Acidic Enviroment.doc

8/16/2019 Acidic Enviroment.doc

1/52

9.3 – The Acidic Environment:

Δ. Construct word and balanced formulae equations of all chemical reactions as they are encountered in this module:

– Note: In chemistry, [x] means “concentration of x” in moles per litre (mol/L).

– E. [H!"] means “concentration of H!" ions” in mol/L.

• Basic reactions to remember:

– Acid reactions:

aci# " $ase salt " %ater H&l(a') " Na!H(a') Na&l(s) " H!(l)

aci# " metal salt " hy#roen as H&l(a') " *(s) *&l(s) " H ()

aci# " car$onate salt " car$on #ioxi#e as " %ater H&l(a') " &a&!(s) &a&l(s) " &!() " H!

aci# " hy#roen car$onate salt " car$on #ioxi#e as " %ater (note: there is &! soli#, its #ry ice)

– !ormation of hydronium:

H" " H! H!"

• Reactions of various oxides with water:

– "on#metal $acidic% o&ides:

&! () " H! (l) H&! (a') (carbonic aci#)

+! () " H! (l) H+! (a') ( sulfurous aci#)

N! () " H! (l) HN! (a') " HN! (a') (nitric an# nitrous aci#)

!- () " H! (l) H! (a') ( phosphoric aci#)

– 'etal $basic% o&ides:

! (s) " H! (l) !H (a') ( potassium hydroxide)

Na! (s) " H! (l) Na!H (a') ( sodium hydroxide)

*! (s) " H! (l) *(!H) (a') (magnesium hydroxide)

• Various equilibrium reactions:

– 0ormation of carbonic aci#: &! () " H! (l) H&! (a')

– &o11er com(leions: &2(H!)"

(a') " &l

3

(a') &2&l3

(a') " H! (l)

– 4ecom1osition of dinitroen tetro&ide: N! () N! ()

– 4ecom1osition of calcium carbonate: &a&! (s) &a! (s) " &! ()

• Non-Arrhenius acid/base reaction (ie no water present and no free ! ions":

– 5aseo2s hy#roen chlori#e an# ammonia react:

H&l () " NH () NH&l (s)


2/52

• #onisation of stron$ and wea% acids:

– )ydrochloric: H&l () " H! (l) H!" (a') " &l3 (a')

– "itric: HN! (l) " H! (l) H!" (a') " N!6

– *ulfuric: H+! (l) " H! (l) H!" (a') " +!3

– Ethanoic: &H&!!H (s) " H! (l) H!" (a') " &H&!!3 (a')

• &ources of sulfur and nitro$en oxides in the atmosphere:

– *ulfur +&ides: !ranic #ecom1osition: H+ () " ! () +! () " H! (l)

72rnin hih6s2lf2r coals: + (s) " ! () +! ()

+meltin metal s2lfi#es: $+ (s) " ! () $! (s) " +!

– "itroen +&ides:

Lihtnin: N () " ! () N! ()

02rther &atalyse# $y oxyen 1articles: N! () " ! () N! ()

• Amphiprotic substances:

– )ydroen carbonate $ie bicarbonate%:

H&!3

(a') " H!"

(a') H&! (a') " H! (l)

H&!3

(a') " !H 3

(a') &!3

(a') " H! (l)

• Natural Buffers:

– 8he car$onic aci#/hy#roen car$onate ion $2ffer in the mammalian $loo# system:

H&! (a') " H! (l) H!"

(a') " H&!3

(a')

• 'sterification:

– ,eneral word#formula:

aci# " alcohol ester " %ater

al9anoic aci# " al9anol ester " %ater

– xam1le:


3/52

$2tanoic aci# " 1entanol 1entyl $2tanoate

&H;&!!H (a') " &-H


4/52

-. ndicators were identified with the observation that the colour of some flowers de(ends on soil com(osition:

• R'*A++:

– 5eneral ro1erties of Bci#s:

8hey taste so2r.

8hey are corrosiCe (ie stin/$2rn s9in)

Dhen in a sol2tion, they can con#2ct electricity (ie electrolytes).

Bci#s are ne2tralise# $y $ases.

1H E ;

0or LI8*F+: blue aci# red (ie turns blue litmus red"

Note: litm2s is a #ye ma#e from lichens

– 5eneral ro1erties of 7ases:

8hey 2s2ally taste $itter.

*ay $e corrosiCe.

*ainly insol2$le in %ater (note: a'2eo2s $ases are calle# al/alis).

Dhen in a sol2tion, they can con#2ct electricity (ie electrolytes), not all $ases are sol2$le.

7ases are ne2tralise# $y aci#s.

7ases are 2s2ally in the form of metal h,droxides (e.. Na!H) !G metal oxides (e.. *!).

1H ;

0or LI8*F+: red $ase blue (ie turns red litmus blue"

– Note: $y #efinition, an# electrolyte is any sol2tions that has free ions that is a$le to con#2ct electricity. Bn aci#

#issociates to form ions, so #oes al9ali $ases. Hence they are a$le to form electrolytes.

– "amin:

0inary Acids A binary compound consists of two elements. Binary acids have the prex hydro

in front of the full name of the nonmetallic element. They have the ending -ic.

Examples include hydrochloric and hydrouoric acid. Hydrouoric Acid H!

Hydrochloric Acid H"lHydrobromic Acid HBrHydrocynide Acid H"nHydrosulfuric Acid H#$

Ternary Acids Ternary acids commonly contain hydrogen% a nonmetal% and oxygen. The name of

the most common form of the acid consists of the nonmetal root name with the


5/52

-ic ending% The acid containing one less oxygen atom than the most common formis designated by the -ous ending. An acid containing one less oxygen atom thanthe -ous acid has the prex hypo- and the -ous ending. The acid containing onemore oxygen than the most common acid has the per- prex and the -ic ending.

&itric Acid H&'(&itrous Acid H&'#Hypochlorous Acid H"l'"hlorous Acid H"l'#"hloric Acid H"l'()erchloric Acid H"l'*$ulfuric Acid H#$'*$ulfurous Acid H#$'()hosphoric Acid H()'*)hosphorous Acid H()'("arbonic Acid H#"'(Acetic Acid H"#H('#'xalic Acid H#"#'*Boric Acid H(B'($ilicic Acid H#$i'(

0ases

$odium Hydroxide &a'H

)otassium Hydroxide +'HAmmonia , &H(

Ammonium Hydroxide &H*'H

"alcium Hydroxide "a-'H#

/agnesium Hydroxide /g-'H#

Barium Hydroxide Ba-'H#

Aluminum Hydroxide Al-'H(

!errous Hydroxide or 0ron -00 Hydroxide !e-'H#

!erric Hydroxide or 0ron -000 Hydroxide !e-'H(

1inc Hydroxide 1n-'H#

2ithium Hydroxide 2i'H

Al/ali 0ases: is a basic1 ionic *A2T of an al/ali metal or al/aline earth metal element.

$odium "arbonate , &a#"'(Bicarbonate -or hydrogen carbonate &aH"'( "alcium "arbonate "a"'(

• *lassif, common substances as acidic basic or neutral:

– Acids:

inear (acetic aci#), Citamin & (ascor$ic aci#), lemon J2ice (citric aci#), as1irin (acetyl salicylic aci#), ?fiKKy@

#rin9s (car$onic aci#).

– 0ases:

4rain cleaners (so#i2m hy#roxi#e), ho2sehol# cleaners (ammonia), antaci# ta$lets (calci2m car$onate), $a9in

1o%#er (so#i2m $icar$onate/so#i2m hy#roen car$onate).


6/52

– "eutral:

2re %ater, mil9, ta$le salt (ex so#i2m chlori#e $2t N!8 all salts are ne2tral),

• #dentif, that indicators such as litmus phenolphthalein meth,l oran$e and bromoth,mol blue can be used to

determine the acidic or basic nature of a material over a ran$e and that the ran$e is identified b, chan$e in indicator

colour:

– Bn indicator is a s2$stance (2s2ally a Ceeta$le #ye) that, in sol2tion, chanes colo2r #e1en#in on %hether the

chemical enCiroment is aci#ic or $asic.

– *ost in#icators 1ro#2ce #ifferent colo2rs one for aci#ic an# one for $asic.

– +itmus , phenolphthalein , meth,l oran$e an# bromoth,mol blue are common in#icators.

• #dentif, data and choose resources to $ather information about the colour chan$es of a ran$e of indicators:

– 8he rane of 1H rane of the common in#icators is sho%n $elo%:

• #dentif, and describe some ever,da, uses of indicators includin$ the testin$ of soil acidit,/basicit,:

– Testin *oil ():

+ome 1lants only ro% %ithin narro% 1H ranes, so the 1H of the soil nee#s to $e re2larly teste#. xam1les

incl2#e aKaleas/camellias nee# aci#ic soil, %hile Ceeta$les (ex c2c2m$ers) nee# al9aline.

B ne2tral %hite 1o%#er (s2ch as talc or $ari2m s2lfate) is s1rin9le# oCer the #am1 soil a fe% #ro1s of in#icator

are 1lace# on to1.

8he %hite 1o%#er allo%s the colo2r chane to $e seen clearly.

– Testin () of ools:

ool %ater m2st $e near ne2tral to aCoi# health 1ro$lems, the 1H re'2ire# for safety is M;.- for less irritation to

eyes an# s9in.


7/52

B fe% #ro1s of in#icator are 1lace# in a sam1le of the 1ool %ater alternatiCely, 1H 1a1er, alrea#y soa9e# in

in#icator can $e 2se#.

– 'onitorin () of Chemical 4astes:

Dastes that are 1ro#2ce# from la$oratories or 1hotora1hic film centres ten# to $e hihly aci#ic.

8he 1H of the %astes m2st $e ne2tralise# $efore they can $e safely #is1ose#.

