Acids and Bases-HL

7/25/2019 Acids and Bases-HL

1/23

ACIDS AND BASES HL

1. Which salts will produce an acidic solution when dissolved in water?

I. CH3COOK

II. NH4NO3

III. Al2(O4!3

A. I and II onl"

#. I and III onl"

C. II and III onl"

$. I% II and III(Total 1 mark)

2. &heK'value or a 'ase is ).* + ,*-2

ol d-3

at 2/0 K. What is theKavalue or its con1uate acid at this

teperature?

A. ).* + ,*-2

#. 2.* + ,*-

C. 2.* + ,*-,2

$. 2.* + ,*-,3

(Total 1 mark)

3. Which copounds can 'e ied toether as solutions o e5ual volue and concentration to or a 'uer

solution?

A. Nitric acid and potassiu h"droide

#. Nitric acid and potassiu nitrate

C. 6ropanoic acid and potassiu h"droide

$. 6ropanoic acid and potassiu propanoate(Total 1 mark)

4. In an eperient conducted at 2).* 7C% the initial concentration o propanoic acid and ethanol were ,. ol d-

3and 2.* ol d-3respectivel". Once e5uili'riu was esta'lished% a saple o the iture was reoved and

anal"sed. It was ound to contain *.0* ol d-3

o copound X.

(i! Calculate the concentrations o the other three species present at e5uili'riu.

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(ii! tate the e5uili'riu constant epression%Kc% and calculate the e5uili'riu constant or this reaction at

2).* 7C.

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(2)(Total 5 marks)

5. &he raph 'elow indicates the pH chane durin the titration o 2*.* c3o *.,** ol d

-3o CH3COOH(a5!

with *.,** ol d-3

KOH(a5!. 8ro the raph% identi" the volue o KOH(a5! and the pH at the e5uivalence

point.

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6. (i! $escri'e how an indicator wor9s.

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(ii! :sin &a'le , o the $ata #oo9let% identi" the ost appropriate indicator or the titration o ethanoic acid

with potassiu h"droide. ;plain "our choice.

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(Total 5 marks)

. ;plain% usin an e5uation% whether a solution o *.,* ol d-3

8eCl3(a5! would 'e acidic% al9aline or neutral.

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!. $eterine the pH o the solution resultin when ,** c3o *.)* ol d

-3HCl(a5! is ied with 2** c

3o

*.,* ol d-3

NaOH(a5!.

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". #ased on inoration in the ta'le 'elow% which acid is the stronest?

A#$% &Ka Ka

A. HA 2.* -

#. H# - , + ,*-3

C. HC 4.* -

$. H$ - , + ,*-)

(Total 1 mark)

1'. Which co'ination will or a 'uer solution?

A. ,** c3o *.,* ol d

-3h"drochloric acid with )* c

3o *.,* ol d

-3sodiu h"droide.

#. ,** c3o *.,* ol d

-3ethanoic acid with )* c

3o *.,* ol d

-3sodiu h"droide.

C. )* c3o *.,* ol d

-3h"drochloric acid with ,** c

3o *.,* ol d

-3sodiu h"droide.

$. )* c3o *.,* ol d

-3ethanoic acid with ,** c

3o *.,* ol d

-3sodiu h"droide.

(Total 1 mark)

11. &he raph 'elow shows the titration curve o 2) c3o *.,** ol d

-3o h"drochloric acid with sodiu

h"droide% o *.,** ol d-3

concentration. &he indicator eth"l orane was used to deterine the e5uivalence

point.


4/23

I the h"drochloric acid was replaced '" ethanoic acid o the sae volue and concentration% which propert" o

the titration would reain the sae?

A. &he initial pH

#. &he pH at the e5uivalence point

C. &he volue o stron 'ase% NaOH% needed to reach the e5uivalence point

$. &he colour o the titration iture 1ust 'eore the e5uivalence point is reached

(Total 1 mark)

12. Aonia% NH3% is a wea9 'ase. It has a pK'value o 4.=).

Calculate the pH o a ,.** + ,*-2

ol d-3

a5ueous solution o aonia at 2/0 K.

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13. (i! 2).* c3o ,.** + ,*

-2ol d

-3h"drochloric acid solution is added to )*.* c

3o

,.** + ,*-2ol d-3a5ueous aonia solution. Calculate the concentrations o 'oth aonia andaoniu ions in the resultin solution and hence deterine the pH o the solution.

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(ii! tate what is eant '" a 'uer solution and eplain how the solution in (i!% which contains aoniu

chloride dissolved in a5ueous aonia% can unction as a 'uer solution.

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(Total ! marks)

14. alts a" or neutral% acidic or al9aline solutions when dissolved in water.

(i! ;plain wh" a solution o sodiu chloride is neutral 'ut sodiu car'onate ors an al9aline solution when

it dissolves in water.

