question in physics?

Question

this one physics teacher at my high school showed an experiment to me last year and it involved him using a straw and a lab cup filled with water(i think or some sort of blue liquid). he blew into the cup with the straw and then made the liquid become green. he never really told me what caused it to become green.

Answer 1

When he blew in the given solution he was actually adding CO2 to it and thus causing a chemical reaction. The blue liquid was bromothymol blue (BTB).

The chemical bromothymol blue (BTB) is a sensitive indicator of the presence of acid. When gas containing is bubbled through a BTB solution, carbonic acid forms and the indicator turns from dark blue to green, yellow, or very pale yellow depending on the concentration (lighter colors mean higher concentrations).
Here are couple of links to a pdf and a site where you will find some such interesting activities for teachers "with" explanation but I don't understand the teachers attitude of keeping knowledge secret from children. It kills the basic Idea of education itself..

http://departments.oxy.edu/tops/Greenhouse/GREENHSE1-T.pdf

http://www.ucar.edu/learn/1_4_2_17t.htm

http://www.ucar.edu/learn/1_4_2.htm

Answer 2

The solution would have contained an indicator maybe, which registered the UNBELIEVABLY TINY increase in carbonic acid caused by co2 dissolving into the water and releasing free protons...I am not convinced by my explanation...as this is sort of a chemistry question...

Answer 3

Not sure what the liquid was, but it was similar to limewater. Limewater starts out clear, then turns milky when you breathe into it because of the CO2 in your exhalations.

Answer 4

It was yellow food coloring. snarf