ASE$2015$
Chemistry$Workshop$
Hands:on$activities!
1
$
For!ease!of!download,!copies!of!the!workshop!activity!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.!
!
!
!
$
!
vASE!2015_DRAFT!
!
!
!!
©CLEAPSS®,!The!Gardiner!Building,!Brunel!Science!Park,!Kingston!Lane,!Uxbridge!UB8!3PQ!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Tel:!01895!251496;!Fax:!01895!814372;!ESmail:[email protected];!Web!site:!www.cleapss.org.uk!
!
Supporting Practical Science, D&T and Art
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"!in!schools!and!colleges!
!
Finding&the&percentage&of&water&in&a&hydrated&salt&&&&&&&&&&&&&&&&&&
(using!an!unbreakable!crucible!)!
&
Procedure&&
Wear!eye!protection!
1. Find!the!mass!of!the!‘crucible’!(M1).!
2. Add!~!0.5!S1.0!g!of!copper(II)!sulfate(VI)S5Swater!to!the!crucible.!!
3. Find!the!mass!of!the!crucible!+!hydrated!salt!(M2).!
4. Using!a!clamp*,!support!the!crucible!above!a!small!spirit!burner.!!
5. Heat!the!crucible!until!the!blue!colour!has!been!lost!and!a!
white/colourless!solid!remains.!!
Remove!the!spirit!burner!(&!extinguish!the!flame).!!
Allow!the!crucible!to!cool.!
6. Find!the!mass!of!the!crucible!+!anhydrous!salt!(M3).!
*If!the!clamp!is!not!suitable!–!use!tongs!or!metal!pliers.!
Using&the&results:&
• Mass!of!copper(II)!sulfate(VI)S5Swater!used!=!M2!–!M1.!
• Mass!of!water!lost!from!the!salt!=!M2!–!M3.!
!
Calculation:&
The!percentage!of!water!in!the!hydrated!salt!=
(!!!!!)×!""
(!!!!!)
!
How!close!is!your!experimental!result!to!the!theoretical!value!of!36.0%?
Chemistry&notes&
Copper(II)!sulfate(VI)S5Swater!loses!4!of!its!water!molecules!at!~100°C.!The!final!water!molecule!is!
lost!at!150°C.!With!a!Bunsen!flame,!a!temperature!of!over!650!°C!is!reached!which!causes!the!
hydrated!copper!sulfate!to!decompose;!the!solid!darkens!and!toxic!and!corrosive!sulfur!di/triS
oxide!gases!are!released.!Using!a!cooler!flame!(!!spirit!burner)!prevents!this!decomposition.!
Other!hydrated!salts!can!also!be!used:&
• Magnesium&sulfate(VI)B7Bwater!loses!all!its!water!at!200°C!and!does!not!decompose!until!1124°C.!!!!!!!!!!!!!
On!heating!it!liquefies!and!then!‘spits’!as!it!reSsolidifies,!so!the!bottle!top!needs!to!be!set!a!little!higher!
and!then!gradually!lowered!as!heating!progresses.!!
• Iron(II)&sulfate(VI)B7Bwater!loses!its!water!at!70°C!and!begins!to!decompose!at!400°C.!Unfortunately,!it!
is!difficult!obtain!the!pure!green!heptahydrate!as!it!loses!water!to!the!atmosphere!(white!specks!will!be!
seen!in!the!solid).!
!
The&apparatus&
The!‘crucible’!is!prepared!by!strongly!heating!a!serrated!steel!bottle!top!(in!
a!fume!cupboard)!to!remove!the!plastic!insert.!!
After!cooling,!a!hole!is!drilled!and!a!metal!bolt!is!fitted!(see!picture).!
!
!
vASE!2015_DRAFT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!©CLEAPSS®,!The!Gardiner!Building,!Brunel!Science!Park,!Kingston!Lane,!Uxbridge!UB8!3PQ!
Page!1!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Tel:!01895!251496;!Fax:!01895!814372;!ESmail:[email protected];!Web!site:!www.cleapss.org.uk!
Structure'and'bonding'
Ionic'compounds,'diffusion'and'precipitates!
'
Procedure!
Wear'eye'protection!
1. Place!a!few!‘grains’!of!copper(II)!sulfate(VI)S5Swater!in!one!of!the!small!white!circles!and!a!few!
‘grains’!of!sodium!carbonate!in!the!other!small!circle!(use!a!microspatula!or!forceps).!
2. Add!drops!of!distilled!water!to!the!centre!of!the!larger!(grey)!circle!until!the!water!comes!close!
to!the!two!solids!but'is'not'touching'them.!
