rate of reaction between sodium thiosulphate courswork chemistry .i..docx

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Stephano Pina

Rate of reaction between sodium thiosulphate

and hydrochloric acid investigation

Contents:

Aim………………………………………………. 2

Chemical ideas ………………………………………………. 2-7

Ris assessment……………………………………………….!

"ethods……………………………………………….#

"aing the standard solution……………………………………………….#

$%periment &……………………………………………….&'-&2

$%periment 2……………………………………………….&(-&)

$%periment (……………………………………………….&*-&!

$%periment+……………………………………………….&!-2'

$%periment )……………………………………………….2'-22

Conclusion……………………………………………….2(

$valuation……………………………………………….2+-27

References……………………………………………….2!



Stephano Pina

Aim:

In this investigation I aim to fnd out the rate o reaction between

sodium thiosulphate and hydrochloric acid and the eect o dierentvariables on it. The reaction consists on the ormation o sulphur as a

precipitate and the rate depends on the time taen or it to orm. I will

use a dierent range o methods and techni!ues to show the

in"uence o some variables on the rate o reaction. I will investigate

the concentration# temperature# catalysts and other acids aect on

the rate reaction. In order to achieve that or the concentration I will

alter concentration o both reactants by diluting them and use the

graphs to determine the order with respect to each reactant# and rom

this I hope to write the rate e!uation and conclude who manymolecules o each reactant are in the rate determining step. $or the

temperature I am hoping to try the e%periment at dierent

temperatures by using water baths and woring out i the rate

increase or decrease with the increase in temperature. $rom this data

I e%pect to plot a graph o ln&'(temp) against '(time wor out the

gradient and use Arrhenius e!uation to calculate an activation energy

or the reaction. $or the catalyst I am looing to try dierent transition

metal catalysts# show their in"uence on the rate and determine which

one is the more eective on speeding up the reaction. And fnally I am

hoping with dierent acids show how the rate ormation o sulphur

precipitate changes with other acids and which one speed the

reaction up or slow it down.



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*hemical ideas:

+ The rate o reaction:

The rate o reaction is the measurement o how !uic a reaction

happens. It,s defned as the change in the amount o reactants or

products per unit o time or the time taen or the reactants to be

used up and the products to orm. Any actor that can increase the

number o successul collisions can increase the rate reaction. -e

have dierent methods to measure the rate o reaction on this

investigation I am going to use the disappearing cross method.

+isappearing cross:

This method measures the time taen or a precipitate to orm. A

glass o beaer is placed on top o a piece o paper with a blac cross

on it. The reactants are added to the beaer and a stopwatch started.

The stopwatch is then stopped when the cross is no longer visible.

This indicates the end point o the reaction with the precipitated ully

ormed.

+Activation energy:

The activation energy o a chemical reaction is the minimum energy

that must be input to a chemical system with potential reactants to

cause a chemical reaction. Activation energy can also be defned as

the minimum energy re!uired to start a chemical reaction.



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+Temperature on reaction rate:

$or a reaction to happen particles need to collide with enough energy#

increasing the temperature maes particles move aster which meansthat they will collide more re!uently and with more energy to mae

the reaction happen. Thereore we can say that increasing the

temperature increases the rate o reaction due to more collisions with

enough energy. This amount o energy needed to mae the reaction

happens is called activation energy. The /olt0mann distribution curve

&graph below) represents the distribution o molecular energies at a

constant temperature.

+*oncentration on reaction rate:

The rate o reaction measures the re!uency o successul collisions

between particles. The concentration is the amount o moles per unit

o volume o a chemical# so the more concentrated a chemical is the

more moles it will have thereore the more particles. Increasing the

number o particles in the same space will increase the the amount o successul collisions that occur that will also lead to an increase on

the reaction rate to increase. This means that as the concentration o

reactants increase rate o reaction will increase because o the



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increase o successul collisions due to the increase in particles.

+1ate e!uation and orders:

The rate e!uation lins the concentration o the reactants with the

rate o reaction. The rate o reaction depends on what is being

measured we could measure the rate at which reactants disappear or

the rate o which products are ormed. The overall rate e!uation

ollows:

-here A and / are the reactants or products depending on what is

being measured. The order o reaction tells you how the a reactantconcentration aects the rate. This can only be wored out rom

e%periment not rom chemical e!uations. The order can be ound by

using graphs either by plotting a concentration(time or

rate(concentration graph. The shapes o these will then allow you to



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determine the order.