In#icators are 2se# to meas2re the 1H, an# s2$stances a##e# to ne2tralise it.

• &olve problems b, appl,in$ information about the colour chan$es of indicators to classif, some household substances

as acidic neutral or basic:

– o2 can $e iCen s2$stance, an# its colo2r in#ication in Cario2s in#icators, to fin# its 1H rane.

• .erform a first-hand investi$ation to prepare and test a natural indicator:

– Aim: to 1re1are an in#icator sol2tion 2sin nat2rally occ2rrin s2$stances, in this case o$taine# from re# ca$$ae,

an# to then test them.

– 5is/ Assessment:

8his 1ractical inColCes $oilin a sol2tion ently, safety lasses an# 1rotectiCe clothin sho2l# $e %orn.

If these safety precautions are taken, then the risk is acceptable.

– 'ethod:

!ne lare re# ca$$ae %as 1eel an# cho11e# it %as then $len#e# thoro2hly 2sin a foo# 1rocessor %ith OO mL

of #istille# %ater.

7oil the mixt2re 2ntil a stronly colo2re# extract forms. Bfter this cools, strain an# transfer the re##ish612r1le

sol2tion to another $ea9er, this is the in#icator.

B## the in#icator sol2tion to #ifferent s2$stances in a etri #ish, leaCin one #ish as the control. !$serCe the

colo2r chanes as the in#icator is a##e# to s2$stances of hih, lo%, an# ne2tral 1H@s.

In se1arate #ishes, one as control, one haCin: mL of #istille# %ater, hy#rochloric aci# (H&l) an# so#i2m

hy#roxi#e (Na!H) sol2tion %as 1lace#.

– 5esult:

In the #istille# %ater, it %as 4BG FGL.

In the H&l sol2tion, it %as IN.

In the Na!H sol2tion, it t2rne# LL!D.

– 6ustification:


8/52

7eetroot %as 2se# as it is a Cery CiCi#ly colo2re# 1lant an# its 1imentation is Cery easily extracte#.

B fresh $eetroot %as 2se# instea# of canne# $eetroot as the canne# Cersion may contain 1reserCatiCes (many of

%hich are %ea9 aci#s) that may affect the res2lts.

H&l an# Na!H %as 2se# as they are on o11osite en#s of the 1H scale this %as to sho% the rane of colo2rs the

in#icator co2l# 1ro#2ce.

– 2imitations:

7eetroot come in many siKes this %as not controlle#.

8he exact 1H at %hich the transition of colo2rs occ2rre# %as not #etermine#.


9/52

7. 4hile we usually thin/ of the air around us as neutral1 the atmos(here naturally contains acidic o&ides of carbon1

nitroen and sulfur. The concentrations of these acidic o&ides have been increasin since the ndustrial 5evolution:

• R'*A++:

– 8he h,dronium ion:

Dhen in a'2eo2s sol2tions, B&I4+ #isassociate into anions an# H" ions (ex H&l H" " &l6 )

8hen the hy#roen ion reacts %ith %ater, ie this reaction occ2rs: H" " H! H!"

8he H!" ion is calle# the hydronium ion, an# is more sta$le than the H" ion.

8h2s, in %ater, acids form h,dronium ions.

• #dentif, oxides of non-metals which act as acids and describe the conditions under which the, act as acids:

– +&ide: is a com1o2n# containin at least one oxyen atom as %ell as at least one other element.

– Nonmetal oxi#es are com1o2n#s %hich contain a non6metal an# oxyen (ex &!), these are forme# $y the

com$2stion of nonmetals or if a com1o2n# contains the nonmetal. xam1les:

&(s) " !() &!()

&H() " !() &!() " H!()

– 8hese non6metal oxi#es:

Geact %ith 4ATE5 to form acids. &! () " H! (l) PH&! (a')

Geact %ith 7B++ to form salts. &!() " Na!H(a') P Na&!(a') " H!(l)

+ome non6metal oxi#es are: C+7 (car$on #ioxi#e), *+7 (s2lf2r #ioxi#e), "+7 (nitroen #ioxi#e) an# 7+8

(1hos1hor2s 1entoxi#e).

– !xi#es of nonmetals, s2ch as car$on, nitroen etc, are aci#ic. 8hey react %ith %ater to form aci#ic sol2tions, hence

they are 9no%n as aci#ic oxi#es.

Geactions:

&! () " H! (l) H&! (a') (carbonic aci#)

+! () " H! (l) H+! (a') ( sulfurous aci#)


!- () " H! (l) H! (a') ( phosphoric aci#)

– Note: the exce1tions are the neutral oxi#es (1refera$ly 9no%n as monoxi#es, are those oxi#es %hich sho% neither

$asic nor aci#ic 1ro1erties in their reaction %ith %ater), incl2#in "7+ (#initroen oxi#e), C+ (car$on monoxi#e) an#

"+ (nitric oxi#e).


10/52

– 'etal o&ides are com1o2n#s %hich contain a metal an# oxyen (ex *!), these are forme# $y the com$2stion of the

metal itself. xam1les:

*(s) " !() *!(s)

&a(s) " !() &a!(s)

– *etal oxi#es:

Geact %ith 4ATE5 to form bases. *! (s) " H!(l) *(!H)(a')

Geact %ith B&I4+ to form salts. *!(s) " H&l(l) *&l(s) " H!(l)

.5. +ome metal oxi#es that act as $ases are: 7+ (1otassi2m oxi#e), "a7+ (so#i2m oxi#e), Ca+ (calci2m

oxi#e) an# '+ (manesi2m oxi#e).

– !xi#es of metals are $asic, s2ch as manesi2m, calci2m etc. 8hey react %ith %ater to form $asic sol2tions, hence they

are 9no%n as $asic oxi#es.

Geactions:

! (s) " H! (l) !H (a') (1otassi2m hy#roxi#e)

Na! (s) " H! (l) Na!H (a') (so#i2m hy#roxi#e)

&a!(s) " H!(l) &a(!H)(a') (calci2m hy#roxi#e)

*! (s) " H! (l) *(!H) (a') (manesi2m hy#roxi#e)

Note: Come to this section, after the topic the rest of topic has been finished

– Am(hoteric oxi#es are oxi#es that can act as 7!8H aci#s an# $ases #e1en#in on the reaction they are 12t in.

– Bm1hoteric oxi#es act li9e $ases/aci#s, $2t #on@t haCe to #onate/acce1t 1rotons. Dhile am1hi1rotic m2st

acce1t/#onate 1roton. Bm1hi1rotic s2$stances are a s2$set of am1hoteric s2$stances, eCery am1hi1rotic s2$stance is

am1hoteric, $2t not the other %ay aro2n#.

– 8he only elements that com$ine to form am1hi1rotic oxi#es are 7e! ($erylli2m oxi#e), Bl ! (al2mini2m oxi#e),

Qn! (Kinc oxi#e), +n! (tin oxi#e) an# $! (lea# oxi#e).

– Bm1hoteric oxi#es:

Geact %ith AC to form salts.

Geact %ith 0A*E to form salts.

Lea# oxi#e

%ith aci#: $! " H&l $&l " H!

http://en.wikipedia.org/wiki/Lead_oxidehttp://en.wikipedia.org/wiki/Lead_oxidehttp://en.wikipedia.org/wiki/Lead_oxide


11/52

%ith $ase: $! " Na!H Na$! " H!

Bl2mini2m !xi#e

%ith aci#: Bl! " RH&l Bl&l " H!

%ith $ase: Bl! " Na!H NaBl! " H!

• Anal,se the position of these non-metals in the .eriodic )able and outline the relationship between position of elements

in the .eriodic )able and acidit,/basicit, of oxides:

– 8he acidic oxi#es are on the GI5H8 si#e of the 1erio#ic ta$le (non6metals).

– 8he basic oxi#es are on the L08 si#e of the 1erio#ic ta$le (metals).

– 8he am(hoteric oxi#es are in6$et%een.

– Note: No$el ases haCe no oxi#es.

• efine +e *hatelier0s principle:

– The Conce(t of Chemical Equilibrium:

*ost chemical reactions o to com1letion. * (s) " H&l (a') *&l (a') " H ()

Ho%eCer not all chemical reactions #o N!8 o to com1letion.

*any reactions are in fact reversible an# t%o6#irectional they can o from left to riht, or riht to left this is

re1resente# 2sin a 6#irectional arro%.

http://en.wikipedia.org/wiki/Zinc_oxidehttp://en.wikipedia.org/wiki/Zinc_oxidehttp://en.wikipedia.org/wiki/Zinc_oxide


12/52

8his reaction from L086to6GI5H8 is calle# the forward reaction, an# the reaction from GI5H86to6L08 is

calle# the bac/ward reaction. 8hese are 9no%n as reversible reactions.

Reversible reactions #o not o to com1letion, $2t they reach a 1osition of +8B7ILI8. 8his is calle# the 1oint of

chemical SFILI7GIF*.

Bt this 1oint there is no loner any chane in the concentrations of the reactants or 1ro#2cts the reaction has

come to a sto1 (macrosco1ically).

8his #oes N!8 mean that all the reactants haCe $ecome 1ro#2cts or Cice6Cersa. Bt the 1oint of e'2ili$ri2m, there

%ill $e reactants BN4 1ro#2cts 1resent reactin to form each other (microsco1ically).

0or exam1le, the reaction of carbon dio&ide T water is a reCersi$le reaction.

E: &! () " H! (l) H&! (a')

♦ 8he ?#o2$le6arro%@ sym$olises the 6#irectional nat2re of the reaction %ater an# &! can react to form

car$onic aci#, an# car$onic aci# can #ecom1ose to form %ater an# &!.

Bt the e'2ili$ri2m the concentration of the reactants an# 1ro#2cts are N!8 e'2al. 8he system is in a $alance.

