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Natural pH Indicator
Making pH Indicator
INTRODUCTION:
A pH indicator is a chemical compound that is added in small amounts to a
solution so that the pH (acidity or alkalinity) of the solution can be
determined easily. pH indicators are
usually weak acids or bases themselves. They detect the presence of hydronium ions (H3O+)
or hydrogen ions (H+). This experiment explores the extraction of natural indicators from
common flowers, fruits, and vegetables and the pH at which these natural
indicators change color. Some indicator solutions and papers will indicate both
an acid and a base, while others are specific to just one. From the pH
indicator that we made, we can test the solution prepared.
OBJECTIVE: Students
will create various pH indicators that can be used to test unknown solutions to
determine if they are an acid or a base.
MATERIALS:
i. 0.1 M HCl solution
ii. 0.1 M NaOH solution
iii. 2-propanol
iv. red cabbage and turmeric
Extracting
the indicator
1.
Finely chopped the red
cabbage and turmeric in different mortar.
2. Add about 10 mL of solvent
and macerate. (Suggested solvents: water, 2-propanol, 50-50 water/2-propanol
mixture,or acetone)
3.
Filter and collect the filtrate
from the macerated plant samples.
Testing
the pH range of the indicator
1. Label 13 test tubes from 1 to 13.
2. Place 9.0 mL of distilled or deionized water in all test tubes
except #1 and #13.
3. Prepare solutions in the acid range in the following manner:
a. Place 10.0 mL of 0.1 M HCl in test tube #1. (pH = 1)
b. Transfer 1.0
mL of 0.1 M acid from test tube #1 to test tube #2 and mix thoroughly. (pH = 2)
c. Transfer 1.0
mL of acid solution from test tube # 2 to test tube #3 and mix thoroughly. (pH
= 3)
d. Continue making
the serial dilutions by transferring 1.0 mL of the most recently diluted acid
solution to the next test tube until six acid solutions of pH 1 to 6 have been
prepared. Be sure to mix each thoroughly before the transfer.
4.
Add 10.0 mL distilled or deionized water to test tube #7. (pH = 7)
5.
Prepare solutions of base in the following manner:
a. Place 10.0 mL of 0.1 M NaOH in test
tube #13. (pH = 13)
b. Transfer 1.0
mL of 0.1 M NaOH from test tube #13 to test tube #12 and mix thoroughly. (pH =
12)
c. Continue
making serial dilutions of the base going from pH 12 down to pH 8 by
transferring 1.0 mL of the most recently diluted basic solution to the next
test tube and mixing thoroughly each time.
6.
Label the wells of a spot plate from 1 to 13. Transfer a few drops of each of
the solutions prepared in steps 3, 4, and 5 to the corresponding well in the
spot plate.
7.
Add a drop or two of the flower/fruit/vegetable extract indicator to each well.
Observe the pH at which the indicator changes color.
serial dilution of NaOH and HCl
Testing
the pH of other liquids
Once the pH ranges of the indicators have been determined, they
can be used in acid-base titrations or to test the pH of household chemicals.
RESULTS:
Testing the pH range of
the indicator:
Type
of pH Indicator
|
pH
Indicator
|
Red Cabbage
|
.jpg) |
Tumeric
|
 |
Both
|
 |
Materials
|
pH
|
Description/Changes
|
Observation
|
Vinegar
|
1
|
Turmeric:
Cloudy yellow
|
 |
1
|
Red Cabbage:
Light purple
|
||
Dish soap
|
13
|
Turmeric:
Reddish
|
 |
12
|
Red Cabbage:
Green
|
||
Johnson`s Talcum Powder
|
8
|
Turmeric:
Cloudy Yellow
|
 |
9
|
Red Cabbage:
Purple
|
||
Soy Sauce
|
7
|
Turmeric:
Cloudy Yellow
|
 |
9
|
Red Cabbage:
Light brown
|
Acids, in
general, are compounds that release hydrogen ions when they are put in water.