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(ii! ;plain wh" iron(III! chloride% >8e(H2O!Cl3% ors an acidic solution in water.

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(Total 4 marks)

15. What is theK'epression or the reaction o eth"laine with water?

A. K'@ >CH3CH2NH3>OH

-

#. K'@?NHCH>CH

??>OHNHCH>CH

223

323+

C. K'@?NHCH>CH

O??>HNHCH>CH

223

2323

+

$. K'@ >CH3CH2NH2>H2O

(Total 1 mark)

16. When these ,.* ol d-3

acidic solutions are arraned in order o increasin strenth (wea9est irst!% what is the

correct order?

acid in solution B Ka@ ,.=4 + ,*-)

ol d-3

at 2/0 K

acid in solution Ka@ ,.30 + ,*-3

ol d-3

at 2/0 K

acid in solution D KaE@ ,.=0 + ,*-)

ol d-3

at 2/0 K

A. B F D F

#. B F F D

C. D F B F

$. F B F D(Total 1 mark)

1. Consider an acidG'ase indicator solution.

HIn(a5! H(a5! In

-(a5!

colour A colour #

What is the eect on this acidG'ase indicator when sodiu h"droide solution is added to it?


6/23

A. ;5uili'riu shits to the riht and ore o colour # is seen.

#. ;5uili'riu shits to the let and ore o colour # is seen.

C. ;5uili'riu shits to the riht and ore o colour A is seen.

$. ;5uili'riu shits to the let and ore o colour A is seen.(Total 1 mark)

1!. (a! (i! tate an e5uation or the reaction o ethanoic acid with water.

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(ii! Calculate the pH o *.2** ol d-3

ethanoic acid (pKa@ 4.=!.

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('! $eterine the pH o a solution ored ro addin )*.* c3o ,.** ol d

-3ethanoic acid%

CH3COOH(a5!% to )*.* c3o *.** ol d

-3sodiu h"droide% NaOH(a5!.

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(c! ;plain how the solution ored in part ('! can act as a 'uer. :se e5uations to support "our answer.

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(Total 1' marks)

1". pKwor water at ,* 7C @ ,4.)4. What is the pH o pure water at this teperature?

A. .=3

#. =.**

C. =.2=

$. =.)4(Total 1 mark)

2'. What isK'or the a5ueous luoride ion iven thatKwis ,.* + ,*-,4andKaor H8 is .0 + ,*-4at 2/0 K?

A. 4

,*0.

,

#. (.0 + ,*-4

!(,.* + ,*-,4

!

C. 4

,4

,*0.

,**.,


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$. .0 + ,*-4

(Total 1 mark)

21. Which o the ollowin could 'e added to a solution o ethanoic acid to prepare a 'uer?

A. odiu h"droide

#. H"drochloric acid

C. odiu chloride

$. 8e(H2O!Cl3(a5!

$. CH3COONa(a5!

(Total 1 mark)

23. Water is an iportant su'stance that is a'undant on the ;arths surace.

(i! tate the epression or the ionic product constant o water%Kw.

(1)

(ii! ;plain wh" even a ver" acidic a5ueous solution still has soe OH-

ions present in it.(1)

(iii! tate and eplain the eect o increasin teperature on the value oKwiven that the ioniation o water

is an endotheric process.(3)

(iv! tate and eplain the eect o increasin teperature on the pH o water.

(2)(Total marks)

24. #uer solutions resist sall chanes in pH. A phosphate 'uer can 'e ade '" dissolvin NaH26O4and

Na2H6O4in water% in which NaH26O4produces the acidic ion and Na2H6O4produces the con1uate 'ase ion.

(i! $educe the acid and con1uate 'ase ions that a9e up the phosphate 'uer and state the ionic e5uation that

represents the phosphate 'uer.(3)

(ii! $escri'e how the phosphate 'uer iniies the eect o the addition o a stron 'ase% OH-

(a5!% to the

'uer. Illustrate "our answer with an ionic e5uation.(2)

(iii! $escri'e how the phosphate 'uer iniies the eect o the addition o a stron acid% H(a5!% to the

'uer. Illustrate "our answer with an ionic e5uation.(2)

(Total marks)

25. A *.,* ol d-3

aonia solution is placed in a las9 and titrated with a *.,* ol d-3

h"drochloric acid

solution.

(i! ;plain wh" the pH o the aonia solution is less than ,3.

(2)

(ii! ;stiate the pH at the e5uivalence point or the titration o h"drochloric acid with aonia and eplain

"our reasonin.(2)

(iii! tate the e5uation or the reaction o aonia with water and write theK'epression or NH3(a5!.


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(2)

(iv! When hal the aonia has 'een neutralied (the halGe5uivalence point!% the pH o the solution is /.2).

$educe the relationship 'etween >NH3 and >NH4 at the halGe5uivalence point.

(1)

(v! $eterine pK'andK'or aonia 'ased on the pH at the halGe5uivalence point.

