ASE$2015$ Chemistry$Workshop$ Exhibition/demo$activities!
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For!ease!of!download,!copies!of!the!workshop! exhibition/demonstration!information!sheets!have!been! combined!together!into!this!single!pdf!document.! Please!note!that!ALL!documents!here!are!in!DRAFT!format,!and! should!be!used!as!such.! If!you!have!ANY!questions!about!how!to!carry!out!an!activity,! please!contact!CLEAPSS!before!carrying!it!out.! !
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This%informa3on%about%the%iron/sulfur%reac3on%%can%be%found%in %‘Safer%chemicals,%safer%reac3ons%(guide%L195). 9.2
Iron/sulfur reaction Myth: We cannot do this activity as it affects asthmatics in the class.
Comment
If the procedure (see Hazcard 96) is not carried out carefully, sulfur burns in air to form sulfur dioxide, a TOXIC and CORROSIVE gas. Any advice suggesting that this activity can be carried out using open-ended equipment, such as bottle tops or heat-resistant paper, should not be followed. Also, if test tubes are too full, sulfur vapour will escape and ignite to form sulfur dioxide. When the iron/sulfur mixture is heated, the sulfur melts and reacts with the iron exothermically to form iron(II) sulfide. This is an important experiment and is one of the few that pupils can do themselves that demonstrates visibly that the properties of a compound are different from its constituent elements. The procedure should be carried out in borosilicate test tubes as a demonstration or in prepared smaller ignition tubes by pupils (see Hazcard 96). Mineral fibre (see section 4.1) stops sulfur vapour leaving the test tube and possibly catching fire.
Procedure
125 x 16 mm borosilicate test tube Mineral fibre plug Position of clamp or holder 2 g of iron/sulfur mix
Heat
• • • •
Controls and hints
Prepare a mixture containing iron powder and sulfur powder in the ratio 7:4 by mass. Place 2 g of the mixture in the borosilicate test tube. Insert a mineral fibre plug in the mouth of the tube and clamp the test tube at the opening. Heat the powder mixture strongly but extinguish the Bunsen burner as soon as the reaction starts.
Wear eye protection. Ensure the room is well-ventilated. Iron powder mixed with either finely-powdered roll sulfur or flowers of sulfur can be used. If fine sulfur powder is mixed with iron filings, separation can occur and a consistent mix is not obtained. Borosilicate glass must be used. The reaction can be initiated using a hot-air paint stripper at about 550 °C. This answers comments from some students who believe the flame penetrates the glass! The reaction can be carried out on a microscale using a 75 x 10 mm test tube (ignition tube). This must never be more than one-quarter full and even 0.2 g of the mixture is sufficient for a good display. The product can be tested with acid quite safely even though hydrogen sulfide (TOXIC) gas is produced. This would have to be done in a fume cupboard unless a microscale procedure45 is used.
Disposal
The test tube should be allowed to cool and placed in the glass bin.
Extension
Unfortunately, there does not appear to be a foolproof method of making nonmagnetic iron(II) sulfide. Fowles46 suggested using a mixture containing 1.5 times as much sulfur as iron but this does not appear to work either. Partington47 suggested that the product is only feebly magnetic. Perhaps weak magnets should be used?
45 46 47
Microscale Chemistry, J Skinner, Royal Society of Chemistry, ISBN 1870343492. This book was sent to all schools in the UK by the RSC. Lecture Experiments in Chemistry, G Fowles, Bell, 3rd edition, 1947. This book may still be on a shelf somewhere in the school, in libraries or in second-hand bookshops. A Textbook of Inorganic Chemistry, J R Partington, MacMillan, 6th Edition, 1950. 31
Supporting Practical Science, D&T and Art - in schools and colleges
Preparing)copper(II))sulfate(VI)555water)crystals:)a)quick)&)safe)method) Nearly'all'pre)16'courses'include'the'reactions'of'acids'and'bases'(or'alkalis)'to'make'salts.'' The'process'is'often'illustrated'by'the'reaction'of'copper(II)'oxide'with'sulfuric'acid'to'produce'the' spectacular'blue'crystals'of'copper(II)'sulfate)5)water'and'water.'This'preparation'of'salts'is' quicker'and'safer'than'the'method'often'suggested'in'textbooks'but'still'involves'several' fundamental'techniques'such'as'filtration'and'crystallization.''' Reference'for'this'method:'Laboratory(Handbook'Section)13.2.6) Wear)eye)protection' 1. Half)fill'a'250'cm3'beaker'with'just)boiled'water'from'a'kettle.' 2. Add'15'cm3'of'1.4'M'sulfuric(VI)'acid'(warning'–'irritant)'to'a'boiling'tube'and' stand'this'in'the'hot'water.''