Hydrogen ions (H+) are hydrogen atoms that have picked up a positive electric
charge. Strong acids such as hydrochloric acid release lots of H+. Weak acids
like the citric acid release only a few H+. Bases, in general, are compounds
that release hydroxide ions when they are put in water. Hydroxide ions are made
of a hydrogen atom attached to an oxygen atom, with a negative charge. They can
be symbolized as OH-. When equal amounts of H+ and OH- in water, they combine
to make water (H2O). If there is not enough OH- to combine with all the H+, the
water will have extra H+ and be acidic. On the other hand, if there is not
enough H+ to combine with all the OH-, the water will have extra OH- and be
basic. Everything has pH value and we could estimate the pH range of some
substances by using the natural pH indicators where we will be using the
turmeric and red cabbage. It is known that turmeric could be use as pH indicators
and the color changes will determine the pH range of that particular
substances being test. Curcume Longa is the scientific names for turmeric and it
is well known being used in Asia where the turmeric being used as antiseptic
towards wounds and cuts so turmeric does has many advantages to wards
human. Suprisingly only recently the scientist are giving attention towards the
properties contain within turmeric.
Red
cabbage contains a pigment molecule called flavin which is
an
anthocyanin. This water-soluble
pigment is also found in apple skin, plums, poppies, cornflowers, and grapes.
Very acidic solutions will turn anthocyanin
a red color. Neutral solutions result in a purplish color. Basic solutions
appear in greenish-yellow. Therefore, it is possible to determine the pH of a
solution based on the color it turns the anthocyanin pigments in red cabbage
juice. The color of the juice
changes in response to changes in its hydrogen ion concentration. pH is the
-log[H+]. Acids will donate hydrogen ions in an aqueous solution and have a low
pH (pH < 7). Bases accept hydrogen ions and have a high pH (pH > 7). What makes anthocyanin an indicator is
that each form of the compound reacts with light differently, so that each form
is a different color.
Following
the procedures we test four several substances which are vinegar, soap, talcum
and sot sauce respectively. All of the substance has different color changes
that enable us to compare the color changes with the pH indicator that has
been set up earlier on so that we could estimate the pH range of the substance.
Concepts of this pH indicator is quiet simple as it regarding the rate of
dissociation either more towards the release of hydrogen ions or the hydroxide
ions.If the hydrogen being release in greater amounts so the pH would be lower
showing that the substances is acidic with the pH range of 1.0- 6.9. Then the
range for hydroxide ion would be 7.1-14 which means that substance is alkaline
and the rate of dissociation of hydroxide ions is very high.
Next
we focus on the color changes and in turmeric the color would be from yellow
to red or dark pink which is the yellow would be the most acidic with pH value
of one as for pH value 14 the color would be pink or red. This color is the
main indicators that helps us to determine the pH range of the substances so it
has to be well prepared according to the procedures. But unfortunately our
indicators are not good as we can not set apart the color from pH value 1
until 11 so the observation of color changes and the indicators cannot being
done accurately.
In
red cabbage, the color changed is observable from pinkish to greenish. When in red or pinkish
show that the substance is acidic while greenish is basic. When test with
talcum powder it’s show purple color which indicate slightly neutral. If we
compared the result obtained by turmeric and red cabbage, red cabbage is better
pH indicator as it can detect or differentiate between the base and acid.
Turmeric only can indicate base.
Based
on the results the pH for vinegar is acidic
with pH 1,then soap with pH 14
followed by talcum with slightly alkaline and the pH value is 8 and pH value 7
is for the soy sauce.It can be seen that the color changes of some of the
substances is not really good and it is hard to determine the pH range but
still we manage ti estimate the proper range and being able to use the turmeric
indicators.
CONCLUSION:
Red
cabbage is a better pH indicator than turmeric as red cabbage is able to indicate
acid and base clearly and has many range of color to be compared.
REFERENCE:
http://sciencesquad.questacon.edu.au/activities/colourful_chemistry.html http://www.ehow.com/how_8497638_make-turmeric-ph-indicator.html http://www.carolina.com/teacher-resources/Interactive/red-cabbage-guice-homemade-ph-indicator/tr10851.tr
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