(3)

(vi! $escri'e the siniicance o the halGe5uivalence point in ters o its eectiveness as a 'uer.

(1)(Total 11 marks)

26. Which itures act as 'uer solutions?

I. ,** c3*., ol d

-3ethanoic acid and ,** c

3*., ol d

-3sodiu ethanoate

II. ,** c3*., ol d

-3ethanoic acid and )* c

3*., ol d

-3sodiu h"droide

III. ,** c3*., ol d

-3ethanoic acid and ,** c

3*.) ol d

-3sodiu h"droide

A. I and II onl"

#. I and III onl"

C. II and III onl"


2. Which solutions have a pH less than =?

I. Na2CO3(a5!

II. >8e(H2O!Cl3(a5!

III. (NH4!2O4(a5!

A. I and II onl"

#. I and III onl"

C. II and III onl"


2!. ;5ual volues and concentrations o h"drochloric acid and ethanoic acid are titrated with sodiu h"droide

solutions o the sae concentration. Which stateent is correct?

A. &he initial pH values o 'oth acids are e5ual.

#. At the e5uivalence points% the solutions o 'oth titrations have pH values o =.

C. &he sae volue o sodiu h"droide is needed to reach the e5uivalence point.

$. &he pH values o 'oth acids increase e5uall" until the e5uivalence points are reached.(Total 1 mark)

2". #roophenol 'lue chanes ro "ellow to 'lue over the pH rane o 3.* to 4.. Which stateent is correct?

A.


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(i! $istinuish 'etween the tersstrongand weak acidand state the e5uations used to show the

dissociation o each acid in a5ueous solution.(3)

(ii! $educe the epression or the ioniation constant%Ka% o h"droc"anic acid and calculate its value

ro the pKavalue iven.

(2)

(iii! :se "our answer ro part (a! (ii! to calculate the >H and the pH o an a5ueous solution o

h"droc"anic acid o concentration *.,*0 ol d-3

. tate oassuption ade in arrivin at "our

answer.(4)

('! A sall piece o anesiu ri''on is added to solutions o nitric and h"droc"anic acid o the sae

concentration at the sae teperature. $escri'e t*oo'servations that would allow "ou to distinuish

'etween the two acids.(2)

(c! A student decided to investiate the reactions o the two acids with separate saples o *.2* ol d-3

sodiu h"droide solution.

(i! Calculate the volue o the sodiu h"droide solution re5uired to react eactl" with a ,).* c

3

solution o *.,* ol d

-3nitric acid.

(1)

(ii! &he ollowin h"pothesis was suested '" the studentJ ince h"droc"anic acid is a wea9 acid it

will react with a saller volue o the *.2* ol d-3

sodiu h"droide solution.L Coent on

whether or not this is a valid h"pothesis.(1)

(iii! :se &a'le , o the $ata #oo9let to identi" a suita'le indicator or the titration o sodiu h"droide

and h"droc"anic acid.(1)

(d! &he raph 'elow shows how the conductivit" o the two acids chanes with concentration.

Identi" A#$% 1and eplain "our choice.(2)

(Total 16 marks)

31. What is the correct epression or the ionic product constant o water%Kw?

A. KW@?OH>

?H>

+

#. KW@?OH?>H>

?OH> 2+

C. KW@ >H >OH-

$. KW@ >H>OH

-


10/23

(Total 1 mark)

32. Which itures could act as 'uers?

I. NaOH(a5! and HCl(a5!

II. NaOH(a5! and CH3COOH(a5!

III. HCl(a5! and CH3COONa(a5!

A. I and II onl"

#. I and III onl"

C. II and III onl"


33. (a! &he pKavalue or propanoic acid is iven in &a'le ,) o the $ata #oo9let.

(i! tate the e5uation or the reaction o propanoic acid with water.

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(1)

(ii! Calculate the h"droen ion concentration (in ol d-3

! o an a5ueous solution o *.,** ol d-3

propanoic acid.

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(2)

('! &he raph 'elow shows a coputer siulation o a titration o 2).* c3o

*.,** ol d-3

h"drochloric acid with *.,** ol d-3

sodiu h"droide and the pH rane o phenol red

indicator.

9etch the raph that would 'e o'tained or the titration o 2).* c3o *.,** ol d

-3propanoic acid

with *.,** ol d-3

potassiu h"droide usin 'roophenol 'lue as an indicator. (&he pH rane o

'roophenol 'lue can 'e ound in &a'le , o the $ata #oo9let!.


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(3)

(Total 6 marks)

34. ,** c3o a NaOH solution o pH ,2 is ied with /** c

3o water. What is the pH o the resultin solution?

