Abstract This is a simple "kitchen chemistry" project about acid/base chemistry. chemistry. Scientists measure the acidity or alkalinity of a solution using a logarithmic scale ca lled the pH scale. In this project you'll learn about the pH scale and you'll make your o!n pH indicator paper using a pH sensiti#e dye that you'll e$tract from red cabbage. %ou %ou can use your pH paper to measure the acidity/alkalinity of #arious household solutions. &bjecti#e The goal of this project is to make your o!n pH indicator paper and use it to measure the acidity and alkanity of #arious solutions from around your house. h ouse. Introduction In this project you'll learn ho! to make your o!n pH paper that you can use to find out if a solution is acidic or basic alkaline(. )hat does it mean for a solution to be acidic or alkaline* It all has to do !ith hydrogen ions abbre#iated !ith the chemical symbol H+(. In !ater H,&( a small number of the molecules dissociate split up(. Some of the !ater molecules lose a hydrogen and become hydro$yl ions &H-(. The "lost" hydrogen ions join up !ith !ater molecules to form hydronium ions H&+(. or simplicity simplicity hydronium ions are referred to as hydrogen ions H+. In pure !ater there are an e0ual number of hydrogen ions and hydro$yl ions. The solution solution is neither acidic or basic. An acid is a substance that donates hydrogen ions. 1ecause of this !hen an acid is dissol#ed in !ater the balance bet!een hydrogen ions and hydro$yl h ydro$yl ions is shifted. 2o! there are more hydrogen ions than hydro$yl ions in the solution. This kind of solution is acidic. A base is a substance that accepts hydrogen ions. )hen a base is dissol#ed in !ater the balance bet!een hydrogen ions and hydro$yl ions shifts the opposite !ay. !ay. 1ecause the base "soaks up" hydrogen ions the result is a solution !ith more hydro$yl h ydro$yl ions than hydrogen ions. This kind of solution is alkaline. Acidity and alkalinity are measured !ith a logarithmic scale called pH. Here's !hy3 !h y3 A strongly acidic solution can ha#e one hundred million million 455555555555555( times more hydrogen ions than a strongly basic solution6 The flip side of course is that a strongly basic solution can ha#e 455555555555555 times more hydro$ide ions than a strongly acidic solution. 7oreo#er the hydrogen ion and hydro$ide ion concentrations con centrations in e#eryday solutions can #ary o#er that entire range. In order o rder to deal !ith these large numbers more easily scientists use a logarithmic scale the pH scale. 8ach oneunit change in the pH scale corresponds to a tenfold change in hydrogen ion concentration. The pH scale ranges from 5 to 49. It's a lot easier to use a logarithmic scale instead of al!ays ha#ing to !rite do!n all a ll those :eros6 1y the !ay notice ho! one hundred million million is a one !ith fourteen :eros after it* It's not coincidence it's logarithms6 To be more precise pH is the negati#e logarithm of the hydrogen ion concentration3
pH ; log 4/
ure !ater has a neutral pH of ?. pH #alues lo!er than ? are acidic and pH #alues higher than ? are alkaline basic(. The table belo! has e$amples of substances !ith different pH #alues @ecelles ,55, 8n#ironment Banada ,55, 8>A date unkno!n(. Table 1. The pH Scale: Some Examples
H+ Boncentration pH Calue 8$ample Delati#e to >ure )ater 5 45 555 555
battery acid
4 4 555 555
sulfuric acid
, 455 555
lemon juice #inegar
45 555
orange juice soda
9 4 555
tomato juice acid rain
E 455
black coffee bananas
F 45
urine milk
? 4
pure !ater
G 5.4
sea !ater eggs
5.54
baking soda
45 5.554
reat Salt Jake milk of magnesia
44 5.555 4
ammonia solution
4, 5.555 54
soapy !ater
4 5.555 554
bleach o#en cleaner
49 5.555 555 4
li0uid drain cleaner
In this project you !ill make your o!n pH paper from a colored indicator that you !ill e$tract from red cabbage by cooking it in !ater. &nce you ha#e the indicator solution you can soak some coffee filter paper in it then allo! the paper to dry. )hen the paper is dry you can cut it into strips and you'll ha#e pH paper that !ill change color. It !ill turn greenish !hen e$posed to bases and reddish !hen e$posed to acids. Ho! green or ho! red* That's your job6 Kse different solutions that you ha#e around the house to find out ho! the color change corresponds to changes in pH.