+*atalyst:

A catalyst is a substance that,s speeds up a reaction but remains

unchanged at the end o the reaction. The catalyst provides an

alternative route or the reaction to happen with a lower activationenergy allowing more successul collisions at a lower energy and this

as a conse!uence maes the rate o reaction speed up. There are two

types o catalysts# homogeneous and heterogeneous. 2omogeneous

is the catalyst that is in the same state as the reactants whereas

heterogeneous catalysts are in a dierent state to the reactants.



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+Transition metals catalytic proprieties:

3any o the transition metals behave as catalysts this is due to their

variable o%idation number# which gives the capacity to tae and give

electrons and o%idi0e or reduce things easily. The ability o transition

metals to be in a variety o o%idation states# the ability to interchange

between the o%idation states and the ability to orm comple%es with

the reagents and be a good source or electrons mae transition

metals good catalysts.

+Acidity:

The strength o an acid or acidity is the ability o the acid to donate a

proton &24). A strong acid tends to dissociate completely in a solution

while a wea acid only dissociate partially.



Stephano Pina

1is assessment:

+ '.& moldm-( ,ydrochloric acid: 5ow ha0ard# may cause harm

to eyes. 6ye protection and lab coat must be worn and small

amounts o it can be poured down the sin with water.+ & moldm-( odium thiosulphate: 5ow ha0ard but can cause

irritation in some cases eye protection and lab coat must be

worn.+ ulphur dio%ide diluted in water/: low ha0ard however the

given o gas is to%ic. 7se eye protection and lab coat and avoid

inhaling the umes i possible by woring on a ume cupboard or

wearing a aceguard.+ olid ulphur: low ha0ard. 6ye protection and lab coat must

be worn. Solid sulphur only causes minor ha0ard unless it is

heated. 8nly small !uantities can be put down the sin because

sulphur doesn,t dissolve in water.+ odium chloride: 5ow ha0ard. 5ab coat and eye protection

must be worn.+ '.& moldm-( 0ron 000/ chloride: low ha0ard. Still can cause

some irritation so lab coat and eye protection must be worn.+ Copper 00 sulphate: low ha0ard. 6ye protection and lab coat

must be worn.+ '.& and '.) moldm-( 0ron 000/ 1itrate: *an cause sin and

eye irritation. 6ye protection and lab coat must be worn.+ '.& moldm-( ulphuric acid: 5ow ha0ard. It may still cause

harm in the eyes or in a cut. 6ye protection and lab coat must

be worn.+ '.& moldm-( phosphoric acid: 5ow ha0ard. *an cause harm

on eyes. -ear lab coat and eye protection. *an be dispose

down the sin with lots o water.+ '.& moldm-( "ethanoic acid: 5ow ha0ard. *an be irritant

when in contact with eyes. 5ab coat and eyes protection must

be worn.+ '.& moldm-( 1itric acid: Irritant or eyes and sin. 5ab coat

and eye protection must be worn.+ '.& moldm-( ropanoic acid: low ha0ard. *an cause eye

irritation. 6ye protection and lab coat must be worn.+ 3ater: no riss.

8ther precautions:

+Any solution on poly bottle need to be labeled.



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+5ong hair must be tied bac.

+Apparatus must be rinsed and washed.

+9o to%ic products can go down the sin with water but all to%ic

products must go in the waste bottle.

3ethods:

"aing of standard solution of sodium thiosulphate:

6!uipment list:

Solid sodium thiosulphate

istilled water

'cm; beaer

' cm; volumetric "as

/alance &< d.p)

$unnel

3agnetic stirrer

"aing the standard solution:

$irst step is to calculate the mass o solid Sodium thiosulphate needed

to produce the volume needed in this case 'ml.

3oles: ' % '('= .' mol

3r o sodium thiosulphate: <>?.'?

