Uncertainty calculation for rate of reaction

Uncertainty calculation for rate of reaction, iodine and sulfur clock kinetics

1. KineticsonIodineClockReactionandUncertaintycalculation
Clickheretoview
Iodineclockreactionhasmanyversions:
Oxidizingagent-H2O2,KIO3,NaIO3,Na2S2O8
Reducingagent-KI,Na2S2O3,NaHSO3,VitaminC
Starchisneed.Blueblackcolourationisseen.
Introductiononsulfurclockreactionanduncertaintycalculation
Thiosulfateionsreactinacid,toproduceaprecipitateofsulfuraccordingtoeqn:
S2O3
2-
(aq)+2H
+
(aq)H2O(l)+S(s)+SO2(g)
Rateofrxnisfollowedbymeasuringtimetakenforafixedamountofsulfurtobeproduced.
Materialsandchemicals
SodiumthiosulfatesolutionNa2S2O3(aq),0.05M Stopwatch
HydrochloricacidHCl(aq),2.0M Whitepaper
Conicalflask,100cm
3
Procedure
PartAEffectofchangeinconcentration
1.Measure5cm
3
of0.05Msodiumthiosulfatesolutionintoaconicalflask.
2.Markacrossonapieceofwhitepaper.Placeflaskonit
3.Measure5cm
3
of2MHCIandaddtheacidtothethiosulfate.Starttimingtherxn.
4.LookdownverticallythroughthesolutionandtimehowlongittakesforthecrosstoJUST
disappear.Stoptimingthereaction.
5.Repeatstep1–5withthevolumeofsodiumthiosulfatesolutionandwaterintable1below.

2. Conc
Na2S2O3
Time/s
Trial1
±0.01
Time/s
Trial2
±0.01
Time/s
Trial3
±0.01
Averagetime Rate
0.05 102.96 103.23 114.80 107.00 0.00046
0.10 45.43 44.08 38.35 42.62 0.0023
0.15 27.36 27.13 26.36 26.95 0.0055
0.20 18.06 18.57 17.53 18.05 0.0111
0.25 15.26 15.44 16.88 15.86 0.0158
Datacollection:
ForConcNa2S2O3,threetrialswereperformedandresultsshown:
1
st
method:(%Uncertainty)
TimetakenforXtodissapear/s
Conc0.05MNa2S2O3
Trial1 Trial2 Trial3
102.96s 103.23s 114.80s
Averagetime= s107
3
80.11423.10396.102


Rate=
timeAverage
Conc
.
=
107
05.0
=0.00046Ms
-1
Uncertaintycalculation:
Averagetime±0.01=(107±0.01)s
%uncertaintytime= %093.0%100
107
01.0

Rate=
timeAverage
Conc
.
%Rate=%Conc+%averagetime(assumingconciscorrect)
%Rate=0.093%
Rate=0.00046±0.093%
Rate=0.00046±0.000000047(Toosmall)Poorchoice!!!!!!

3. 2
nd
method:(Usingstandarddeviation)
TimetakenforXtodissapear/s
Conc0.05MNa2S2O3
Trial1 Trial2 Trial3
102.96s 103.23s 114.80s
Rate1=
1.time
conc
= 00049.0
96.102
05.0

Rate2=
2.time
conc
= 00048.0
23.103
05.0

Rate3=
3.time
conc
= 00043.0
80.114
05.0

Averagerate=
3
3.2.1. rateraterate 
= 00047.0
3
00043.000048.000049.0


Standarddeviationforrate=0.000032
Averagerate±sd=0.00047±0.000032(Goodchoice)
3
rd
method:(Max-Minmethodfortime)
TimetakenforXtodissapear/s
Conc0.05MNa2S2O3
Trial1 Trial2 Trial3
102.96s 103.23s 114.80s
Uncertaintyfortime=UsingMaxtimeandMintime
Mintime=102.96s
Maxtime=114.80s
Uncertaintytime=Range=
2
)( MinMax
= s92.5
2
)96.10280.114(


Averagetime= s107
3
80.11423.10396.102


Averagetime±time=(107±5.92)s
%uncertaintytime= %5.5%100
107
92.5

Rate=
timeAverage
Conc
.
=
107
05.0
=0.00046Ms
-1
%Rate=%Conc+%averagetime(assumingconciscorrect)
%Rate=%averagetime=5.5%
Rate=0.00046±5.5%
Rate=0.00046±0.000026(Goodchoice)

4. 4
th
method:(Max-Minmethodforrate)
TimetakenforXtodissapear/s
Conc0.05MNa2S2O3
Trial1 Trial2 Trial3
102.96s 103.23s 114.80s
Rate1=
1.time
conc
= 00049.0
96.102
05.0