Terms Boncepts and Luestions to Start 1ackground Desearch To do this project you should do research that enables you to understand the follo!ing terms and concepts3
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Acids 1ases
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Jogarithms
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pH
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pH indicators
Luestions
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)hat #alue of pH is neutral* )hat range of pH #alues is acidic*
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)hat range of pH #alues is basic*
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)hat color is red cabbage pH paper !hen dipped in acidic solutions*
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)hat color is red cabbage pH paper !hen dipped in basic solutions*
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1ibliography •
Here is t!o good !ebsites about acids and bases including information about indicators3 Barboni . ,559. "8$periments !ith Acids and 1ases" un Science allery o
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1ogren S. et al. n.d. "Acids 1ases and pH Scale" Krbana 7iddle School Teachers Krbana IJ
This !ebpage has instructions for making se#eral different colored pH indicators including beet juice phenolphthalein from la$ati#e tablets( red cabbage and turmeric3 1eckham D. date unkno!n. "pH Indicators and Tests for Acids and 1ases" Jearn 2B School of 8ducation Kni#ersity of 2orth Barolina Bhapel Hill aper" Dobert Orampf Science 8ducation Bo.
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K of 72 ,559a. ")hat Is an 8$ponent*" 7ath De#ie!3 Kseful 7ath for 8#eryone Kni#ersity of 7innesota School of >ublic Health ublic Health
or more information about the pH scale try these references3 o
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8n#ironment Banada ,55,. "Oids' Borner pH Scale" The reen Jane3 Acid Dain 8n#ironment Banada !ebsite . ,55,. "The pH Scale" Cirtually 1iology Bourse 1asic Bhemistry Boncepts Mohnson Bounty Bommunity Bollege
7aterials and 80uipment To do this e$periment you !ill need the follo!ing materials and e0uipment3
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Ded cabbage lea#es 40uart cooking pot
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)ater
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40uart bo!l
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Strainer
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)hite coffee filters coneshaped ones are good(
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Alternati#ely you can use filter paper or chromatography paper .
Acidic and basic solutions to test for e$ample3 o
Jemon juice #inegar
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&range juice soda
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Tomato juice acid rain
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1lack coffee bananas
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7ilk sali#a
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>ure !ater
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Sea !ater eggs
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1aking soda solution
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7ilk of magnesia
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Ammonia solution
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Soapy !ater
8$perimental >rocedure Safety Notes: • •
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Adult super#ision re0uired. @o not mi$ strong acids and bases. Kse appropriate caution !hen testing the pH of household cleaning solutions like ammonia(. A#oid skin contact and follo! all precautions on the product label.
4. @o your background research so that you are kno!ledgeable about the terms concepts and 0uestions abo#e. ,. >repare a red cabbage indicator solution the "8$periments !ith Acids and 1ases" !ebpage Barboni ,559( has great pictures illustrating all of the steps( a. Slice a head of cabbage at appro$imately cm 4 in( inter#als or peel the lea#es from the head and tear them into pieces. b. >lace the lea#es in the cooking pot and co#er !ith !ater. c. Book on medium heat for half an hour lo! boil is good(. d. Allo! the cooked cabbage to cool then pour off the li0uid into a bo!l. %ou can pour through a strainer to catch the cabbage pieces or hold them back !ith a large flat ladle !ith holesQsee the photographs on the "8$periments !ith Acids and 1ases" !ebpage Barboni ,559(. e. The solution is a deep blue but !ill change color !hen the pH changes. %ou can e$periment !ith using the li0uid as a pH indicator.( . Here's ho! to make pH paper using the red cabbage solution and coffee filters3 a. Soak the !hite coffee filters in the red cabbage solution for about 5 minutes. b. @rain the e$cess solution from the filters and set them out in a single layer on some paper to!els to dry o#ernight. To speed up the drying process you can put them on a cookie sheet and put them in your o#en at lo! temperature 4E5R,55. c. )hen the coffee filters are dry cut them into cm G cm about 4 in in( strips.
d. The strips are no! ready to test the pH of #arious solutions. They start out blue but !ill turn green in basic solutions and red in acidic solutions. 9. Kse the strips to test the acidity/alkalinity of #arious solutions around your house. or e$ample3 a. Jemon juice #inegar b. &range juice soda c. Tomato juice acid rain d. 1lack coffee bananas e. 7ilk sali#a f. >ure !ater g. Sea !ater eggs h. 1aking soda solution i.
