lesson plan16

8/8/2019 Lesson Plan16

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Lesson Plan 16 | Page 1 2007 | ABC Science Online

Lesson Plan 16

Cool Chemistry - DIY pH Indicator Brief descriptionRed cabbage juice is a natural pH indicator makingthis classic activity one of the most popular chemistry experiments for children. The indicator changes frompurple to bright pink in acids to blue or yellow-greenin bases. Preparation time and consumables havebeen greatly reduced in this lesson plan and thewhole activity can be conducted at virtually no cost.The pH indicator is extracted as a teacherdemonstration while students build their own

MiniLabs using clear straws as test tubes todramatically reduce the amount of indicator andchemicals used. They use the pH indicator to classify avariety of safe household chemicals including vinegar,laundry powder and lemonade.

Duration: 60 - 80 minutes

Year level: Lower to upper primary*

Topics: Natural and process materials, Energy and Change

Preparation: 10 to 20 minutes

Extensions: Investigate the effect of carbon dioxide gas on water using pHIndicators, Investigate antioxidants (anthocyanin is a powerfulantioxidant)

Overview Whole class Discuss acids and bases and pH (Teacher Notes P 5) , (15 20 min)

Perform Teacher Demo 1 Extracting Red Cabbage Acid-Base Indicator (see Teacher Notes)

Perform Teacher Demo 2 Preparing Test Chemicals (Teacher Notes P 6)Distribute worksheets, discuss small group activitiesand safety precautions

Allocate groups and jobs

Small groups Construct MiniLabs and Classify Chemicals (30 40 min)Students follow worksheet instructions to construct MiniLabsStudents filter the cooled pH indicator solutionsextracted in Teacher Demo 1.Students test household chemicals and record observations

Whole class Discuss the activity (15 20 min)Teacher Demo 2: Test pH of soluble aspirin (see Teacher Notes)

Beautiful Results usingRed Cabbage pH Indicator


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Materials and equipment

These quantities are for 6 separate groups

Total Quantity Description

Making pH Indicator (sufficient for whole class and demonstrations)

Red cabbage

1 Chopping board and knife

1 Kettle (to boil water for extracting indicator)

1 Small funnel (for filtering cabbage extract)

6 Takeaway containers (1 per group)

6 Plain facial tissues (1 per Group - for filtering cabbage extract)

14 Clear plastic cups (1 per group, 1 Demo + 7 test chemicals)

8 Plastic pipettes or eye-droppers (1 per test chemical)

7 Shish-kebab sticks (1 per chemical - snap off sharp ends)

cup Chemical 1 Tap Water

cup Chemical 2 White vinegar

1 tsp Chemical 3 Baking Soda (dissolved in cup tap water)

cup Chemical 4 Lemonade (375ml can sufficient for whole class)

1 tsp Chemical 5 Laundry powder (any brand in cup water)

cup Chemical 6 Lemon Juice (squeeze bottle type is suitable)

1 tsp Chemical 7 Tartaric Acid (available from supermarket)

1 Soluble aspirin for Teacher Demo (optional)

1 Tall glass for Teacher Demo

Materials for making Min-Labs

24 Clear plastic straws (4 per group)

6 Strips of adhesive poster putty (1 per group)

6 Plastic plates (1 per group) 1 Absorbent table cloth (or towel)

PreparationPurchase and/or collect red cabbage (half is sufficient), vinegar, baking soda, laundry powder, lemonade, lemon juice, tartaric acid and soluble aspirin from home and/orsupermarket. Snap off sharp ends of shish-kebab skewers for safety.

Photocopy sufficient quantity of student worksheets for whole class.



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ObjectivesStudents prior knowledgeNo prior knowledge is required or assumed for this lesson plan. The objectives listedbelow are suggestions only and may not be appropriate for every year level.

