SCIENCE DEMONSTRATIONS
CHEMISTRY - VITAMIN C CLOCK REACTION
Vitamin C Clock Reaction
Two colorless liquids are
mixed together and after a few moments the mixture turns a dark blue color.
There are actually a couple of simple chemical reactions going on at the same
time to make this “clock reaction” occur. This version of the classic “VITAMIN
C clock reaction” uses safe household chemicals available easily at home.
AIM: To study the VITAMIN C clock reaction
Materials required:
·
distilled water (tap water will work OK
as well)
·
a couple of plastic cups
·
1000 mg vitamin C tablets
·
tincture of iodine (2%)
·
hydrogen peroxide (3%)
·
liquid laundry starch
PROCEDURE
1. Make a
vitamin C solution by crushing a 1000 mg vitamin C tablet and dissolving it in
2 oz of water. Label this as “vitamin C stock solution”.
2. Combine
1 tsp of the vitamin C stock solution with 1 tsp of iodine and 2 oz of water.
Label this “solution A”.
3. Prepare
“solution B” by adding 2 oz of water to 3 tsp of hydrogen peroxide and 1/2 tsp
of liquid starch solution.
4. Pour
solution A into solution B, and pour the resulting solution back into the empty
cup to mix them thoroughly. Keep pouring the liquid back and forth between the
cups.
RESULT: The iodine which is colorless in vitamin C solution becomes
blue black when mixed with solution of starch and hydrogen peroxide.
Explanation: There are two forms of iodine:
Element
form (Iodine): I2 + starch -------> blue
Ion form
(Iodide): I- + starch --------> colorless
There are two reactions taking
place simultaneously in the solution:
#1. 2I- + H2O2 ---(slow)------->
I2 + H2O
#2. I2 +
Vitamin C ----(fast)----> I (colorless)
In
Reaction # 1 iodide ions react with hydrogen peroxide to produce iodine element
which is blue in the presence of starch
In
Reaction # 2 The Vitamin C is immediately reacting with any iodine formed in
reaction # 1. The net result, at least for part of the time is that the
solution remains colorless with excess of iodide ions being present.
Now
after a short time as the reactions keep proceeding in this fashion, the
Vitamin C gets gradually used up. The Vitamin C creates a clock reaction (1 - 2
minutes) and once it is used up, the solution turns blue, because now the
iodine element and starch are present.
PHYSICS EXPERIMENT
SPOON OR BELL EXPERIMENT
Aim:
To prove vibrating spoon can sound like a bell.
Apparatus
required: Spoon ,fork ,wooden ladle
Procedure:
--->
Tie a spoon in the middle of the string
---->
And hold the ends of the string with the index fingers and
bring it close to
ears.
--->
Ask your friend to hit gently the spoon with another spoon.
This
step can be repeated using fork, other shaped spoons,or by decreasing the
length of string etc.
Observation:
If
we listen carefully, we hear the sound which resembles like a bell lasting for
a while.
Conclusion:
Sound
is produced by Vibrating Bodies. Sound travels faster in solid medium.
BIOLOGY EXPERIMENT
EFFECT OF BROMELAIN ON GELATIN
Pineapple Enzyme
Many people love gelatin-based desserts. Many of us love pineapples too. Should
you put them together? As many a gelatin-loving cook has discovered, certain
fruits can change gelatin’s ability to set. In this experiment, we can discover
what happens when gelatin meets pineapple.
AIM: To study
effect of Bromelain (enzyme present in pineapple) on setting of gelatin
MATERIALS
REQUIRED: Fresh pineapple, boiled pineapple, frozen pineapple, measuring cup
Kettle Water Spoon Two quarters, 3 containers of gelatin
PROCEDURE:
1. Mix the
gelatin powder with warm or hot water according to the package's instructions.
2. Pour an equal amount of gelatin into each of three bowls.
3. Add ten small
chunks of fresh pineapple to one bowl, in another put boiled one and in last
one put frozen pineapple chunks.
4. Put all the bowls of gelatin in the
refrigerator to set, and wait for several hours.
RESULTS: The
gelatin with the fresh and frozen pineapple in it gets very watery, while the
gelatin in the other bowl with boiled pine apple gets firm. A quarter will sink
into the liquid in the pineapple gelatin, but it will sit on top of the gelatin
in the plain gelatin bowl.
CONCLUSION:
Pineapples contain the protein-digesting enzyme called bromelain. Bromelain is also
used as a meat tenderizer; Gelatin is made out of animal proteins, particularly
collagen. When you add water to the gelatin, long chains of protein form,
making invisible protein “spaghetti”. Water gets trapped in the middle of these
long chains, turning what should be a liquid into a semi-solid. Since pineapple
bromelain digests proteins, when the pineapple meets the gelatin, it begins to
eat away at it. The long protein chains collapse, making everything watery again.
The bowl with boiled pineapple sets as normal as bromelain enzyme is heat
sensitive and heating inactivates this enzyme.
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