INTRODUCTION
Liquids all
around us have either acidic or basic. For example acid taste sour while bases
taste bitter and feel slippery. However, both strong acids and strong bases can
be very dangerous and burn our skin, so it is important to be careful when
using such chemicals.
The strength
of the pH scale is determined by the concentration of hydrogen ions (H+)
where a high concentration of H+ ions indicate a low pH and a high
concentration of H+ indicate a high pH. The pH scale range from 1 to
14 where 1 to 6 is classified as acidic, 7 neutral and 8 to 14 is classified as
basic.
In this experiment, the juice from red cabbage is use as a
pH indicator to test common household liquids and determine their pH levels.
Moreover, explores the extraction of natural indicators from common flowers,
fruits, and vegetables and the pH at which these natural indicators change
colour. Some indicators solutions and papers will indicate both an acid and a
base, while others are specific to just one.
MATERIALS
- 0.1M HCl & NaOH solution
- 2-propanol/acetone
- Purple cabbage
- Flowers
METHOD
Extracting the indicator
- A few flower petals were chopped. 10mL of
solvent was added and the petal flowers were macerated.
- The macerated petal flowers were filtered and
the filtrate was collected.
Testing the pH range of the indicator
- 13 test tubes were labelled 1 to 13.
- 9mL of distilled water was added in all test tubes,
except test tube 1, 7 and 13.
- A series of dilution was prepared according to
the table below:
Test
tubes
|
Distilled
water/mL
|
Acid
or base
|
pH
|
1
|
-
|
10mL of HCl
|
1
|
2
|
9
|
1mL acid from test tube 1
|
2
|
3
|
9
|
1mL acid from test tube 2
|
3
|
4
|
9
|
1mL acid from test tube 3
|
4
|
5
|
9
|
1mL acid from test tube 4
|
5
|
6
|
9
|
1mL acid from test tube 5
|
6
|
7
|
10
|
-
|
7
|
8
|
9
|
1mL basic from test tube 9
|
8
|
9
|
9
|
1mL basic from test tube 10
|
9
|
10
|
9
|
1mL basic from test tube 11
|
10
|
11
|
9
|
1mL basic from test tube 12
|
11
|
12
|
9
|
1mL basic from test tube 13
|
12
|
13
|
-
|
10mL of NaOH
|
13
|
- A few drops of flower indicator and purple
cabbage indicator was added into the test tube 1 to 13.
- The colour changes was observed
Testing the pH of other liquids
- 5 types of household items were put in wells of
the spot plate.
- A few drops of flower indicators and purple
cabbage indicator were added into each of the household items.
- The observation was recorded.
RESULT
 |
| pH indicator for purple cabbage |
 |
| pH indicator for flowers |
 |
| Purple cabbage indicator in household items |
 |
| Flowers indicator in household items |
Household
items
|
Observation
|
pH
|
||
Purple
cabbage
|
Flowers
|
Purple
cabbage
|
Flowers
|
|
Toothpaste
|
From white to light blue
|
From white to purple
|
11
|
11
|
Soap
|
From white to blue
|
From white to green
|
11
|
12
|
Flour
|
From white to orange
|
From white to orange
|
13
|
13
|
Salts
|
From crystal clear to purple
|
From crystal clear to purple
|
10
|
9
|
Hair gel
|
From colourless to purple
|
From colourless to purple
|
3
|
5
|
DISCUSSION
In this project, we made our own pH Indicator by purple
cabbage and flower. Indicators are chemical compounds that can be added to a
solution to determine either it is acidic or alkaline. The indicator will change colour depend on
whether an acid or an alkali is added.
Purple cabbage contains a pigment molecule called flavin (anthocyanin). The anthocyanin makes a
very good indicator. This water-soluble pigment is also found in apple skin,
plums, poppies, cornflowers, and grapes. A very acidic solution will turn
anthocyanin a red colour. Neutral solutions result in a purplish colour. Basic
solutions appear in greenish-yellow. Therefore, it is possible to determine the
pH of a solution based on the colour it turns the anthocyanin pigments in purple
cabbage juice. The colour of the juice changes in response to changes in its
hydrogen ion concentration.
Purple Cabbage pH Indicator Colours:
pH
|
2
|
4
|
6
|
8
|
10
|
12
|
Colour
|
Red
|
Purple
|
Violet
|
Blue
|
Blue-green
|
Greenish-yellow
|
The strength of the pH scale is determined by the
concentration of hydrogen ions (H+)
where a high concentration of H+ ions indicate a low pH and a
high concentration of (H+) ions indicate a high pH. The pH scale
ranges from 1 to 14 where 1 to 6 is classified as acidic, 7 neutral (either a
base or an acid) and 8 to 14 is classified as basic.
Both purple cabbage and flowers give us a similar result. We
used five household materials to test the pH indicators. Based on our result, toothpaste,
soap, flour and salt is alkali, meanwhile, hair gel is acidic. We mix our
household materials with purple cabbage and flower sample, and then observe the
colour changes. After that, we compare
with the two indicators (purple cabbage and flower sample) to determine the
materials are acid, base or neutral.
Purple cabbage juice
turns red colour when it mixes with something acidic and turns green when it
mixes with something basic. Purple cabbage juice is considered to be an
indicator because it shows us something about the chemical composition of other
substances. It same goes with our own flower sample, but in purple cabbage the
colour of indicator is clearer than flower sample.
Purple cabbage is just one of many indicators that are
available to scientists. Some indicators start out colourless and turn blue or pink,
as an example, when they mix with a base. If there is no colour change at all,
the substance that you are testing is probably neutral, just like water.
In this project, precaution steps must be taken to avoid any
bad incident. We must make use that we use safety goggles and gloves,
particularly when handling strong acids and strong bases. Beside, make sure the
test tube is rinsed with distilled water before pour any solution.
CONCLUSION
As a conclusion, we are able to determine our household
materials pH by test it with purple cabbage indicator and flower sample
indicator. Both samples indicate an acid
and a base not just specific for one. Purple cabbage is a very good indicator
because of the anthocyanin pigment found on it.
REFERENCES
1. Voet, D.,
& Voet, J. G. (2003). Biochemistry (3rd ed.). N.p.: Wiley, John
& Sons, Incorporated. Retrieved March 15, 2017.
2. (n.d.). In
http://www.sciencekiddo.com/red-cabbage-ph-indicator/.
3. Red
Cabbage Chemistry. (2003). In https://www.stevespanglerscience.com/lab/experiments/red-
cabbage-chemistry/
4. Alexander Thomas
Cameron (1928), Biochemistry (1st
Edition), The Macmillan Company.
5. Jeremy M Berg, John L Tymoczko and LubertStryer (2002), Biochemistry (5th Edition),
W. H. Freeman and
Company.
6. https://www.stevespanglerscience.com/lab/experiments/red-cabbage-chemistry/