'
3. Leave'to'warm'up'while'preparing'for'the'steps'below.' 4. Weigh'out'between'1.8'and'2.0'g'of'copper(II)'oxide'(warning')'harmful).' 5. Add'~'half'the'copper(II)'oxide'powder'to'the'hot'acid'in'the'boiling'tube.' 6. Every'half)minute'or'so,'remove'the'boiling'tube'from'the'hot'water'to'agitate' the'reaction'mixture.'Return'tube'to'the'hot'water'to'keep'warm.' 7. Once'the'solution'clears,'add'the'rest'of'the'copper(II)'oxide'and'keep'agitating' the'mixture'until'there'appears'to'be'no'further'reaction.'' How(could(you(check(that(the(reaction(is(complete?(
'
8. Set'up'a'filter'funnel'with'a'fluted'filter'paper'in'a'100'cm3'conical'flask.'' 9. Pour'the'contents'of'the'boiling'tube'into'the'filter'funnel.' 10. Once'filtered,'place'the'conical'flask'with'salt'solution'on'a'tripod'and'gauze.''
'
This(next(operation(can(be(difficult(to(judge.' 11. Add'a'few'anti)bumping'granules'to'the'solution'in'the'conical'flask'(optional).' 12. Heat'the'solution'to'boiling')'then'boil'for'~'3'minutes'maximum.'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' If'you'hear'‘spitting’'before'the'time'is'up')'immediately'turn'off'the'Bunsen.'' DO'NOT'BOIL'THE'SOLUTION'DRY'' ' 13. Switch'off'the'Bunsen'burner.'' 14. Carefully'place'a'rolled–up'paper'towel'around'the'neck'of'the'conical'flask'and' use'this'to'lift'the'flask'and'place'it'on'the'bench.'(TAKE'CARE'–'HOT!)'' 15. Once'the'liquid'has'stopped'boiling'and'spitting,'pour'the'hot'contents'into'the' Petri'dish.'What’s'the'best'way'to'pour'out'the'solution?'(TAKE'CARE'–'still'HOT!)' '
Leave'the'Petri'dish'to'cool.'Some'of'you'will'observe'dramatic'crystal'formation'almost'immediately.'' Some'of'you'may'be'initially'disappointed'but'be'patient!'Leave'the'Petri'dish'for'a'little'longer'and'you’ll' almost'certainly'obtain'some'good'(and'larger!)'crystals.'(Take'a'photo'of'the'crystals'you'prepare).'
vASE 2015_DRAFT
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Conductivity+ Wear+eye+protection+ If#not#already#laminated,#insert#this#sheet#into#a#plastic#folder.#You#will#also#need#a#beaker#of#pure#water# (distilled#or#deionised)#and#a#beaker#of#tap#water#(which#should#be#at#least#moderately#hard).## Make#a#‘spatula’:#cut#one#end#of#a#wood#splint#to#a#point#(use#scissors).## 1.#Place#3C4#drops#of#pure#water#in#the# leftChand#circle.#Dip#the#electrodes#in#C# does#the#LED#light#up?#Repeat#the#test# with#tap#water#in#leftChand#circle.#
#
##
3.#Salt#water#
#
4.#Now#add#1#drop#of#phenolphthalein#or#Universal# Indicator#solution.##
Add#3#C#4#drops#of#pure#water#to#the# circle.#Put#a#few#grains#of#salt#in#the# black#oblong.#Move#1#grain#of#salt#into# the#water#drop.#Test#for#conductivity# but#stir#with#the#electrodes.##
2.#Now#add#1#drop#of#phenolphthalein# or#Universal#Indicator#solution#and# insert#the#electrode#again.#
Stir#the#solution#with#the#spatula#so#the#colour#is# even.#Insert#the#electrodes,#keeping#them#still.## What#do#you#observe?## Cut#off#the#contaminated#end#of#the#spatula.##
What#else#do#you#observe?# 5.#Sugar#(sucrose)#in#water#
6.#Now#try#using#brown#sugar# and#add#a#few#more#grains.##
#
Repeat#the#procedure#above#but#this# time#use#white#sugar.##
#
Your#observations#here#might#help#explain#….#http://en.wikipedia.org/wiki/Brown_sugar#
(There#will#need#to#be#time#for#interpretation/#explanation#of#the#results)#
Extension+(there#is#a#palette#below#for#carrying#out#the#tests#on#but#you’ll#need#be#organised!)+ Serial#dilution:#Place#10+drops#of#1%#sodium#chloride#solution#in#circle#A.#Remove#1#drop#into#circle#B#and#add#9# drops#of#pure#water.#Does#the#solution#conduct#electricity?#How#dilute#can#the#solution#be#yet#still#give#a#positive# response#on#the#LED?# #
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A#
B#
C#
D#
E#
F#
G#
• Other#waters#can#be#investigated:#water#from#the#freezer,#bottled#waters,#boiled#water#&#freshly# collected#rainwater.# • Other#activities?#Try#other#chemicals?#Magnesium#sulfate(VI),#copper#sulfate(VI)#crystals,#potassium# iodide,#glucose,#sodium#sulfate(VI)#(add#a#drop#of#phenolphthalein#or#Universal#indicator?).# vASE 2015_DRAFT Page 1 of 1
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Supporting Practical Science, D&T and Art - in schools and colleges