A. ,

#. 3

C. ,,

$. ,3(Total 1 mark)

35. Aonia acts as a wea9 'ase when it reacts with water. What is theK'epression or this reaction?

A.O>H>NH

OH>NH>

23

4+

#. ??>OH>NH

O?H?>NH>

4

23

+

C. ??>OH>NH

?NH>

4

3

+

$. ?>NH

?OH?>NH>

3

4+

(Total 1 mark)

36. &he indicator% HIn is used in a titration 'etween an acid and 'ase. Which stateent a'out the dissociation o theindicator% HIn is correct?

HIn (a5! H(a5! In

-(a5!

colour A colour #

A. In a stronl" al9aline solution% colour # would 'e o'served.

#. In a stronl" acidic solution% colour # would 'e o'served.

C. >In-

is reater than >HIn at the e5uivalence point.

$. In a wea9l" acidic solution colour # would 'e o'served.(Total 1 mark)

3. At the sae concentration% which acid would have the lowest pH?

A. HNO2 Ka@ ). + ,*-4

ol d-3

#. H8 Ka@ .0 + ,*-4

ol d-3

C. CH)COOH Ka@ .3 + ,*-)

ol d-3

$. HCN Ka@ 4./ + ,*-,*

ol d-3

(Total 1 mark)

3!. oe o the ost iportant processes in cheistr" involve acidG'ase reactions.

(i! Calculate theKavalue o 'enoic acid% CH)COOH% usin &a'le ,) in the $ata #oo9let.


12/23

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(ii! #ased on itsKavalue% state and eplain whether 'enoic acid is a stron or wea9 acid.

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(iii! $eterine the h"droen ion concentration and the pH o a *.*,* ol d-3

'enoic acid solution. tate o

assuption ade in "our calculation.

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(4)(Total marks)

MM3".I 2* c3saples o *., ol d

-3solutions o the acids 'elow are ta9en% which acid would re5uire a dierent

volue o *., ol d-3

sodiu h"droide or coplete neutraliation?

A. Nitric acid

#. uluric acid

C. ;thanoic acid

$. H"drochloric acid(Total 1 mark)

4'. Which iture o acid and al9ali would produce a 'uer solution?

A#$% Alkal$

A. 4* c3*., ol d

-3HCl * c

3*., ol d

-3NaOH

#. * c3*., ol d

-3HCl 4* c

3*., ol d

-3NaOH

C. 4* c3*., ol d

-3HCl * c

3*., ol d

-3NH3

$.* c

3

*., ol d

-3

HCl 4* c

3

*., ol d

-3

NH3(Total 1 mark)

41

Which a5ueous solution would have a pH =?

A. odiu sulate

#. Aoniu nitrate

C. odiu ethanoate


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D. Aluminium nitrat

e(Total 1 mark)

42. Which indicator would 'e the ost appropriate or titratin a5ueous eth"laine% CH3CH2NH2% with nitric acid%

HNO3?

A. #roophenol 'lue (pKa@ 4.,!

#. #rooth"ol 'lue (pKa@ =.3!

C. 6henol red (pKa@ 0.*!

$. &h"olphthalein (pKa@ ,*.*!(Total 1 mark)

43. A 2).* c3solution o a wea9 onoprotic acid% HA(a5!% is titrated with *.,)) ol d

-3sodiu h"droide%

NaOH(a5!% and the ollowin raph is o'tained.

(i! $eterine the pH at the e5uivalence point.(1)

(ii! ;plain% usin an e5uation% wh" the e5uivalence point is not at pH @ =.(3)

(iii! Calculate the concentration o the wea9 acid 'eore the addition o an" NaOH(a5!.(2)

(iv! ;stiate% usin data ro the raph% the dissociation constant%Ka% o the wea9 acid% HA% showin "our

wor9in.(3)

(v! uest an appropriate indicator or this titration.(1)

(Total 1' marks)

44. $escri'e 5ualitativel" the action o an acidG'ase indicator.(Total 3 marks)

45. (i! ;plain what is eant '" the ter buffer solution.(2)


14/23

(ii! Calculate the pH o a solution prepared '" iin )*.* c3o *.2** ol d

-3CH3COOH(a5! and )*.*

c3o *.,** ol d

-3NaOH(a5!% showin "our wor9in.

(3)

(Total 5 marks)

46. tate whether AlCl3is acidic% 'asic or neutral in an a5ueous solution. Write an e5uation to support "our answer.

(Total 2 marks)

4. *.,** ol o aonia% NH3% was dissolved in water to a9e ,.** d3o solution.

&his solution has a h"droide ion concentration o ,.20 + ,*-3

ol d-3

.

(i! $eterine the pH o the solution.(2)

(ii! Calculate the 'ase dissociation constant%K'% or aonia.

(3)

(Total 5 marks)

4!. Which values are correct or a *.*,* ol d-3

solution o NaOH(a5! at 2/0 K?

(Kw@ ,.*+,*-,4

ol2d

-at 2/0 K!