3. Now!take!a!wooden!splint!in!each!hand!and!push!both!solids!until!they!are!just!into!the!outer!
edge!of!the!water!droplet.!!
4. Observe!what!happens.!
•
•
Is!the!precipitate!that!forms!blue!(i.e.!contains!copper)!or!white!(i.e.!contains!sodium)?!
Explain!your!observations.!
5. Now!try!repeating!the!experiment!with!other!chemicals!to!see!if!precipitates!form.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
You!could!try!combinations!including:!
!
•
lead(II)!nitrate(V)!
•
barium!chloride!
•
potassium!iodide!
Use!the!‘palette’!below!(one!lecturer!has!called!this!a!labtop!).!Just!wipe!off!the!liquid!and!solid!
with!a!paper!towel!when!you!have!finished!and!place!in!the!bin.!Wash'your'hands.!
!
!
!
!
!
!
!
vASE!2015_DRAFT!
!©CLEAPSS®,!The!Gardiner!Building,!Brunel!Science!Park,!Kingston!Lane,!Uxbridge!UB8!3PQ!
Page!1&of&2!!!!!!!!!Tel:!01895!251496;!Fax:!01895!814372;!ESmail:[email protected];!Web!site:!www.cleapss.org.uk!
Structure'and'bonding'
Ionic'compounds,'diffusion'and'precipitates!
!
'
Some'results!
Sodium!carbonate!solid!was!placed!in!the!rightShand!circle!and!barium!chloride!solid!was!in!the!
leftShand!circle.!
The!precipitate!(of!barium!carbonate)!can!be!seen!forming!in!the!droplet.!!
!
!
An'alternative'approach:!
Here,!the!bulb!of!a!plastic!dropper!pipette!has!been!cut!in!half!(longways)!and!the!solids!placed!at!
either!end!of!the!open!bulb.!!
Water!was!then!added!in!drops!between!the!solids!so!that!the!two!solids!began!to!dissolve!at!the!
same!time.!!
The!picture!below!shows!the!precipitate!of!yellow!lead'iodide!forming!from!lead(II)!nitrate(V)!and!
potassium!iodide.!
!
!
!
!
vASE!2015_DRAFT!
!©CLEAPSS®,!The!Gardiner!Building,!Brunel!Science!Park,!Kingston!Lane,!Uxbridge!UB8!3PQ!
Page!2&of&2!!!!!!!!!Tel:!01895!251496;!Fax:!01895!814372;!ESmail:[email protected];!Web!site:!www.cleapss.org.uk!
Exploring*Indicators*
*
INDICATORS!change!colour!when!added!to!solutions!of!different!pH.!!Carry!out!Steps*145!to!investigate!three!indicators!(bromothymol*blue,*methyl*
orange*and!phenolphthalein).!Follow*the*instructions*carefully.!WEAR*EYE*PROTECTION.!
Step*1:!!*
Step*2:**
Step*3:*
Step*4:*
Step*5:*
Put!4*drops!of!0.1!M!HCl(aq)!into!circle!A1!to!create!one!large!drop.!Repeat!for!each!circle!A2!S!A4.*
Now!use!the!solutions!named!at!the!top!of!the!other!columns!(i.e.!instead!of!HCl)!to!repeat!Step*1!for!B1*S!B4,!C1!S!C4,!D1!S!D4!&!E1!S!E4.*
Put!1*drop!of!bromothymol*blue!into!each!circle!A1!to!E1;!1!drop!of!methyl*orange!in!A2!–!E2!and!1*drop!of!phenolphthalein!in!A3!–!E3.*
Make!a!mixture!of!indicators!(do!this!in!the!glass!vial!or!well!plate)!using!the!recipe!in!the!greenSshaded!box!below.!
Put!1*drop!of!your!mixed!indicator!into!each!solution!in!circles!A4!–!E4.!Make!a!note!of!your!observations!(take!a!photo?).!
*
0.1*M*HCl(aq)*
(strong*acid,*pH*=*1)*
*
pH*4*buffer*
pure*water**
(neutral,*pH*=*7)*
(weak*acid)*
A1!
B1!
C1!
pH*9*buffer*
(weak*alkali)*
!
0.1*M*NaOH(aq)*
(strong*alkali,*pH*=*13)*
D1!
!
E1!!
INDICATOR*
bromothymol*blue*
(BB)*
A2!
!
B2!
!!
C2!
!!
D2!
!
E2!
A3!
!
B3!
!!
C3!
!!!!
D3!
!!!!
E3!
A4!
!!!
B4!
!!