Thin%layer%chromatography%of%chloroplasts%% TLC%plates% The%plates%used%here%have%silica%applied%on%a%polyester%backing.%They%are% expensive%T%costing%about%£80%for%50%plates%(20%x%5%cm).%However,%a%plate% can%easily%be%cut%(with%sharp%scissors)%into%smaller%strips.%One%large%plate% can%be%cut%into%15%smaller%plates%(1.3%x%5%cm)%T%cost%~%13%p%per%strip.% Aluminium%oxide%plates%are%also%available.%% Some%plates%are%doped%with%a%UV254%fluorescent%material%to%allow%detection% of%colourless%spots%using%a%UV%light%in%the%254%nm%range.%
Procedure%for%chromatography% Wear%eye%protection.%Do%not%inhale%the%solvents.% 1. Add%a%small%spatula%measure%of%anhydrous%sodium%sulfate(VI)%to%the%bottom%of%a%plastic% Eppendorf%tube%(see%right).%This%is%to%remove%any%moisture%that%may%be%present.% 2. Place%small%pieces%of%a%soft%green%leaf%in%the%bottom%of%the%Eppendorf%tube%(see%right).%%%%%%%%%%%%%%%%%% Add%5%drops%of%Solvent%A.%consisting%of%2%parts%ethyl%ethanoate%and%3%parts%propanone.%% Notes:'% • An'Eppendorf'tube'is'used'here'but'any'small'container'or'test'tube'would'work.'' • Solvent'A'consists'of'2'parts'ethyl'ethanoate'and'3'parts'propanone.' 3. Press/stir%the%leaf%with%a%metal%probe%(eg,%the%end%of%forceps)%to%extract%as%much%colour%as%possible!%% 4. Now%use%a%fine%brush%to%place%a%small%dot%of%the%coloured%solvent%about%5%mm%from%the%bottom%edge%of% the%TLC%plate.%Mark%this%position%on%the%side%of%the%plate.% % % 5. Gently%blow%on%the%dot%to%dry%it%before%putting%another%dot%of%coloured%solution%on%top%of%it.% • Check'with'the'tutor'that'the'dot'is'not'too'faint/strong'before'going'on'to'the'next'step.' 6. Use%a%dropper%pipette%to%place%~%0.5%cm3%of%Solvent%B%(the%developing%or%‘eluting’%solvent)%into%a%clean% vial%so%that%the%depth%is%about%5%mm.%The%level%of%the%solvent%must%be%below%the%level%of%the%dot%on%the% chromatography%plate% • Solvent'B'is'a'5:3:2'mixture'(by'volume)'of'cyclohexane,'ethyl'ethanoate'and'propanone.% 7. Put%the%TLC%plate%into%the%vial%(see%picture,%right)%and%replace%the%screwTtop%lid.%% • Ensure'that'the'vial'is'kept'still'while'the'chromatogram'is'running.%
Vial
8. After%a%few%minutes,%when%the%‘solvent%front’%has%moved%7/8ths%of%the%way%up%the%plate,% remove%the%plate%from%the%vial%(use%forceps/tweezers)%and%let%it%dry.%Mark%the%position%of% the%solvent%front.%
13 mm
9. Take%a%photograph%of%the%result%as%soon%as%the%solvent%has%evaporated%away.%The%coloured% This spot is about compounds%detected%are%light%sensitive%and%will%fade.% 8 mm from the bottom of the plate
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%©CLEAPSS ,%The%Gardiner%Building,%Brunel%Science%Park,%Kingston%Lane,%Uxbridge%UB8%3PQ% % %%%%%%%%%%%%%%%%%%%%%%Tel:%01895%251496;%Fax:%01895%814372;%ETmail:%
[email protected];%Web%site:%www.cleapss.org.uk%
50 x 13 mm pre-coated TLC plate
Supporting Practical Science, D&T and Art - in schools and colleges
% Notes/results% Our%results%from%geranium%leaves%are%compared%below%to%some%published%values%that%used%a%slightly% different%solvent%but%the%arrangement%of%spots%is%very%similar.%Separation'of'Plant'Pigments'by'Thin'Layer' Chromatography%from%Quach,%H.%T.;%Steeper,%R%L.;%Griffin,%G.%W.%J.'Chem.'Educ.%2004,%81,%385T7.%
β-carotene pheophytins chlorophyll a and b lutein
other xanthophylls
% • The%green%in%leaves%is%due%mainly%to%chlorophyll%a%and%chlorophyll%b.% • Pheophytins%are%decomposition%products%in%which%chlorophylls%%%%%%%%%%%%%% a%and%b%have%lost%their%magnesium%ions.% • The%yellow%dyes%include%betaTcarotene%and%xanthophylls.% • Xanthophylls%are%derivatives%of%betaTcarotene%that%contain%oxygen.%%%%%%%%% The%xanthophyll%in%spinach%is%about%96%%lutein%and%4%%zeaxanthin.%% % % % % beta%carotene% % %
% Lutein%%
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Zeaxanthin%
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Zeaxanthin%differs%from%lutein%in%the%position%of%a%double%bond%in%the%ring%on%the%right.%
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[email protected];%Web%site:%www.cleapss.org.uk%
Supporting Practical Science, D&T and Art - in schools and colleges
Finding&the&Formula&of&Magnesium&Oxide& Why&do&this?& This%practical%illustrates%the%idea%that%oxygen%has%mass,%and%that%burning%can%involve%an%increase%in%mass%as% an%element%reacts%to%become%an%oxide.%The%activity%also%introduces%the%idea%that%the%relative%mass%of% elements%in%a%compound%is%in%the%same%proportion%as%the%atoms%in%the%chemical%formula.%
Using&bottle&tops& This%method%replaces%the%usual%procedure%with%a%crucible.%Crucibles%are%expensive%and%removing%the%lid%can% lead%to%breakages,%and%the%loss%of%magnesium%oxide,%giving%an%unreliable%result.%Bottle%tops%are%typically% made%of%steel.%Do%not%use%any%made%of%aluminium.%Before%use,%the%bottle%top%needs%to%be%heated%strongly% in%a%fume%cupboard%to%burn%out%the%plastic%insert.% &