3ass needed= .' % <>?.'?= <>.?< &<dp)

') 7sing a 'cm; beaer weigh out <>.?<g o sodium

thiosulphate# add about @cm; distilled water and use a

magnetic stirrer to mi% the solution together until all the solid is

dissolved.<) 7sing a unnel transer the solution made into the 'cm;

volumetric "as washing both the beaer and the unnel into

the volumetric "as so no solution is lost.;) Top up the volumetric "as to the 'cm; line with distilled

water. 3ae sure the bottom o the meniscus is resting on the

line. Then put the stopper on the top and shae it well to mi% allthe content eeping your thumb frmly on the stopper.



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>) Transer the solution to a poly bottle# label it maring the

concentration and volume and store it in a sae place to use it

when needed.

$%periment &:

Changing the concentration of sodium thiosulphate:

In this e%periment I used a disappearing cross method and changed

the concentration o sodium thiosulphate. -ith the recorded data I

plotted a concentration(time graph and a rate(concentration graph.

-ith this I hope to wor out the order o reaction with respect to

sodium thiosulphate and use it to later produce a rate e!uation.

6!uipment list:

'@cm; 2ydrochloric acid .' moldm+;

cm; Sodium thiosulphate solution 'moldm+;

Bcm; istilled water

;% 'cm; pipettes

;% '@cm; beaers

@% @cm; beaers

@% test tubes

/lac cross

Stopwatch

3ethod:

') $ill three dierent '@cm; beaers with sodium thiosulphate#

hydrochloric acid and water.

<) 7sing a 'cm; pipette fll @ @cm; beaers with 'cm; o 2*land fll @ test tubes with the amount o sodium thiosulphate and

distilled water shown in the table below using the other two

pipettes. 5abel the test tube ' to @ according to the e%periment

number.

6%pt -ater(cm; 'moldm+;

Sodium

thiosulphate(cm;

.'moldm+;

2ydrochloric

acid(cm;

' ' '



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< < ? '

; > B '

> B > '

@ ? < '

;) Place the frst beaer containing hydrochloric acid over the

blac cross and add test tube ' to it at the same time start the

stopwatch and swirl the solution to mi% the contents together.

1ecord the time taen or the cross to disappear in a table o

results. 1epeat this process mi%ing the other test tubes with the

rest o the beaers containing hydrochloric acid.>) 1epeat the process < times and also record the results.



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1esults:

6%pt Time'&s) Time<&s) Time;&s) Timeave&s)

' '@.<@ '>.? '>.> '@.;

< '.' '?.C? '?.?< '?.

; <C.B< <C.B <B.< <C.''

> ;C.<? ;B.B ;C.< ;?.

@ C>.C@ C@.< C>.' C>.?

Analysis:

1ate='(time

e%pt 1ate

' .BB@

< .@<

; .;B

> .<B;

@ .';>

$inding the concentration o each e%periment:

6%pt': n=' % &'(') =.'mol

6%pt<: n=' % &?(') = .?mol

6%pt;: n=' % &B(') = .Bmol

6%pt>: n=' % &>(') = .>mol

6%pt@: n=' % &<(') = .<mol

8verall concentration= moles(total volume

6%pt': n=.'( &<(') = .@moldm+;

6%pt<: n=.?( &<(') = .>moldm+;

6%pt;: n=.B( &<(') = .;moldm+;

6%pt>: n=.>( &<(') = .<moldm+;



Stephano Pina

6%pt@: n=.<( &<(') = .'moldm+;

I have then used this data to plot a concentration(time graph and a

rate(concentration graph &graphs are attached to the page).

/y analysing the concentration(time graph we can see that the hallie o sodium thiosulphate is constant o ;'s# which indicates that

sodium thiosulphate should be frst order. The rate(concentration

graph also shows that the rate is directly proportional to the

concentration we can then conclude that sodium thiosulphate has a

frst order D9a<S<8;E'.

$%periment 2:

Changing the concentration of hydrochloric acid

In this e%periment I used a disappearing cross method and changed

the concentration o hydrochloric acid. I then used the data to I plot a

concentration(time graph and a rate(concentration graph. -ith this I

hope to wor out the order o reaction with respect to hydrochloric

acid and write a rate e!uation or the reaction.