C4!
D4!
!!!!
E4!
methyl*orange*
(MO)*
Phenolphthalein*
(PP)*
Mixed*indicator:*
BB!!!=!10!drops!
MO!=!!!5!drops!
PP!!!=!!!5!drops*
!
! !
!!!!!!vASE!2015_DRAFT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!©CLEAPSS®,!The!Gardiner!Building,!Brunel!Science!Park,!Kingston!Lane,!Uxbridge!UB8!3PQ!
!!!!!Page!1!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Tel:!01895!251496;!Fax:!01895!814372;!ESmail:[email protected];!Web!site:!www.cleapss.org.uk!
Supporting Practical Science, D&T and Art
- in schools and colleges
Ammonia'chemistry'in'a'Petri'dish'
Why'do'this?'
Ammonia'dissolves'in'water'to'produce'an'alkaline'solution'(sometimes'referred'to'as'ammonium'
hydroxide).'Ammonia'solution'can'be'used'to'identify'metal'ions'as'it'produces'precipitates'–'
some'of'which'are'highly'coloured'if'transition'elements'are'present.'This'activity'provides'a'quick'
and'simple'way'to'explore'some'of'the'chemistry'of'ammonia'and'metal'ions.'
Possible(curriculum(links:(ammonia,(qualitative(analysis,(metal(ions,(acid7base(chemistry.'
Suitability'
Y7'
Personal'protective'equipment'and'essential'safety'measures'
Wear'eye'protection.''
This'Practical(Procedure'should'be'read'in'conjunction'with'the'following'guidance:'
•
Hazcards(5'and'6'
Outline'method'and'control'measures'
Ensure'that'the'2'M'ammonia'solution'is'freshly'prepared.'
Disposal'
Place'the'Petri'dish'in'water'in'a'bowl'of'water.'Remove'any'solid'materials'and'then'pour'the'
solution'down'a'foul'water'drain.'Place'indicator'paper'in'a'rubbish'bin.'
Chemistry'notes'
If'all'the'ammonia'is'released'(which'it'isn’t),'then'24'cm3,'or'17'mg,'of'the'gas'would'be'released.'
Although'we'can'detect'the'gas'by'our'sense'of'smell'(odour'level'is'3.5'mg'm–3),'the'ammonia'
levels'will'be'below'the'Short'Term'Exposure'Level'(STEL)'level'of'25'mg'm–3''in''a'large'room'(of'
300'm3)'averaged'over'15'minutes.'
Expected'results'
Indicator'paper'indicates'a'pH'of'11.'
Sulfuric(VI)'acid'is'neutralised'and'finally'becomes'alkaline.'
Some'of'the'metal'salts'form'precipitates'(as'hydroxides).'
Some'of'the'metal'salts'form'hydroxide'precipitates'which'then'dissolve'in'excess'ammonia'
solution'as'complex'ions'are'formed.'
At'any'one'time'in'a'1'M'aqueous'ammonia'solution,'only'about'one'molecule'of'ammonia'in'240'
is'converted'to'ammonium,'NH4+(aq),'and'hydroxide,'OH–(aq)'ions.'Ammonia'is'an'example'of'a'
weak'alkali'because'not'all'the'ammonia'molecules'form'a'hydroxide'ion.'The'hydroxide'ions'
produced'neutralise'acids'and'react'with'metal'ions.'
1.
2.
3.
4.
'
'
vASE 2015_DRAFT
Page 1
©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
Ammonia'chemistry'
Wear'eye'protection.'Work'in'a'well5ventilated'lab.'
'
! If#not#already#laminated,#place#it#in#a#plastic#wallet/folder.#
! Place#a#9#cm#diameter#Petri#dish#on#the#large#solid:line#circle#(left).#Remove#lid.#
! Place#the#test#solutions/papers#in#the#Petri#dish#in#the#numbered#positions,###########
1'–'6,#as#described#below.##
1
6
Also#place#1:2#drops#of#solutions#2:6#in#the#matching#outer:ring#circles#(i.e.#
outside#the#Petri#dish)#:#you#will#then#be#able#to#compare#with#those#inside#the#
Petri#dish#to#see#what#effect#the#ammonia#has.#
2
RV
*
3
5
1.
2.
3.
4.
5.
6.