A. >H @ ,.*+,*

-,2ol d

-3and pH @ ,2.**

#. >OH-

@ ,.*+,*-,2

ol d-3

and pH @ ,2.**

C. >H @ ,.*+,*

-,2ol d

-3and pOH @ ,2.**

$. >OH-

@ ,.*+,*-,2

ol d-3

and pOH @ ,2.**(Total 1 mark)

4". At 2) 7C%Kaor an acid is ,.*+,*-2

. What is the value oK'or its con1uate 'ase?

A. ,.*+,*2

#. ,.*+,*-2

C. ,.*+,*,2

$. ,.*+,*-,2

(Total 1 mark)

5'. Which stateent a'out indicators is al*a+scorrect?

A. &he idGpoint o the pH rane o an indicator is =.

#. &he pH rane is reater or indicators with hiher pKavalues.

C. &he colour red indicates an acidic solution.

$. &he pKavalue o the indicator is within its pH rane.

(Total 1 mark)

51. (a! 6redict and eplain% usin e5uations where appropriate% whether the ollowin solutions are acidic% al9aline

or neutral.

(i! *., ol d-3

8eCl3(a5!

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(ii! *., ol d-3

NaNO3(a5!

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(iii! *., ol d-3

Na2CO3(a5!

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('! Acidic ases can 'e released into the atosphere that have an environental ipact when the" are

deposited as acid rain. tate t*o eleents that or the acidic ases and descri'e t*oipacts the" have on

the natural environent.

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(Total 6 marks)

52. An eperient was carried out to deterine the concentration o a5ueous aonia '" titratin it with a *.,)*

ol d-3

suluric acid solution. It was ound that 2).* c3o the a5ueous aonia re5uired 2*., c

3o the

suluric acid solution or neutraliation.

(a! Write the e5uation or the reaction and calculate the concentration% in ol d-3

% o the a5ueous aonia.(4)

('! everal acidG'ase indicators are listed in &a'le , o the $ata #oo9let. Identi" o indicator that could 'e

used or this eperient. ;plain "our answer.(3)

(c! (i! $eterine the pOH o *.,2, ol d-3

a5ueous aonia (pK'@ 4.=)!.

(4)

(ii! tate what is eant '" the ter buffer solution% and descri'e the coposition o an acid 'uer

solution in eneral ters.

(3)

(iii! Calculate the pH o a iture o )*.* c3o *.,** ol d

-3a5ueous aonia and )*.* c

3o

*.*)** ol d-3

h"drochloric acid solution.(4)

(Total 1! marks)


16/23

,A-SCHE,E

1. C>, 2. $>, 3. $>,

4. (i! [CH3CH2COOH]:

(,. - *.0* @! *.0 (ol d-3

!

[CH3OH]:

(2.* - *.0* @! ,.2 (ol d-3![H2O]:

*.0* (ol d-3

! 3

(ii! (Kc@!OHCOOH>CHCHCH>

OH>COOCHCHCH>

323

2323

(Kc@!?0.*2.,>(

?!0*.*>( 2

@! *.= 2

Allow 0.6.

Award[1 max]for 0.!3. /50

5. "olu#e of KOHJ 2* (c3!

Allow an$ %alue between 20 and 2& 'c#3(.

)H at t*e e+ui%alence )oint: 0.*-,*.* 2/20

6. (i! HIn is a wea9 acid P wea9 'ase

HIn H In

-

colour , colour 2

re+uired.

Award[2]for ,2 alone.

in 'ase e5uili'riu oves to riht P in acid e5uili'riu oves to let 3

(ii! phenolphthalein

indicator colour chane occurs in rane o pH at the e5uivalence

point P O-/ 2

,2 can be scored inde)endentl$ e%en if indicator is incorrect./50

. acidic

>8e(H2O!3

>8e(H2O!)(OH!2

HP

>8e(H2O!3

H2O >8e(H2O!)(OH!2

H3O 2

Acce)t e+uations indicating t*e for#ation of

[e'H2O(1'OH(2]

[e'H2O(3'OH(3]

[e'H2O(2'OH(1]

4o not )enali5e Q./20

!. n(HCl! @ (*.,** + *.)*! @ *.*)* (ol!

n(NaOH! @ (*.2** + *.,*! @ *.*2* (ol!n(HCl!reainin@ (*.*)* - *.*2*! @ *.*3* (ol!

>HCl @

3*.*

*3*.*

@ *.,* (ol d-3

!

pH @ ,.* )

Award[2 max]for ust )H 7 &.0 wit*out working.