8his #oes not mean that there are moles of reactant an# moles of 1ro#2ct, for instance. U2st that $oth the

for%ar# an# reCerse reaction is moCin at the same rate.

8he chemical e'2ili$ri2m is #oes "+T haCe to $e fixe#. !ne si#e of the reaction can $e faCo2re# to another

#e1en#in on the con#itions of the reaction this is the $asis of Le &hatelier@s rinci1le.

– 2e Chatelier;s rinci(le:

Le &hatelier@s rinci1le states that:

B system %ill always see9 the 1oint of e'2ili$ri2m.

+o %hen a system at e'2ili$ri2m has a chane im1ose# on in, it %ill “rea#J2st” to !!+ the chane to ret2rn

to a 1oint of e'2ili$ri2m.

• #dentif, factors which can affect the equilibrium in a reversible reaction:

– 0actors that affect (or shift ) the e'2ili$ri2m 1osition are a chane in concentration of a s1ecies, a chane in (ressure

in the system an# chane in tem(erature of the system.

– 1" *han$e in *oncentration:

If the concentration of a 1artic2lar s2$stance (s1ecies) is:

IN&GB+4, the e'2ili$ri2m 1oint %ill shift to%ar#s the o((osite si#e of the e'2ation this o11oses the

chane, as it re#2ces the concentration of the s1ecies $y 1ro#2cin more 1ro#2cts on the o11osite si#e.


13/52

4&GB+4, the e'2ili$ri2m 1oint %ill shift to%ar#s the same si#e of the e'2ation the s1ecies is on this

o11oses the chane, as it increases the concentration of the s1ecies $y the o11osite reaction.

8a9e for exam1le, the copper complex ion e'2ili$ri2m:

E: &2(H!)"

(a') " &l3(a') &2&l

3(a') " H! (l)

(7LF) (5GN)

-. If Cl3 ions are increase# the e'2ili$ri2m %ill shift to the GI5H8, as more &2&l3is forme# hence the

system %ill $ecome more reen.

7. If more water is a##e# the e'2ili$ri2m %ill shift to the L08, as more &2(H!)" is forme#, an# the

system %ill $ecome more $l2e.

3. If water is remoCe# the e'2ili$ri2m %ill shift to the GI5H8, so that the %ater lost %ill $e re1lace# $y the

for%ar# reaction.

– 2" *han$e in 3as .ressure (or chan$e in Volume":

If the 8!8BL 1ress2re on the system is:

IN&GB+4, the e'2ili$ri2m %ill faCo2r the si#e that re#2ces 1ress2re, that is, has less moles th2s

o11osin the chane.

4&GB+4, the e'2ili$ri2m %ill faCo2r the si#e that increases 1ress2re, that is, 1ro#2ces more moles

th2s o11osin the chane.

ress2re is increase# is $y reducin the Col2me, or #ecrease $y increasin the Col2me.

8a9e, for exam1le, the e'2ili$ri2m $et%een #initroen tetroxi#e an# nitroen #ioxi#e:

E: N! () N! ()

(< mole) ( moles)

-. If the 8!8BL 1ress2re is increased, the e'2ili$ri2m %ill shift to the left, to #ecrease 1ress2re, as there

are less moles 1ro#2ce on the left.

7. If the 8!8BL 1ress2re is decreased, the e'2ili$ri2m %ill shift to the riht, to increase the 1ress2re, as

more moles are 1ro#2ce# on the riht.

– 4" *han$e in )emperature:

5ecall:

Bn exothermic reaction is one that (roduces heat enery. 0or exothermic reactions, the sin of the change in

heat (VH) is N5B8I.

♦ In terms of reCersi$le reactions, exothermic reactions 1ro#2ce heat thro2h the forward reaction, $2t

a$sor$ heat in the reverse reaction.

Bn en#othermic reaction is one that absorbs heat enery. 0or en#othermic reactions, the sin of the change

in heat (VH) is !+I8I.


14/52

♦ In terms of reCersi$le reactions, en#othermic reactions a$sor$ heat thro2h the forward reaction, $2t

release heat in the reverse reaction.

If a system is e&othermic, an# the tem1erat2re is:

IN&GB+4, the e'2ili$ri2m %ill shift to the left, as the reCerse reaction is en#othermic, an# %ill cool the

system to o11ose the heatin.

4&GB+4, the e'2ili$ri2m %ill shift to the riht, as the for%ar# reaction is exothermic, an# %ill heat the

system to o11ose the coolin.

8a9e for exam1le, the #ecom1osition of calci2m car$onate (%ithin a close# system that is, nothin is allo%e# to

esca1e). It is an en#othermic reaction the change in heat is 1ositiCe:

E: &a&! (s) &a! (s) " &! () VH >


15/52

If it is IN&GB+4, the e'2ili$ri2m %ill faCo2r the reCerse reaction, as it is en#othermic an# %ill o11ose

the chane $y coolin the system.

If it is 4&GB+4, the e'2ili$ri2m %ill faCo2r the for%ar# reaction, as it is exothermic an# %ill o11ose

the chane $y heatin the system.

ffect of acids (H") an# bases (!H6), accor#in to Le &hatelier@s rinci1le:

&! () " H! (l) H"

(a') " &!3

(a')

If an B&I4 is a##e#, the concentration of H" %ill increase, an# hence the e'2ili$ri2m %ill shift to the left,

1ro#2cin more as.

If a 7B+ is a##e#, the !H3 %ill react %ith the H" (creatin %ater) reatly shiftin the e'2ili$ri2m to the

riht, as more H" is 1ro#2ce# to co2nteract the chane. If eno2h $asic s2$stance is a##e#, the reaction co2l#

o to com1letion, an# no loner haCe an e'2ili$ri2m 1oint.

• #dentif, natural and industrial sources of sulfur dioxide and oxides of nitro$en:

– *ulfur io&ide (+!):

NB8FGBL so2rces: olcanic ases, $2shfires, #ecom1osition of oranic matter ($y $acteria)

IN4F+8GIBL so2rces: rocessin an# $2rnin of coal %ith s2lf2r im12rities an# extractin metals from s2lf2r6

rich ores, s2ch as alena ($+).

– "itroen 'ono&ide (or Nitric oxi#e, N!):

NB8FGBL so2rces: 8he reaction of nitroen an# oxyen in the atmos1here #2e to hih tem1erat2res of lihtnin.

IN4F+8GIBL so2rces: 8he nitroen in the air reacts %ith oxyen in the hot enines an# 1o%er stations.

– "itroen io&ide (N!):

NB8FGBL so2rces: Bfter nitric oxi#e is 1ro#2ce# $y lihtnin, it slo%ly reacts %ith oxyen to 1ro#2ce nitroen

#ioxi#e.

IN4F+8GIBL so2rces: Nitroen reacts %ith oxyen in enines an# 1o%er stations.

• escribe usin$ equations examples of chemical reactions which release sulfur dioxide and chemical reactions which

release oxides of nitro$en:

– *ulfur io&ide:

"atural: Dhen oranic matter #ecom1oses it 1ro#2ces hy#roen s2lfi#e (H+), %hich then reacts %ith oxyen to

1ro#2ce s2lf2r #ioxi#e:

H+ () " ! () +! () " H! (l)

ndustrial: 8he $2rnin of s2lf2r6rich coal theses #irectly com$ine %ith oxyen:

+ (s) " ! () +! ()


16/52

ndustrial: 8he extraction of metals from metal s2lfi#es also releases s2lf2r #ioxi#e. .. smeltin of alena for

lea#:

$+ (s) " ! () $! (s) " +!

– +&ides of "itroen:

"atural and ndustrial: Nitric oxi#e is 1ro#2ce# either %hen lihtnin, %ith its hih tem1erat2res com$ines

nitroen an# oxyen:

N () " ! () N! ()

8he same reaction occ2rs in the hih tem1erat2res of enines or 1o%er 1lants, also com$inin nitroen an#

oxyen.

Nitroen #ioxi#e is forme# %hen nitric oxi#e reacts %ith oxyen in the air:

N! () " ! () N! ()

• Assess the evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitro$en:

– It is #iffic2lt to quantitativel, state that oxi#es of s2lf2r an# nitroen haCe $een increasin in the atmos1here $eca2se

these oxi#es occ2r in relatiCely lo% concentrations, ie O.O< 11m (1arts 1er million) an# chemical instr2ments a$le to

meas2re Cery lo% concentrations (li9e those for +!), haCe only $een aCaila$le since the


17/52


8hese aci#s then com$ine %ith rain #ro1lets, formin aci# rain. Bci# rain is Cery #estr2ctiCe it can #ecimate

entire forests, corro#e limestone str2ct2res an# #isr21t nat2ral ecosystems $y alterin nat2ral 1H leCels.

Health ro$lems: Sulfur dioxide is a respirator, irritant an# can ca2se $reathin #iffic2lties at concentrations as

lo% as < 11m. It triers asthma attac9s an# araCates em1hysema. Nitrogen dioxide is also a respirator,

irritant . Bt concentrations a$oCe 11m, it can $ein to #estroy tiss2e.

• 'xplain the formation and effects of acid rain:

– 2re %ater has a 1H of ;.

– Acid rain is any rain that has a 1H of less than -.

– 0!G*B8I!N of aci# rain:

Sulfur dioxide reacts %ith rain in the atmos1here formin sulfurous aci#:

+! () " H! (l) H+! (a')

Sulfurous acid then reacts %ith oxygen this is catalyse# $y air 1articles:

H+! (a') " ! () H+! (a')

Nitrogen dioxide also reacts %ith rain, ma9in nitrous an# nitric aci#s:

N! () " H! (l) HN! (a') " HN! (a')

Nitrous aci# then reacts %ith oxygen, this is catalyse# $y air 1articles:

HN! (a') " ! () HN! (a')

8h2s, in in#2strialise# areas, rain can contain relatiCely hih leCels of Cery stron aci#s that is nitric an# s2lf2ric

aci#s.