Universal#indicator#paper#–#damp#(a#1:2#cm#strip).#
Hydrochloric#acid,#0.1#M#(2#drops)#containing#Universal#indicator.#
Copper(II)#salt#solution,#0.1#M#(2#drops).#
Iron(II)#salt#solution,#0.1#M#(2#drops)#
Iron(III)#salt#solution,#0.1#M#(2#drops)#
Zinc#salt#solution,#0.1#M#(2#drops)#
! Place#an#empty#‘reaction#vessel’#(eg,#small#watch#glass)#in#the#‘RV’#circle.#
4
! To#generate#ammonia#gas#(TOXIC):#use#tweezers#to#place#2:3#granules#of#
anhydrous#calcium#chloride#in#the#reaction#vessel#(gas#generator).#############################
Add#0.5#cm3#(approximately#10#drops)#of#ammonia#solution#(2#M)#to#the#reaction#
vessel.#Immediately'place'the'lid'on'the'Petri'dish.#
! Watch#carefully#and#record#your#observations#over#the#next#5:10#minutes###############
(eg,#take%photographs).#
! Explain#as#much#of#the#chemistry#going#on#in#the#Petri#dish#as#you#can.#
! Disposal:#refer#to#notes#on#page#1.#
vASE 2015_DRAFT
Page 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
Investigating*iron*chemistry*
• Wear*eye*protection*
• Use$a$wooden$splint$for$stirring.$After$use,$
break$off$the$end$&$place$in$the$waste$bin.*
- in schools and colleges
Make*Solution*A:$$Put$a$small$spatula$measure$(~0.2$g)$of$iron(II)$salt$in$a$vial.$$Add$1.5$cm3$of$distilled$water.$$Swirl$to$dissolve$solid.$
1.$
$
2.$
Place$3$drops$of$solution*A$
in$circle$1."Observe"at"
intervals"while"carrying"out"
the"rest"of"this"activity.$
$
6.$
4.$
5.$
Put$2<3$magnesium$pieces$in$ 1*drop$of$solution*A.$
circle$2.$Add$3*drops$of$
Add$5*drops$of$sodium$
solution*A.$Slide$a$magnet$
hydroxide.*
slowly$towards$the$mixture.$
1*drop$of$solution*A.$
Add$1*drop$of$potassium$
hexacyanoferrate(II).$
1*drop$of$solution*A.$
Add$1*drop$of$potassium$
thiocyanate.$
Now*go*to*Step*6.*
$
$
7.$
8.$$
9.$$
1*drop$of$solution$A.$
$
Add$2*drops$of$hydrochloric$
acid$and$3*drops*of*hydrogen$
peroxide.$Mix.$$
This*is*Solution*B.*
$
1*drop$of$solution*B.$
Add$5*drops$of$sodium$
hydroxide.$
1*drop$of$solution*B.$
Add$1*drop$of$potassium$
hexacyanoferrate(II).$
1*drop$of$solution*B.$
Add$1*drop$of$potassium$
thiocyanate.$
10.$
Note:$the$reactions$in$Steps$10$
and$11$are$difficult,$as$they$
need$speedy$action!$
The$aim$is$to$reduce$iron(III)$
ions$back$to$iron(II)$ions$with$
the$thiosulfate$ions.$
1*drop$of$solution*B.$
If$you’ve$been$successful$–$you$
Observe$carefully$as$you$add$
should$get$a$green$precipitate$
5*drops$of$sodium$thiosulfate$
in$Step$11.*
solution.$Mix*.$$
11.$$
3.$
$
$
Now*go*to*Step*10.$
Solutions*used:*
• sodium$hydroxide,$NaOH(aq),$0.4$M$
• hydrochloric$acid,$HCl(aq),$1$M$
• hydrogen$peroxide,$H2O2(aq),$20$‘vol’$
• sodium$thiosulfate,$Na2S2O3(aq),$0.5$M$
Take$1*drop$from$the$
mixture$in$circle*10.$$
Add$5*drops$of$sodium$
hydroxide$solution.$
• potassium$hexacyanoferrate(II),$K4Fe(CN)6(aq),$0.1$M$
• potassium$thiocyanate,$KSCN(aq),$0.1$M$
*If$a$brown$ppte$appears,$add$drops$of$HCl(aq)$until$the$ppte$just$dissolves.$
vASE 2015_DRAFT
Page 1 of 1
©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
!
Exploring!equilibria!
Reactions*that*‘go*both*ways’*and*dynamic*equilibria*are*commonly*studied*in*both*pre916*and*
post916*courses.*The*reaction*described*here*can*be*used*to*explore*the*effect*of*changing*
conditions*(temperature*or*concentration)*on*a*system*at*equilibrium.**
*
Cobalt(II)!complexes!–!investigating!the!effect!of!temperature!