17/23

/50

". A>, 1'. #>, 11. C/10

12. K'@?NH>

?OH>

3

2

@ ,*-4.=)

P ,.=0 + ,*-)

>OH-

@!,*,***.,(

=).42

@ 4.22 + ,*-4

(ol d-3

!

pOH @ -lo,*(4.22 + ,*-4

! @ 3.3= P >H @

4

,4

,*22.4,***.,

@ 2.3= + ,*-,,

pH @ ,4 - 3.3= @ ,*. 4

Award[2 max]for correct final answer if no working s*own./40

13. (a! initial aount o HCl @ ,***

*.2)

+ ,.** + ,*-2

@ 2.)* + ,*-4

ol

a% initial aount o NH3@ ,***

*.)*

+ ,.** + ,*-2

@ ).** + ,*-4

ol

inal aount o NH4

and NH3'oth @ 2.)* + ,*-4

ol

inal >NH4 and >NH3 'oth @

3

4

,**.=)

,*)*.2

@ 3.33 + ,*-3

ol d-3

>OH-

@K'+?NH>

?NH>

4

3

+@K'@ ,*

-4.=)P,.=0 + ,*

-)

pOH @ 4.=) hence pH @ /.2) )

Award final two #arking )oints if *alf8e+ui%alence #et*od used.

('! a 'uer solution resists a chane in pH when sall aounts o

acid or 'ase are added to it

4o not acce)t descri)tion in ter#s of co#)osition of buffer.

when H is added it reacts with NH3to or NH4

when OH-

is added it reacts with NH4to or NH3and H2O 3

Acce)t e+uations for last two #arking )oints./!0

14. (i! NaCl is the salt o a stron acid and a stron 'ase P no h"drol"sis

with (Naand C,

-ion!

the CO32-

ions co'ine with Hro water to or a wea9 acid

leavin OH

-

ions P CO3

2-

H2O HCO3

-

OH

-

P O-/ 2

(ii! 8e3

has a sall radius and a hih chare P 8e3

has a hih

chare densit"

it ors 'onds with the OH-

ions ro water leavin Hions P

it increases the polarit" o the O-H 'ond (in the water liands! P

>8e(H2O!3

>8e(H2O!)(OH!2

Hetc 2

/40

15. #/10

16. A/10

1. A

/10

1!. (a! (i! CH3COOH(a5! H2O(l! CH3COO-

(a5! H3O(a5!

-

CH3COOH(l! H2O(l! CH3COO-

(a5! H3O(a5!


18/23

-

CH3COOH(a5! CH3COO-

(a5! H(a5!

,ust include .

9gnore state s$#bols. ,

(ii! Ka@,*-4.=

P ,.=4 + ,*-)

,.=4 + ,*-)@ 2**.*

H>2+

P >H @ *.**,0=pH @ 2.=3

Award [3] for correct final answer allow #ark for correct

con%ersion of [H] to )H e%en if [H

] incorrect. 3

('! (initial!>CH3COOH @ *.)** ol d-3

and! e5 >CH3COOH @ *.2** ol d-3

(initial!>CH3COO-

@ *.3** ol d-3

and! e5 >CH3COO-

@ *.3** ol d-3

Allow 0.02 #oles and 0.03 #oles instead of 0.200 and 0.300 #ol d#3

.

>H @Ka ?COOCH>

COOH?CH>

-3

3

@ ,., + ,*-)ol d-3P pH @ pKa lo>ACI$?

AR&?>

pH @ 4./4

Award[3 max]for correct final answer if no working s*own. 4

(c! (i acid added! CH3COO-

HQ CH3COOH

(i al9ali added! CH3COOH OH-

Q CH3COO-

H2O

/;)lanation #arks cannot be awarded wit*out e+uations.

Acce)t H OH

< H2O as OH

reacts wit* H

in t*e buffer to for# water. 2

/1'0

1". C>, 2'. C>, 21. A>, 22. C>,

23. (i! (Kw! @ >H>OH

- P (Kw! @ >H3O

>OH

-

4o not award #ark if [ ] o#itted or ot*er brackets are used. ,

(ii! >H increases% >OH

- decreases 'ut still soe present (Kwconstant! P

>OH-

cannot o to ero as e5uili'riu present P >OH-

@ >H

w

+

K

%

thus >OH-

cannot 'e ero P O-/ ,

(iii! (chanin & distur's e5uili'riu! endotheric reaction P orward reactionavoured P e5uili'riu shits to the riht

to use up (soe o the! heat supplied

Kwincreases (as 'oth >H Sand >OH

- increase! 3

(iv! (as >H increases! pH decreases P pH F =

=o #ark for #ore acidic.

inverse relationship 'etween pH and >HPpH @ -lo>H

PpH @ lo,*

?H>

,+

Acce)t [H3O] in )lace of [H]. 2

/0

24. (i! AcidJ H26O4-

'Conugate( base:H6O42-

=o #ark for =aH2>O1or =a2H>O1.


19/23

H26O4-

(a5! H(a5! H6O4

2-(a5!

Acce)t re%erse e+uation or reaction wit* water.

9gnore state s$#bols but e+uilibriu# sign is re+uired.

