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9.3 The Acidic Environment


(1-i) Classify common substances as acidic, basic or neutral

Acidic Basic Neutral

ulfuric Acid !istilled "ater #otassium $ydro%ideCarbonic Acid &il' odium $ydro%ide

oda "ater il Ammonia

(1-ii) dentify that indicators such as litmus, *henol*hthalein, methyl

oran+e and bromothymol blue can be used to determine the acidic or

basic nature of a material over a ran+e is identied by chan+e in indicator

colour.

These indicators have a s*ecic *$ ran+e at hich they chan+e colour this ran+e is

useful in identifyin+ the nature of a substance

(1-iii) dentify and describe some everyday uses of indicators includin+ the

testin+ of soil acidity/basicity

- oil testin+- ome *lants +ro best at a certain *$ therefore farmers/+ardeners

use indicators to test the soil, as they may need to ad0ust the *$ of it, for e%am*le

a farm ould *refer the soil to be at the o*timum *$ for the cro* they are tryin+to +ro to *roduce the +reatest yield

- "ater testin+- immin+ *ools and auariums need re+ular testin+ to monitor *$

level hich maintains the ater uality, health of inhabitants or *revention of

+roth of certain or+anisms- E2uent Testin+- ndicators are used to monitor the *$ levels of aste aters from

industry to reduce the im*act on the environment.

(1-a) #erform a rst-hand investi+ation to *re*are and test a natural

indicator

"e tested the *$ of a ran+e of substances usin+ beetroot 0uice cabba+e 0uice and

universal indicator then $ibiscus e%tract.

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btain the natural indicator by boilin+ cabba+e and/or beetroot in ater (se*arate

bea'ers)

$ibiscus indicator is made by crushin+ the oer in a mortar and *estle ith metholated

s*rits

&ethod-

1. btain 3 identical test tubes and *ut eual amount of 4.1 mol $Cl into each before

*uttin+ a fe mls of cabba+e 0uice and notin+ the colour chan+e.

5. 6e*eat ith all other acids and bases (7ine+ar, soda ater, salt ater, 8a$ and

Cloudy Ammonia) notin+ all colour chan+es

3. 6e*eat for the other indicators includin+ universal indicator

"e found that cabba+e 0uice (ori+inally *ur*le) has a *$ ran+e of -: ith it been +reen

in basic solution and red in acidic solution, hilst beetroot (ori+inal red) as *ur*le in

acid and bron/oran+e in base ith a *$ ran+e of 3-:

(1-b) dentify data and choose resources to +ather information about the

colour chan+es of a ran+e of indicators

ee +ra*h in (1-ii)

(1-c) olve *roblems by a**lyin+ information about the colour chan+es of

indicators to classify some household substances as acidic, neutral or

basic

;y usin+ the information +iven on the colour a variety of indicator is in certain

substances, e can classify a ran+e of substances as acidic or basic

(5-i) dentify %ides of non-metals hich acts as acids and describe the

conditions under hich they act as acids

The o%ides of non-metals and semi-metal such as carbon dio%ide can acts as acids under

certain conditions these conditions include reactin+ ith ater to form an acid

E+ C5 < $5 $5C3

they can also act as acids in neutralisin+ bases to form ater and a salt

E+ C5 < 58a$ 5$5 < 8a5C3

(5-ii) Analyse the *osition of these non-metals in the *eriodic table and

outline the relationshi* beteen *osition of elements in the *eriodic tableand the acidity/basicity of o%ides

8on metal %ides located at the ri+ht hand side of the *eriodic table act as acids, hilst

metal o%ides located on the left hand side of the *eriodic table act as bases, also the

o%ides of the ve elements close to the borderline beteen metals and non-metals are

am*hoteric

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(3-iii) !ene =e Chatelier>s *rinci*le

f a system of euilibrium is disturbed the *osition of the euilibrium ill ad0ust itself in

the direction hich counteracts the disturbance

(5-iv) dentify factors hich can a?ect the euilibrium in a reversible

reaction

@actors hich can a?ect the *osition of the euilibrium in a reaction include

- A chan+e in tem*erature- A chan+e in *ressure (#ressure is *ro*ortional to the number of moles)- Chan+e in concentration (addin+ more reactant or *roduct)

(5-v) !escribe the solubility of carbon dio%ide in ater under various

conditions and e%*lain in terms of =e Chatelier>s *rinci*le

The dissolvin+ of C5 in ater to form carbonic acid is an e%othermic reaction therefore

heat ener+y may be considered one of the *roducts.