The*three*sealed*tubes*each*contain*192*cm3*of*a*violet<coloured*cobalt(II)*solution*.**
The*solution*contains*an*approximately*equimolar*mixture*of*two*complex*ions:**
• [Co(H2O)6]2+*which*is*pink**
• [CoCl4]2–*which*is*blue*
!
Procedure*
Wear!eye!protection*
1. Keep*one*of*the*tubes*at*room*temperature*as*a*control.*
2. Place*one*of*the*tubes*in*a*beaker*of*hot*water*from*a*just9boiled*kettle.*************************************
What(do(you(observe?*
3. Place*the*third*tube*in*an*ice9cold*water*bath.************************************************************************************
What(do(you(observe?*
4. Explain*your*observations.***************************************************************************************************************************
In(which(direction(is(the(ligand7exchange(reaction((below)(exothermic?*
*
[Co(H2O)6]2+(aq)!+!4Cl–(aq)!!!
!!!!![CoCl4]2–(aq)!+!6H2O(l)!
*********************************pink**************************************************************************blue*
*See*notes*on*page*2.*
*
!
!
!
!
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: [email protected]; Web site: www.cleapss.org.uk
*Notes:!
Cobalt(II)!chloride!
Harmful*if*swallowed.*May*cause*an*allergic*skin*reaction.*May*cause*
allergy*or*asthma*symptoms*or*breathing*difficulties*if*inhaled.*Suspected*
of*causing*genetic*defects.*May*cause*cancer*by*inhalation.*May*damage*
fertility.*Very*toxic*to*aquatic*life*with*long*lasting*effects.*
*
Hydrochloric!acid!
Causes*severe*skin*burns*and*eye*damage.*May*cause*respiratory*irritation.*
*
*
!
To!prepare!the!cobalt(II)!chloride!equilibrium!mixture((
Wear!splash<proof!goggles!&!chemical!resistant!gloves!to!prepare!the!solution.!Work!in!a!fume!cupboard.*
•
In*a*conical*flask,*dissolve*2*g*of*cobalt(II)*chloride*hexahydrate*in*20*cm3*of*distilled/deionised*water.**********************
A*pink*solution*of*Co(H2O)62+(aq)*is*formed.*Pour*the*cobalt(II)*solution*into*a*50*cm3*measuring*cylinder.*
•
Carefully,*add*concentrated*hydrochloric*to*the*cobalt(II)*solution*to*give*a*total*solution*volume*of*50*cm3.*********
A*blue*solution*containing*CoCl429*is*formed.*Pour*this*mixture*back*into*the*conical*flask.*
•
•
Using*‘trial*and*error’*additions*of*small*volumes*of*water*and*concentrated*hydrochloric*acid,*produce*a*
solution*with*an*‘in7between’*violet*colour.**
Once*prepared*as*described,*the*cobalt(II)*complex*solution*should*be*treated*as*a*serious*health*hazard*and*
will*also*be*at(least*a*skin,*eye*and*respiratory*irritant.*However,*if*used*as*suggested*here*(in*sealed*test9
tubes),*it*presents*minimal*risk*of*harm*to*health.**
The*prepared*solution*can*be*stored*in*a*suitable,*appropriately*labelled*reagent*bottle*for*future*use.**
See*also*CLEAPSS*Hazcards.**
•
Use*a*plastic*dropper*pipette*to*transfer*293*cm3*of*the*cobalt*equilibrium*mixture*into*small*test9tubes.*******
Stopper/seal*the*tubes.*
(
The!chemistry:*the*equilibrium*between*the*two*complexes*can*be*disturbed*by*changing*the*temperature*(or(
by(adding(Cl–(ions).*The*equilibrium*is:*
[Co(H2O)6]2+(aq)*+*4Cl–(aq)***
*****[CoCl4]2–(aq)*+*6H2O(l)*******
!!!!!!!!!!!!pink****************************************************blue*
The*shifts*in*equilibrium*position*produced*by*temperature*changes*are*in*accordance*with*Le*Chatelier’s*
principle.*ΔH*is*+ve*(endothermic)*in*the*forward(direction(as(written(above.*Warming*the*solution*causes*a*
‘shift’*to*the*right*and*the*solution*becomes*blue*(and*vice*versa*because*ΔH*for*the*reaction*is*–ve,*exothermic,*
in*the*reverse*direction).*
(Adapted*from*RSC*Classic(Chemistry(Demonstrations.*http://media.rsc.org/Classic*Chem*Demos/CCD98.pdf)!