– ffects of aci# rain:

lants destruction:

Bci# rain settles into soil an# ca2ses chemical reactions there %hich affect 1lants, ca2sin #efoliation an# a

#ecrease a$ility to %ithstan# frost.

+2lfate ions in aci# rain react %ith calci2m an# manesi2m in soil so that these essential minerals $ecome

2naCaila$le for 1lants, hence #efoliatin an# re#2cin ro%th as%ell, exam1le spruce trees. *ore than half

the trees in 5ermany@s 7lac9 0orest %ere #amae# $y aci# rain.

Animal life:

Bci# rain lo%ers the 1h of la9es an# streams e.. in +can#inaCia, #2e to emissions from &entral 2ro1e,

9illin fish es an# other a'2atic life. In some 1H6sensitiCe fish s1ecies, s2ch as broo% trout , many

1o12lations haCe $een com1letely %i1e# o2t.


18/52

In other areas the aci# has $een a$le to react %ith al2mini2m com1o2n#s an# releasin toxic al2mini2m that

ca2ses the fish ills to clo %ith m2c2s.

Erosion of marble and limestone buildins: 8hese contain car$onate (es1. calci2m car$onate) %hich reacts

rea#ily %ith aci# formin salt.

&a&! (s) " H+! (a') &a+! (s) " H! (l) " &! ()

&a&! (s) " HN! (a') &a(N!) (s) " H! (l) " &! ()

• *alculate volumes of $ases $iven masses of some substances in reactions and calculate masses of substances $iven

$aseous volumes in reactions involvin$ $ases at 56* and 155%.a or 276* and 155%.a:

– 8h2s, the list of &hemistry e'2ations so far are:

– Note: 8he concentration (ie molarity/molar) of a sol2tion is #efine# as moles 1er litre or mol/L, ie < molar > < * > <

mole/litre.

– 0asic *toichiometry:

Stoichiometry is the st2#y of the calc2lation of '2antitatiCe (meas2ra$le) relationshi1s of the reactants an#

1ro#2cts in chemical reactions.

!ne of the basic la%s of stoichiometry is the ?La% of 4efinite ro1ortions@:

In chemical reactions, reactants com$ine in fixe#, #efinite 1ro1ortions (or GB8I!+) to form 1ro#2cts. 8he

ratios are #etermine# $y the coefficients of the s1ecies in a 7BLBN&4 chemical reaction. 8he coefficient

of a s1ecies is the n2m$er $efore the s1ecies:


19/52

♦ E: + (s) " ! () +! ()

Loo9in at the coefficients, yo2 can see that in this reaction, + %ill react %ith ! in the ratio of -O/( Y < " . .<

>


20/52

E,: Calculate the volume of sulfur dioxide produced when !g of hydrogen sulfide is oxidised at "#C and

$!!k%a.

♦ 0rom the %or9in 1ro#2ce# a$oCe, %e 9no% that


21/52

8he ass2m1tion that all ases lost %as from the car$on #ioxi#e 12m1e# into the $ottle – some oxyen (%hich has

a lo% sol2$ility) may haCe $een lost.


22/52

3. Acids occur in many foods1 drin/s and even within our stomachs:

• efine acids as proton donors and describe the ionisation of acids in water:

– Bn aci# is a s2$stance that releases ) ions.

– Bnother name for the H" ion is a ?(roton@ this is $eca2se a 1ositiCe hy#roen atom (H") is J2st a hy#roen n2cle2s

(no electrons) an# hence is J2st a 1roton.

– Dhen aci#s react %ith other s2$stances, the H" ion is transferre# to another s1ecies that is %hy aci#s can $e #efine#

as (roton#donors.

– In %ater, aci#s I!NI+ (se1arate into its ions).

– E: 2re hy#roen chlori#e a##e# to %ater:

H&l () H"

(a') " &l3(a')

– Ho%eCer, H" ions are Cery reactiCe, they imme#iately react %ith %ater molec2les close $y.

H&l () " H! (l) H!

"

(a') " &l3

(a')

– Bci#s ionise to form hydronium ions (H!")

• #dentif, acids includin$ acetic (ethanoic" citric (2-h,drox,propane-124-tricarbox,lic" h,drochloric and sulfuric

acid:

– Acetic Acid:

+ystematic name: thanoic aci#

*olec2lar form2la: &H&!!H

It is the aci# 1resent in Cinear.

It is classifie# as a %ea9 aci#.

– Citric Acid:

6hy#roxy1ro1ane6


23/52

It is also in#2strially ma#e in lare '2antities, %ith many 2ses.

– *ulfuric Acid:

*olec2lar form2la: H+!

It is also a stron aci#.

*ost in#2strially 1ro#2ce# chemical. Fse# to ma9e $atteries, fertiliKers etc.

• escribe the use of the p scale in comparin$ acids and bases:

– (): ?1o%er of hy#roen”, is a meas2re of the aci#ity or $asicity of a sol2tion #e1en#in on the concentration of

hy#roen ions.

– 8he () scale is 2se# to #etermine the aci#ity or $asicity of a s2$stance.

It is n2m$ere# from O to 6lo


24/52

– B chane in 1H of < means a 6lo -@

[)][+)#] > -B#-@

• .rocess information from secondar, sources to calculate p of stron$ acids $iven appropriate h,dro$en ion

concentrations:

– 8he 1H of a strong aci# can $e calc2late#, iCen the molar concentration, as BLL its 1rotons are release# into sol2tion.

– Ho%eCer, an aci# may $e a$le to release *!G than one 1roton. 8hese aci#s are calle# 1oly1rotic aci#s.

– &BL&FLB8IN5 1H of a stron, mono(rotic aci#:

*ono1rotic aci#s release only one 1roton, e.. H&l:

H&l H" " &l6

E: &alc2late the 1H of O.O< * hy#rochloric aci#.

* means mol/L hence this is O.O< mol/L, or 6lo


25/52

[H"] > O.OO 6lo 6lo O.R=

1H > Y O.< > O., the Col2me of the sol2tion remains the same, hence v- > O.O< L an# v7 > O.- L

Hence: c7 > (c- Y v-% \ v7 D $O. Y O.O O.OOW *

8herefore the oriinal concentration of hy#roen ions ie [H"] %as O.< mol/L, after #il2tion this has #ro11e#

#o%n to O.OOW.

8he oriinal 1H %o2l# $e –lo O.R=

8he ne% 1H is –lo .<

– xtra: &alc2latin the 1H of a sol2tion after "ET5A2*AT+":

8he ne2tralisation of a aci# an# a $ase can leaCe a sol2tion that is slihtly aci#ic or $asic the Col2mes an#

concentrations of sol2tions 2se# #etermines the 1H of the final 1ro#2ct.

Note: 8he sol2tion %ill only $e ne2tral %hen there are exactly the same n2m$er of moles of H" an# !H6 reacte#.


26/52

E: O.OO-

♦ 7ase: n > O.- Y O.O- > O.OOW;-

8here are more moles of $ase than there are aci# hence there %ill $e an excess of $ase after ne2tralisation

com1letes.

*oles of $ase remainin > O.OOW;- – O.OO- > O.OO;-

Bs Na!H only releases one !H6 ion, [!H6] > O.OO;-

♦ 1!H > 6lo .R

♦ Hence 1H >


27/52

)Cl: O.


28/52

– In the L08 $ea9er, there is a sol2tion of sulfuric aci#. Bll the molec2les haCe com1letely ionise#, as it is a stron

aci#s. ach H+! molec2le has release# 1rotons, as it is a #i1rotic aci#.

– Ho%eCer, in the GI5H8 $ea9er, there is a sol2tion of ethanoic aci#, of e'2al concentration. !nly half of the aci#

molec2les haCe ionise# (in reality the 1ercentae is m2ch lo%er,


29/52

It is 9no%n that methyl orane is re# in stronly aci#ic sol2tions, an# yello% in slihtly aci#ic to hihly al9aline

sol2tions.

– art 0: 8estin &ommon +2$stances Fsin a () 'eter:

B small amo2nt of each sol2tion %as 1lace# in a se1arate $ea9er, an# a fe% #ro1s of 2niCersal in#icator sol2tion

a##e#. 8he colo2r chane of the sol2tion %as matche# %ith a 1roCi#e# colo2r chart to #etermine the sol2tion@s

a11roximate 1H.

B 1H 1ro$e connecte# to a #ata loer %as then cali$rate# 2sin a sol2tion of 9no%n 1H, $efore $ein 2se# to

meas2re the 1H of the sol2tion more exactly.

– 5esults:

1H of sol2tions %as fo2n#.

– 6ustification:

*ethyl orane is only re# in stronly aci#ic sol2tions, so eCen a Cery %ea9 $ase %o2l# haCe $een a$le to elicit a

colo2r chane.

B %i#e rane of s2$stances %as 2se# to 1ortray the %i#e rane of 1ossi$le $ases. 8his sho%e# that $ases are not

only limite# to metal hy#roxi#es.

B 1H meter aCe instantaneo2s acc2rate res2lts.

– 2imitations:

8he methyl orane test %as not a$le to #istin2ish $asic an# ne2tral s2$stances, as $oth ca2se# no colo2r chane

from the re#.

Fsin a 1H meter or 1ro$e is a non6#estr2ctiCe %ay of testin %hether a chemical sol2tion is aci#ic, $asic or

ne2tral. roCi#e# the 1H meter electro#e or 1ro$e is %ashe# %ell %ith #istille# %ater $et%een meas2rements, the

sol2tions teste# sho2l# $e 2naffecte#, $2t the in#icator %ill contaminate the 1ortion of sol2tion teste#.