Rate2=
2.time
conc
= 00048.0
23.103
05.0

Rate3=
3.time
conc
= 00043.0
80.114
05.0

Averagerate=
3
3.2.1. rateraterate 
= 00047.0
3
00043.000048.000049.0


MaxRate=0.00049
MinRate=0.00043
Uncertaintyrate=Range= 00003.0
2
)00043.000049.0(
2
)(



MinMax
Averagerate±rate=0.00047±0.00003(Consistentandgoodchoice)
5
th
method:(MaxandMinmethod)
TimetakenforXtodissapear/s
Conc0.05MNa2S2O3
Trial1 Trial2 Trial3
102.96s 103.23s 114.80s
Averagetime= s107
3
80.11423.10396.102


Rate=
timeAverage
Conc
.
=
107
05.0
=0.00046Ms
-1
Maxrate=
timeMin
Conc
.
= 00048.0
96.102
05.0
 Ms
-1
Minrate=
timeMax
Conc
.
= 00043.0
80.114
05.0
 Ms
-1
Uncertaintyrate=Range= 000025.0
2
)00043.000048.0(
2
)(



MinMax
Rate±rate=0.00046±0.000025(Goodchoice)

5. KineticsonIodine/SulfurClockrxnandUncertaintycalculation
Part1:
Introduction
Thiosulfateionsreactinacid,toproduceaprecipitateofsulfuraccordingtoeqn:
S2O3
2-
(aq)+2H
+
(aq)H2O(l)+S(s)+SO2(g)
Rateofrxnisfollowedbymeasuringtimetakenforafixedamountofsulfurtobeproduced.
Materialsandchemicals
SodiumthiosulfatesolutionNa2S2O3(aq),0.200M Stopwatch
HydrochloricacidHCl(aq),2.0M Whitepaper
Conicalflask,100cm
3
Procedure
PartAEffectofchangeinconcentration
6.Measure5cm
3
of0.2Msodiumthiosulfatesolutionintoaconicalflask.
7.Markacrossonapieceofwhitepaper.Placeflaskonit
8.Measure5cm
3
of2MHCIandaddtheacidtothethiosulfate.Starttimingtherxn.
9.LookdownverticallythroughthesolutionandtimehowlongittakesforthecrosstoJUST
disappear.Stoptimingthereaction.
10.Repeatstep1–5withthevolumeofsodiumthiosulfatesolutionandwaterintable1below.
Table1Volsodiumthiosulfatesolution(Volineachbeakeris5cm
3
befaddingtogether)
TrialVolof0.2MNa2S2O3
(cm
3
)
Volof
deionized
water(cm
3
)
Conc
Na2S2O3/M
(5mleach)
Conc
HCI/M
(5mleach)
1 5 0 0.20 2
2 4 1 0.16 2
3 3 2 0.12 2
4 2 3 0.08 2
5 1 4 0.04 2
TrialVolof0.2MNa2S2O3
(cm
3
)
Volumeof
deionized
water(cm
3
)
FinalConc
Na2S2O3/M
(5mleach)
FinalConc
HCI/M
(5mleach)
1 5 0 0.10 1
2 4 1 0.08 1
3 3 2 0.06 1
4 2 3 0.04 1
5 1 4 0.02 1
Questions.
Plotagraphofconcentrationofthiosulfatesolutionagainstthereciprocalofthetime(
t
1
).The
reciprocaloftimeisameasureoftherateofthereaction.

6. Part2
Determineactivationenergyofareaction.
Introduction.(Iodineclockreaction)
Peroxodisulphate(VI)ionsreactinacid,toproduceiodine,I2accordingtoeqn:
S2O8
2-
(aq)+2I
-
(aq)2SO4
2-
(aq)+I2(aq)
2S2O3
2-
+I2→S4O6
2-
+2I
-
RateofrxncanbefollowedbymeasuringthetimetakenfortheI2formingtoreactwithstarch,
appearanceofblueblack.AmtS2O3
2-
addedtoindicatecertainamtofI2hastobeformedbefore
excessI2reactswithstarch.Experimentexamineshowratevarieswithtemperatureforafixed
concentrationofallsolutions.
Materialsandchemicals
SodiumthiosulfateNa2S2O3,0.001M Stopwatch
Kl,0.5M Whitepaper
SodiumperoxodisulphateNa2S2O8,0.05M
Waterbath
0.2%starch
Procedure
PartBEffectoftemperature
1.Measure2mlof0.001MsodiumthiosulfatesolutionintoatesttubeA.
2.Add1ml0.5MKItosametesttubeA,and2dropsstarch.
3.Add1ml0.05MNa2S2O8,totesttubeB.
4.IncubatetesttubeAandBatroomtemperaturefor10mins.
5.After10mins,poursolutionfromtesttubeBtoA.Recordtimebluecolourationtoform
6.Repeatstep1–5attemperatureof4,30,50and70°C.Adjusttempbyahotwaterbath.
TestTubeA TestTubeB
Temp/C Totalvol
1ml,0.5MKI
2ml,0.001MS2O3
0.5ml0.2%starch
Conc0.05MNa2S2O8
1mleach
Time/s Rate=
1/Time
4 2.5 1
RT 2.5 1
30 2.5 1
50 2.5 1
70 2.5 1

