Making!Slime!
Category:!''
Chemistry'
Group!Size:'
1'
Estimated!Length:!
30'minutes'
Objective:!!!
Making' bouncy,' rubbery,' gooey' slime' using' simple' ingredients' found' at' home.' ' The'
effect' of' changing' the' ratio' of' the' ingredients' on' the' consistency' of' the' slime' is'
explored.'
Materials:'
Elmer’s'glue'(white'or'transparent)'
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Borax'
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3'(or'4)'plastic'cups'
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spoons'
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food'colouring'
Safety:!
There' are' no' known' toxic' effects' produced' by' borax,' Elmer’s' glue' or' the' gel' unless'
ingested.' To' be' on' the' safe' side,' make' sure' that' anyone' who' touches' the' gel' washes'
their'hands'afterwards.'Warn'the'students'not'to'get'it'on'their'clothing'and'of'course,'
not'to'eat'it!'You'can'throw'the'gel'in'the'trash.'
Introduction:!
Polymers+and+polymer+cross0linking+
Tiny'molecules'commonly'referred'to'as'monomers,'strung'in'long'repeating'chains'and'held'together'
by'chemical'bonds'form'polymers.'Why'should'you'care?'Well'for'one'thing,'your'body'is'made'of'them.'
DNA,'the'genetic'blueprint'that'defines'people'and'other'living'things,'is'a'polymer.'So'are'the'proteins'
and'starches'in'the'foods'we'eat,'the'wheels'on'our'skateboards'and'inAline'skates,'and'the'tires'on'our'
bikes'and'cars.'There'are'two'types'of'polymers:'natural'and'synthetic.''Natural'polymers'include'wool,'
hair,'rubber'and'silk.'Examples'of'synthetic'polymers'on'the'other'hand'are'polyester'(clothes),'Teflon'
(cooking'pots'nonAstick'coating),'polystyrene'(styrofoam'food'containers)'and'polycarbonate'(plastic'
bottles).'Depending'on'the'formulation,'the'same'kind'of'polymer'can'be'made'soft'and'flexible'or'hard'
and'sturdy.'A'good'example'is'the'polymer'polyethylene;'it'is'used'to'make'lab'coats,'plastic'bottles'as'
well'as'bullet'proof'vests.'
How!to!teach!it:!
1.
2.
Introduce'polymers'and'their'application'like'in'the'Introduction.'
Show'them'the'reagents'for'the'experiment'describe'how'they'look'like'and'tell'them'most'of'
the' materials' could' actually' be' bought' in' groceries.' Warn' the' students' not' to' eat' any' of' the'
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materials'and'the'products.'They'should'wash'their'hands'with'soap'and'lots'of'water'after'the'
experiment.'
3.
Group'the'students'in'pairs'and'each'pair'should'be'instructed'to'follow'the'steps'presented'in'
the'procedure.'
4.
During'the'experiment,'ask'questions'like'the'ones'suggested'in'the'section:'Questions'that'you'
can' think' about.' You' can' also' ask' questions' regarding' solubility' (like' dissolves' like)' in' this'
experiment.'
5.
Make'them'report'the'difference'between'the'two'batches'of'slime'that'they'made.'
6.
Discuss'the'science'behind'the'scenes.'
Procedure'
1. To' avoid' confusing' the' children' with' the' instructions,' demonstrate' the' experiment' while' they' are'
doing'it'step'by'step.'After'demonstrating'each'step'give'the'children'time'to'do'it'themselves.'
2. To'make'the'borax'solution,'in'a'plastic'cup,'mix'1'spoon'borax'powder'with'approximately'1'cup'of'
water.' ' Mix' well' with' a' plastic' spoon.' ' If' all' of' the' borax' powder' dissolves,' then' you' need' to' add'
more.' ' Keep' adding' a' little' bit' and' stirring' very' well.' When' you' get' to' the' point' where' no' more'
borax'will'dissolve,'then'the'solution'is'saturated'and'it’s'ready'for'use.'
3. In'two'other'plastic'cups,'add'the'Elmer’s'glue'and'the'water'as'per'the'table'below.''Add'a'drop'or'
two'of'food'colouring.''Try'to'make'your'measurement'as'consistent'as'possible.''Mix1well1before1
adding1the1Borax.'
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Experiment!
1!
2!
3!
Glue!
1'spoon'
1'spoon'
1'spoon'
Water!
1'spoon'
3'spoons'
3'spoons'
Borax!
1'spoon'
1'spoon'
2'spoons'
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4. Add' the' borax' solution' into' the' first' plastic' cup' with' glue,' and' stir' fast' and' well.' ' The' resulting'
mixture'should'be'slimy'and'gooey.''
5. To' the' remaining' plastic' cups' with' glue,' add' the' borax' as' per' the' table.' ' Stir' fast' and' well' until'
completely'mixed.'
6. Compare'the'elasticity'and'hardness'of'the'mixtures'in'the'cups.'
7. Shape'the'two'(or'three)'mixtures'into'a'ball'and'throw'it'on'the'table.''Which'one'bounces'better?'
8. Leave'the'balled'mixture'on'the'table'for'two'minutes,'observe'what'happens.'Is'the'slime'a'solid'or'
a'liquid?'
