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7/31/2019 Red Cabbage Juice
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Red Cabbage Juice
Written by : Abdul Wahab
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Red Cabbage Juice.
As we have seen, acids and bases have the property ofmodifying the color of certain substances. This is thecase with the juice of the red cabbage. This liquid has ablue-violet color, but when it comes in contact withacidic substances it becomes red, while in contact withbasic substances it becomes green and even yellow.Let's see how it is possible to use the juice of the redcabbage to measure the pH of various substances.
Red cabbage. Cut the cabbage intoslices and put them in a pot.
Add water enough to cover
the slices and boil for half an hour.
Pour the juice
in a low container.
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During winter and spring, it is easy to find a redcabbage at the produce market or greengrocer. It is a
cabbage which has a red-violet color. Buy one of themand cut it in little slices . Put them in a pot and pour
enough water to cover them. Boil for half an hour, thenturn off the heat and let the temperature come down.Pour the blue-violet liquid you have obtained into alarge, low container. The boiled cabbage slices areedible and you can use them in a recipe.
Use of the red cabbage juice as an indicator in theliquid state.Pour some drops of this liquid on a white surface and
observe its changes of color when it is mixed withvinegar or with baking soda. You will see that this liquidbecomes red in contact with vinegar or lemon juice,while it becomes green in contact with baking soda.
This behavior is unusual, and later on we will try toexplain it.
Pour one centimeter of the red cabbage juice indicatorliquid into a transparent glass. Add water up to half of
the glass. Now, pour vinegar into the glass and observethe color changes of the liquid. Repeat the experimentby adding, this time, a little baking soda instead of thevinegar. Also in this case, you will see color changes.
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Preparing red cabbage pH papers.
Cut some porous white paper or card sheets intorectangles and soak them in the juice so they well
absorb it. After about half an hour, remove the cardsand put them away to dry. To do it quicker, you canalso dry them with a hairdryer. Cut the cards in strips.Put away the red cabbage cards which are not usedimmediately: they will last some months. If you storethem in a closed envelope to reduce their oxidization,they will last longer. Put the remaining juice in a bottle.After a few days, this juice goes bad and you have tothrow it away. To keep it longer, store it in a
refrigerator.
Soaking cards with red cabbage Drying the cards.
Red cabbage paper in solution oflemon juice.
Red cabbage paper in solution oflemon juice.
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Red cabbage card in a saturatedsolution of baking soda.
DETERMINE THE pH OF SOME SUBSTANCES
In this paragraph, we will measure the pH of somecommon substances. We will do this with litmus paperand with the pH meter (if available). We will use alsothe red cabbage paper we prepared.
In the following table, write the values of pH you
determine for each substance, using litmus paper andthe pH meter. By means of colored pencils, draw thecorresponding color of the red cabbage paper.
TABLE 1 - MEASURING THE pH OF SOME SUBSTANCES
SUBSTANCES
pH(litmus
p.)
pH(pH
meter)
COLOR(red
cabbagepaper)
distilled water
tap water
rain water
soda water
vinegar
lemon juice
wine
beer
Coca-Cola
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milk
baking soda (saturatedsolution)
ammonia (20% sol. about,to be diluted again with 3
parts of water). To be keptin a closed bottle.
normal aspirin (1 tb in 20 mlof distilled water)
buffered aspirin (1 tb in 20ml of distilled water)
shampoo
soap
other substances commonly
used at home and not
dangerous. Do not usestrong acids or basesbecause they are dangerous.
Do not use bleach.
EQUIPMENTS
pH meter if available
litmus paper a roll
red cabbage paper strips
beakers or glass pots 20
glass or plastic rods 1
At the end of the measurements, compare the valuessupplied by the litmus paper and by the pH meter.Observe the corresponding colors of the red cabbagepaper.Highlight the two more acidic substances.
Highlight the two more basic substances.
Observations:
Vinegar, lemon and Coca-Cola are acidic substances.Baking soda and ammonia are basic substances.Distilled water has a neutral pH.
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THE COLOR SCALE OF RED CABBAGE
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