Procedure&
Note:%an%alternative%version%of%the%bottle%top% ‘crucible’%may%be%used%in%some%workshops.%
Wear&eye&protection.&Make&sure&that&any&long&hair&is&tied&back.& 1. Find%the%total%mass%of%2%bottleAtops%and%15%cm%of%nichrome%wire.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Record%this%mass%as%M1.%% 2. Roll%a%10%to%15%cm%length%of%magnesium%ribbon%around%a%pencil%and%place%the% ribbon%in%one%of%the%bottleAtops.% 3. Find%the%mass%of%the%2%bottleAtops%+%nichrome%wire%+%magnesium%ribbon.% Record%this%mass%as%M2.% 4. Set%up%a%Bunsen%burner%and%tripod%on%a%heatAproof%mat.%On%the%tripod%place% a%pipeAclay%triangle%small%enough%to%support%the%bottleAtop%‘parcel’.% 5. Sandwich%the%magnesium%between%the%two%bottleAtops%(serrated%edges% together).%Wrap%the%wire%round%the%bottleAtops%to%keep%them%together.% 6. Place%the%bottleAtops%securely%on%the%pipeAclay%triangle.%% 7. Heat%the%bottleAtops%with%a%strong,%nonAluminous%flame.%When%the% % magnesium%ignites,%you%will%be%able%to%see%the%bright%glow.%%%%%%%%%%%%%%%%%%%%%%%%%%% M1%=% Keep%heating%for%5%minutes%or%until%you%can%no%longer%see%a%bright%light% % between%the%bottleAtops.% M2%=% 8. Switch%off%the%Bunsen%burner%and%allow%the%tops%to%cool%(for%~%5%minutes).% % 9. Find%the%mass%of%the%bottleAtop%+%nichrome%wire%+%magnesium%oxide.%%%%%%%%%% M3%=% Record%this%mass%as%M3.% % Using&the&experimental&results& • Calculate%the%mass%of%magnesium%ribbon%you%have%used%(M2%A%M1)% • Work%out%the%mass%of%magnesium%oxide%produced%(M3%A%M1).% • Use%the%graph%(next%page)%to%see%the%relationship%between%the%mass%of% magnesium%and%the%mass%of%magnesium%oxide.%
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% M2%A%M1%=% & M3%A%M1%=% %
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vASE 2015_DRAFT Page 1 of 2
© CLEAPSS®, The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ Tel: 01895 251496; Fax: 01895 814372; E-mail:
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& The&variation&of&the&mass&of&magnesium&oxide&with&the&mass&of&magnesium& The%green%line%corresponds%to%the%formula%Mg20.%The%blue%line%corresponds%to%the%formula%Mg0.%The%red%line% corresponds%to%the%formula%Mg02.%
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Extension& Magnesium%reacts%with%nitrogen%to%form%magnesium%nitride%(Mg3N2),%which%reacts%with%water%to%produce% ammonia%that%changes%moist%red%litmus%paper%to%blue.% % Add%the%solid%in%the%bottle%tops%to%a%small%container% (a%vial).%Place%damp%red%litmus%paper%over%the%top.%
%
Remove%the%paper%and%add%boiling%water%to%the%vial.% Replace%the%litmus%paper.%
%
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vASE 2015_DRAFT Page 2 of 2
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Supporting Practical Science, D&T and Art - in schools and colleges
Heating(marble(chips:(a(quantitative(approach(( Wear(eye(protection( You$are$provided$with$a$weighing$boat$and$a$marble$chip.$$ Record$the$following:$$ M1$(mass$of$the$weighing$boat)$=$$ M2$(mass$of$the$weighing$boat$+$marble$chip)$=$$ M3$(mass$of$marble$chip)$=$ • Put$the$marble$chip$in$the$wire$holder$(see$right).$$ • Place$the$holder$on$the$tripod$and$heat$the$marble$chip$as$strongly$as$possible$ for$10$minutes.$At$intervals,$try$moving$the$Bunsen$burner$away$and$you$may$ be$able$to$see$‘limelight’.$$ You%could%take%a%picture%of%this.$$ • After$10$minutes,$remove$the$heat$and$allow$the$chip$to$cool$(~$5$mins).$ • Use$forceps$to$transfer$the$marble$chip$into$a$weighing$ boat.$$ Important:%hold%the%weighing%boat%near%the%heated%chip% while%you%do%this%to%avoid%losing%product.$$ • Find$the$mass$of$the$heated$chip$(M4).$$
CaCO3(s)(→(CaO(s)(+(CO2(g)( How$much$calcium$carbonate$has$reacted?$$ $ 100$g$of$calcium$carbonate$should$leave$56$g$ of$calcium$oxide,$CaO,$after$heating.$$ Your%mass$of$calcium$carbonate$$(M3)$should$ leave$(56$x$M3)/100$g.$
( M4$(mass$of$the$heated$chip)$=$
Compare$this$value$with$what$you$have$ actually$obtained$(M4).$
$ • Now$put$the$heated$chip$into$a$test$tube.$Use$a$dropper$ pipette$to$drip$in$2$cm3$of$water.$$
Observation(s)?( $ $
Extension)(1):%%
Observation(s)?(
• Filter$the$solution$(normal$method)$into$a$2nd$test$ tube/vial.$ • Use$a$straw$to$BLOW$into$the$solution.$ Extension)(2):%%
Observation(s)?)
