Science Demonstrations

Biology:

Citrate Test

Showing the citrate slant toAnna maam 

explaining the principle of the test

Requirements: test sample, citrate agar slant.

Principle: this test is used to check the ability of microorganisms to utilise citrate as a sole source of carbon for growth. The agar is incorporated with bromothymol blue indicator which changes its color from green to blue on production of acid. Oragnisms that utilise citrate as sole carbon source (Aerobacter) degrade it to form acetate, pyruvate and CO₂ . So the acid that is formed is responsible for the change in color.

Procedure:

1) Prepare 3 citrate agar slants (1 for the test, 1 for +ve control and 1 for –ve control).

1) Streak a loopful of test sample (drinking water) on a citrate slant.

2) For +ve control streak a 24 hr old culture of Aerobacter

3) For –ve control incubate a slant without inoculation.

4) Incubate all 3 tubes for 24 hrs at 37⁰C

Result: there was no color change in the test tube indicating the absence of citrate utilising bacteria.

Chemistry:

Neutralisation Reaction.

Performing the neutralisation reaction.

Requirements: NaOH, HCl, beaker, dropper

Principle: The reaction between an acid and a base to form salt and water is called neutralisation reaction.

                      HCl + NaOH                     NaCl + H₂O

There are various applications of this reaction in everyday life.

1)    An ant bite releases formic acid which is neutralised by adding calamine which contains ZnCO₃ which is a base.

2)    Due to indigestion when there is production of more acid in the stomach resulting in acidity, a base milk of magnesia (MgOH) is used.

Procedure:

1)    Take 2ml of NaOH in a beaker.

2)    Add 2 drops of phenolphthalein indicator. ( the solution turns pink)

3)    Add a few drops of HCl in the above beaker and check for color change.

4)    Colour change from pink to colourless indicates neutralisation reaction.

Result: the colour of the solution changed from pink to colourless.

Physics

Attracting paper

Requirements: pieces of paper, ruler

Principle: This experiment is based on static electricity. Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge.

When the ruler is rubbed against the hair the –ve charges of the hair get transferred to the surface of the ruler making it –vely charged and the hair surface positively charged. So in such a situation when the ruler is brought close to the pieces of paper the bits of paper get attracted to the ruler.

Procedure: Take a ruler and rub it over your hair for about 1 min, and further move it above the pieces of paper.

Result: The papers get attracted to the surface of the ruler.

My experiences:

through the demonstrations i got an opportunity to perform the experiments. I even got to learn lot many other experiments based on different concepts performed by my colleagues.