C5 (+)< $5(l) $5C3 (a)< heat ener+y

An increase of tem*erature reduces the amount of C5 dissolved hilst increasin+ the

*ressure allos for more C5 to dissolve

Therefore if the tem*erature is raised the euilibrium ill shift to the left in order to use

u* some of the heat and loer the tem*erature.

f the tem*erature is loered the euilibrium shifts to the ri+ht in order to release more

heat ener+y to raise the tem*erature

f the *ressure is increased the euilibrium ill shift to the ri+ht in order to relieve the

*ressure by usin+ u* some of the C5 as +ases ta'e u* more s*ace than liuid therefore

by usin+ some of the C5 some of the *ressure is relieved

f the concentration of a reactant is increased the euilibrium ill shift to the ri+ht, but if

the concentration of the *roduct is increased then it ill shift to the left, this is in order touse u* some of the e%tra thin+ added

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(5-vi) dentify natural and industrial sources of sulfur dio%ide and o%ides of

nitro+en

ulfur !io%ide is created naturally by volcanic eru*tions and hot s*rin+s, but is made in

lo levels. n industry sulfur dio%ide is made by the smeltin+ of ulde ores (e+ #b < 5

#b < 5) and the burnin+ of fossil fuels hich contain sulfur such as coal hich u*on

combustion reacts ith the o%y+en to for ulfur !io%ide

8% (85(+)t certain, but from the increasin+ e?ects

of these +ases e can see that they are increasin+ in concentration, ill it causin+ severe

dama+e to cro*s *lants and statues ith acid rain

(5-i%) calculate volumes of +ases +iven masses of some substances in

reactions, and calculate masses of substances +iven +aseous volumes, in

reactions involvin+ +ases at 4oC and 144'#a or 5oC and 144'#a

7olume of 1 mole ideal +as at 144 '#a andat 4C (5D3.1 ) ...................... 55.D1 = (T#)At 5C (59:.1 ).................... 5F.D9 = (=C)

(5-%) E%*lain the formation and e?ects of acid rain

ince all rain contains dissolved carbon dio%ide even un*olluted rain is sli+htly acidic as itforms carbonic acid. Acid rain normally forms hen rain dissolved sulfur o%ides and 8%formin+ sul*hurous ($53) sulfuric ($5F) and nitric acids ($83). These then ionisesformin+ $< hich do the dama+e to buildin+ etc. The e?ects of acid rain are-

F

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1. Causes aterays to become acidic a?ectin+ auatic life, in some case too acidto su**ort life

5. !ama+es *lants and cro*s by alterin+ the *$ of soil thereby a?ectin+ +roth as*lants need a s*ecic *$ soil

3. !ama+es stone and metal buildin+ by erodin+ them, such as the hydro+en ionsbrea'in+ ho calcium carbonate in statues

(5-a) identify data, *lan and *erform a rst-hand investi+ation todecarbonate soft drin' and +ather data to measure the mass chan+esinvolved and calculate the volume of +as released at 5C and 144'#a

Aim- To determine the amount of C5 +as dissolved in a soft drin'

nde*endent variable- #ressure at hich the soft drin' is contained

!e*endent 7ariable-

&ethod- 1. "ei+ht and record an uno*ened can of co'e

5. Carefully o*en the can, tryin+ not to s*ill any

3. Allo the can to rest in a cool *lace (room tem*erature) aay from direct

sunli+ht (to reduce eva*oration). "ei+h and record daily for a D day *eriodF. Create a control by sub0ectin+ an uno*ened can to identical conditions

em*tyin+ and also to im*rove e%*erimental result create an identical can and

re*lacin+ it ith an euivalent amount of distilled ater and sub0ect it to the same

conditions as the e%*erimental can recordin+ the ei+ht of the can daily

6esults

Day Weight of experimental can

Weight ofunopened can

Weight of atercan

! F4G.F F4D.34 3:4.F1

" !idn>t ei+h !idn>t ei+h !idn>t ei+h

3 !idn>t ei+h !idn>t ei+h !idn>t ei+h

# F41.D1 F4D.34 3DD.5$ F44.94 F4D.34 3DD.F4

% F44.F1 F4D.59 3DG.F1

ver the *eriod of si% days the control lost F.G5 +rams

&ass of carbonated cola H F4G.F+

&ass of decarbonated cola H F44.F1+

&ass of C5 lost H G.4F+ but the ater can lost F.G5 +rams due to eva*oration

Therefore 1.F5+ of C5 as lost

&oles H +rams/molecular mass

H 1.F5/FF.41

7olume H &oles % &olar 7olume

H 1.F5/FF.41 % 5F.D9

7olume of C5 H 4.D99=

I Error@actory su**lied data states 44mls of Cola *roduces 1.9= of C5

The e%*eriment *roduced 4.D99= for 3D mls

Therefore 44mls of this e%*eriment Cola ould *roduces 1.4GD=

I Error H reference value J e%*erimental value/ reference value % 144

H 1.9 J 1.4GD/1.9 % 144

H F3.:GI

ources of error-

- &ass loss- &ass loss not cause by eva*oration or the loss of C5 caused by thin+s

such as s*illa+es can cause an e%*erimental error but chan+in+ the ei+ht values

thereby ma'in+ the results less accurate.