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Questions!that!you!can!think!about!
1.'What'is'a'saturated'solution?'What'happens'in'step'4'if'the'solution'is'not'saturated?'
2.'What'happens'when'more'borax'is'added'to'one'of'the'slime'products'(i.e.''step'7)?'
3.'What'happens'when'you'add'6'plastic'spoons'of'water'in'step'1'instead'of'using'5'plastic'spoons?'
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Behind!the!Scene!Science!
Polymerization1Reaction1
Sodium' borate' or' borax' (Na2B4O7.10H2O)' is' the' salt' of' a' strong' base' and' a' weak' acid.' In' water,' it'
hydrolyses'to'form'a'boric'acidAborate'buffer,'the'equilibrium'of'which'is:'
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B(OH)3'+'2'H2O'AA>''B(OH)4A'+'H3O'+''''
Note'that'boric'acid'is'so'weak'that'it'does'not'give'up'a'proton,'but'instead,'accepts'hydroxide'from'
water.'At'low'concentrations'both'boric'acid'and'borate'ions'are'present'as'the'monomeric'species.''
The' polymers' in' Elmer's' Glue' may' be' a' copolymer' of' polyvinyl' alcohol' and' polyvinyl' acetate.' The'
cross' linking' with' Elmer's' Glue' is' primarily' with' the' polyvinyl' alcohol.' When' dissolved' in' water' the'
polymers'give'a'freeAflowing'but'viscous'solution.'The'borax'solution'is'a'"crossAlinking"'substance'that'
binds'the'polymer'chains'together,'which'makes'the'polymers'thicker.''Boric'acid/borate'ion'from'the'
borax'solution'can'complex'with'polyvinyl'alcohol'as'shown:'
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How1 does1 polyvinyl1 alcohol1 interact1 with1 the1 borate1 ion?' Each' borate' can' complex' with' two' different'
chains' of' polyvinyl' alcohol,' thus' crossAlinking' the' different' polymer' chains' and' making' a' threeA
dimensional' network' of' connected' chains.' ' CrossAlinking' means' that' the' polymers' get' connected' to'
other' polymers' making' it' harder' for' them' to' move' around.' When' the' concentration' of' crossAlinked'
chains'is'high,'water'gets'trapped'within'the'network,'and'a'semisolid'gel'is'the'product.'Examples'of'
networks'and'gels'are'rubber,'rubber'cement,'Jello,'fruit'jellies,'tofu,'and'yogurt.'Commercial'slime'is'
the'crossAlinked'product'of'guar'gum'and'borax.'1
Polyvinyl'acetate'from'Elmers'glue'can'also'participate'in'the'crossAlinking'as'follows.'Polyvinyl'acetate'
reacts' with' water' (slowly)' producing' acetic' acid' and' a' hydroxyl' group' remaining' in' the' polymer'
backbone,'especially'if'the'Elmer's'Glue'is'old.'In'this'case'the'hydroxyl'group'could'also'crosslink'with'
the'borax.'The'fundamental'reaction'is'between'the'hydroxyl'group'and'the'boric'acid'from'the'borax.'
Effects1of1Concentration1of1Reagents1
As'mentioned'above,'when'the'polymer'chains'get'more'crossAlinked,'it'gets'harder'for'them'to'move'
around,'and'the'slime'starts'to'get'thicker.'Adding'more'borax'solution'in'procedure'7'should'make'the'
slime'thicker,'harder,'less'elastic'and'less'bouncy.'When'the'Elmer’s'glue'is'more'dilute'(e.g.'more'water'
is'added),'the'resulting'slime'becomes'softer.'''Also,'when'the'trapped'water'evaporates'from'the'crossA
linked'polymer,'the'slime'gets'hard.'Adding'water'can'rehydrate'the'slime'and'bring'it'back'to'its'soft'
texture'provided'it'was'not'kept'in'its'hard'state'for'a'long'period'of'time.'In'addition,'when'making'the'
slime,'adding'more'water'to'the'waterAglue'solution'will'make'the'slime'more'stretchable'and'softer.'
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Saturated1Solutions1
When'adding'more'solid'to'a'solution'and'it'appears'that'the'added'solid'is'not'dissolving'anymore,'the'
solution'is'said'to'be'a'saturated'solution.'The'perception'that'it'is'not'dissolving'anymore'is'however'
not'true.'In'fact,'the'solid'continues'to'be'dissolved,'however,'the'solids'that'were'previously'dissolved'
continuously'precipitate'as'well.'The'rates'of'dissolution'and'precipitation'are'equal'and'the'system'is'
said'to'be'at'equilibrium.'
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States1of1Matter1
When' the' balled' slime' was' left' on' the' table,' it' spreads' after' a' few' minutes,' that' is,' the' shape' is' not'
retained.' Is' it' then' a' solid' or' a' liquid?' Recall' that' solids' retain' their' shape' unless' an' external' force' is'
applied'and'liquids'follow'the'shape'of'the'container.'Slime'has'actually'properties'that'are'both'solid'
and'liquidAlike.''
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