Blood And Buffers

Biology, Chemistry:	Buffer Solutions
Grade Range:	Elementary School, Middle School, High School
Format:	Hands-on, Stage

This Demonstration is Under Construction

Materials

• Bromothymol Blue Indicator
• Water (DI Water ideal, but will work with Tap Water)
• Dry Ice
• Calcium Carbonate
• Phosphate Buffer Solution
• Three 500mL (Stage) or Four 100mL (Hands-on) Beakers
• Optional: Poster Board

Safety Precautions

Please read the Dry Chemical, Liquid Chemical, and Cryogen sections of the Demonstration Safety page before performing this demonstration. The solutions for this demonstration can be poured down the drain, and do not need to go into a waste container.

This demonstration requires: Cryogen Gloves, Goggles, Disposable Gloves

Demonstration

Preparation

• Make the Phosphate Buffer Solution: In a 600mL beaker, add 13.8g of NaH₂PO₄ to 500mL of DI water, and stir until completely dissolved. In a separate 600mL beaker, add 14.2g of Na₂ HPO₄ 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

1. 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?
2. 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.
3. Ask the audience what they think might happen if you add calcium carbonate to the last two solutions. What do they think it will do to the solutions?
4. Add the Calcium Carbonate to both solutions, and watch what happens. The water solution will start turning blue, while the buffer solution still stays unchanged!
5. 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 calcium carbonate. You can leave all the solutions with their solvents; the buffer solutions should hold up to any changes for 30 minutes to an hour.

Why This Works

Short Explanation

This is where you would provide a basic, easy-to-understand explanation of the demonstration. Try not to use too much "Science Jargon", and if needed add any explanation tips, like comparing the demo to something kids are familiar with.

Full Explanation

This is where you will explain the demonstration in full, and provide all additional information that pertains to the demo. Unlike the short explanation above, this should be worded so someone who is familiar with the topics might understand it. If needed, you can provide equations and citations for additional sources of information on the topic. This is also where you will find some answers for trickier questions, such as "How does a plane fly upside-down?" for the Bernoulli's Principle demo. If you want to add a floating box for equations, copy the following:

This will give you	a floating box.
The box will be	centered for you.

Additional Information

• Any extra tidbits that do not fit into other sections
• This demonstration is a part of the (insert Stage Show here)