equilibria quiq
TRANSCRIPT
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1. A saturated solution of calcium hydroxide, Ca(OH)2(aq), has a pH of 9.6.
(a) rite an expression lin!in" hydro"en ion concentration and pH. #se this to calculate
the concentration of hydro"en ions in this solution.
(3)
($) (i) %he ionisation constant for &ater, K&' . * +mol2dm+6.
rite the expression for K&.
K&'
(1)
(ii) Calculate the concentration of hydroxide ions in the saturated solution of
calcium hydroxide.
(1)
(iii) Calculate the concentration of calcium hydroxide in the saturated solution.
(1)
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(i-) Calculate the solu$ility of calcium hydroxide in " dm+
.
/i-e your ans&er to three si"nificant fi"ures.
(1)
(-) 0u""est &hy your calculated -alue may differ si"nificantly from the -alue in
chemistry reference $oo!s.
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.........................................................................................................................
(1)
(c) An alternati-e method for findin" the solu$ility of calcium hydroxide is to titrate
cmof the saturated solution &ith hydrochloric acid of concentration . mol dm
+
.
Ca(OH)2(aq) 1 2HCl (aq) CaCl2(aq) 1 2H2O (l)
(i) Calculate the pH of the hydrochloric acid.
(1)
(ii) #se your ans&er to ($)(iii) and the information a$o-e to calculate the -olume of
hydrochloric acid needed to neutralise cmof the saturated calcium
hydroxide solution.
(3)
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(iii) 0!etch the titration cur-e for this reaction.
(2)
(i-) 0u""est &hy phenolphthalein is not a suita$le indicator for this reaction.
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(1)
(Total 15 marks)
2. n the Ost&ald process for the production of nitric acid, ammonia is oxidised at 9 3C o-er
a platinum4 rhodium alloy catalyst accordin" to the equation5
H(") 1 7O2(") O(") 1 6H2O(")
%he reaction is -ery exothermic.
(a) (i) hy do the concentrations of the su$stances in an equili$rium mixture remain
constant8
....
....
(1)
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(ii) 0tate &ith a reason the effect of an increase in pressure on this equili$rium
system.
....
....
....
(2)
($) %he mixture o$tained from the catalyst cham$er contains excess oxy"en.
rite the equation for the further reaction that occurs on coolin" this mixture.
....
(1)
(ii) 0ho&, $y means of an equation, ho& the product in ($) (i) is used to ma!e
nitric acid.
....
(2)
(c) (i) 0!etch a :axℓ
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(ii) #se your dia"ram and any necessary explanation to sho& ho& the presence of a
catalyst leads to an increase in reaction rate at the same temperature.
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....
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....
....
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(4)
(Total 12 marks)
3. (a) >efine the follo&in" terms.
(i) pH .....................................................................................................................
(1)
(ii) K& ......................................................................................................................
(1)
($) ?xplain the meanin" of the term strong, as applied to an acid or a $ase.
......
......
(1)
(c) Calculate the pH of the follo&in" solutions.
(i) HCl(aq) of concentration .2 mol dm+
.
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(1)
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(ii) aOH (aq) of concentration .@ mol dm+
(K&' + . * +
mol2dm
+6).
(2)
(d) HA is a &ea! acid &ith a dissociation constant Ka' 7.62 * +7
mol dm+
.
(i) rite an expression for the dissociation constant, Ka, of HA.
(1)
(ii) Calculate the pH of a . mol dm+
solution of HA.
(3)
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(e) A $uffer solution contains HA(aq) at a concentration of . mol dm+
, and its
sodium salt, aA, at a concentration of .6 mol dm+
. Calculate the pH of this
$uffer solution.
(3)
(Total 13 marks)
4. Consider the follo&in" equation5
20O21 O2 20O
2. moles of 0O2and . mole of O2&ere allo&ed to react in a -essel of -olume 6 dm.
At equili$rium .@ moles of 0Ohad formed and the pressure in the flas! &as 2 atm.
(a) (i) rite the expression for Kcfor this reaction $et&een 0O2and O2.
(1)
(ii) Calculate the -alue of Kc, &ith units.