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
Micro&electrolysis,of,copper(II),chloride,solution,
Procedure,
Wear,eye,protection,
1. Place(the(following(in(the(Petri(dish((see(diagram(below)(in(the(following(order:((
(i)
(ii)
(iii)
(iv)
1&2,drops(of(potassium(bromide(solution((~(0.5(M(–(2(M);(
1&2,drops(of(potassium(iodide(solution((~(0.1(M(–(0.5(M);(
a(piece(of(damp(blue(litmus(paper(
drops(of(0.5(M(copper(II)(chloride(solution(until(the(‘merged’(drop(just(touches(both(electrodes.(
A few drops of 0.5 M
copper(II) chloride
solution
Moist blue litmus
paper
Carbon-fibre
electrodes
Two drops of 0.1 to
0.5 M potassium
1V2(drops(of(KI((aq)(
iodide solution
Two drops of 0.5 to
1V2(drops(of(KBr((aq)(
2M potassium
bromide solution
2. Place(the(lid(on(the(Petri(dish(and(then(connect(the(electrodes(to(a(DC(source((~(6(to(9(volts).(
3. Switch(on(and(observe(what(happens:((i)(at(the(electrodes,((ii)(to(the(test(solutions(&(indicator(paper.(
4. Look(carefully(at(the(electrode(regions(using(the(digital(microscope.(
Warning:,please,disconnect,the,battery,as,soon,as,you,have,completed,your,observations.(
(
Note:(To(avoid(inhaling(chlorine(gas((which)could)result)in)triggering)breathing)difficulties)to)those)who)are)
susceptible),(do(not(remove(the(cover(of(the(Petri(dish(and(at(the(same(time(lean(closely(over(the(top.((
The(chlorine(can(be(quickly(diffused(away(with(a(waft(of(the(hand.(The(chlorine(levels(are,(on(average,(
well(below(the(workplace(exposure(levels((see(note(on(reverse).(
Results,
((((
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: [email protected]; Web site: www.cleapss.org.uk
(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((
Notes,
During,the,electrolysis:((
• copper,(Cu(s),(is(produced(at(the(cathode((see(picture(on(page(1).(
• chlorine,(Cl2(g)(formed(at(the(anode(reacts(with(the(salt(solutions(to(form(bromine,(Br2,(and(iodine,(I2((in(
solution).((
• moist(blue(litmus(paper(turns(red(due(to(formation(of(hydrochloric(acid,(HCl(aq),(and(chloric(I)(acid,(
HClO(aq).(The(latter(then(oxidises(the(litmus(dye(to(give(colourless(products.(
• The(results(are(even(more(effective(if(the(procedure(is(viewed(via(a(visualizer/digital(microscope.(
(
Equipment,and,safety,notes,
• The(electrodes(are(1mm(carbon(fibre(rods(available(from(suppliers(of(kite(materials.(
3
• In(this(procedure,(4(drops((i.e.(0.2(cm )(of(0.5(M(copper(II)(chloride(solution(are(used.(The(maximum(
amount(of(chlorine(that(could(be(produced(is(~(7.1(mg((i.e.(~(2.4(cm3(at(room(temperature).((
If(15(sets(of(equipment(were(all(working(at(the(same(time,(the(Workplace(Exposure(Limit((WEL)(of(1.5(
mg(mV3((averaged(over(the(whole(room)(would(not(be(reached.(However,(it(would(be(exceeded(in(
localised(areas,(i.e.,(just(above(the(Petri(dish(when(the(lid(is(removed.(Hence,(great(care(must(be(taken(
to(avoid(inhaling(the(chlorine(gas.(
,
Possible,extensions,
Find(out(what(happens(with(other(salt(solutions.(
Potassium(
bromide(
Place(1(drop(of(2M(potassium(bromide(in(a(Petri(dish(and(add(9(drops(of(water.((
Place(this(mixture(between(the(electrodes.(Based(on(the(experiment(with(copper(II)(
chloride(solution,(design(some(additional(investigations.(
Iron(II)(
sulfate(VI)((
Place(iron(II)(sulfate(VI)(solution(between(the(electrodes.((
If(iron(is(produced(at(an(electrode,(it(ought(to(be(magnetic.(Is(it?(
Zinc(sulfate(VI)((
Place(0.1M(zinc(sulfate(VI)(solution(between(the(electrodes.(Follow(the(electrolysis(
using(a(digital(microscope.(Further(dilution(will(slow(down(the(rate(of(electrolysis(
but(will(this(make(the(appearance(of(any(metal(crystals(easier(to(see?(Investigate.(
Lead(nitrate(V)((
Place(0.1(M(lead(nitrate(V)(solution(between(the(electrodes(and(follow(the(
electrolysis(using(a(digital(microscope.(
Silver(nitrate(V)(
Place(0.05M(silver(nitrate(V)solution(between(the(electrodes(and(follow(the(
electrolysis(using(a(digital(microscope.(
Hint:(the(electrodes(can(be(moved(closer(together(or(further(apart(to(speed(up(or(slow(down(the(rate(of(electrolysis.(
(
Disposal,
All(the(liquids(can(be(washed(down(the(sink(into(the(foul(water(drain.(
(
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
Zinc%electroplating%
Why%do%this?%