• Add%3%cm3%of%water%to%the%filter%funnel%and%obtain%some% more%clear%solution.%% • Add%1%drop%of%Universal%indicator%and%blow%into%the%testC tube/vial%with%the%straw.%% • Keep%blowing!%BLOWING)NOT)SUCKING!% vASE 2015_DRAFT
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%
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$ Limelight) Below$is$a$limelight$spotlight$used$in$London$in$1860.$Limelight$was$used$in$the$first$theatrical$ spotlights.$$ The$Scottish$engineer$Thomas$Drummond$invented$the$limelight$in$1816.$He$used$a$core$of$ limestone$(calcium$carbonate)$that$was$heated$to$incandescence$by$a$burning$mixture$of$oxygen$ and$hydrogen.$The$incandescent$limestone$provided$very$brilliant$light$that$could$be$directed$and$ focused.$The$limelight$was$first$employed$in$the$theatre$in$1855$and$became$widely$used$by$the$ 1860s.$Its$intensity$made$it$useful$for$spotlighting$and$for$the$realistic$simulation$of$effects$such$as$ sunlight$and$moonlight.$It$could$also$be$used$for$general$stage$illumination.$The$limelight$required$ constant$attention$of$an$individual$operator,$who$had$to$keep$adjusting$the$block$of$limestone$as$ it$burned$and$to$tend$to$the$gas$that$fuelled$it.$$ $
$$
$$
Blow]Through$Limelight$Burners:$ The$oxygen$and$hydrogen$gases$were$mixed$at$the$burner.$
$ Different$type$burners$had$different$orifices.$Common$burner$types$were:$
$ A.$Blow]through$jet;$B.$Mixed$gas$jet;$C.$Gwyer's$jet$$ These$blow]through$burners$date$from$the$middle$of$the$19th$century.$
$ $
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This%informa3on%about%the%thiosulfate/acid%reac3on%can%be%found%in %‘Safer%chemicals,%safer%reac3ons’%(guide%L195).
13. A safer procedure for the thiosulfate/acid reaction Comment: So much sulfur dioxide is given off at higher temperatures that we have had to give up this activity.
Comment
The reaction between sodium thiosulfate solution and dilute hydrochloric acid (both MINIMAL HAZARD) produces sulfur dioxide, a TOXIC and CORROSIVE gas, and colloidal sulfur as a precipitate. The gas can induce an asthmatic attack in some pupils. The release of gas is a particular problem if the activity involves studying the effect of increasing the temperature of the reaction. In addition, the precipitate ‘sticks’ to the glass and, unless the container is washed immediately, it becomes difficult to remove. This version of the procedure attempts to minimise the effects of sulfur dioxide, by reducing the volume of sodium thiosulfate solution used. It also uses a stop bath containing sodium hydrogencarbonate solution to avoid the production of sulfur dioxide after measurements have been taken. A simple water bath avoids the need for a Bunsen burner as long as there is hot water (about 50-60 °C) in the laboratory. At temperatures above 55 °C, the reaction time is so short that the results are unreliable. By using cold water (kept in a refrigerator overnight) in the water bath, the procedure can be carried out at temperatures below ambient. The reaction time is longer although the water bath becomes warmer as time passes. Temperature readings can be taken before and after and the average used in the results. This is an extra complication and is discussed in the ‘Extension’ notes overleaf.
Special equipment
The vials. Their capacity should exceed 10 ml, eg, 48 x 25 mm (h x d) vials from Griffin & George, TUL-490-062E. The water bath. Use a microwavable plastic61 container (capacity 500 cm3) with lid. Holes can be made by pushing into the lid a very hot metal disc a little larger than the diameter of the vials, eg, a coin, or a cork borer62. Unused holes can be stoppered with bungs. If a 1 litre container is used as the water bath, test tubes can be inserted in place of vials. The water bath can be used for any procedures which require a more or less steady temperature and do not take too long to complete.
