Bouncing Raisins: Difference between revisions

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== Age ==
{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Chemistry]]:
| Density, Decomposition Reactions
|-
| Grade Range:
| [[Elementary School]]
|-
| Format:
| [[Hands-on]]
|}


Elementary School
A twist on the classic "Baking Soda and Vinegar Volcano" experiment, this will help students look at the reaction closely, and see more than just a foamy explosion. This demonstration is easy to run, and after initial setup you can let it run, only adding more reactants as needed throughout an entire science night!
 
== Format ==
 
Hands-on


== Materials ==
== Materials ==


    Raisins
* Raisins
    Roughly 40 mL of vinegar per performance
* Vinegar
    A heaping teaspoon of sodium bicarbonate (baking soda or alka seltzer) per performance
* Baking Soda
    A skinny glass or graduated cylinder
* Clear Container (Graduated Cylinder, Beakers, Large Bowl, etc.), able to hold at least 500 mL


== Safety Precautions ==
== Safety Precautions ==


Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. Whenever a demonstration involves food, students may ask to eat or taste the materials - NEVER let the students eat demonstration materials. You may explain that the materials have been near other, more harmful chemicals that we use in other demonstrations.
Please read the Liquid Chemical and Dry Chemical sections of the [[Demonstration Safety]] page before performing this demonstration.
 
    Vinegar/Acetic Acid MSDS
    Sodium Bicarbonate MSDS
 
== Preparation ==


Assemble your materials.


== Demonstration ==
== Demonstration ==


Fill the glass with the vinegar and SLOWLY add the baking soda. If you do it too fast, you will get an acid/base volcano! Let the foam settle back down. Add raisins to the mixture. You will see CO2 bubbles collect on the raisin. Once enough bubbles collect, the raisin will float. If the raising hits the surface of the liquid and the bubbles leave the raisin, the raisin will fall back down. The bouncing may take a few minutes to get going. You can watch the raisins bounce for at least 20 minutes or more! However, if you are doing the demonstration for several groups of students, you should make a new solution each time so that they can see the chemicals you are using.
# Set out your container, and first pour in your vinegar, filling it a third of the way. Then add your baking soda, being careful to not add too much at one time. Otherwise, you'll have a mess!
 
# As it bubbles, drop in 6-10 raisins. After the initial reaction, the solution will still bubble slowly, and students can come up to see the raisins bouncing!
Note for those using alka seltzer instead of plain baking soda: the alka seltzer seems to make the solution much more fizzy than baking soda and, as a result, the raisin can be harder to see.
# If the reaction slows too much to continue, add more vinegar or baking soda. If you see a lot of baking soda in the bottom, only add vinegar. Likewise, if there is very little or no visible baking soda, add more of it.
 
== What to Say ==
 
Here I have some baking soda and vinegar - these are two chemicals that your parents probably have in the kitchen. They're used in cooking and baking, and also cleaning.
 
Have you guys ever made a volcano out of baking soda and vinegar? It's really easy to do - you just need to mix vinegar, which is an acid, and baking soda, which is a base, together. You get an acid/base reaction which produces a ton of carbon dioxide bubbles! It's pretty messy, so don't do it without help from your parents.
 
Carbon dioxide is just a gas - it's part of the air we breathe. It's also the stuff in soda that makes it so fizzy!
 
When I mix the baking soda and vinegar, you will see lots and lots of CO2 bubbles forming!
 
OK, now I'm going to add some more food to the mixture. These are just raisins from the grocery store.
 
What's happening to the raisins? They're bouncing! Can anyone guess why?
 
Let me give you a hint - things that are less dense than water float in water. To be less dense just means that a bit of it weighs less than the same amount of water. Our mixture of baking soda and vinegar is really mostly water because the vinegar is very watered down.
 
Well, those carbon dioxide bubbles are gas. Like almost all gases we see around us, carbon dioxide is much less dense than water. Do you see the gas bubbles collecting on the raisin? The bubbles definitely float in water, so if you cover the raisin in lots of bubbles, they will help the raisin float.
 
Do you know why the raisin sinks back down? It's because it's losing some of those bubbles! If the raisin has less bubbles on it, its overall density is higher. If its density is higher than water, it will sink.
 