• .lan and perform a first-hand investi$ation to measure the p of identical concentrations of stron$ and wea% acids:

– B 1H meter %as 2se# to meas2re the 1H@s of the sol2tions.

– 5E*2T*:

+2lf2ric aci# 1H > O.;

Hy#rochloric aci# 1H > .=

thanoic aci# 1H > .


30/52

@. 0ecause of the (revalence and im(ortance of acids1 they have been used and studied for hundreds of years. +ver

time1 the definitions of acid and base have been refined:

•


31/52

•


32/52

– 8he oriinal aci# is NH its conJ2ate $ase is NH6

– 8he oriinal $ase is H its conJ2ate aci# is H"

– *(eacial case: Geactin hy#roen chlori#e as an# ammonia:

H&l () " NH () NH" " &l

6 NH&l(s)

– 8he oriinal aci# is H&l its conJ2ate $ase is &l 6

– 8he oriinal $ase is NH its conJ2ate aci# is NH"

– 7F8 Bmmoni2m &hlori#e is a salt com1o2n#.

– Note


33/52

– 8he reason %hy many salts sol2tions are N!8 ne2tral (1H ` ;.O) is that the ions ma9in that salt, can act as 7r^nste#6

Lo%ry aci#s/$ases, that is they are calle# conJ2ate aci#s " conJ2ate $ases.

– 0rom a$oCe %e ac9no%le#e# the fact that 76L theory #oes not reconise salts/solCents etc , there is only conJ2ate

1airs. Hence %hen these ions $rin alon their 1ro1erties to the salt forme#.

– 8he aci#ity or al9alinity of a salt #e1en#s on the reactants of the ne2tralisation reaction:

B stron aci# an# a stron $ase %ill ma9e a ne2tral salt

B wea/ aci# an# a wea/ $ase %ill ma9e a ne2tral salt

B stron aci# an# a wea/ $ase %ill ma9e a slightly B&I4I& salt

B wea/ aci# an# a stron $ase %ill ma9e a slightly 7B+I& salt

– 8hese are the eneral r2les for ne2tralisation reactions, $2t the aci#ity/al9alinity of a salt m2st $e 1roCe# $y

hy#rolysis.

– )ydrolysis is sim1ly reactin the salt@s ions %ith %ater or more s1ecifically 8he reaction of an anion %ith %ater to

1ro#2ce !H6 or the reaction of a cation to 1ro#2ce H!" (its is the o11osite of ne2tralisation).

U2st as ne2tralisation is reaction of aci# an# $ase to form salt an# %ater, salt can react %ith %ater to o the other

%ay aro2n#.

Geaction $et%een a +8G!N5 aci# an# a DB $ase:

8heoretically the salt %ill $e slightly aci#ic 1H E ;.

♦ E: HN! (a') " NH (a') NH N! (a')

Nitric aci# is a stron aci#, an# ammonia is wea/ $ase hence ammonium nitrate %ill $e a slihtly aci#ic

salt.

H!DG yo2 m2st 1roCe it. Geact the salt@s ions %ith %ater:

♦ NH" " H! NH " H!

"

♦ N!6 " H! No reaction

8he 1resence of hydronium ions 1roCes it is an aci#ic sol2tion.

Geaction $et%een a DB aci# an# a +8G!N5 $ase:

8he salt %ill $e slightly $asic 1H ;.

♦ E: Na!H (a') " &H&!!H (a') &H&!!Na (a') " H! (l)

Sodium hydroxide is a stron $ase, an# ethanoic acid is a wea/ aci# hence sodium ethanoate %ill $e a

slihtly $asic salt.

8o 1roCe it:

♦ Na" " H! No Geaction


34/52

♦ &H&!!3 " H! &H&!!H " !H

3

8he 1resence of hy#roxi#e ions 1roCes it is a $asic sol2tion.

Geaction $et%een a +8G!N5 aci# an# a +8G!N5 $ase:

8his salt %ill $e ne2tral 1H close to ;.

♦ E: !H (a') " H&l (a') &l (a') " H! (l)

Neither of the ions in the 1ro#2ct reacts %ith %ater hence it is ne2tral.

• *hoose equipment and perform a first-hand investi$ation to identif, the p of a ran$e of salt solutions:

– Aim: 8o test the 1H of a rane of salt sol2tions.

– 'ethod:

ach salt %as 1lace# in a $ea9er an# their res1ectiCe 1Hs %ere first estimate# $y loo9in at %hat aci# an# $ase

constit2tes the salt, 8he aci#ity of salt sol2tions can $e ex1laine# $y the 7ronste#6Lo%ry aci#6$ase $ehaCio2r of

their constit2ent ions.

8hey %ere then meas2re# %ith a 1H meter. 8hen seCeral #ro1s of 2niCersal in#icator %ere a##e# to each.

Note: neCer learn these J2st remem$er com$inations of %ea9/stron aci#6$ases.

– 5esults:

Na&!: B11roximately


35/52

• #dentif, neutralisation as a proton transfer reaction which is exothermic:

– Ne2tralisation reactions are reactions $et%een aci#s an# $ases. Bs acids are proton-donors bases are proton-

acceptors, ne2tralisation reactions $et%een aci#s an# $ases are proton-transfer reaction reactions. Ie 1rotons (H") are

transferre# from the aci# to the $ase.

– 8he first #efinition of ne2tralisation %as “acid / base 0 salt and water ”, $2t not all ne2tralisation reactions release

%ater, $2t all ne2tralisation #onate/acce1t H " hence it nee#e# to $e chane#.

– Note: nearly eCery hsc '2estion 2ses the #efintion aci# " $ase > salt " %ater, 9ee1 it in han#, an# 9no% a$o2t 1roton

transfer as a secon# #efintion.

– E: H&l (a') " !H (a') &l (a') " H! (l)

H" " &l6 " " " !H6 " " &l6 " H!

If %e remoCe all the spectator ions, the $asic 2n#erlyin 1roton6transfer reaction is easily seen:

H" (a') " !H 3

(a') H! (l)

Hence, the 1roton is transferre# to the hy#roxi#e ion, formin %ater.

– E: H" (a') " NH (a') NH" (a')

8his reaction is ta9en 2n#er ?net ionic e'2ation@ the oriinal reaction is (H7r " NH NH7r), an# it can

$e #one rihtf2lly so.

8he 1roton is transferre# to the ammonia, formin ammoni2m.

Bs can $e seen, no %ater is 1ro#2ce# it is still consi#ere# ne2tralisation.

– Note: *ost ne2tralisation reactions are exothermic they li$erate heat enery, (exam1le of en#othermic reaction is

Cinear an# $a9in 1o%#er)

– 8he VH 6-R 9U/mol, #e1en#in on the strenth of the reactants.

5ecall: xothermic reactions release enery as more enery is release# in $on# formation than is a$sor$e# in

$on# $rea9in.

• Anal,se information from secondar, sources to assess the use of neutralisation reactions as a safet, measure or to

minimise dama$e in accidents or chemical spills:

– It is im1ortant to imme#iately ne2tralise any chemical s1ills inColCin stron$ aci#s an# $ases, as they are corrosiCe

an# #anero2s.

– Ne2tralisation reactions (conCertin an aci#/$ase into salt) are 2se# as safety meas2res in cleanin 21 after s2ch

inci#ents.

– Dhen ne2tralisin an aci# or a $ase the follo%in 1roce#2re is follo%e#:

8he most 1referre# aents of ne2tralisation has the 1ro1erties of $ein stable, easily transported , solid

(1o%#ere#), cheap an# wea/ly am(hi(rotic (so it can act as a DB aci# or a DB $ase). 8his is the safest


36/52

material, as it can ne2tralise $oth aci#s an# $ases eCen if an excess is 2se#, it is Cery %ea9, an# so #oes not 1ose

any safety ris9s.

– 8he most common s2$stance 2se# to ne2tralise s1ills in la$oratories is 1o%#ere# so#i2m hy#roen car$onate, 9no%n

as so#i2m $icar$onate (NaH&!) this is $eca2se the hy#roen car$onate ion (H&!6) is an am1hi1rotic s1ecies.

NaH&! " H&l Na&l " H! " &! (actin as $ase)

NaH&! " Na!H Na&! " H! (actin as an aci#)

– *tron aci#s an# $ases m2st neCer $e 2se# to ne2tralise s1ills if an excess is 2se#, the s1ill %ill $ecome #anero2s

aain.

• escribe the correct technique for conductin$ titrations and preparation of standard solutions:

– Titration is a chemical analysis techni'2e in %hich ne2tralisation is 2se# to experimentally #etermine the 2n9no%n

concentration of a sol2tion thro2h the reaction of that sol2tion an# a sol2tion of a 9no%n 2ntil the reaction $et%een

them is com1lete.

– The Chemical Theory of Titration:

8he 1oint of acid1base titration is to #etermine the concentration of an 2n9no%n sol2tion (secondar, solution) $y

slo%ly reactin a certain Col2me of this sol2tion %ith another sol2tion of 9no%n concentration (standard

solution), 2ntil the equivalence point/endpoint is reache#.

8he e'2iCalence 1oint of a chemical reaction occ2rs %hen all aCaila$le molec2les haCe reacte#, an# the reaction

comes to an en#. 8he en#1oint is %hen the in#icator (%hich is 2se# to iCe a Cis2al in#ication of the molec2les

haCe reacte#), chanes colo2r.

8he volumes of the reactants at this en#/e'2iC 1oints are caref2lly meas2re# 2sin the 9no%le#e of these

Col2mes, an# the oriinal concentration of the stan#ar# sol2tion, the concentration of the 2n9no%n sol2tion can

$e calc2late#.

Note: $eca2se Col2me meas2rements 1lay a 9ey role in titration, it is also 9no%n as volumetric anal,sis.