7ilk of magnesia
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Ammonia solution
k. Soapy !ater l. 2ote3 if you test the pH of sali#a do not put the pH paper in your mouth6 Instead spit some sali#a into a clean container and dip the paper into the sali#a. E. After testing put the pH strips in order of increasing pH of the solution tested. a. %ou can use the table in the Introduction as a guide. b. The Cariations section has some additional suggestions for independent confirmations of the pH readings. F. @o you see a gradual change in color as the pH of the tested solutions #aries* Ban you match specific colors to certain pH le#els* &#er !hat range of pH does the color continue to change* Ho! accurately do you think you can determine the pH of a solution !ith your test papers* )ithin 4 , or pH units* Cariations •
Bompare the performance of your homemade pH paper !ith commercial pH paper can be found in a !ellstocked tropical fish store(. &r buy an ine$pensi#e pH meter and use it to calibrate your homemade pH paper. Kse the table in the Introduction to make a series of different solutions form lo! to high pH. 7easure the pH of each solution !ith the pH meter rinse off the tip bet!een solutions( and !rite do!n the results. 2o! check each solution !ith your pH paper. Ban you see color differences that correspond to the
measured changes in pH* &#er !hat pH range do you see color changes* Ho! large does the shift in pH need to be in order to see a change in color* Try making pH indicator solutions and/or indicator papers( from other natural dyes3 for e$ample beet juice phenolphthalein or turmeric po!der 1eckham date unkno!n Orampf ,55F(. Test your household solutions !ith each of the indicators. @oes the additional information from multiple indicators gi#e you a better measure of the pH of your solutions*
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@oes the pH of your sali#a change after eating #arious types of food* If so ho! much time does it take to return to normal* @esign an e$periment to find out. Again do not put the pH paper in your mouth. Instead spit some sali#a into a clean container and dip the pH paper into the sali#a. Also don't try changing the pH of your sali#a !ith anything non edible6
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)hat is the pH of rain!ater in your area* Ban you measure it !ith your pH paper or pH indicator solutions* or a simpler e$periment that uses a pH indicator solution instead of pH paper see the Science 1uddies project Babbage Bhemistry. or more science project ideas in this area of science see Bhemistry >roject Ideas.
Bredits Andre! &lson >h.@. Science 1uddies
Jast edit date3 ,55?455E 4435355
Career Focus
Bhemist 8#erything in the en#ironment !hether naturally occurring or of human design is composed of chemicals. Bhemists search for and use ne! kno!ledge about chemicals to de#elop ne! processes or products.
Bh Bh aff pri in de car fut
Bhemical Technician The role that the chemical technician plays is the backbone of e#ery chemical semiconductor and pharmaceutical manufacturing operation. Bhemical technicians conduct e$periments record data and help to implement ne! processes and procedures in the laboratory. If you enjoy handson !ork then you might be interested in the career of a chemical technician. If you like this project you might enjoy e$ploring careers in Bhemistry.
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Home and Garden pH &ndicators Common Household Items 1y Anne 7arie Helmenstine >h.@. About.com uide See (ore *bout:
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ph indicators pigment chemistry
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anthocyanins
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organic chemistry
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Red cabbage juice can be used to test the pH of common household chemicals. From left to right, the colors result from lemon juice, natural red cabbage juice, ammonia, and laundry detergent. Anne Helmenstine
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1uy 7ona#ie in 7alaysia 1ecome a >referred Bustomer 1uy @irect 1est >rices6 !!!.mona#ie#o.my >h 7eters V Accessories1enchtop V portable field models pH probes cables kits etc. !!!.>reiser.com Taman Hiburan di 7alaysiaJa!ati Taman Hiburan di 7alaysia 1ersukaria dgn Dakan V Sekeluarga6 !!!.?54panduan.com Chemistry Ads Chemistry Chemistry on Line Chemistry Help For Chemistry Lab able !! Chemistry com here are many common household products and garden plants that can be used as pH indicators. "ost plants contain pH sensiti#e anthocyanins, so e$periment %ith other plants, too.
!lants •
Beets A #ery basic solution %ill change the color of beets or beet juice from red to purple.