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- "ei+hin+ Error- The scales only measure to to decimal *laces, therefore each

ei+hin+ can cause a

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The *$ scale is used to com*are the concentration of hydro+en ions in solutions of acids

and bases thereby alloin+ us to determine the acidity or basicity of a substance. $ence,

the *$ scale allos us to com*are acids and bases, and their stren+ths

(3-iv) !escribe acids and their solutions ith a**ro*riate use of the termsstron+, ea', concentrated and dilute

tron+ acid H Total ioniLation in solution

"ea' Acid H #artial ioniLation in solution

Concentrated Acid H $i+h molarity

!ilute Acid H lo molarity

(3-v) identify *$ as Jlo+14M$

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(3-a) olve *roblems and *erform a rst-hand investi+ation to use *$

meters/*robes and indicators to distin+uish beteen acidic, basic and

neutral chemicals

;y usin+ *$ meters and universal indicators e ere able to see the *$ of many

chemicals thus alloin+ us to classify them as acidic, basic or neutral

(3-b) #lan and *erform a rst-hand investi+ation to measure the *$ of

identical concentrations of stron+ and ea' acidsTested the *$ of di?erent acids hich the same molarity and found the *$ can vary

de*endin+ on the stren+th of the acid. Tested 4.1 mol $Cl and acetic acid and found that

the stron+er acid in $Cl had a loer *$ than the ea' acid in acetic acid, ualitatively

and uantitatively ie ith both universal indicator and a *$ meter.

(3-c) Oather and *rocess information from secondary sources to riteionic euations to re*resent the ionisation of acids"e search many sources, hi+hli+hted and summarise relevant information, before

chec'in+ validity.

(3-d)Pse available evidence to model the molecular nature of acids and

simulate the ionisation of stron+ and ea' acids

Throu+h usin+ models e shoed ho stron+ acid ionise more than ea' acids

(3-e) Oather and *rocess information from secondary sources to e%*lain

the use of acids as food additives

- #reservatives- Addin+ acids to a food loers the *$ and ma'es it more diQcult for

some bacteria or fun+i to +ro ithin thereby hel* it last lon+er, acid hich do

thins include ethanoic and sulfur dio%ide- @lavour- &any food such as soft drin' and 0ams uses citric and ethanoic acids to

ith it a shar* sour taste- -8utrition- some foods have vitamins added to increase their nutritional value

such as ascorbic acid (vitamin C)

(3-f) dentify data, +ather and *rocess information from secondary sources

to indentify e%am*les of naturally occurrin+ acids and bases and theirchemical com*osition

;ull ants or bee stin+s contain formic acid (methanoic acid). Ethanoic acid is the main

chemical in vine+ar. &any fruit es*ecially citrus contain citrus acid

Common bases include lime hich is Ca and is used in cement as ell as =ye hich is

mainly $ and 8a$ and is obtained by soa'in+ ood ashes in ater

(3-+) #rocess information from secondary sources to calculate *$ of stron+

acids +iven a**ro*riate hydro+en ion concentrations

Jlo+14M$

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nd the molarity of $< if it ionised. To nd the molarity from the *$ use shit-lo+ molarity,if the solution is di*rotic half the molarity to nd the molarity of the acidE+ hat is the *$ of 4.4m $Cl

M$

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(F-iii) !escribe the relationshi* beteen an acid and its con0u+ate base

and a base and its con0u+ate acid

"hen an acid donates a *roton, it forms its con0u+ate base this ould act as a base if

the reaction as reversed as it ould acce*t a *roton. "hen a base acce*ts a *roton, it

forms its con0u+ate acid, this ould act as an acid if the reaction as reversed as it oulddonate a *roton.