Acce)t OH

'ions( react wit* H'ions( to for# H2O. 3

(ii! stron 'asePOH-

replaced '" wea9 'ase (H26O42-

% and eect iniied! P

stron 'ase reacts with acid o 'uer P e5uili'riu in (i! shits in orward

direction

OH-(a5! H26O4-(a5! Q H2O(l! H6O42-(a5!9gnore state s$#bols acce)t e+uilibriu# sign.

Acce)t OH

added reacts wit* Hto for# H2O. 2

(iii! stron acidPHreplaced '" wea9 acid (H26O4

-% and eect iniied! P

stron acid reacts with 'ase o 'uer P e5uili'riu in (i! shits in

reverse direction

H(a5! H6O4

2-(a5! Q H26O4

-(a5!

Acce)t reaction wit* H3O.

9gnore state s$#bols. 2

/0

25. (i! NH3wea9(er! 'asePpartial dissociation

>OH-

F *.,(*! PpOH , (thus pH F ,3 P pH pOH @ ,4! 2

(ii! around pH @ )

Acce)t a %alue between 1 and 6.

stron acid-wea9 'ase titration% (thus acidic! P at e5uivalence point% NH4

present is acidic P NH4 NH3 H

2

(iii! NH3(a5! H2O(l! NH4(a5! OH-(a5!9gnore state s$#bols but e+uilibriu# sign re+uired.

K'@?NH>

?OH?>NH>

3

4+

2

(iv! >NH3 @ >NH4 ,

(v! pOH @ ,4.** - /.2) @ 4.=)

pK'(@ pOH! @ 4.=)

K'@ ,.=0 + ,*-)

9gnore units.

Award[3]for correct final answer. 3

(vi! optiuPost eectivePhihest 'uer capacit"P)* T-)* T 'uerPe5uall"

eective as an acidic 'uer and a 'asic 'uer P O-/ ,/110

26. A>, 2. C>, 2!. C>, 29. C[1

3'. (a! (i! stron acid copletel" dissociatedPionied a% wea9 acid partiall"

dissociatedPionied

HNO3(a5! Q H(a5! NO3

-(a5!

HCN(a5! H(a5! CN

-(a5!

9nsist on bot* arrows as s*own.

?tate s$#bols not needed.


20/23

Acce)t H2O and H3O. 3

(ii! Ka@>HCN

>CN>H +

Allow H3Oinstead of H

.

Ka@ ,*-/.2,

@ .,= + ,*-,*

2

(iii! >H

@

!,*0.*,*,=.(PHCN> ,*a K

@ 0., + ,*

-

Allow in t*e range !.&3 @ &06

to !.&6 @ &06

.

pH @ ).*/

-

pH @ 2,

(pKa- lo>HCN! P 2,

(/.2, - lo *.,*0!

@ ).*/

>H @ ,*

-).*/@ 0., + ,*

-

Allow in t*e range !.&3 @ &06

to !.&6 @ &06

.

9f e;)ression for [H] #issing but bot* answers correct award[3]

if one answer correct award[2].

assue >H FF *.,*0 P nelii'le dissociation 4

('! -it* H=O3J

aster rate o 'u''lePh"droenPas production

aster rate o anesiu dissolvin

hiher teperature chane

Acce)t o))osite argu#ent for HC=.

eference to s)ecific obser%ations needed.

Award[1]if 2 obser%ations gi%en but acid is not identified. 2 a

(c! (i! (nitric acid! =.) c3 ,

(ii! not valid as h"droc"anic acid reacts with sae volueP =.) c3 ,

(iii! 'rooth"ol 'lue P phenol red P phenolphthalein ,

(d! HNO3

(hiher conductivit" or solutions with sae concentration as! there areore ions in solution 2

/160

31. $>, 32. C>,

33. (a! (i! CH3CH2COOH H2O CH3CH2COO-

H3O

P CH3CH2COOH CH3CH2COO-

H

re+uired for #ark. ,

(ii! (pKaor propanoic acid @ 4.0=!

>H2@ *.,** +Ka

>H @ ,., + ,*

-3(ol d

-3! 2

('! s9etch to showJ


21/23

indicator rane 'etween pH 3.* and pH 4. (with "ellowL atpH 3.* and 'lueL at pH 4.!

initial pH o acid at 2./ U ,.* (when no KOH has 'een added!

halGe5uivalence point (does not need to 'e naed! at pH 4./

when ,2.) c3o KOH have 'een added

e5uivalence point at appro pH 0.)-/.* when 2).* c3o KOH(a5!

added

upper part o curve ro 2).*-)*.* c3added identical to oriinal

curve

Award[1]eac* for an$ t*ree )oints. 3 a/60

34. C>, 35. $(, 36. A>,

3. #>,

3!. (i! Ka@ .3,* + ,*-)

P .3, + ,*-)

Acce)t 6.3 @ &0B

,

(ii! wea9 (acid!