(3)
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($) %he reaction $et&een 0O2and O2is exothermic. 0tate the effect on the follo&in", if
the experiment is repeated at a hi"her temperature5
(i) Kc..
(1)
(ii) the equili$rium position ....................................................................................
(1)
(c) 0tate the effect of a catalyst on5
(i) Kc..
(1)
(ii) the equili$rium position ....................................................................................
(1)
(d) (i) rite the expression for Kpfor the reaction $et&een 0O2and O2.
(1)
(ii) Calculate the mole fractions of 0O2, O2and 0Oat equili$rium.
(2)
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(iii) Calculate the partial pressures of 0O2, O2and 0Oat equili$rium.
(1)
(i-) Calculate the -alue of Kp, &ith units.
(2)
(Total 14 marks)
111. (a) %he electronic confi"uration of a co$alt atom can $e &ritten as ArBds
2.
/i-e the electronic confi"uratin of the Co1
ion.
......
(1)
($) (i)
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O2(") 1 2H1(aq) 1 2e
+ H2O2(aq) 1.6@
Co1
(aq) 1 e+
Co21
(aq) 1.@2
0uita$le reducin" a"ent ....
Geasonin" .....
.......
(3)
(ii) 0u""est twofactors that mi"ht pre-ent a reducin" a"ent from $ein" as effecti-e
as the electrode potentials mi"ht seem to su""est.
.......
.......
.......
.......
(2)
(c) (i) rite the formula of the hexaaquaco$alt() ion.
.......
(1)
(ii) /i-e an equation, in-ol-in" the hexaaquaco$alt()ion, to illustrate the process
of li"and exchan"e.
.......
(2)
(Total 9 marks)
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5. (a) A mixture of hydro"en iodide, hydro"en and iodine (all in the "aseous state)
esta$lishes dynamic equili$rium if a constant temperature is maintained.
2H (") H2(") 1 2(") H' 19.6 !I mol+
(i) ?xplain the meanin" of the term dynamic equilibrium.
............................................................................................................................
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............................................................................................................................
(2)
(ii) Ho&, if at all, &ould the proportion of hydro"en iodide present at equili$rium
chan"e if the temperature &ere to $e increased8 Iustify your ans&er.
............................................................................................................................
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............................................................................................................................
............................................................................................................................
(2)
(iii) %he reaction is catalysed $y metals such as "old and platinum. Ho&, if at all,
&ould the proportion of hydro"en iodide present at equili$rium chan"e if the
reaction &ere to $e catalysed8 Iustify your ans&er.
............................................................................................................................
............................................................................................................................
(1)
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($) Jart of an ener"y profile for this reaction is sho&n $elo&. t is not intended to $e to
scale.
Complete the profile sho&in"5
the productsK
the pro"ress of both uncatalysed and catalysed reactionsK
la$elled arro&s to indicate the acti-ation ener"ies of both the uncatalysed andcatalysed reactions.
(4)
(Total 9 marks)
. %hermochemical data, at 29@ L, for the equili$rium $et&een =inc car$onate, =inc oxide and
car$on dioxide is sho&n $elo&.
EnCO(s) EnO(s) 1 CO2(") MH
N' 1. !I mol
+
SNEnO(s)B ' 1.6 I mol
+L
+
SNEnCO(s)B ' 1@2. I mol
+L
+
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SNCO2(")B ' 12.6 I mol
+L
+
(a) (i) 0u""est reasons for the differences $et&een the three standard entropies.
............................................................................................................................
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............................................................................................................................
............................................................................................................................
(2)
(ii) Calculate the entropy chan"e for the system, MSN
system, for this reaction. nclude
the si"n and units in your ans&er.
(2)
($) Calculate the entropy chan"e for the surroundin"s, MSN
surroundin"s, at 29@ L, sho&in"
your method clearly.
(2)
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(c) (i) Calculate the total entropy chan"e for this reaction, MSN
total,at 29@ L.
(1)
(ii) hat does the result of your calculation in (c)(i) indicate a$out the natural
direction of this reaction at 29@ L8
Iustify your ans&er.
............................................................................................................................
............................................................................................................................