6!uipment list:

'@cm; o ' moldm+; Sodium thiosulphate

cm; o .' moldm+; 2ydrochloric acid

Bcm; distilled water

;% 'cm; pipettes

;% '@cm; beaers

@% @cm; beaers

@% test tubes

/lac cross

Stopwatch

3ethod:

') $ill three dierent '@cm; beaers with sodium thiosulphate#

hydrochloric acid and water.

<) 7sing a 'cm;

pipette fll @ @cm;

beaers with 'cm;

o sodiumthiosulphate and fll the @ test tubes with the amount o



Stephano Pina

hydrochloric acid and distilled water shown in the table below

with the other two pipettes. 5abel the test tube '+@ in relation to

the amount o solutions you have put in them.

6%pt -ater(cm; 'moldm+; Sodium

thiosulphate(cm;

.'moldm+; 2ydrochloric

acid(cm;

' ' '

< < ' ?

; > ' B

> B ' >

@ ? ' <

;) Place the frst beaer containing sodium thiosulphate over the

blac cross and add test tube ' to it at the same time start the

stopwatch and swirl the solution to mi% the contents together.

1ecord the time taen or the cross to disappear in a table o

results. 1epeat this process by mi%ing the rest o the beaers

with the other test tubes recording the time taen.>) 1epeat the process < times and also record the results.

1esults:

6%pt Time'&s) Time<&s) Time;&s) timeave&s)

' ';.? '>.< '>.<< '>.C

< 'B.' '@.C< '@.C@ '@.?;

; '?.< '?.?B '?.C@ '?.?>

> <>.C <>.< <>.'@ <>.'>

@ ;?.< ;C.C ;C.< ;C.C



Stephano Pina

Analysis:

1ate= '(time

6%pt 1ate

' .C''

< .B;<

; .@>

> .>'>

@ .<B;

$inding the concentration o each e%periment:

6%pt': n=.' % &'(') =.'mol

6%pt<: n=.' % &?(') = .?mol

6%pt;: n=.' % &B(') = .Bmol

6%pt>: n=.' % &>(') = .>mol

6%pt@: n=.' % &<(') = .<mol

8verall concentration= moles(total volume

6%pt': n=.'( &<(') = .@moldm+;

6%pt<: n=.?( &<(') = .>moldm+;

6%pt;: n=.B( &<(') = .;moldm+;

6%pt>: n=.>( &<(') = .<moldm+;

6%pt@: n=.<( &<(') = .'moldm+;

I have then used this data to plot a concentration(time graph and a

rate(concentration graph &graphs are attached to the page).

/y analysing the concentration(time graph we can see that hal lie o

hydrochloric acid is not constant &'sF '@.@). This dierence in hal lie

can be the evidence that hydrochloric acid isn,t frst order since frst

order reactants have constant hal lie. /ut rom the

rate(concentration graph we can see that the rate is directly

proportional to the concentration indicating the hydrochloric acid has

a frst order. So by analysing my results and consulting my notes and



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because the dierence between the time o the hal lie &;.@s) is small

we can then assume that this dierence is due to errors on the

e%periment that I will later comment on the evaluation section. -e

can then conclude that hydrochloric acid is frst order D2*lE '. $rom the

previous e%periment we now that sodium thiosulphate is also frstorder# the rate o reaction is then frst with respect to each reactants.

-hich implies that the rate e!uation or this e!uation can be written

as r45,Cl6&51a22(6&.

$%periment (:

Changing temperature:

In this e%periment I used a disappearing cross method and tried the

e%periment at dierent temperatures. -ith the results I e%pect to

investigate the eect o the temperature on the reaction rate by

plotting a temperature(rate graph and a time(temperature graph. I

will also plot a ln&'(time)(&'(temperature) and use the Arrhenius

e!uation to fnd the activation energy o the reaction.