KaFF ,P sallKa 2

(iii! >H3O

P>H

@

*,*.*a K

>H3O

P>H

@ =./ + ,*

-4(ol d

-3!

pH @ 3.,*P3.,P3.,2

Award[3]for correct final answer of )H.

assue FF *.*,* (ol d-3

!P ioniation o water is insiniicant P

>CH)COOHinitial@ >CH)COOHa5P teperature 2) 7CP2/0 K 4

/0

3". #>, 4'. C>, 41. C>,

42. A>,

43. (i! /.)

Acce)t an$ %alue in t*e range .1.6. ,

(ii! titration involves a wea9 acid a% a stron 'ase

salt ored at e5uivalence point is 'asic due to h"drol"sis

A-

(a5! H2O(l! HA(a5! OH-

(a5!

9gnore state s$#bols. 3

(iii!,*.2)

,*.22,)).*

@ *.,3 (ol d

-3! 2

(iv! at hal neutraliation point% pH @ pKa

pKa@ ).3

Acce)t an$ %alue in t*e range B.2B.1.


22/23

Ka@ ).* + ,*-

(ol d-3

!

Acce)t calculations based on initial )H or on )H of salt. 3

(v! phenolphthalein

Acce)t t*$#ol)*t*alein.

Allow /C fro# 'a('i(. ,/1'0

44. HIn(a5! H(a5! In

-(a5!

colour A colour #

in presence o acidPH% e5uili'riu shits to let% colour A

in presence o 'asePOH-

% e5uili'riu shits to riht% colour # 3/30

45. (i! 'uer solution resists chane in pH

on addition o sall aount o acid or 'ase 2

(ii! ater iin >CH3COO-

@ >CH3COOH @ *.*)* ol d-3

Ka@ >HP pKa@ pH

pH @ 4.=

-orking #ust be s*own to score[3]

.Award[1]if 1.6 stated wit* no working. 3/50

46. acidic

>Al(H2O!3

(a5! >Al(H2O!)(OH!2

(a5! H(a5!

Acce)t AlCl3 3H2O < Al'OH(3 3HCl. 2

/20

4. (i! >H @

3

,4

,*20.,

,***.,

@ =.0, + ,*-,2

ol d-3

P pOH @ -lo,.20 + ,*-3

@ 2./*

pH @ (,4.* - 2./*! @ ,,.,Award[2]for t*e correct final answer 2

(ii! K'@?NH>

?OH?>NH>

3

48+

@ ,**.*

!,*20.,(P

**,20.*,**.*

!,*20.,( 2323

@ ,. + ,*-)

P,.4 + ,*-)

3/50

4!. A>, 4". $>,

5'. $>,

51. (a! (i! acidic a% >8e(H2O!3

is a wea9 acid

>8e(H2O!3

(a5! >8e(OH!(H2O!)2

(a5! H(a5! ,

DeCl3is acidicE is not acce)table.

(ii! neutral a%NaNO3P sodiu nitrate is ored ro stron 'ase

and stron acid P ions do not h"drol"se ,

(iii! al9aline a% CO32-is a wea9 'ase P

CO32-

(a5! H2O(l! HCO3-

(a5! OH-

(a5! ,

Award[1] onl$ for correct identification of solutions as acidic neutral and

alkaline onl$ wit*out e;)lanation.


23/23

('! nitroen a% sulur

9illsPhars ishPa5uatic lie in la9esPrivers

leachin o soils daaes plant liePtrees 3/60

52. (a! 2NH3(a5! H2O4(a5! (NH4!2O4(a5! 4

Acce)t correct e+uation wit* =H1OH instead of =H3n'H2?O1( 7 0.020&@0.&B0 '#ol(F

n'=H3( 7 6.03@&03

'#ol(F

[=H3] 7 0.21& '#ol d#3(F

Award[3]for t*e correct final answer for t*e concentration calculation.

('! 'roocresol reen

reaction o wea9 'ase and stron acid

pH rane o 'roocresol reen is 3.0 to ).4Poccurs at pH F = 3

(c! (i! K'@ ,*-4.=)

@ ,.=0+,*-)

K'@

?NH>?OHP>?NH>

?OH?>NH>3'

3

4K=

+

>OH-

@ ,2,.*,*=0., )

pOH @ 2.03 4

Award[4]for t*e correct final answer.

Allow /C for e;a#)le an$ correct con%ersion of [OH] to )OH.

(ii! a solution which resists chane in pH P chanes pH ver" slihtl"

when sall aounts o acid or 'ase are added

wea9 acid and its salt P wea9 acid and its con1uate 'ase 3

(iii! n(NH3! @ *.**)** (ol! a% n(HCl! @ *.**2)* (ol!

NH>NH> 34 =+

>OH-

@K'@ ,.=0+,*-)

(pOH @ 4.=) so! pH @ /.2) 'allow .2 to .3( 4

Award[4]for correct final answer.

Acce)t ot*er %alid #et*ods./1!0

Documents

Acids and Bases-HL