(1)
(d) (i) rite an expression for the equili$rium constant, Kp, for this reaction.
(1)
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(ii) 0tate ho& you &ould alter O? condition to increase the yield of car$on
dioxide from this equili$rium reaction.
Iustify your ans&er.
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(2)
(Total 11 marks)
!. %he reaction in the Ha$er Jrocess that is used to produce ammonia is a homo"eneous
dynamic equili$rium5
2(") 1 H2(") 2H(") H' +92 !I mol+
(a) 0tate the meanin" of the terms5
(i) dynamic equili$riumK
............................................................................................................................
............................................................................................................................
(2)
(ii) homo"eneous.
............................................................................................................................
(1)
($) /i-e, &ith a reason in each case, the effect of the follo&in" on the "osition of the
equili$rium a$o-e5
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(i) an increase inpressureK
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
(ii) an increase in temperature.
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(2)
(Total ! marks)
#. (a) :ethane reacts &ith steam in a re-ersi$le reaction. n industry this reaction, carried
out at a pressure of atm, is used to produce hydro"en for the manufacture of
ammonia
CH(") 1 H2O(") CO(") 1 H2(") H ' 12 !I mol+
(i) >efine the term "artial "ressure as applied to a "as mixture.
............................................................................................................................
............................................................................................................................
(1)
(ii) rite an expression for the equili$rium constant, Kp, for this reaction.
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(1)
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(iii) 0tate and explain the effect of increasin" the total pressure on the position of
this equili$riumK
............................................................................................................................
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............................................................................................................................
............................................................................................................................
(2)
($) 0tate the effect on the -alue of Kpfor this equili$rium of the follo&in".
(i) ncreasin" the total pressure.
............................................................................................................................
(1)
(ii) ncreasin" the temperature.
............................................................................................................................
(1)
(iii) Addin" a catalyst.
............................................................................................................................
(1)
(c) %here is a theory that methane, CH, constantly lea!s from the earths crust. %his is notnoticea$le on land $ut at the $ottom of a cold sea, such as off the Canadian coast, the
methane is trapped in a solid ca"e of &ater molecules.
CH(") 1 6H2O(s) CH(H2O)6B(s)
methane hydrate
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At +29 3C the equili$rium pressure of the methane is . !Ja.
(i) rite an expression for Kpfor this equili$rium.
(1)
(ii) >educe the -alue of Kpat +29 3C, statin" its units.
(1)
(iii) At 3C the equili$rium pressure of methane rises to 26 !Ja. hat does this
tell you a$out the effect of temperature chan"e on the position of equili$rium
and a$out the enthalpy chan"e for this reaction8
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
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(i-) 0ome people ha-e su""ested collectin" the methane hydrate from the $ottom of
the sea and allo&in" it to &arm up to 3C on $oard a ship. Comment on
&hether this &ould $e a useful method for collectin" methane.
............................................................................................................................
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(1)
(Total 12 marks)
9. ?thanoic acid, CHCOOH, is a &ea! acid &hich can $e used, &ith its salts, to ma!e $uffersolutions.
(a) ?xplain &hat is meant $y the term weak acid.
....................................................................................................................................
....................................................................................................................................
(1)
($) ?xplain &hat is meant $y the term bu$$er solution.
....................................................................................................................................
....................................................................................................................................
(2)
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(c) An aqueous solution of ethanoic acid of concentration . mol dm+
has a pH of 2.@.
0!etch, &ith care, ho& the pH chan"es durin" the titration of 27. cm. mol dm
+
aqueous ethanoic acid &ith aqueous sodium hydroxide of the same concentration.
( ,
( 2
( )
@
6
,
2
)) ( ) 2 ) . ) , ) 7 )
D o l u m e o f a l ! a l i a d d e d 4 c m
p H
.
(4)
(d) ndicate on your s!etch the portion of the cur-e &here the mixture is $eha-in" as a
$uffer.
(1)
(e) (i) rite an expression for the dissociation constant, Ka, for ethanoic acid.
(1)
(ii) ?xplain ho& the pKa of ethanoic could $e found from the "raph.
............................................................................................................................
............................................................................................................................(2)
(Total 11 marks)
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