Editing Blood And Buffers (section)

== Demonstration ==

;Preparation: 
* Make the Phosphate Buffer Solution: In a 600mL beaker, add 13.8g of NaH<sub>2</sub>PO<sub>4</sub> to 500mL of DI water, and stir until completely dissolved. In a separate 600mL beaker, add 14.2g of Na<sub>2</sub> HPO<sub>4</sub> to 500mL of DI water, and stir until completely dissolved. Pour both solutions into a 1L bottle and mix. Label the solution as a 0.2M Phosphate Buffer Solution and write the date it was made. Be sure to test the pH of the solution to make sure it stays within two decimals of 7.0. If it is below, add a small amount of NaOH. If it is above, add a small amount of HCl.
* Setup the demonstration: In the first and last beakers, pour 100mL/500mL of water in, add 20 drops of the Bromothymol Blue indicator and stir. In the center beaker(s), add 100mL/500mL of the Phosphate Buffer Solution, then add 20 drops of the indicator and stir. All the solutions should be green, and should be the same shade as each other. Keep the buffer solution(s) in the center.
;Presentation:
# Show the Audience that the solutions look the same, and that the indicator you added shows that they are at or close to the same pH. Ask the audience what might happen to the first two solutions if you were to add a small amount of dry ice to them. What do they think it will do?
# Place a piece of dry ice into each solution, and watch what happens. The water solution will start turning yellow, while the buffer solution will stay unchanged! For the stage show, remove the dry ice from the buffer solution once the color change happens.
# Ask the audience what they think might happen if you add baking soda to the last two solutions. What do they think it will do to the solutions?
# Add the baking soda to both solutions, and watch what happens. The water solution will start turning blue, while the buffer solution still stays unchanged!
# For a hands-on show, use two beakers with the buffer solution so that one can have a piece of dry ice and the other can have the baking soda. You can leave all the solutions with their solvents; the buffer solutions should hold up to any changes for 30 minutes to an hour.