Electroplating-is-an-important-industrial-application-of-electrolysis-and-is-studied-in-many-pre416-and-post4
16-courses.-Electroplating-processes-often-involve-coating-a-metal-object-with-another-metal-to-protect-orenhance-the-surface-properties-of-the-object.-This-small4scale-activity-provides-a-simple-method-forobserving-electroplating-in-action-and-is-a-safer-alternative-to-methods-which-use-nickel-salts-(seeAdditional%information).Possible(curriculum(links:(electrolysis,(redox,(ionic(compounds,(industrial(chemistry-
Suitability%
Teacher/technician-(for-preparation)Y9-
Personal%protective%equipment%and%essential%safety%measures%
Wear-eye-protectionThis%Practical%Procedure%should%be%read%in%conjunction%with%the%following%guidance:%
•
•
Hazcards-67,-91-and-108B-Recipe(Book-61,-85-and-106-
Outline%method%and%control%measures%
Preparation%
•
A-plating-‘bath’-can-be-made-from-a-small-plastic-food-container-(~-6-cm-x-6-cm-x-3-cm).-Drill-a-holethrough-a-zinc-foil-strip-(the-anode)-then-fix-this-in-place-with-a-bolt/screw-through-the-plastic-container(if-necessary,-first-melt-a-hole-in-the-container-wall-–-work-in-a-fume-cupboard-when-doing-this).-For-theelectroplating-procedure,-support-the-‘bath’-in-a-clamp-or-glue-it-to-a-corrugated-plastic-(eg,-‘Corriflute’)base.-[Alternatively,(a(zinc(foil(strip(can(simply(be(hooked(over(the(rim(of(a(100(cm3(beaker.]zinc%foil%strip
plastic%container
(~%6%cm%x%6%cm%x%3%cm)
screw/bolt%&%nut
-
%
PP 0005 vASE2015_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: [email protected]; Web site: www.cleapss.org.uk
Procedure%
Wear%eye%protection%
1. To-clean-the-copper-cathode:-hold-a-strip-of-copper-foil-with-plastic-forceps-and-dip-it-into-0.25-–-0.4-Mnitric-acid-for-about-1-minute-–-or-just-until-the-surface-of-the-metal-becomes-bright-and-shiny.-Rinsethe-foil-strip-in-water-and-dry-with-a-paper-towel/tissue.2. To%prepare%the%zinc%plating%solution:-add-30-cm3-of-0.4-M-sodium-hydroxide-solution-to-5-cm3-of-0.1-Mzinc-sulfate(VI)-solution-and-stir.-Any-white-precipitate-of-zinc-hydroxide-should-dissolve-to-give-a-clearsolution.-Pour-the-solution-into-the-plating-‘bath’.3. Connect-the-+ve-pole-of-a-6-V-DC-source-(or-use-a-9-V-battery)-to-the-zinc-anode.-4. Connect-a-cleaned-copper-foil-strip-(cathode)-to-the-–ve-pole-of-the-battery/DC-source-then-dip-thecopper-strip-into-the-plating-solution-to-complete-the-circuit.Within-a-few-seconds,-the-copper-foil-quickly-becomes-coated-with-zinc-and-looks-like-‘silver’.-Afterrinsing-and-drying-it-can-be-rubbed-with-a-cloth-to-make-it-shine-(see-Extensions).-
copper&cathode&(,)
zinc&anode&(+)
-----
zinc&plating&
solution
-
Extensions%%
•
Turning-‘silver’-into-‘gold’:-pass-the-dry,-plated-copper-foil-quickly-through-a-hot-flame.-The-zinc-meltsinto-the-top-layer-of-the-copper-to-produce-a-brass-alloy-surface-–-thus-giving-a-‘gold-effect’.-
•
Copper4plated-pennies-could-also-be-used.-These-can-be-stuck-into-students’-notes-and-not-used-aslegal-tender-afterwards.-
•
If-required-–-it-can-be-shown-that-the-zinc-plating-(from-step-3)-can-be-removed-by-immersing-thecopper-strip-in-1-M-sulfuric(VI)-acid-and-warming.-
Disposal%
The-used-plating-solution-can-be-diluted-in-a-bucket-of-water-and-poured-down-a-foul-water-drain.-
Chemistry%notes%
The-best-conditions-for-electroplating-involve-using-a-low-concentration-of-the-hydrated-metal-ion-requiredfor-plating-and-a-good-conductivity-in-the-electrolyte-solution-(i.e.-a-high-total-concentration-of-ions).In-this-activity,-the-zinc-is-in-equilibrium-(as-below)-but-the-position-of-equilibrium-lies-well-to-the-right-sothe-concentration-of-hydrated-zinc-ion,-Zn2+(aq),-is-extremely-small.Zn2+(aq)---+---4OH–(aq)-
-
Zn(OH)42–-(aq)-
Additional%information%
Many-published-resources-often-suggest-using-nickel-electroplating-as-an-example-of-the-electroplatingprocess-but-nickel-salts-are-classified-as-presenting-potentially-long4term-health-hazards.-Following-COSHHprinciples,-it-is-preferable-to-illustrate-the-electroplating-process-using-less-toxic-materials.®,
PP 0005 vASE2015_DRAFT
©CLEAPSS The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ
Page 2 of 2
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!