– rimary *tandards:

rimary stan#ar#s are the s2$stances %hich can $e 2se# to 1re1are stan#ar# sol2tions (ie they are the sol2tes of

the solCent sol2tion).

8here are certain criteria chemicals nee# to satisfy $efore they can $e 2se# to create stan#ar# sol2tions these

m2st haCe the follo%in 1ro1erties:

HI5H FGI8:

♦ 8his is to 1ro#2ce acc2rate res2lts, 2ntainte# $y chemical im12rities (ex H&l can Cary from $atch to

$atch).

&H*I&BL +8B7ILI8 (low reactivity):


37/52

♦ +tan#ar#s m2st $e chemically sta$le so they #o not react %ith the %ater/ases in the air (e.. &!).

N!N6H5G!+!I& BN4 N!N600L!G+&N8:

♦ Hyrosco1ic s2$stances absorb water from their s2rro2n#ins, %hile efflorescent s2$stances release

water into their s2rro2n#ins.

♦ 7oth these 1rocesses chane the concentration of sol2tions, res2ltin in im1recise stan#ar# sol2tions.

HI5H +!LF7ILI8:

♦ rimary stan#ar#s nee# to #issolCe com1letely into their sol2tions.

HI5H *!L&FLBG DI5H8:

♦ 8he hih molec2lar %eiht of 1rimary stan#ar#s minimiKes many errors in meas2rement.

Fns2ita$le chemicals to 2se as 1rimary stan#ar#s incl2#e so#i2m hy#roxi#e, %hich in sol2tion %ill react %ith

ases in the air, hy#rochloric aci#, %hich is efflorescent, an# s2lf2ric aci#, %hich is hyrosco1ic.

– re(arin *tandard *olutions:

– &alc2latin the amo2nt of 1rimary stan#ar# nee#e#:

7efore ma9in stan#ar# sol2tions, the amo2nt of 1rimary stan#ar# to $e 2se#, nee#s to $e

calc2late#. 8he ty1ical la$oratory lass%are in %hich stan#ar# sol2tions are ma#e are calle#

volumetric flasks -O mL flas9s are most commonly 2se#.

De %ill #etermine the amo2nt of primar, standard nee#e# to create -O mL of the O.O- *

stan#ar# sol2tion of so#i2m car$onate.

&BL&FLB8I!N+:

*olar *ass (Na&!) > (.==O) " (


38/52

-. 0ill the flas9 half6%ay 21 to the -O mL ra#2ation mar9, an# ently s%irl the flas9 2ntil all the sol2te has

#issolCe#. +et the flas9 on the $ench.

R. Fsin the %ash6$ottle, fill the flas9 %ith %ater 2ntil it is J2st 2n#er the ra#2ation mar9. Fsin a aste2r 1i1ette,

a## #istille# %ater 2ntil the menisc2s sits exactly on the -O mL mar9.

;. &oCer the flas9 %ith its lass sto11er an# inCert the entire flas9 three times. If the menisc2s has lo%ere#, a## a

fe% more #ro1s. If not, the stan#ar# sol2tion is com1lete.

– The Correct Technique for Conductin Titrations:

8here is a Cery 1recise an# s1ecific techni'2e to titration, %hich 2ses a Cariety of cali$rate# lass%are. 8hese

incl2#e:

2olumetric 3lask : 8his is 2se# to 1re1are an# hol# stan#ar# sol2tions.

Conical 3lask 4ie &rlenmeyer flask5: 8his is 2se# to hol# the reactants #2rin titration. Its sha1e 1reCents the

reactants from s1illin as they are s%irle# toether.

6urette: 8he $2rette is a 1iece of cylin#rical lass%are, hel# Certically, %ith Col2metric #iCisions on its f2ll

lenth an# a 1recision ta1 ( stopcock ), on the $ottom. It is 2se# to #is1ense 1recise amo2nts of a li'2i# reaent

in titration. 72rettes are extremely 1recise an# acc2rate to bO.O- mL.

%ipette: 8he 1i1ette is a lass t2$e 2se# to transfer 1recise Col2mes of li'2i# reaents. i1ettes are 2s2ally

#esine# to transfer one meas2rement of Col2me, s2ch as only - mL. 8he reaent is #ra%n 21 the 1i1ette

2sin a 1i1ette filler (e.. a r2$$er $2l$).

7efore titration, all lass%are m2st $e GIN+4 a11ro1riately. 8he techni'2e for the #ifferent lass%are is:

ol2metric flas9s (incl2#in lass sto11ers) are rinse# thoro2hly %ith distilled water , 1refera$ly m2lti1le

times. &lose the flas9 %ith the sto11er 2ntil it is oin to $e 2se# it is left %et.


39/52

&onical flas9s are rinse# thoro2hly %ith #istille# %ater an# left %et.

72rettes: the #istille# %ater is fille# into the $2rette an# the ta1 o1ene#. Dater is allo%e# to flo% o2t an#

thoro2hly rinse the ti1. *ore %ater is then a##e#, an# the entire lass t2$e is s%irle# in yo2r han#s to %ash

the si#es of the $2rette. 72rettes are rinse# 8HG 8I*+ %ith #istille# %ater an# then !N& more %ith

the sol2tion it is oin to contain.

i1ettes are also rinse# 8HG times %ith #istille# %ater, an# then !N& %ith the sol2tion it is oin to

contain.

Bfter eCerythin is rinse# a11ro1riately, the lass%are is fille#.

7y conCention, the aci# is 1lace# in the $2rette (2n9no%n), an# the $ase in the conical flas9

Fsin the a$oCe exam1le aain:

Fsin a f2nnel, the nitric aci# is 1o2re# into the $2rette 2ntil B7! the Kero mar9. Hol# a %hite car#

$ehin# the Kero mar9, an# o1en the ta1 slo%ly 2ntil the menisc2s sits UF+8 on to1 of the mar9. 8he %hite

car# ma9es the menisc2s clearer the Col2me #eliCere# $y the $2rette is calle# a titre.

Fsin a 1i1ette, a fixe# Col2me (ali'2ot) of so#i2m car$onate (say - mL) is #ra%n from the Col2metric flas9

an# #e1osite# into the conical flas9 the Col2me meas2re# o2t $y a 1i1ette is calle# an aliquot .

– In#icators:

8o #etermine the en#1oint (ie to also #etermine the 1H), %e 2se in#icators. B s2ita$le in#icator sho2l# $e chosen,

1refera$ly one that %ill ex1erience a chane in color (ie en# 1oint) close to the e'2iCalence 1oint of the reaction.

Ho%eCer, a s2ita$le in#icator m2st $e 2se#.

0or stron6aci#/%ea96$ase titrations, as a$oCe, methyl orange is the most s2ita$le in#icator. 8his is $eca2se it

chanes from yello% to 1ale orane/1in9 %ithin the slihtly aci#ic rane, corres1on#in %ith the en#1oint of 1H

> .-.

0or the follo%in titrations, these in#icators are s2ita$le.

– The Titration $ie where location of the end(oint is determined%:


40/52

3inally, the titration can $e 1erforme#. B fe% #ro1s of methyl orane in#icator are a##e# to the conical flas9, an#

the sol2tion t2rns a clear yello% colo2r (ie yello% $eca2se of %ea9 $ase).

8he conical flas9 is 1lace# on a %hite tile (to ma9e the sol2tion@s colo2r clear) 2n#er the $2rette, %hich is hel# in

a retort stan#.

8he ta1 is slo%ly o1ene#, an# the conical flas9 is contin2o2sly s%irle#.

Dhen the first colo2r chane is notice#, the ta1 is close#. B s%irl of the conical flas9 %ill li9ely ret2rn the

sol2tion $ac9 to its oriinal colo2r.

+lo%ly o1en the ta1 so that sol2tion flo%s o2t in #ro1s, an# sto1 %hen the en#1oint is reache#, as sho%n $y the

colo2r of the in#icator.

8he en#1oint of a chemical reaction is the 1oint %here the reaction +8!+, $eca2se all the s1ecies haCe reacte#.

In aci#/$ase titration, the reaction is a ne2tralisation reaction an# hence 1H can #etermine %hen the en#1oint has

$een reache#, however , this #oes N!8 mean that the 1H at the en#1oint is ;.

8he 1H at the en#1oint #e1en#s on the aci# an# $ase $ein 2se#.

E: 0or the titration a$oCe, nitric aci# is titrate# into the so#i2m car$onate:

7efore titration occ2rs, for so#i2m car$onate, 1H is m2ch reater than ;.

Bs nitric aci# is slo%ly a##e#, the 1H #ecreases stea#ily, 2ntil the en#1oint is reache#, at . mL of aci#.

7F8 the salt forme# $et%een a stron aci# an# a %ea9 $ase is slihtly aci#ic hence at the en#1oint, the

sol2tion in the flas9 is slihtly aci#ic.

8he first titration 1erforme# is a ro2h #raft an# often oCershoots the en#1oint. 8his first titration is reJecte#.

8itration is 1erforme# m2lti1le times to achieCe the acc2rate res2lts.

– E: Nitric Bci# T +o#i2m &ar$onate:

8he titration of a sol2tion of nitric acid (HN!) of FNN!DN concentration %ith a 9no%n sol2tion of $asic,

O.O- * sodium carbonate (Na&!). Note: yo2 can haCe the concentrations other %ay aro2n#.

8he sol2tion of 9no%n concentration is calle# the standard sol2tion.

8he first step in any aci#/$ase titration is to i#entify the chemical reaction that is oin to occ2r, $y %ritin a

$alance# chemical e'2ation. In this case:

HN! (a') " Na&! (a') NaN! (a') " &! () " H! (l)

O mL of the O.O- * so#i2m car$onate %as titrate# %ith the nitric aci# an# the en#1oint %as reache# after .

mL of nitric %as 2se#.