== Why It Is ==
 
Vinegar and baking soda react together as acids and bases, respectively, and produce carbon dioxide. More specifically, the baking soda dissolves in the water to produce bicarbonate ions (HCO3):
 
NaHCO3 ---> Na+(aq) + HCO3-(aq)
 
At the same time, the vinegar dissociates and produces hydrogen ions:
 
CH3COOH <--> H+(aq) + CH3COO-(aq)
 
These two products form carbonic acid:
 
H+ + HCO3- ---> H2CO3


Finally, the carbonic acid decomposes into carbon dioxide gas:


H2CO3 ---> H2O + CO2
== Why This Works ==


The carbon dioxide gas produces gas bubbles in the water that collect on the raisin and cause it to float. The CO2/raisin pair floats because it is of much lower density than water. The density of water is 1 g/ml, but the density of CO2 is only 0.00197 g/ml! Even a little bit of CO2 can lower the average density of the CO2/raisin pair by a lot. Once the density of the pair is a little lower than water, it floats! When some CO2 is lost and the density edges closer to that of the raisin itself, which is higher than water, it sinks.
We are all pretty familiar with the Baking Soda and Vinegar reaction: It is a decomposition reaction, which generates Carbon Dioxide gas:


== Real Life Examples ==
NaHCO<sub>3</sub>(s) + C<sub>2</sub>H<sub>4</sub>O<sub>2</sub>(aq) ---> Na<sup>+</sup>(aq) + C<sub>2</sub>H<sub>3</sub>O<sub>2</sub><sup>-</sup>(aq) + H<sub>2</sub>O(l) + CO<sub>2</sub>(g)


Carbon dioxide dissolved in soda produces soda's fizzy sensation on your tongue.
Some of the gas that generates tries to stay in solution, but will come out of solution if it is able to collect onto something. The raisins do just that! Since the raisins have a lot of surface area (with the many wrinkles and gaps), they provide a spot for the bubbles to collect onto. When they do, they make the raisin a little more ''Buoyant''. In other words, because the raisins have a lot of gas collecting on them, they will start to float! Once they reach the surface, however, some or all of the bubbles will pop, and the raisin will lose that buoyancy and sink back to the bottom. This will repeat over and over again, as long as there is enough dissolved gas to collect on the raisins.


A helium balloon floats because the helium gas is less dense than air.
== Additional Information ==


Also see the Exploding Soda and Density Rainbow demonstrations.
* This demonstration pairs well with the [[Density Rainbow]] and the [[Exploding Soda]]

Latest revision as of 15:39, 5 April 2016

Chemistry: Density, Decomposition Reactions
Grade Range: Elementary School
Format: Hands-on

A twist on the classic "Baking Soda and Vinegar Volcano" experiment, this will help students look at the reaction closely, and see more than just a foamy explosion. This demonstration is easy to run, and after initial setup you can let it run, only adding more reactants as needed throughout an entire science night!

Materials

  • Raisins
  • Vinegar
  • Baking Soda
  • Clear Container (Graduated Cylinder, Beakers, Large Bowl, etc.), able to hold at least 500 mL

Safety Precautions

Please read the Liquid Chemical and Dry Chemical sections of the Demonstration Safety page before performing this demonstration.


Demonstration

  1. Set out your container, and first pour in your vinegar, filling it a third of the way. Then add your baking soda, being careful to not add too much at one time. Otherwise, you'll have a mess!
  2. As it bubbles, drop in 6-10 raisins. After the initial reaction, the solution will still bubble slowly, and students can come up to see the raisins bouncing!
  3. If the reaction slows too much to continue, add more vinegar or baking soda. If you see a lot of baking soda in the bottom, only add vinegar. Likewise, if there is very little or no visible baking soda, add more of it.


Why This Works

We are all pretty familiar with the Baking Soda and Vinegar reaction: It is a decomposition reaction, which generates Carbon Dioxide gas:

NaHCO3(s) + C2H4O2(aq) ---> Na+(aq) + C2H3O2-(aq) + H2O(l) + CO2(g)

Some of the gas that generates tries to stay in solution, but will come out of solution if it is able to collect onto something. The raisins do just that! Since the raisins have a lot of surface area (with the many wrinkles and gaps), they provide a spot for the bubbles to collect onto. When they do, they make the raisin a little more Buoyant. In other words, because the raisins have a lot of gas collecting on them, they will start to float! Once they reach the surface, however, some or all of the bubbles will pop, and the raisin will lose that buoyancy and sink back to the bottom. This will repeat over and over again, as long as there is enough dissolved gas to collect on the raisins.

Additional Information

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