!
Electrochemical,cells,and,electrode,potentials,
Why,do,this?,
Redox!reactions,!reactivity!and!electrochemical!cells!are!studied!in!both!preS16!and!postS16!courses!
although!more!detailed!work!involving!electrode!potentials!is!usually!only!met!at!postS16!level.!Younger!
students!could!use!the!apparatus!to!investigate!the!relationship!between!the!reactivity!of!metals!and!the!
voltage!measured!in!a!simple!electrical!cell.!Older!students!could!carry!out!a!range!of!activities!involving!
electrode!potentials.!!
Suitability,
Y7!
Personal,protective,equipment,and,essential,safety,measures,
Wear!eye!protection.!Use!tweezers!for!manipulating!metal!pieces.!
This,Practical(Procedure,should,be,read,in,conjunction,with,the,following,guidance:,
•
Hazcards!for!the!metals!and!solutions!used!
Outline,method,and,control,measures,
1. Place!a!plastic!Petri!dish!on!a!flat!surface.!Place!a!strip!of!filter!paper!in!the!dish.!!
2. Add!2S4!drops!of!copper(II)!sulfate(VI)!solution!(0.1M)!to!one!end!of!the!strip.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Place!a!small!piece!of!copper!foil!on!top!of!the!copper(II)!sulfate(VI)!solution.!
3. Add!2S4!drops!of!zinc!sulfate(VI)!solution!(0.1M)!to!the!opposite!end!of!the!strip.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Place!a!small!piece!of!zinc!foil!(or!a!zinc!granule)!on!top!of!the!zinc!sulfate(VI)!solution.!
4. Carefully,!add!drops!of!potassium!nitrate!solution!(0.1!M)!to!the!centre!of!the!filter!paper!S!allowing!the!
solution!to!spread!out!so!that!it!just!touches!the!other!two!solution!areas!(i.e.!the!‘salt!bridge’).!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
5. Set!the!multiSmeter!to!a!convenient!scale,!e.g.,!2000!mV.!
6. Place!one!probe!on!the!top!(i.e.!dry)!surface!of!each!of!the!metals!and!take!a!reading.!
,
,Filter paper strip
Copper foil on filter
paper dampened
2+
with Cu (aq).
Petri dish
,
Zinc foil on filter
paper dampened
2+
with Zn (aq).
More,metals:,place!another!strip!at!right!angles.!Repeat!the!experiment!using!other!metals!with!their!salts!at!
each!end!of!the!filter!paper!strips.!
Extension,,,
Concentration:,Concentration!cells!can!be!set!up!using!1M!copper(II)!sulfate!at!one!end!of!a!filter!paper!
strip!and!more!dilute!copper(II)!solutions!at!the!other!end!of!the!strip.,
Complexing:!0.1M!copper(II)!sulfate!made!up!in!water!is!placed!at!one!end!of!a!filter!paper!strip!and!0.1!M!
copper,sulfate,made,up,in,2M,ammonia,solution!is!placed!at!the!other.,
vASE!2015_DRAFT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!©CLEAPSS®,!The!Gardiner!Building,!Brunel!Science!Park,!Kingston!Lane,!Uxbridge!UB8!3PQ!
Page!1!of!1!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Tel:!01895!251496;!Fax:!01895!814372;!ESmail:[email protected];!Web!site:!www.cleapss.org.uk!