(F-iv) dentify a ran+e of salts hich form acidic, basic or neutral solutions

and e%*lain their acidic, neutral or basic nature

Acidic (alts Neutral (alts Basic (alts

8a$F 8aCl 8a5C3

8$FCl 83 C$3C8a

8$F83 8a5F odium ethanoate

(F-v) dentify con0u+ate acid/base *airs

"henever an acid and a base react, they form their con0u+ates

$Cl < $5 Cl- < $3

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3. have an accurately 'non formula

F. be stable in air, i.e. it does not lose or +ain ater or react ith o%y+en orcarbon dio%ide in airE%am*les of suitable solutions are Acid- o%alic acid (C$C$) hich isdi*rotic, and base- anhydrous sodium carbonate (8a5C3)

The solution is *re*ared by

1. Accurately ei+hin+ a calculated amount of solid5. !issolvin+ it in distilled ater3. Transferrin+ all of the dissolved solid to a volumetric as'F. @lushin+ out the bea'er ith distilled ater to +et the entire solid into thevolumetric as'. Addin+ ater to the as' to *re*are a %ed volume of solution.G. ha'in+ to com*letely dissolve the solid into the aterD. Calculate the &olarity

ou must have a suitable indicator for a titration-- tron+ Acid < tron+ ;ase, has an e.* around *$ D so ;romothymol blue ould be

a +ood indicator, yello in acid and blue in base.- tron+ Acid < "ea' base has an e.* around *$ F- therefore methyl oran+e

ould be a +ood indicator, red in acid and yello in base- "ea' acid < stron+ base has an e.* around *$ 9-14 therefore *henol*hthalein

ould be a +ood indicator, colourless in acid and *in' in base&ethod for titrations

1. &i% u* the *rimary standard5. Choose the suitable indicator3. 6inse the burette ith *rimary standardF. @ill the burette ith the *rimary standard to the Lero mar'. 6inse a *i*ette ith the un'non then add an 5ml aliuot of un'non into a

volumetric as' (hich has been rinsed ith distilled ater) ith the *i*ette, then

add a fe dro*s of the indicatorG. Carefully add the solution from the burette into the as' until the indicatorchan+es, record the amount of standard used and re*eat

(F-i%) Uualitatively describe the e?ect of bu?ers ith reference to a

s*ecic e%am*le of a natural system

A bu?er or bu?ered solution is a solution hich can absorb si+nicant amounts of acid orbase ith minimal chan+e in *$. ;u?ers control the level of acidity or basicity in asolution. A bu?er solution is usually a mi%ture of a ea' acid and its con0u+ate base suchas hydro+en carbonate ions, $C3

-, and its con0u+ate base carbonate ions, C35-.

$ydro+en carbonate ions are im*ortant in maintainin+ the *$ of human blood at aboutD.F.f an acid is added to the bu?er, the hydro+en ions are removed by

$s *rinci*le that been an increase of a *roduct or reactant ill alter to *osition ofthe euilibrium accordin+ly as to use of some of this e%tra substance. This is the same

for if a base is added to the bu?er, hydro%ide ions are removed by $-< $C3- $5 t react anymore thereby reducin+ harm, if a base

as used to neutralise an acid you ould need to 'no the e%actly molarity to ma'e it

com*letely safe

(-i) !escribe the di?erences beteen the al'anols and al'anoic acid

functional +rou*s in carbon com*ounds

The functional +rou* in al'anols is a hydro%ide ion (hydro%y) *rovidin+ it ith

characteristic *ro*erties, such as hi+h meltin+ *oints and boilin+ *oints hilst an

al'anoic acid has a double bond +rou* in addition to the hydro%ide +rou* attached to

the same carbon, this is 'non as the carbo%ylic acid functional +rou*, -C$, al'anoicacids, can act as acids if they lose a hydro+en

(-ii) dentify the P#AC nomenclature for describin+ the esters *roduced

by reactions of strai+ht-chained al'anoic acids from C1 to C: and strai+ht-

chained *rimary al'anols from C1 to C:

Al-anol

Methanoic Acid

Ethanoic

acid

Propanoic

Acid

Butanoic

Acid

Petanoic

Acid

Hexanoic

Acid

Heptanoic

Acid

Octanoic

AcidMetha methyl

methanoatmethylethanoat

methyl*ro*anoat

methylbutanoat

methyl*entanoa

methylhe%anoat

methylhe*tanoat

methyloctanoat

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nol e e e e te e e e

Ethanol

ethylmethanoate

ethylethanoate

ethyl*ro*anoate

ethylbutanoate

ethyl*entanoate

ethylhe%anoate

ethylhe*tanoate

ethyloctanoate

Propanol

*ro*ylmethanoate

*ro*ylethanoate

*ro*yl*ro*anoate

*ro*ylbutanoate

*ro*yl*entanoate

*ro*ylhe%anoate

*ro*ylhe*tanoate

*ro*yloctanoate

Butanol

butylmethanoate

butylethanoate

butyl*ro*anoate

butylbutanoate

butyl*entanoate

butylhe%anoate

butylhe*tanoate

butyloctanoate

Pentanol

*entylmethanoate

*entylethanoate

*entyl*ro*anoate

*entylbutanoate

*entyl*entanoate

*entylhe%anoate

*entylhe*tanoate

*entyloctanoate

Hexanol

he%ylmethanoate

he%ylethanoate

he%yl*ro*anoate

he%ylbutanoate

he%yl*entanoate

he%ylhe%anoate

he%ylhe*tanoate

he%yloctanoate

Heptanol

he*tylmethanoate

he*tylethanoate

he*tyl*ro*anoate

he*tylbutanoate

he*tyl*entanoate

he*tylhe%anoate

he*tylhe*tanoate

he*tyloctanoate

Octanol

octylmethanoate

octylethanoate

octyl*ro*anoate

octylbutanoate

octyl*entanoate

octylhe%anoate

octylhe*tanoate

octyloctanoate

(-iii) E%*lain the di?erence in meltin+ *oint and boilin+ *oint caused by

strai+ht Jchained al'anoic acid and strai+ht-chained *rimary al'anols

structures

Al'anoic acids have much hi+her meltin+ *oint and boilin+ *oints than their

corres*ondin+ al'anols due to Al'anoic acids havin+ double the amount of hydro+en

bonds beteen molecules thereby +ivin+ it a hi+her meltin+ and boilin+ *oint due to it

therefore needin+ more ener+y to brea' the bonds. Al'anes only have dis*ersion forces

beteen each molecules, +ivin+ them the loest boilin+ *oint of the three as dis*ersion

forces are much ea'er than hydro+en bonds.

Ethane Ethanol Ethanoic Acid

Boiling *t &/ -:9

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(-v) !escribe the *ur*ose of usin+ acid in esterication for catalysis

Concentrated sulfuric Acid is used to catalyse esterication for to reasons-

- Acts as a dehydration a+ent, absorbin+ ater (and inducin+ condensation

reactionsX), thereby increasin+ the yield of ester as the euilibrium reaction is

shifted to the ri+ht as accordin+ to =e Chatelier>s *rinci*le- t acts as at catalyst, s*eedin+ u* the reaction rate reachin+ euilibrium faster

(-vi) E%*lain the need for reu%in+ durin+ esterication

6eu%in+ allos the mi%ture to react at hi+h tem*eratures ithout fear that the reactants

or *roducts ill eva*orate aay

(-vii) utline some e%am*les of the occurrence, *roduction and uses of

esters

Esters occur idely in nature es*ecially in fruit and oers, in hich they are res*onsiblefor the smell and taste.

(-a) dentify data *lan select eui*ment and *erform a rst-hand

investi+ation to *re*are an ester usin+ reu%

Aim to *roduce an ester usin+ a reu%

&ethod-

1. #lace *ro*ortional molar (ie correct ratio to match the stachiometry) amounts of then

al'anol and the acid ith 1 ml of concentrated sulfuric acid into a 4ml as'

5. Add a fe boilin+ chi*s and assemble the reu% a**aratus ith a condenser

3. Connect a tube beteen a ater sources and the condenser and turn the ta* until a

moderate uniform o is achieved

F. teadily heat the mi%ture over a busen ame for 34 minutes

. Carefully remove the as' and *our the contents into a se*aratin+ funnel containin+

1mls of distilled ater, sto**er the funnel and sha'e carefully before carefully decantin+

the aueous layer (loer layer)

G. Add 1 ml of 1 mol 8a5C3 solution before sha'in+ and removin+ the loer layer

leavin+ the ester in the se*aratin+ funnel

D. Carefully smell, and record.

!iscussion-

The reaction mi%ture is ashed ith ater in order to remove the aueous layer hich ismiscousable ith the ester, but the ester is imiscousable ith ater hilst the aueous

layer isn>t thereby se*aratin+ them

The ester is ashed ith 8a5C3 to neutralise and remove the catalyst.

(-b) #rocess information from secondary sources to identify and describe

the uses of esters as avours and *erfumes in *rocessed foods and

cosmetics

Pses of esters include-

- Articial avours for drin's and various *rocessed foods

1F

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- olvents Ethyl ethanoate is idely used as an industrial solvent, and is also used

as a solvent in nail varnish- n+redients in many *roducts includin+ sham*oo and cosmetic *roducts.

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