontaining Na+ ions-and CI-"'~'. :!:., ..• ~. . "" .

ions;

3. Reactions like this one; il1'whichorte or mo;~ electrons. are transferred, are. called

6~,t>A110rJ;' RlfDvcn(),J~ reactions,or' t<t1:>O~'

';4.- '," >,:.; ..-\"--,

. ,':, ;;:,

Mostreactio~~us~d for energy produc!ilon '~~~,~ed~~readions~. i

Oxidation States

I. Theconcept of oxidation states provides a war to keep track of electrons in redox reactions.. ,

2. This is particularly useful for redo"r~actioJ1Sinvolving covalent substance. ,,..~-' .

. -'.

3: For acovalent bond between two identic,al atoms.jfieelectronsaresplit equally between the two.

- ~', . - -

4. Whentwo differ~~t atoms a~einvolved,and JheeJectrons'at~ shared.unequally, theelectrons are

assigned to the atom that.has th¢ str~ngerattr~ct'ion for-the electrons.

5. Oxid~tion states are assigned .accordtng to ~he~les 011 page -'--:-"':""' _

~.-,. .,:

6. While: uncommon, noninteger oxidationstates can exist."

~., '..

~- ..,.

C\

* •••• Assign oxidation states to all atoms in each of the following compounds:

AS203

O~ -JAs c +3

HAsO.::

0 z: -~As > + 3H z: f I

r-'j t: t- 'J-

P s: t 5(j s: - J..

Characteristics of Oxidation- Reduction Reactions

I. In some cases the transfer of electrons is very obvious.

2. In other cases the transfer is less obvious.

3. 6'i.1 DA770 JJ is the increase in oxidation state; a loss of electrons.

4. i(EJ)vtT70,J is the decrease in oxidation state; a gain of electrons.

5. The OXI D/:c,tJ6 AGEiJT

is the --~--------------~----LEO Gl-:127. says _

Los~ of J=:"LECn2.0A.,./S,OX/DAT10,J

OVER

***** Identify the oxidizing agent, the reducing agent, the substance being oxidized, and the substance

being reduced.

Cu (5) + 2 Ag" (aq) - 2 Ag (5) + Cu2+ (aq)

OXIDl~"J6 A6t:N1; -'b +RftlUCltJ6 A6eJT ~ &

SiCI4 (I) + 2 Mg (s) - 2 MgCb (s) + Si (s)

O)(IDlcIN6 AGeJT : Slc.P'IOX/,;)lctD: I11j

IZtDlJCrD : S i

BALANCING OXIDATION - REDUCTION EOUATIONS

I. Difficult to do by simple inspection.

Half - Reaction Method

I. Separate the reaction into two half-reactions, one involving oxidation and one involving reduction.

2. Balance them separately.

3. Add them together.

In Acidic Solution

I. Write separate equations for the oxidation and reduction half-reactions.

2. Balance all the elements except hydrogen and oxygen.

3. Balance oxygen using H20.

4. Balance hydrogen using W.

.. ,_. , ..

•

5. Balance the charge using electrons.

6. Multiply one, or both. balanced half-reactions by an integer to equalize the number of electrons

transferred in the two half-reactions.

7. Add the half-reactions and cancel identical species.

8. Check that the elements and charges are balanced.

***** Balance the following oxidation-reduction reaction that occurs in acidic solution using the half-

reaction method.

Cr~Oi- (aq) + CI- (aq) - Cr.3+ (aq) + Cl- (g)

C 0J.-

~e- ./- I~Ht ~ ,.:}. 7 -->

!? 01-I'II/t of e-ra. 07 -7

fI CJ - -7

7 1-6-0

Cld 1- Je-

OVER

In Basic Solution

1. Use the half-reaction method specified for acidic solutions to obtain the final balanced equation as if W

ions were present.

2. To both sides of the equation, add a number ofOH' ions that is equal to the number of H" ions.

3. Form H20 on the side containing both Wand OH" ions, and eliminate the number of H20 molecules

that appear on both sides of the equation.

***** Balance the following oxidation-reduction reaction that occurs in basic solution.

CN" (aq) + Mn04" (aq) -+ CNO" (aq) + Mn02 (5)

!I~0 f ~rJ - -'7 CAf 0 - t- c2 H of -I d e -

3~- + '-11-++ + MVlO\( - -;;:. MY) Oa- 4- OJ 1Ia.- 0

3 CJJ 0 - + ~ 1-/7 of- & e -

-"7 ;;) 1111 ()a -I ;; /la- 0 •