The vials are placed in the container. Hot or cold water can be added to adjust the temperature. Up to six holes can be placed in the lid.
The capped vial is placed horizontally on the tile and held in place with Blutac. The mark is viewed from above.
Monitoring the reaction A black mark is made with a suitable pen on a white tile.
The stop bath: Another plastic container should be filled with 5% sodium hydrogencarbonate solution to which a small volume of universal indicator solution is added. The vials with the reactants are placed in this bath to stop the reaction and absorb sulfur dioxide gas. Use the colour of the indicator to check that the solution has not become acidic. If it does, add more sodium hydrogencarbonate.
61 62
They are usually made of polypropylene and can be obtained from supermarkets or other general stores. For this task, use an old borer, no longer employed to make holes in corks or bungs. Heating a cork borer will soften the metal and ruin it for its normal use. 43
Procedure
• • • • •
• • • • • • • •
Extension
On a white tile, draw a black line with a suitable marker pen. Wear eye protection. Using a 10 ml measuring cylinder, pipette or burette, place 10 ml samples of 0.1 M sodium thiosulfate solution into 6 glass vials. Place a cap on each vial. Have ready a thermometer and the apparatus to deliver quickly 1 ml of 1 M hydrochloric acid. A 10 ml measuring cylinder, burette, syringe or graduated pipette could be used. Remove the cap from a vial, add 1 ml of 1 M hydrochloric acid to the sodium thiosulfate solution, start a stop clock, cap the vial and place it horizontally on the white tile over the black mark. It is held in place with Blutac. Note the time when the black mark can no longer be seen when viewed from above. Take the vial off the white tile, remove the cap and quickly insert a thermometer to note the temperature. Immerse the vial and its contents in the stop bath solution. Fill the water bath with warm water from a tap or kettle (50-60 °C). Insert a vial of sodium thiosulfate solution into the water bath. Remove the cap and stir the solution with a thermometer until the temperature increases to about 6 °C above room temperature. Remove the vial from the water bath. Repeat the instructions in the 5th bullet point to obtain a second set of readings. Insert a third vial of sodium thiosulfate solution into the hot water bath. Remove the cap of the vial and stir the solution with a thermometer until the temperature increases to about 12 °C above room temperature. Remove the vial from the water bath. Repeat the instructions in the 5th bullet point to obtain a third set of readings. Obtain two further readings at higher temperatures. Do not exceed 55 °C. Remove all the vials from the stop bath and rinse them out with water.
Empty the water bath. Half-fill it with cold water which has been stored in a refrigerator overnight and insert a vial containing sodium thiosulfate solution. Remove the cap and stir the solution with a thermometer until the temperature drops to about 6 °C below room temperature. Remove the vial from the water bath. The rate of reaction is proportional to the reciprocal of the time taken for the black mark to disappear. At KS4, it should be possible to plot this value against the temperature to show that, for every rise of 10 °C, the rate of reaction doubles. An example is shown below with results obtained using the method described here. Two results below room temperature were obtained. An Excel spreadsheet can be used to manipulate the results and produce a chart. 0.07 0.06 0.05
1/Time -1 (sec )
0.04 0.03 0.02 0.01 0 0
5
10
15
20
25
30
35
40
45
Temperature (°C)
In Y12 or 13, the procedure can be used to find the energy of activation of the reaction using the Arrhenius equation. These results gave an energy of activation of 54.4 kJ mol-1.
Disposal
All solutions can be disposed of down a foul-water drain.
44
The Acid / Thiosulfate Reaction
a We
1
1M
10 ml of 0. M sodium thiosulfate solution.
acid. 3 ml
Eye protection This method uses about a fifth of other published procedures.
2 ml
1 ml
Transfer 1 ml of acid to the thiosulfate solution and start the clock.
Once the thiosulfate solution is so cloudy you cannot see the black cross stop the clock. Note the time
Enter the results in the table below.
Empty the contents of the cloudy thiosulfate vial into the coloured stop bath.
in seconds. Take the temperature. 1 ml
2 ml
3 ml
2
re
te pro e y
n ctio
Acid Rinse out the vial with water.
3
Acid
Add hot water from the tap to the container.
These are polypropylene microwave boxes with holes and cross on the base.
The hazards are the reactants but the sulfur dioxide. By adding the mixture to sodium carbonate, sulfur dioxide and the hydrochloric acid are neutralised
Replace the thiosulfate vial with an empty clean vial and add another 10 ml of thiosulfate solution.
Care with hot water. 3 ml
2 ml
4
Wait 3 minutes before repeating the procedure in 2.
1 ml
Using hot water the need for Bunsen burners, tripods and stands.
Acid 5
Try other temperatures but never exceed 60 oC as the time is so short it is difficult to measure.