6!uipment list:

'cm; o .'moldm+; 2ydrochloric acid

Bcm; o ' moldm+; Sodium thiosulphate

>cm; distilled water

;% 'cm; pipettes

<% boiling tube

'% @cm; beaer

/lac cross

Stopwatch

Thermometer

>% <@cm; beaers

>% -ater baths &set to ;o# >o# @o# Bo)

3ethod:

') Into @ boiling tubes measure out 'cm; o hydrochloric acid

and place > o these into the water baths# one in each water

bath. Into another fve boiling tubes measure out ?cm; o



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water and <cm; o sodium thiosulphate and place > o them

into each o the our water baths.<) uring the time that the boiling tubes are in the water bath

add the boiling tube that is not in the water to a @cm;

beaer and place it on top o a blac cross. Put a

thermometer in the beaer then add the sodium thiosulphate

and water and start the stopwatch. 8nce the cross has

disappeared record the time and temperature.;) Tae the hydrochloric acid test tube in the frst water bath

and transer it to a @cm; beaer and place it on top o a

blac cross. Put a thermometer in the beaer then tae the

sodium thiosulphate and water solution on the water bath

and add it to the beaer. 8nce the cross has disappeared

record the time and temperature.

>) 1epeat stage ; or the beaers on the rest o the waterbaths.

@) 1epeat stages '+> again and record the results.

1esults:

Temperature&o*) Time'&s) Time<&s) timeave&s)

<; B?.@> C.; B.<

; >C.?> >?.< >C.;

;C ;<.?' ;<.C@ ;<.C?

>B '.?C <.; '.@

@C ';.<@ ';.;> ';.;

Analysis:

e%pt rate

' .'>>

< .<

; .;@

> .@'

@ .C@'



Stephano Pina

$rom the e%periment and analy0ing temperature(rate and a

time(temperature graphs we can see that the time o reaction

decreases as the temperature increases# that means that rate

decreases when temperature goes up. -e can say that there is a

positive correlation between temperature and rate and a negativecorrelation between time and temperature. This means that by

increasing the temperature we increase the speed o the reaction and

thereore the rate. The higher temperature the aster the reaction

since the particles have more energy and are colliding more. -e can

then calculate the activation energy needed or the reaction to occur

using the ln&'(time)(&'(temperature) graph.

Activation energy= gradient % Ggas constant

5n&'(time) Temperature&H) '(T % '

;

+>.<> <B ;.;?

+;.?C ;; ;.;

+;.@ ;' ;.<;

+<. ;' ;.';

+<.@ ;; ;.;

$rom the graph:

radient= &+<.@4>.<)( &;.'%'+;+;.;C%'+;) = +>C<<

6a= gradient % G gas constant = +>C<< % ?.;' = ;<>' Jmol+'

;<>' Jmol+' is the activation energy that means that a particle should

have a minimum o ;<>'J in order to collide successully and cause

the reaction to happen.

$%periment +:

Adding a catalyst:

In this e%periment tried using dierent catalyst. -ith this I hope to

see their eect on the rate reaction and determine which one is more

eective on speeding the reaction up by putting the date on a bar

chart and comparing the results with the reaction without a catalyst.

6!uipment list:



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' cm; o .'moldm+; 2ydrochloric acid

'cm; o ' moldm+; sodium thiosulphate

>cm; o istilled water

>cm; o .'moldm+; Iron III chloride

>cm; o .'moldm+; *opper II sulphate

>cm; o .'moldm+; Iron III nitrate

>cm; o .@moldm+; Iron III nitrate

'% 'cm; beaers

'% boiling tubes

Stopwatch

/lac cross

<cm; pipette

<% 'cm; pipettes

3ethod:

') 7sing a pipette fll @ dierent beaer with 'cm;

o hydrochloricacid. 5abel these beaers with numbers rom ' to @.

<) $ill @ boiling tubes with 'cm; o sodium thiosulphate also

labeling it ' to @.;) 7sing a <cm; pipette measure out the dierent solution and

transer it to the respective test tubes:+<cm; o water to test tube '+<cm; o .'moldm+; Iron III chloride to test tube <+<cm; o .'moldm+; *opper II sulphate to test tube ;+<cm; o .'moldm+; Iron III nitrate to test tube >

+<cm;

o .@moldm+;

Iron III nitrate to test tube @

;) Tae beaer ' containing hydrochloric acid and place it over a

blac cross add test tube ' content to it mi% it and record the time

when the cross disappear.

>) 1epeat the same procedure mi%ing test tube < and beaer <# test

tube ; and beaer ;# test tube > and beaer > and test tube @ and

beaer @ always recording the time.