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'Black' Berries &lackberries, black currants, and black raspberries change from red in an acidic en#ironment to blue or #iolet in a basic en#ironment. Blueberries &lueberries are blue around pH '.()*.', but turn red as the solution becomes e#en more acidic. Carrots Cherries Cherries and their juice are red in an acidic solution, but turn blue to purple in a basic solution. Curry Powder Curry contains the pigment curcumin, %hich changes from yello% at pH +. to red at pH (.-. Delphinium Petals he anthocyanin delphinin changes from bluish)red in an acidic solution to #iolet blue in a basic solution. Geranium Petals eraniums contain the anthocyanin pelargonin, %hich changes from orange) red in an acidic solution to blue in a basic solution. Grapes Red and purple grapes contain multiple anthocyanins. &lue grapes contain a monoglucoside of mal#inidin %hich changes from deep red in an acidic solution to #iolet in a basic solution. Horse Chestnut Leaves Soak horse chestnut lea#es in alcohol to e$tract the /uorescent dye esculin. 0sculin is colorless at pH 1.2 but becomes /uorescent blue at pH '. et the best e3ect by shining a black light on the indicator. Mornin Glories "orning glories contain a pigment named 4hea#enly blue anthocyanin4 %hich changes from purplish)red at pH -.- to blue at pH +.+. !nion 5nions are olfactory indicators. 6ou don4t smell onions in strongly basic solutions. Red onion also changes from pale red in an acidic solution to green in a basic solution. Pansy Petals Petunia Petals he anthocyanin petunin changes from reddish)purple in an acidic solution to #iolet in a basic solution. Poison Primrose Primula sinensis has orange or blue /o%ers. he orange /o%ers contain a
mi$ture of pelargonins 7see eranium8. he blue /o%ers contain mal#in, %hich turns from red to purple as a solution goes from acidic to basic. •
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Poppy Petals Purple Peonies 9eonin changes from reddish)purple or magenta in an acidic solution to deep purple in basic solution. "ed #Purple$ Cabbae Red cabbage contains a mi$ture of pigments used to indicate a %ide pH range.
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"ed "adish
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"hubarb
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"ose Petals he o$onium salt of cyanin turns from red to blue in basic solution.
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%trawberries
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&ea
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&hyme (tract in )lcohol
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&urmeric his spice contains a yello% pigment, curcumin, %hich changes from yello% at pH +. to red at pH (.-.
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&ulip Petals
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*iolet Petals
Household Chemicals •
Bakin %oda #+aHC! ,$ &aking soda %ill :;; %hen added to an acidic solution 7such as #inegar8, but %ill not :;; in an alkaline solution. he reaction doesn4t readily re#erse itself, so baking soda can be used to test a solution, but can4t be 4reused4. he reaction is<
HB&a0( + H+a0( ; H,&l( + B&,g( •
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Colorchane Lipstick 6ou4ll need to test your colorchange lipstick to determine its pH range, but most cosmetics that change color respond to changes in pH 7di3erent from cosmetics that change color according to angle of light8. (La( &ablets he tablets contain contain phenolphthalein, %hich is a pH indicator that is colorless in solutions more acidic than pH (.* and pink to deep red at solutions more basic than pH =.
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*anilla (tract >anilla e$tract is an olfactory indicator. 6ou can4t smell the characteristic scent at high pH 7alkaline solution8 because the molecule is in its ionic form. -ashin %oda As %ith baking soda, %ashing soda :;;es in an acidic solution but not in a basic solution.