6
Extension
Temperature
For temperatures colder than room temperature, you need to measure the temperature BEFORE and AFTER and take the average. The time to go cloudy takes so long that the temperature of the water bath starts to rise.
Dispose of all liquids down the sink .
Time (seconds)
The procedure is so quick that more readings can be obtained than in the more traditional method. Safe disposal of residues.
For further information on risk assessments, see guide L196, Managing Risk Assessment in Science.
This%version%of%the%thiosulfate/acid%reac3on%is%from% ‘Making%and%recording%risk%assessments’%(guidance%leaflet,%GL%90).%
GL 90 PTB 12/09 Page 5 of 5
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Microscale*cracking*of*paraffin*and*dehydration*of*alcohols*
!
!
* Procedure* Wear*eye*protection! 1.
Seal!a!glass!Pasteur!pipette!by!heating!the!end!(tip)!in!a!Bunsen!burner!flame.!!Cool.!
2.
Add!~!0.5!cm3!of!liquid!paraffin1!to!the!pipette.!!
3.
Insert!mineral!wool!into!the!pipette!so!that!the!wool!absorbs!the!liquid!paraffin.!
4.
Use!a!‘microIscale!spatula’!to!place!some!aluminium!oxide!powder!into!the!pipette.!!
5.
Set!up!the!pipette!as!shown!in!the!diagram!above.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Support/hold+the+pipette+(at+its+wide+end,+around+the+silicone+tubing)+with+a+clamp.!! Arrange!a!small!testItube!containing!~!1!cm3!of!bromine!water!so!the!product!gas!can!pass! through2.!!
6.
Acidified+0.002+M+potassium+manganate(VII)+solution+could+be+used+in+place+of+the+bromine+water.+++++++++++++++++++++++++++++++++ The+colour+change+may+be+more+noticeable.+
7.
Light!the!spirit!burner!then!place!it!so!that!the!flame!is!at!the!junction!of!the!mineral!wool!and! aluminium!oxide.! Once+bubbling+through+quickly,+the+product+gas+can+be+lit+as+it+emerges+from+the+pipette.+
* Notes* 1. An!alcohol!such!as!propanI1Iol!or!propanI2Iol!can!replace!the!liquid!paraffin.!These!alcohols!will! dehydrate!to!produce!the!relevant!alkenes.! 2. This!smallIscale!procedure!avoids!the!problems!(explosions!)!caused!by!‘suckIback’.! !
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Supporting Practical Science, D&T and Art - in schools and colleges
pH#and#indicators#(1):#using#a#plastic#Comboplate®# Procedure# Wear#eye#protection#<#solution#B#is#IRRITANT.%% 1. Use%the%pipette%to%fill%the%wells%E1#–%E6%and%F1%–%F5%as%follows:% E1#
20%drops%of%A%
E2#
18%drops%of%A%+%2%drops%of%B%
E3#
16%drops%of%A%+%4%drops%of%B%
E4#
14%drops%of%A%+%6%drops%of%B%
E5#
12%drops%of%A%+%8%drops%of%B%
E6#
10%drops%of%A%+%10%drops%of%B%
F1#
8%drops%of%A%+%12%drops%of%B%
F2#
6%drops%of%A%+%14%drops%of%B%
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F4#
2%drops%of%A%+%18%drops%of%B%
F5#
20%drops%of%B%
F6#
empty%
1
2
3
4
5
6
8
7
9
10
11
12
A B C D
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1
2
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4
5
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%
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2. Add%water%to%each%of%the%wells%so%the%level%is%about%3mm%from%the%top.% 3. Rinse%a%pH%meter*%in%clean%water.%Remove%as%much%water%as%possible%then%dip%it%into%the%liquid%in%well%E1.%Note% the%reading%(to%1%decimal%place).% 4. Dip%the%pH%meter%into%water%and%take%a%reading%of%well%E2.%Continue%in%this%way%up%to%F5.%Write%the%readings%on% the%diagram%above.%% 5. Fill%wells%A1,%B1,%C1%and%D1%each%with%3%drops%from%E1.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% *A%calibrated%Checker%pH% Fill%wells%A2,%B2,%C2%and%D2%each%with%3%drops%from%E2.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% probe%(about%£30)%can%be% Continue%until%wells%A11,%B11,%C11%and%D11%are%full.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% used%to%find%the%pH%values.% If"you"have"used"well"F6,"you"can"also"fill"A12,"B12,"C12"and"D12.% 6. Add%1%drop%of%Universal%indicator%to%wells%A1%to%A11.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Repeat%using%the%different%pure%indicators%e.g.,%methyl%orange%to%row%B1%T%B11.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Extracts%from%flowers%and%vegetables%can%also%be%used%(e.g.%red%cabbage;%petunia%flowers).% Notes:"""If"you"have"another"Comboplate®,"more"wells"can"be"filled."" Photograph"the"Comboplate®"for"a"lasting"record."Label"the"photograph.% Solutions# •