@) 1epeat the whole e%periment again recording the results to mae

it more accurate.



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6%pt 2*l(cm; 9a<S<8;(cm; 2<8(cm; *atalyst(cm;

' ' ' <

<#;#>#@ ' ' <

1esults:

6%pt Time'&s) Time<&s) Timeave&s)

' 9o catalyst 'B.'@ 'B. 'B.'<

< .'moldm+;

Iron III

chloride

'@.; '@.;C '@.;>

; .'moldm+;

*opper II

sulphate

'B.' '@.B@ '@.?;

> .'moldm+;

Iron III

nitrate

'B.C '@.@; '@.?

@ .@moldm+;

Iron III

nitrate

<.>@ <.'< <.<

Analysis:

@

'

'@

<

<@

;

;@

Catalyst

average time&s)



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The bar chart shows that the catalysts have a very low eect on

speeding the reaction up. The most eective o the catalysts on

maing the reaction aster is iron III chloride. .@moldm+; slows the

reaction down this is due to its high concentration and instead o

speeding up it has the opposite eect.$%periment ):

8i9erent acids:

In this e%periment I will use dierent types o acids to replace

hydrochloric acid. -ith the results I will plot a bar chart and determine

the ones who speed the reaction up and the ones that slow it down.

6!uipment list:

'cm; o 'moldm+; Sodium thiosulphate

<cm; o .'moldm+; sulphuric acid

<cm; o .'moldm+; phosphoric acid

<cm; o .'moldm+; propanoic acid

<cm; o .'moldm+; methanoic acid

<cm; o .'moldm+; nitric acid

<% 'cm; pipette

'% 'cm; beaer

'% boiling tube

/lac cross

Stopwatch

3ethod:

') 7sing a pipette fll @ dierent beaers with 'cm;

o sodiumthiosulphate labeling them rom ' to @.

<) 7sing another 'cm; pipette fll @ dierent boiling tubes with

the @ dierent acids labeling it also rom ' to @.+ $ill test tube ' with 'cm; o sulphuric acid+ Test tube < with 'cm; o phosphoric acid+ Test tube ; with 'cm; propanoic acid+ Test tube > with 'cm; methanoic acid+ Test tube @ with 'cm; nitric acid;) Place the beaer labeled ' on top o the blac cross. Add the

solution on test tube ' to it mi% it and record the time taen orthe cross to disappear.



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>) 1epeat that process mi%ing the beaers and test tubes with the

same label and recording the time taen to disappear.@) 1epeat the whole process &rom stage '+>) and record the

results.

1esults:

6%pt Time'&s) Time<&s) timeave&s)

' Sulphuric

acid

'.?' '.< '.?C

< Phosphoric

acid

<'.?? <'.<@ <'.@C

; Propanoicacid

''B.> ''?.>B ''C.;

> 3ethanoic

acid

@.;? @.'< @.<@

@ 9itric acid '>.?> '>. '>.?C

<

>

B

?

'

'<

'>

Acids

average time &s)



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/y analy0ing the bar chart we can see that sulphuric acid is the most

eective on speeding the reaction up and propanoic acid the less

eective. -e can also observe that the strongest the acid the aster

the reaction. This is due to the act that wea acids lie propanoic

acid and methanoic acid don,t dissociate completely and is harder toor them and re!uires more energy to give away the 24 that triggers

the reaction allowing the ormation o sulphur that causes the

precipitate to orm. That e%plains why a stronger acid will speed up

the reaction while a wea acid slows it down. Sulphuric acid also

contains sulphur and the presence o more sulphur in the reaction

maes it aster or the precipitate to orm because an e%cess o

molecules are involved in the process.