7. Temp/K Totalvol
1ml,0.5MKI
2ml,0.001MS2O3
0.5ml0.2%starch
Conc0.05MNa2S2O8
1mleach
Time/s Rate=
1/Time
277 2.5 1
RT 2.5 1
303 2.5 1
323 2.5 1
343 2.5 1
Questions
1.Rateofrxnisgivenbyreciprocalofthetime(
t
1
).Usingyourresultscollected,
-PlotagraphofTemp/CvsRate(
t
1
).
-PlotagraphofTemp/KvsRate(
t
1
).
2.PlotanothergraphoflnkverticalvsTemp(
T
1
)horizontal.TempinKelvin.
3.Calculateactivationenergy,EainkJmol
-1
4.Howdoesrateofreactionchangewithtemperature?(Whatisyourassumptions?)

8. Part3
Determineorderreactionbetweeniodineandpropanoneinaqueoussolution.
Introduction.(Iodinationofpropanone)
Propanonereactwithiodine,I2accordingtoeqn:Reactioncatalyzedbyacid,H
+
I2+CH3COCH3CH3COCH2I+I
-
Rate=k[CH3COCH3]
x
[I2]
y
[H
+
]
z
RateofrxndeterminebychangeofabsorbanceI2overtime.Asintensity/concentrationofI2
decreases,absorbancedecreases.HowchangingconcCH3COCH3,H
+
andI2affectrateofrxn?
Materialsandchemicals
Acetone,7M Stopwatch
I2,0.002M Cuvette
HCI,2M
Colorimeter
Visiblespec
Micropipette
Procedure
Effectofacetoneconcentrationonabsorbance(at520nm)
1.Measure2mlofwaterincuvette.Pressblanktocalibrate.Removeitout.
2.PlacecuvettecontainingI2solutionintovisiblespec.Scancompletespectrumto
determineʎmaxwhichabsorbanceismax.(Around520nm)
3.Pipette1.5mlwater,0.5mlHCI,0.5mlI2tocuvette.Presscollectforabsorbancereading
4.Pipette0.5ml,7Macetonetocuvette.Mix.Reactionstartwhenacetonemixesand
absorbancestarttodecreasewithtime.
5.Saveeverylatestrun.
6.Repeatstep1-5withdifferentacetoneconc(3.5M,1.75M,0.875M,0.4375M)
7.Measurechangeofabsorbanceovertimefordifferentacetoneconcentration.(5s)
8.Plotacetoneconcagainstaveragerateofrxn.Averagerateofrxn=
time
Absorbance

9. Part4
Determineorderreactionbetweeniodineandpropanoneinaqueoussolution.
Introduction.(Iodinationofpropanone)
Propanonereactwithiodine,I2accordingtoeqn:Reactioncatalyzedbyacid,H
+
I2+CH3COCH3CH3COCH2I+I
-
Rate=k[CH3COCH3]
x
[I2]
y
[H
+
]
z
RateofrxndeterminebychangeofabsorbanceI2overtime.Asintensity/concentrationofI2
decreases,absorbancedecreases.HowchangingconcCH3COCH3,H
+
andI2affecttherateofrxn?
Materialsandchemicals
Acetone,7M Stopwatch
I2,0.002M water
HCI,2M
Colorimeter
Micropipette
Procedure
Effectofacetoneconcentrationonabsorbance(at520nm)
1.Measure5mlofwaterincuvette.Pressblanktocalibrate.Removeitout.
2.Pipette1.5mlwater,0.5mlHCIand0.5mlI2intocuvette.
3.Insertcuvettetocolorimeter,andpipette0.5ml,7Macetonetocuvette.Mix,press
collect.
4.Recordabsorbancechangeovertimewithstopwatch.
5.Repeatstep1-4withdifferentacetoneconc(3.5M,1.75M,0.875M,0.4375M)
6.Measurethechangeofabsorbanceovertimefordifferentacetoneconcentration.(5s)
7.Plotacetoneconcagainstaveragerateofrxn.Averagerateofrxn=
time
Absorbance