Decent Bhemistry Articles Suggested Reading Acid)&ase ?ndicators pH of Household ?tems @ui; • •
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"ake Red Cabbage pH ?ndicator
"ore 9lant 9igments Autumn Leaf Chemistry &iochemistry of Lycopene • •
Summary Some of the most important kinds of chemicals in science are acids and bases. Although you may not reali;e it, you use acids and bases in your home e#eryday. 6ou can recogni;e an acid because it makes food and drinks taste sour. ?f you ha#e e#er tasted something chalky or e#er felt a liuid that feels slippery like soap, those substances are probably bases. 5ne %ay to test if a substance is an acid or base is to test its pH. pH is the scale used in science to rate acids and bases. he scale is numbered from 1 B 1'. Acids ha#e a pH bet%een 1 and -. &ases ha#e a pH bet%een ( and 1'. ?f your pH is at +, that means the substance is neutral, and it is neither an acid nor a base. ust like %e use a temperature scale on a thermometer to :nd out if something is hot or cold, %e can use the pH scale to :nd out if something is an acid or a base. An easy %ay to do this is to use pH paper, %hich is a piece of paper %ith a chemical on it that %ill change colors if it is mi$ed %ith acids or bases. Some fruits and #egetables contain this special type of chemical. 5ne e$ample is red cabbage. ?n this acti#ity you %ill learn ho% to make your o%n pH paper using juice from red cabbage. 5nce you make your red cabbage juice, you %ill %ant to kno% ho% to use it. ?f the color of your red cabbage juice is a purple color, then you kno% that the pH of your solution should be around +, %hich means that your solution is neutral. !hen you :rst make the red cabbage juice, the liuid should be this color. !hen you begin to test the pH of other liuids, the juice %ill change di3erent colors if it is mi$ed %ith an acid or a base. "atch the colors you get %hile you are testing liuids to the chart belo% to see %hat pH you ha#e. p H s ca le f or R ed C ab ba ge ui ce pH 1)' *) 2)- +)( =)1D 11)1' Color 9ink Eark Red >iolet &lue &lue)reen reenish)6ello% Acid&ase Acid Acid Acid Geutral)&ase &ase &ase
oals
"ake red cabbage pH paper
Ise pH paper to test the pH of some common products around the house to determine if they are acidic or basic
Cabbae .uice / pH indicator Area of Science< Chemistry "eant for at least rade )- 7age ()1D8. his e$periment is edible. An adult need not be present.
+,er,ie": 7ake your o!n acid/base indicator by boiling red cabbage. Kse the juice to pH different fluids. E-uipment: 4. 4/, head of WredW cabbage or so. ,. 7etal grater. . >ot filled !ith enough !ater to co#er the grated cabbage. 9. Strainer E. Some acid/base solutions3 for an acid try #inegar for a base mi$ some detergent in !ater. Safety: 1e careful !ith the fingers !hen grating the cabbage. Ho" to do the experiment: 4. rate the cabbage into small pieces and place them in the pot + !ater. ,. 1oil the mi$ture for ,55 minutes until the li0uid turns a dark purplish color. . @ecant the fluid into a glass or jar pouring through a strainer to remo#e the cabbage. Sa#e the cabbage.. mi$ !ith a little #inegar and you can eat it on hot dogs etc.. The collected fluid should be bluish/dark purple in color. 9. 7ake up some 'test' acid/base solutions. A good acid to use !ould be !hite #inegar. %ou could also try soda !ater/sprite or diluted juice from a lemon or o range. %ou can make a basic solution
by mi$ing some !ashing detergent in !ater or by adding some baking soda sodium bicarbonate( to !ater. It's useful to ha#e a control solution of neutral( !ater distilled !ater is best if you ha#e access to it. E. Add a fe! drops of the cabbage juice to your solutions and note any color changes. The juice should turn pink in acidic solutions and green in basic solutions. F. %ou can use the indicator on any other solutions of interest or try drying it on coffee filters to create a simple form of "pH paper." Explanation: Ded cabbage contains pigments call anthocyanins . The pigments gi#e it the red/purplish color. Anthocyanins belong to group of chemical compounds called fla,onoids .
or most pH indicators the compound ac0uires a proton at lo! pH lots of H+( but looses it at higher pH. This seemingly minor alteration is sufficient to alter the !a#elengths of light reflected by the compound thus creating the color change !ith respect to pH. Anthocyanins beha#e some!hat in#ersely in that the pigments "gain" an &H at basic pH but loose it at acidic pH. The ))) link belo! describes the chemistry !ith structures if you !ant to see the details. The chemistry behind pH acids and bases.. An acidic solution contains an e$cess of protons or H+. pH is a measure of ho! 'acidic' a solution is. The lo!er the pH the more acidic the solution. In chemical terms pH means "the negati#e log of the concentration of protons" in solution. Bhemistry students should recogni:e this as pH / 0lo#H23 . If the concentration of H+ is .547 the pH !ill be3
log<.54= ; log<45X,= ; ,( ; , #ery acidic6(. "2eutral" solutions !ater e.g.( ha#e a pH of ?. This number coicides !ith the amount of H+ naturally formed in !ater from the e0uilibrium reaction3 H,& YZ H+ + &H H+ e$perimentally kno!n to be [45X?7 &H is also the same concentration(. "1asic" solutions ha#e a pH greater than ? meaning they ha#e less free H+ than that of neutral !ater.