Science skills

Students will: Follow worksheet instructions to construct MiniLabs Use funnels and cups to carefully filter the pH indicator solution

from red cabbage leaves Use eye-droppers to carefully add pH indicator and test

chemicals to test tubes (clear straws) Record their observations on the student worksheet Classify each test chemical as an acid or base on their worksheet

Science concepts pH is a measure of how acidic or basic a chemical The pH scale ranges from 1 to 14 A pH of 7 is neutral it is neither basic nor acidic A pH less than 7 is acidic A pH greater than 7 is basic pH indicators are chemicals that change colour when added to

an acid or base red cabbage juice contains natural pH indicators red cabbage pH indicator turns pink or red in acids red cabbage pH indicator turns blue to yellow-green in bases the pH indicators in red cabbage juice belong to the

anthocyanin family of chemicals

Positive attitudes

Students will Develop an understanding of and appreciation for the scientificmethod

Work cooperatively with partners/group members and ensure Handle all equipment and water carefully and responsibly Dispose of waste responsibly (eg pour waste water onto plants

or garden beds instead of down the sink)



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Procedure Teacher Demonstration Extract pH Indicator Whole Class (1015 min)

Discuss students perceptions of chemicals by asking leading questions such aswhat are chemicals?are all chemicals dangerous? are all chemicals liquids?is water a chemical? what about lemonade or vinegar?what do you know about acids and bases?are all acids dangerous?

Display the red cabbage and ask students whether it contains any unusual orinteresting chemicals. Explain that it contains many thousands of amazing chemicalswhich scientists are still learning about including some that change colour whenmixed with acids or bases.

Students who have a pool at home may already be familiar with pH indicators becausepool maintenance includes measurement of pH using indicators

Introduce the lesson you are going to demonstrate how to extract the natural,colour changing acid-base indicator from the cabbage. The class will then break into

small groups, build their own mini chemistry lab complete with micro test tubes anduse some of the red cabbage indicator to test the pH of various household chemicals.

Follow the procedure on page 5 of the Teacher Notes to extract the pH IndicatorSolution stop when hot water is added at Step 5 and continue class discussion (thefinal filtering steps will be performed by students in small groups when the solutionhas cooled)

Discuss the procedure for small group activities Allocate groups and jobs (allocating job badges will minimise classroom traffic and the

risk of accidents and spills)

Build Mini Labs and Test Chemicals Small Groups (1520 min)

All group members read the worksheet instructions Equipment Manager collects materials required for activity from science store Group members cooperate to build the MiniLabs Equipment Manager collects cooled cabbage juice for straining Each group member has a turn at adding chemicals to test tubes All group members record observations and classify chemicals on their worksheets Free Experimentation students will enjoy mixing several chemicals together to

observe the colour change. Allow up to 15 minutes of free time for experimentation. All the chemicals are safe to mix and can be discarded onto a garden or poured downthe sink.

All group members cooperate to clean up Equipment manager returns equipment to science store Place red cabbage scraps and tissues in compost bin if possible

Discussion Whole Class (1015 min)

Discuss the activity and observations Scientists and industrial chemists use a variety of pH indicators to measure the pH and

concentrations of solutions very accurately Perform Teacher Demo 2: Testing Soluble Aspirin and discuss



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Teachers notes

TEACHER DEMO 1:Preparing Red Cabbage pH Indicator Solution

There are no critical steps in this procedure. Chopping the cabbage more finely, using

hotter water and longer soaking times will all extract more of the desired chemicalfrom the cabbage.

Perform this as a demonstration rather than preparing in advance students willenjoy seeing the process and will be more amazed if the realise how simple theextraction of the pH indicators from red cabbage is.

The finer you chop the cabbage, the better but it is not critical.

2. Finely chop the cabbage on a large chopping board.

1. Half a red cabbage will provide ample pH indicator forthe whole class, plus teacher demonstrations

3. Evenly distribute the chopped cabbage into 6 takeaway containers.

4. Pour enough boiling or hot water into each container to just cover the cabbage.

The volumes and water temperature are not critical hotter water isbetter.

Each group will only need a tiny amount of the final solution so this isnot critical less than of a cup.

5. Stirring will extract more of the pH indicators but is notcritical stop at this point and continue class discussion.

This step is not critical a longer soak time will extract more pHindicator



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6. Line a small funnel with a facial tissue and strain thewater from the cabbage into a plastic cup.

NOTE: This step can be completed by students in small groups or by the teacher once the water has cooled sufficiently 10 to 15 minutes is sufficient extraction time but you could begin the lesson prior to a break and allow soaking

7. Remove tissue and leftover cabbage and place back incontainer compost leftovers and tissue if possible.

TEACHER DEMO 2:

8. Less than cup for each group is more than sufficient pHIndicator solution to perform all the chemical tests.

Preparing Chemical Solutions for Testing

Label six plastic and fill as follows. Only one set is required for the whole class and willbe rotated through each of the groups:

1. Tap water cup2. Vinegar cup undiluted3. Baking Soda 1 tsp in cup water (stir until clear)4. Lemonade cup undiluted5. Laundry Powder 1 tsp in cup water (stir until mostly dissolved)6. Lemon Juice 1 / 8 cup undiluted7. Tartaric Acid 1 tsp dissolved in cup water

Bi-Carb

Soda

Laundry

Powder

White

Vinegar

Tartaric Acid Lemon

Juice

Lemonade



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SMALL GROUP ACTIVITY:

Preparing Straw Test Tubes and Mini Lab

Each group will require: 1 Plastic plate4 Straws (cut in half to make 8 micro test tubes) 1 Blob of poster wall putty

1. Cut the four straws neatly in half.

2. Place eight small blobs of poster putty evenly spaced onthe plastic plate. Push halved straws firmly into the putty.

3. Completed Mini-Lab with straw test tubes ready forexperiments.

Testing pH of Household ChemicalsRotate the chemicals to be tested around the groups the pipette and stirrers shouldremain with their solutions to avoid mixing/contamination.

1. Use a pipette or eye-dropper to add pH Indicator solutionto each test tube so they are all roughly one third full.

2. Add tap water to the first test tube so it is roughly twothirds full (do not overfill so solution can be stirred with the shish-kebab stick stirrer if necessary).

3. Gently stir the solution by inserting the skewer into thestraw several times students record their observationsand classify the chemical on their worksheets.



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Testing pH of Household Chemicals /continued

4. Add each test chemical in succession, stir with shish-kebab skewer, record resulting colour change and classify the chemical.

5. Continue until each chemical has been tested andclassified. Cleaning up is easy and simple and materialscan be used again if washed in warm soapy water.

Results

The following results will be obtained the concentration of pH indicator will affectthe colour intensities but not the hue (colour).

Chemical Colour Change Acid/BaseTap Water No noticeable colour change pH neutralBaking Soda Blue to blue-green BaseVinegar Red to purplish-red AcidTartaric Acid Bright red AcidLaundry Powder Yellow-green BaseLemonade Purple Acid

Lemon Juice Bright Red Acid

B a k

i n g

S o d a

( b l u e o r

b l u - g r e e n )

V i n e g a r

( r e d - p u r p l e )

T a r

t a r i c

A c i

d

( b r i g

h t r e

d )

L a u n

d r y

P o w

d e r

( y e l

l o w - g r e e n

)

L e m o n a d e

( p u r p l e )

L e m o n

J u i c e

( b r i g

h t r e

d )

T a p

W a t e r

( v i o l e t - n o c h a n g e

)



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TEACHER DEMO 2 - CONCLUSION:Testing Soluble Aspirin

During the concluding discussion, use a large glass to observe the change in pH of water as a soluble aspirin dissolves. Use a large, tall glass so the whole class can seethe change.

The solution slowly turns pink indicating that the pH isdecreasing (ie the solution is becoming acidic).

Acids, Bases and pH Indicators

The pH scale ranges from 1 to 14. A chemical with a pH of 7 is neutral it is neitherand acid or a base. The nomenclature pH means the potential of hydrogen andrefers to the ability of a chemical to donate or accept hydrogen ions to otherchemicals. Acids donate hydrogen ions while bases can accept them.

Acids are chemicals with a pH less than 7. The word acid comes from the Latinacidus meaning sour because acids generally have a sour taste. Some acids such assulfuring and nitric acid are particularly strong and can severely burn skin while otheracids are much weaker and safer. Most of the foods humans eat are acidic.

A base is a chemical with a pH greater than 7. Bases generally have a bitter taste anda slimy or soapy feel to the skin (this sensation is very noticeable in laundry powders).Bases react violently with acids even weak acids and bases such as acetic acid(vinegar) and sodium bicarbonate (baking soda) fizz violently to release carbondioxide gas yet both are safe to consume.

Acids and bases react with each other to produce a salt and water (there are many types of salts of which sodium chloride which is common table salt is just one).

pH indicators (acid-base indicators) are chemicals which change colour in thepresence of an acid or a base. The change is reversible. Adding an acid or base towater decreases or increases the solutions pH and the indicator colour will changeaccordingly.