Solution#A:%3.1%g%of%boric%acid%+%2.65%g%of%citric%acid%made%up%to%250%cm3%of%solution%in%total.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
•
Solution#B:%9.0%g%of%disodium%hydrogen%phosphateT12Twater%+%1%g%of%sodium%hydroxide%made%up%to%250%cm3%of% solution%in%total.%%
•
Universal%indicator%solution.%Other%chemical%indicators%(e.g.%methyl%orange).%%Plant%extracts.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
# #
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®
©CLEAPSS , The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ Tel: 01895 251496; Fax: 01895 814372; E-mail:
[email protected]; Web site: www.cleapss.org.uk
Some#results# %
%
The%following%pictures%were%sent%to%CLEAPSS%by%a%technician.%The%students%did%this%in%their%science%club.%
vASE 2015_DRAFT Page%2"of"2
®
©CLEAPSS , The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ Tel: 01895 251496; Fax: 01895 814372; E-mail:
[email protected]; Web site: www.cleapss.org.uk
Supporting Practical Science, D&T and Art - in schools and colleges
Wear#eye#protection%%
2:#Using#Petri#dishes#
Indicators%to%use%include:%litmus%solution%(L),%methyl%orange% (M),%phenolphthalein%(P),%bromothymol%blue%(B)%%
How#the#colours#of#indicators#change#with#acids#and#alkalis#
#
% % %
L
M
L
M
L
M
L
M
L
M
P
B
P
B
P
B
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B
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B
% % % % % %
0.1M## hydrochloric#acid#
0.1M## ethanoic#acid#
0.1M## ammonium#ethanoate#
0.1M## sodium#carbonate#
0.1M## sodium#hydroxide#
% %
• • % • % • % % %
Insert%this%sheet%into%a%plastic%folder.%% Place%a%small%plastic%Petri%dish%on%each%green%circle.%Place%one%drop%of%the%named%acid/alkali/salt%in%each%of%the%small%circles%in%the%dish.%% Add%a%drop%of%the%correct%indicator%to%each%small%circle.%Now%take%a%photo%of%the%final%result%(or%make%a%note%of%the%colours).% % Disposal:%Place%the%Petri%dish%under%running%water%from%the%tap%and%dry%the%dish%with%a%paper%towel.%
%
% The%solutions%are%arranged%(left%!%right)%from%most%acidic,%weakly%acidic,%neutral,%weakly%alkaline,%strongly%alkaline.%% % Look%for%a%pattern%in%the%colours%of%the%indicators.% %
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Supporting Practical Science, D&T and Art - in schools and colleges
Extension:#more#reagents#to#put#into#order#
%
L
M
L
M
L
M
L
M
L
M
P
B
P
B
P
B
P
B
P
B
% % %
Carbonic#acid## (soda#water)# %
0.1M## sodium#hydrogen#carbonate#
0.1M## ammonium#chloride#
0.1M## boric#acid#
0.1M## Sodium#ethanoate##
%
%
This%time%the%solutions%are%not%in%any%specific%order.%Look%for%a%pattern%in%the%colours%of%the%indicators.%
% % % %
Other%reagents%that%could%be%tried%are%0.1M%solutions%of%citric%acid,%phosphoric%acid,%magnesium%sulfate(VI),%sodium%chloride,%ammonia%and%lime%water.%
% # #
#Further#extension:%Find%out%what%happens%if%you%made%a%mixture%of%methyl%orange,%bromothymol%blue%and%phenolphthalein%and%add%this%to%the%test% #solutions.% #
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# #
3:##Indicators#at#home#(you%must%have%the%agreement%of%the%adults%in%the%home)# Wear#eye#protection:#this#can#be#bought#from#a#DIY#shop#if#it#is#not#already#in#the#house#toolbox!# Dropping%pipettes%can%be%made%from%drinking%straws.%Just%keep%your%finger%over%one%end%to%allow%drops%of%the%reagent%onto%a%plastic%folder.%
Reagents# Baking%soda,%washing%soda,%colourless%vinegar,%tap%water,%citric%acid.% Fruits,#cordials,#teas#and#infusions:%blackberries,%black%currants,%red%grapes%skins,%blueberries,%bherries%and%cherry%juice.%cranberries,%strawberries,%tea.%% Flower#petals:%Dahlia,%Chrysanthemum,%Delphinium,%Geranium,%Pansy,%Peonies,%Petunia,%Poppy,%Rose,%Tulip,%Violets,%% Vegetables:%beetroot,%carrots,%onion%(red),%red%cabbage.%%(Also:%try%onion%and%garlic%which%are%olfactory%indicators%T%the%odours%disappear%with%acidity%or% alkalinity).% • Spices/herbs:%curry%powder%and%tumeric%(these%are%spices%that%contain%a%bright%yellow%pigment%called%curcumin),%thyme.% • Miscellaneous:%‘Mood’%lipsticks.% • ….%you%may%find%more.% • • • •
% NB:%Some%dyes%can%be%extracted%with%hot%water%but%others%require%an%alcohol.%With%adult%permission,%you%may%be%able%to%obtain%rubbing%alcohol%(propanT2Tol)%from%a%DIY% shop.% % %
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