Loo9in at the chemical e'2ation, the molar ratio of reaction is :<

Hence, . mL of nitric aci# contains 8DI& as many moles as O mL of so#i2m car$onate. &alc2latin:

n c O.OO< mol of so#i2m car$onate.


41/52

n > Y n O.OO mol of nitric aci#.

c > n / C > O.OO / O.O > O.O= *

0rom this titration, the concentration of nitric aci# %as calc2late# to $e O.O= *

– *any r2les m2st $e a#here# to for an acc2rate titration.

– *ost im1ortant is the 1re1aration of an extremely 1recise stan#ar# sol2tion.

8his is the titration c2rCe of the a$oCe reaction:

– The Calculations nvolved 4ith Titration:

Bll the calc2lations re'2ire# are #etaile# a$oCe all titration concentrations can $e calc2lation 2sin the e'2ation

n > c Y C.

72t another %ay to calc2late the concentration:


42/52

• ?ualitativel, describe the effect of buffers with reference to a specific example in a natural s,stem:

– B buffer is a sol2tion that is a$le to maintain a constant p eCen the a##ition of a stron aci# or $ase #oes not

chane its 1H. 8hey can #o this $y acce1tin or 1roCi#in H" ions as necessary to res1on# to the chane in 1H,

9ee1in the concentration of H" in sol2tion relatiCely constant, an# th2s resiste# a chane in 1H.

– 8he $2ffer sol2tion contains a11roximately e'2al amo2nts of a wea/ acid an# its con=uate base at equilibrium.

– 8he e'2ili$ri2m inColCe# can $e re1resente# as:

HB " H! H!" " B6

– ?HB@ is the %ea9 aci#, %hich iCes its 1roton to %ater, formin its conJ2ate $ase, ?B6@

– Bn exam1le of a NB8FGBL $2ffer system is the car$onic aci# system:

&! from res1iration #issolCes in the $loo#, formin the H&!6 ion.

H&! (a') " H! (l) H!"

(a') " H&!3

(a')

– Fsin Le &hatelier@s 1rinci1le, %e can #e#2ce %hy the 1H remains constant:

B##ition of any aci# (rear#less of its strenth) increases [H !"]. Ho%eCer, this #oes not #ecrease the 1H the

a##itional aci# sim1ly reacts %ith the conJ2ate $ase an# forces the e'2ili$ri2m to the left, formin more of the

%ea9 aci# to eCen o2t the a##e# concentration, so the concentrations cancels each other o2t an# the 1H ret2rns to

its oriinal Cal2e.

B##ition of any $ase (that is !H 6 ions) #oes not increase the 1H as the $ase reacts %ith the hy#roni2m, [H !"],

th2s this #ecreases. 8his shifts the e'2ili$ri2m to the riht, to re1lenish the lost [H !]". !r another reason is the

fact that %ater is create#, hence increasin the concentration of %ater, this %ants to re#2ce this, hence e'2ili$ri2m

12she# to the riht to minimise this. 8h2s the 1H ret2rns to its oriinal Cal2e.


43/52

• .erform a first-hand investi$ation and solve problems usin$ titrations and includin$ the preparation of standard

solutions and use available evidence to quantitativel, and qualitativel, describe the reaction between selected acids and

bases:

– Bnother titration 1erforme# %as $et%een 1otassi2m hy#roen 1hthalate (a %ea9 aci#) an# so#i2m hy#roxi#e (a stron

$ase), 2sin 1henol1hthalein in#icator.

• .erform a first-hand investi$ation to determine the concentration of a domestic acidic substance usin$ computer-based

technolo$ies:

– -O mL of ho2sehol# Cinear %as 1lace# in a small $ea9er.

– B 1H 1ro$e %as attache# to the la$oratory com12ter the 1ro$e %as rinse# %ith #istille# %ater, an# then rinse# %ith

left6oCer sol2tion.

– 8he 1ro$e %as then 1lace# in the sol2tion, an# the 1H meas2re#.

– 5iCen the fact that foo#6ra#e ethanoic aci# only has a$o2t O.X ionisation, the concentration of ethanoic aci# %asthen calc2late#.

– 5esults:

8he aCerae 1H meas2re# %as .-

[H"] > O.OO


44/52

8. Esterification is a naturally occurrin (rocess which can be (erformed in the laboratory:

• R'*A++:

– B functional rou( is a s1ecific ro21 of atoms %ithin a molec2le that is res1onsi$le for the chemical 1ro1erties of

that molec2le.

– olarity occ2rs %ithin a $on# %hen one of the atoms is more electroneatiCe than the other the $on# has a sliht

chare.

– Al/yl ,rou(: Bn al9yl is a f2nctional ro21 of an oranic chemical that contains only car$on an# hy#roen atoms,

%hich are arrane# in a chain. 8hey haCe eneral form2la Cn)7n-.

• escribe the differences between the al%anol and al%anoic acid functional $roups in carbon compounds:

– Al/anols: !ranic com1o2n#s containin the h,drox,l $roup (6!H), attach to an al9yl ro21. 8heir eneral form2la

is G!H, %here G stan#s for a sat2rate# al9yl ro21.

– Al/anoic Acids: !ranic com1o2n#s containin the carbox,l $roup (6&!!H), attache# to an al9yl ro21. 8heir

eneral form2la is G&!!H, %here G stan#s for a sat2rate# al9yl ro21.

– 8he f2nctional ro21 of al9anols is the hydro&yl rou( (–!H):

Structure: Bn oxyen an# a hy#roen molec2le coCalently $on#e#.

Note: the ?H@ ion is Cery har# to remoCe in al9anols.

– 8he f2nctional ro21 of al9anoic aci#s is the carbo&yl rou( (–&!!H).

Structure: Bn oxyen is #o2$le6$on#e# to a central car$on, an# an –!H ro21 is sinle6$on#e# to the same

car$on.

Note: 8he –!H is not calle# a hy#roxyl ro21 %hen %ithin a car$oxyl ro21. Bn# they can release there

?H@ ions, J2st the e'2il$ir2m lies %ell to the reacatant si#e.

– 8he #ifferences $et%een the f2nctional ro21s, also #ifferentiates the car$on com1o2n#s containin each res1ectiCely.

– .olar Bondin$: 7oth the hy#roxyl an# car$oxyl ro21 contain 1olar $on#s (ie &6! T !6H $on#s), allo%in the

molec2les to form hy#roen $on#s. Ho%eCer, the hy#roxyl ro21 contains t%o 1olar coCalent $on#, %hilst the

car$oxyl ro21 contains three 1olar coCalent $on#s (&6!, !6H an# &>! $on#s) this is sinificant in infl2encin the

meltin 1oints an# $oilin 1oints of these com1o2n#s.

– 'xtra molecules: 8he car$oxyl &!!H has &>! %hich a##s to the 1olarity of al9anoic aci#s. 8his means that they

haCe stroner #i1ole6#i1ole interacts as %ell as $on#in an# #is1ersion forces an# a##e# molec2lar %eiht. Dhich

means they re'2ire more enery to oCercome these forces than their res1ectiCe al9anols.


45/52

– Nature of atoms: 8he H atom in the hy#roxyl f2nctional ro21 is har# to remoCe, %hilst the H ro21 in the car$oxyl

f2nctional ro21 can $e reCersi$ly lost &!!H &!!6 " H". 8his ena$les the car$oxyl ro21 to act as a %ea9

aci#, iCin the name “al9anoic aci#”. Bl9anols, ho%eCer, cannot act as aci#s or $ases, they are n2etral.

– Note: a dimer is a molec2le consistin of t%o i#entical sim1ler molec2les, if molec2les share hy#roen

$on#s/#i1ole6#i1ole interactions.

• 'xplain the difference in meltin$ point and boilin$ point caused b, strai$ht-chained al%anoic acid and strai$ht-

chained primar, al%anol structures:

– 0or the same n2m$er of car$ons in a straiht car$on6chain, the hihest $oilin 1oints an# meltin 1oints are in the

follo%in or#er: al9anes al9anols al9anoic aci#s

– 8he intermolecular forces $et%een molec2les #etermines %hat 1hysical state they %ill exist in (soli#, li'2i# or as)

for a iCen 1ress2re an# tem1erat2re. 8he intramolec2lar (ie coCalent $on#s) hol#in the molec2les toether are Cery

stron, $2t these are larely irreleCant to the 1hysical 1ro1erties of the s2$stance. hysical 1ro1erties are oCerne# $y

the intermolec2lar forces. 0or exam1le %hen yo2 heat %ater, yo2 #on@t #ecom1ose it to oxyen an# hy#roen as, yo2chane the state in %hich the molec2les exist in.

– 8he stroner the intermolec2lar forces, the more ?tihtly $o2n#@ the molec2les are to each other, an# hence more

enery nee#s to $e force# into the system to oCercome these forces (i.e. hiher meltin or $oilin 1oint).

– BLBN+: the only intermolec2lar forces $et%een molec2les are #is1ersion forces. 8hese forces are ca2se# $y the

moCement of electrons aro2n# the molec2le, %hich create instantaneo2s moments of chare. 8hese chares attract

each other, creatin these #is1ersion forces. 8hey are very %ea9, an# hence the $oilin an# meltin 1oints of al9anes

are lo%. Note: BLL al9anes are non61olar.

– BLBN!L+: they haCe #is1ersion forces, as %ell as #i1ole6#i1ole forces (ie interactions $et%een the 1olar $on#s of

molec2les). Bl9anols contain the 1olar &6! an# !6H $on#s, as these haCe a 1artial chare, they attract near$y

molec2les this is #i1ole6#i1ole interactions, the !6H molec2le can also 2n#ero hy#roen $on#in (form of #i1ole

#i1ole interaction %here hy#roen is inColCe#) %hich occ2rs $et%een molec2les. 8heir intermolec2lar interactions are

stroner than those of al9anes, an# hence they haCe hiher meltin an# $oilin 1oints.

