Equilibria Quiq

7/24/2019 Equilibria Quiq

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A2 CHEMISTRY EQULIBRIA SAHAM

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.

.........................................................................................................................

.........................................................................................................................

(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.

..........................................................................................................................

..........................................................................................................................

(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 :ax&ell;


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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.

....

....

....

....

....

....

(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.

............................................................................................................................

............................................................................................................................

............................................................................................................................

(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.

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................

(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.

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................

(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.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

(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.

............................................................................................................................

............................................................................................................................

............................................................................................................................

(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

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................

(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.

............................................................................................................................

............................................................................................................................

............................................................................................................................

(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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Equilibria Quiq