Conclusion:

$rom e%periment ' the frst graph shows us that sodium thiosulphate

has frst order has frst order in respect to the order o reaction as the

rate against concentration graph has produced a directly proportional

line and its hal lie is constant on the concentration against time

graph. 8n e%periment <# hydrochloric acid also appears to be a frst

order as the graph shows a directly proportional line or rate against

concentration even i the hal lie is not constant which is due to

errors that will be commented on the evaluation section that couldaect my results. -hich gives a overall order o reaction o < and a

rate e!uation r45,Cl6&51a22(6& . This means that both reactants

have one molecule reacting on the rate determining step. The results

rom e%periment ; o temperature change support the chemical idea

that the rate o reaction increases as temperature increases which

means that reaction happens aster. This also support the collision

theory that states the aster the molecules are moving more

molecules will have enough energy to successully collide and mae

the reaction happen. $rom that I plotted a graph and wored out theactivation energy or my reaction which was ;<>' Jmol+' which is the

minimum value o energy that a particle should have in order to

collide and react with success. $rom my e%periment > with the

catalyst we can see that transition metal catalyst have a small

increase in the speed o the reaction. -e can see that all the catalyst

used were heterogeneous and all e%cept rom .@moldm+; Iron III

nitrate made the reaction go aster. This catalyst eect o transition

metals is due to their unpaired electrons in the d orbital# and their

ability to orm a variety o o%idation states. This means they can

readily accept and(or donate electrons to orm intermediate



Stephano Pina

compounds providing a dierent and aster path or the reaction to

tae place which e%plains why the reaction happened aster with the

addition o a catalyst. 8n e%periment @ we can see the dierent acids

and their eect on the reaction time. -e conclude that sulphuric acid

is the best acid to use in order to speed the reaction up this is due tothe presence o sulphur which maes the precipitate o sulphur to

orm !uicer due to the presence o more molecules and thereore

more probability o fnd sulphur molecules with enough energy to

react. The less eective acid is propanoic acid this is due to the act o

being a wea acid who doesn,t dissociate completely not providing 24

ions that can act has a catalyst on the ormation o sulphur.



Stephano Pina

$valuation:

3aing o standard solution:

-hile maing the standard solution some procedural errors aecting

the results may have been made. -hen calculating the mass o

sodium thiosulphate is important to remember that it was hydrated

and it has to be included on the calculations. -hen rinsing the unnel

and beaer it is possible that some o the solution is let in the in the

beaer maing the moles o the solution not accurate and smaller

than e%pected. It is also very important that the bottom o the

meniscus is on the mar when water is added to the solution in the

volumetric "as because the concentration will not be correct and it

will aect the results. -hile measuring the mass o solid sodium

thiosulphate needed the <dp balance has an error o 4(+ .@g. The

precision error or measuring the solid will then be:

.@(<>.?<=.<'@ % ' = .<'@ K o percentage o error

The precision error or the 'cm; is 4(+ .;cm;

.; ( ' = .< % ' = .;K o error

*hanging concentrations:

In this e%periment some errors may have been incurred as I was using

a stop watch with precision error 4(+ .@s I could have started it at

dierent times allowing the reaction to start without a ull indication

to the actual time taen. -ith using the disappearing cross method it

was diLcult to Mudge the e%act time the cross disappeared and the

longer the reaction the harder it was to determine thereore stopping

the stopwatch at the same time was more diLcult maing my results

probably a ew seconds out. Also while mi%ing the reactions together

while timing them I may have mi%ed some more than others resulting

in a !uicer reaction. The change in room temperature on dierent

tries and dierent days was also a possible source o uncertainty

since a higher temperature can lead to a aster reaction and thereore

aecting the results o my e%periment. The 'cm; pipette used to

measure the solutions had a precision error o 4(+ .>cm;. The

percentage or each try is calculated below:



Stephano Pina

6%periment ':

6%pt K o error rom

water reading

K o error rom

sodium

thiosulphate

reading

K o error

rom

hydrochlori

c acid

reading

K o error

rom

stopwatch

reading

' + .> .> .;;

< <. .@ .> .<B

; '. .BC .> .'?

> .BC '. .> .';

@ .@ <. .> .B?

6%periment <:

6%pt K o error

rom water

reading

K o error

rom sodium

thiosulphate

reading

K o error

rom

hydrochloric

acid reading

K o error

rom

stopwatch

reading' + .> .> .;B

< <. .> .@ .;<

; '. .> .BC .<C

> .BC .> '. .<'

@ .@ .> <. .';



Stephano Pina

*hanging temperature:

In this e%periment some errors may have come rom the use o the

stopwatch while recording the time# the human reaction was the mainreason maing my time results probably be a ew seconds out.