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pH of some common substances

pH Substance1.0 Battery Acid (sulfuric acid)1.8-2.0 limes2.2-2.4 lemon juice

2.2 vinegar (acetic acid)2.9-3.3 apple juice, cola3.7 orange juice4.0-4.5 tomatoes5.6 unpolluted rain5.8-6.4 peas6.4 cow's milk6.5-7.5 human saliva7.0 distilled water7.3-7.5 human blood

8.3 baking soda9.2 borax11.0 laundry ammonia12.0 lime water14.0

Red Cabbage Indicator - Anthocyanin

The chemicals responsible for the red colour in red cabbage and many othervegetables, fruits and flower petals belong to the anthocyanin family. Over 300 kinds

of anthocyanin have been discovered so far. They are also powerful antioxidantswhich have been shown to be very beneficial to human health. The following linksprovide further reading about anthocyanin.

Food Pigments Stop Cancer in its Tracks (20/08/07)Sydney Morning Herald Articlewww.smh.com.au/news/national/food-pigments-stop-cancer-in-its-tracts/2007/08/20/1187462176713.html

Red Leaves (23/02/05)

ABC TV Catalyst (Transcript)www.abc.net.au/catalyst/stories/s1310369.htm

Red Leaves (May 2003)Tropical Topics No. 77 Page 6 (Queensland Environmental Protection Authority)www.epa.qld.gov.au/register/p00820ak.pdf

Anthocyanin in the Rainforest (05/09/92)Tropical Topics - Queensland Environmental Protection Authority www.epa.qld.gov.au/register/p00820ar.pdf


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In this activity, you will extract amazing natural chemicals from red cabbage.These chemicals change colour when added to acids or bases.

You will build a MiniLab complete with Micro Test Tubes made from straws. Add your cabbage acid-base indicator to test various chemicals are an acid or base.

Objectives

To build a MiniLab with Micro Test TubesTo extract the natural acid-base indicators from red cabbage leaves.To use the acid-base indicators and MiniLab to test whether chemicals are acids or bases.To work cooperatively so every group member contributes to the activity To conserve water by using the minimum amount requiredTo conserve materials and recycle them where possible

Making the MiniLab

Materials required

Plastic Plate Adhesive poster putty 4 Clear Straws Scissors

Procedure

Work cooperatively to build your MiniLab and try to make sure everyone has a turn at part of the procedure.The equipment manager collects the materials required from the science store.

1. Cut the four straws neatly in half. You should now have eight shorter straws of equal length. These willbecome your MiniLabs Micro Test Tubes.

2. Place seven small blobs of poster putty evenly spacedon the plastic plate (it doesnt matter if your plate isround or square).

3. Push seven of the halved straws firmly into the putty.

This is how your completed MiniLab should look.

2007 | ABC Science Online


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Preparing the Acid-Base Indicator

Materials required

Red Cabbage 1 Clear Plastic Cup1 Tissue Small funnel

ProcedureThe equipment manager collects the red cabbage prepared by the teacher.

Testing the Chemicals ProcedureCollect one of the chemicals to test. Once you have finished testing, pass the chemical onto another groupand collect the next chemical to be tested.

1. Line the funnel with a facial tissue. Carefully pour the waterfrom the red cabbage into funnel. Try not to spill any of cabbage.

2. Carefully put the leftover cabbage and tissue back into thecontainer. Compost the leftover cabbage and tissue if possible.

3. Use the eye-dropper to add Acid-Base Indicator solution toeach test tube so they are all roughly one third full. You need toleave room for the chemicals you will test.

1. Add tap water to the first test tube so it is roughly two thirdsfull.

This test tube will act as your reference colour for a neutralchemical (one that is neither an acid nor a base).

2. Gently stir the water into the acid-base indicator solution withthe shish-kebab skewer.

3. Repeat steps 1 and 2 for each chemical to be tested.

Record your observations in your science journal.


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Red Cabbage Indicator Colour Chart

pH less than 7 = Acid pH more than 7 = BasepH

2 4 6 8 10 12

ColourRed Purple Violet Blue Blu-Grn Grn-Yel

Note: This colour chart is a guide only as colours may vary depending on your printer

Table 1. Acid Indicator Tests Results & Analysis

Chemical Indicator Colour Acid or Base

1. Tap Water

2. White Vinegar

3. Baking Soda (Sodium Bicarbonate)

4. Lemonade

5. Laundry Powder

6. Lemon Juice

7. Tartaric Acid

Free ExperimentationWhen you have completed all your tests, try mixing several chemicals to see if you can change the indicatorcolour from purple to pink, then to blue and back to pink again. Using very small quantities of acids andbases is the best way to achieve this result. Apart from the colour change, you will also notice that somechemicals produce bubbles of gas when they react.

2007 | ABC Science Online

lesson plan16

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