– BLBN!I& B&I4+: haCe the stronest intermolec2lar interactions, as they haCe three 1olar $on#s in each molec2le:

&6!, &>! an# !6H $on#s hence more #i1ole #i1ole interactions. In a##ition, hy#roen $on#in ($et%een –!H

molec2les) an# #is1ersion forces occ2r. 8his reatly increases the meltin an# $oilin 1oints of al9anoic aci#s.

– Blso the loner the car$on chains, the hiher the $oilin an# meltin 1oints are, $2t less sol2$le they $ecome.


46/52

– Note: Ho%eCer, as the al9anes an# corres1on#in al9anoic aci#s/al9anols start to et loner, then the effect of the 1olar f2nctional ro21s $ecome less im1ortant in com1arison to the lare non61olar car$on6car$on section, %hich has

only #is1ersion forces. 8h2s, as al9anoic aci#s an# al9anols $ein to $ecome loner, their meltin an# $oilin 1oints

start to $ecome closer to the corres1on#in al9anes.

– 8h2s, if %e loo9 at a homoloo2s series of al9anes, al9anols an# aci#s, %hich is a se'2ence of com1o2n#s %ith

increasin n2m$ers of car$ons, %e see that the al9anes $oilin 1oints start to c2rCe to%ar#s the other t%o.

0oilin oints of Al/anes1 Al/anols and Al/anoic Acids


47/52

• #dentif, esterification as the reaction between an acid and an al%anol and describe usin$ equations examples of

esterification:

– Esters are oranic com1o2n#s, Colatile (rea#ily eCa1oratin) containin the ester functional $roup: “–&!!–”. 8hey

are ma#e thro2h the condensation reaction (%here H! con#ensers o2t) $et%een an al9anol an# al9anoic aci#s.

– 8heir eneral form2la is G&!!G ;

– In the #iaram, G an# G re1resent a hy#roen, or car$on chains (mainly). Hence the sim1lest ester is H&!!&H this

is calle# methyl methanoate.

– !ther eneral forms of esters can $e %ritten as:

– Esterification is the 1rocess %hich forms esters. In the most eneral sense it is the reaction $et%een an acid an# an

alcohol .

0or the H+& co2rse, %e limit o2r 9no%le#e of esterification as the reaction $et%een straiht6chaine# 1rimary

BLBN!I& (ie car$oxylic) aci#s, an# straiht6chaine# 1rimary BLBN!Ls. 8his forms carbox,late esters.

– *arbox,late esters are forme# %hen a car$oxyl f2nctional ro21 (–&!!H) of an al9anoic aci# reacts %ith the

hy#roxyl f2nctional ro21 (–!H) of an al9anol.

– sterification is a

condensation

reaction a %ater

molec2le is

enerate#.

– Bn interestin 1oint is

that in eliminatin the

%ater molec2le, it is the car$oxylic aci# (6&!!H) that s211lies the !H, an# the al9anol (6!H) that s211lies J2st an H.


48/52

– sterification is a reCersi$le reaction in %hich e'2ili$ri2m lies m2ch to the left at room tem1erat2re. It is a mo#erately

slo% en#othermic reaction an# the reaction comes to an e'2ili$ri2m rather than to com1letion.

al9anoic aci# " al9anol " M-O9J ester " %ater VH O (ie "Ce, en#othermic)

– 8h2s to alter the system, 2n#erstan# of Le &hateliers 1rinci1le is nee#e#.

• escribe the purpose of usin$ acid in esterification for catal,sis:

– &oncentrate# s2lf2ric aci# is often a##e# #2rin the 1rocess of esterification this serCes 12r1oses:

+2lf2ric aci# acts as a catalyst, ie it s(eeds u( the rate of reaction $y lo%erin the actiCation enery, an# th2s the

rates of the for%ar# an# reCerse reactions %ill $e increase# e'2ally allo%in the 1oint of e'2ili$ri2m to $e

reache# faster.

+2lf2ric aci# increases the yield of the reaction. It #oes this $y actin as a #ehy#ratin aent it a$sor$s the %ater,

enco2rain the for%ar# reaction, shiftin e'2ili$ri2m to the riht accor#in to Le &hatelier@s 1rinci1le.

• 'xplain the need for refluxin$ durin$ esterification:

– 5eflu&in: a techni'2e inColCin the con#ensation of Ca1ors an# the ret2rn of this con#ensate to the system from

%hich it oriinate#, this is #one $y a reflu&in a((aratus %hich is $asically a con#enser 1lace#

Certically onto a $oilin flas9 it cools any Ca1o2rs that $oil off so that they #ri1 $ac9 into the flas9.

– 8he nee# for it incl2#es the fact that the nat2ral 1ro#2ction of ester is a slow 1rocess (es1 at normal

+L&) an# a hi$h un-,eildin$ 1rocess an# dan$erous.

– Heatin the reaction flas9 has main $enefits:

8he hiher the tem1erat2re (more 9inetic enery), the faster the rate of reaction e'2ili$ri2m

can $e reache# m2ch faster than if it %as left at room tem1erat2re.

Blso, esterification is an endothermic reaction increasin the heat of the flas9 enco2raes the

for%ar# reaction, creatin more ester.

– Hence thro2h refl2xin the reaction can $e reache# faster , %ith more yiel#s.

– Blso the 1ro#2cts an# reactants of an esterification reaction (aci#s, alcohols, esters) are Colatile s2$stances, an# th2s

%o2l# esca1e from the container as they %ere heate#, 1resentin a haKar# to st2#ents an# loss of reactant an#

1ro#2ces. Gefl2x ena$les safe techni'2e an# more Cia$le reaction.

http://upload.wikimedia.org/wikipedia/en/5/51/Reflux_labled.svg


49/52

• #dentif, the #;.A* nomenclature for describin$ the esters produced b, reactions of strai$ht-chained al%anoic acids

from *1 to *@ and strai$ht-chained primar, al%anols from *1 to *@:

– +traiht6chaine# al9anoic aci#s only haCe one car$oxyl f2nctional ro21, locate# on one of the en#6car$ons.

– Namin al/anols:

&o2nt the n2m$er of car$ons, ta9e the 1arent al9ane name, #ro1 the ?e@ an# a## on an ?6ol@.

8here are no exce1tions. 8he IFB& names coinci#e %ith all the systematic names methanol an# ethanol are

consi#ere# correct.

– Namin al/anoic acids:

&o2nt the n2m$er of car$ons ta9in the name of the 1arent al9ane %ith the same n2m$er of car$ons, #ro1 the ?e@

an# a## on ?6oic aci#@.

E: 8he 6& al9ane is 1ro1ane. Hence 6& al9anoic aci# is 1ro1anoic aci#.

8here are exce1tions to the r2le the IFB&61referre# name for the al9anoic aci#s for


50/52

No% that the aci# an# al9anol has $een i#entifie#, the ste1s a$oCe are easily follo%e#.

E,: Name the follo%in ester:

♦ Fsin an imainary sha#e, coCer the 1art %hich incl2#es the &>! $on#, an# anythin $efore it. Ie

♦ 8o the left, there is the &>! $on#, an# car$ons (co2ntin the &>!) hence, the al9anoic aci# 2se# ha#

car$ons. It %as $2tanoic aci#.

♦ Note: )he *< bond belon$s to al%anoic acids hence it0s $iven to it in the ester namin$ process8

♦ It follo%s then that the riht si#e is the al9anol, %hich has car$ons. 8herefore 1ro1anol %as 2se#.

♦ 8herefore the ester is 1ro1yl $2tanoate.

Note: In most of the ester exam1les, the ester $on# %ill $e attache# to the en#s of $oth the car$oxylic aci# (%hich

m2st $e tr2e, as the car$oxyl ro21 is al%ays on the en# of a molec2le) an# the alcohol. 72t, as a hy#roxyl ro21

can $e any%here on a molec2le, it is 1ossi$le to et esters %here the $on# is not attache# to the en# of the

alcohol.

In this case, n2m$erin is 2se# to in#icate %hich car$on of the alcohol the ester $on# is attache# to. +o for

exam1le, yo2 %o2l# name 61ro1yl acetate to in#icate (61ro1yl ethenate is %ron, from a$oCe):

•


51/52

irritant.

thyl Bcetate sterification of acetic aci#, ethyl

alcohol an# s2lf2ric aci#.• Brtificial fr2it essence

• +olCent for Carnishes, lac'2ers an# l2es

($oth 1olar an# non61olar com1o2n#s).

• .rocess information from secondar, sources to identif, and describe the uses of esters as flavours and perfumes in

processed foods and cosmetics:

– sters are in#2strially 1ro#2ce# to mimic flaCo2rs an# scents fo2n# in nat2re

– 8hese are for 2se in 1rocesse# foo#s, or mixe# to 1ro#2ce 2ni'2e 1erf2mes.

– *any 1rocesse# foo#s are flaCo2re# artificially, e.. $anana6flaCo2re# mil9 is flaCo2re# %ith the ester iso-pentyl

acetate.

– &osmetics contain esters as scents, s2ch as 1erf2mes, %ith are com1rise# almost excl2siCely of a mixt2re of esters in a

solCent, or to iCe soa1s, han#6lotions or other cosmetics a 1leasant smell.

• #dentif, data plan select equipment and perform a firsthand investi$ation to prepare an ester usin$ reflux:

– Aim: 8his 1ractical aime# to 1re1are the ester $2tyl ethanoate $y refl2x from


52/52

thanol an# ethanoic aci# %ere 2se# as the reactants.

ethanol ethanoic acid ethyl ethanoate water

In a ro2n#6$ottom flas9, O mL of ethanol, O mL of ethanoic aci# an#

Documents

Acidic Enviroment.doc