Another source o error could be the act that I have only measured

the temperature at the end o the reaction instead o measuring the

beore and ater and mae an average. The thermometer I used to

measure the temperature also has a precision error o 4(+ .@o which

also adds some uncertainty to my measurements. The pipette used to

measure water# sodium thiosulphate and hydrochloric acid has a

precision error o 4(+ .>cm;. The percentage o error or each try is

listed below:

e%pt K o error

rom water

reading

K o error

rom

sodium

thiosulphat

e reading

K o error

rom

hydrochlori

c acid

reading

K o error

rom

stopwatch

reading

K o error

rom

thermomet

er reading

' .@ <. .> .C< <.<

< .@ <. .> .' '.C

; .@ <. .> .'@ '.>

> .@ <. .> .<@ '.'

@ .@ <. .> .;? .??

*atalyst e%periment:

Procedural error may have incurred as I used a stop watch# I could

have started it at dierent times allowing the reaction to start without

ull indication to the actual time taen. /y using the disappearing

cross method it is diLcult to Mudge the e%act point the cross ully

disappears and dierent persons can have dierent Mudgments aboutit adding or taing a ew seconds to the actual value o time. Also the



Stephano Pina

longer the reaction taes the more diLcult is to stay concentrate on

stopping the stopwatch at the e%act moment. Another source o error

can be while mi%ing the solutions together and swirling it with more

or less orce maing some more mi%ed than others thereore aster or

the reaction to happen. The percentage o error or each try iscalculated below:

6%pt K o error

rom

water

reading

K o error

rom

sodium

thiosulph

ate

reading

K o error

rom

hydrochlo

ric acid

reading

K o error

rom

catalyst

reading

K o error

rom

stopwatc

h reading

' < .> .> + .;'

< + .> .> < .;;

; + .> .> < .;<

> + .> .> < .;<

@ + .> .> < .'C

ierent acids e%periment:

Procedural error may have incurred as I used a stop watch# I could

have started it at dierent times allowing the reaction to start without

ull indication to the actual time taen. /y using the disappearing

cross method it is diLcult to Mudge the e%act point the cross ully

disappears and dierent persons can have dierent Mudgments about

it adding or taing a ew seconds to the actual value o time. Also the

longer the reaction taes the more diLcult is to stay concentrate on

stopping the stopwatch at the e%act moment. Another source o error

can be while mi%ing the solutions together and swirling it with more

or less orce maing some more mi%ed than others thereore aster or

the reaction to happen. The percentage o error or each try is

calculated below:

6%pt K o errorrom sodium

K o errorrom acid

K o error romstopwatch



Stephano Pina

thiosulphate

reading

reading reading

' .> .> .>B

< .> .> .<;; .> .> .>> .> .> .'@ .> .> .;>

References:

'. *lassroom notes<. A< level chemistry 8*1 / revision guide;. 1is assessment+ *leapss saety cheets>. http:((www.chemguide.co.u(physical(catalysis(introduction.html

<(<(<'@ dierent types o catalysts@. http:((en.wiipedia.org(wii(1eactionNrateNconstant 'C('(<'>@

reaction rate and rate constantB. http:((en.wiipedia.org(wii(1ateNe!uation 'C('(<'@ rate

e!uationC. http:((www.chemguide.co.u(physical(basicrates(catalyst.html

'C('(<'@ catalysts on rate reaction?. http:((www.chemguide.co.u(physical(basicrates(arrhenius.html

'?('(<'@ arrhenius e!uation. http:((www.ehow.com(aboutNBB?BC?Ntransition+metals+good+

catalystsN.html'. http:((en.wiipedia.org(wii(StandardNsolution '?('(<'@

http://www.chemguide.co.uk/physical/catalysis/introduction.html%2002/02/2015


http://www.chemguide.co.uk/physical/basicrates/catalyst.html%2017/01/2015


http://www.chemguide.co.uk/physical/basicrates/arrhenius.html%2018/01/2015


http://www.ehow.com/about_6686789_transition-metals-good-catalysts_.html


http://en.wikipedia.org/wiki/Standard_solution%2018/01/2015







http://en.wikipedia.org/wiki/Standard_solution%2018/01/2015



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