Month: October 2015

Drinking Straw Explosion

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Demo #7 – Drinking Straw Explosion

Useful in Units:  Gas Laws

Background and Uses

This is a fun and easy demonstration showing that as the volume of a sample of gas is decreased at constant temperature, the pressure of the gas increases (Boyle’s Law).  I find that very few of the students have ever seen this party trick and they are surprised by the result.

Alterations to try and pitfalls to avoid for this demo:  

  1. Some brands of straws work better than others.  Make sure to test the straws ahead of time.
  2. Make sure to get more than enough straws for your students.  This is a trick that can fail when the students first try.

Concepts the Demo Illustrates:

Boyle’s Law, Combined Gas Law, Volume, Pressure

Where I found this demonstration:

My older cousin Mike showed this cool straw trick to me when I was a kid after he got a job at McDonald’s.  He learned it from some of the other employees.  McDonald’s straws do work really well.  

Procedure (Drinking Straw Explosion)

Materials required:

  • Straws
  • 2 people

Procedure:

  1. Student 1:  Pinch each end of a drinking straw tightly.  Roll the straw end over end so that the straw is winding up and the volume within the straw gets smaller and smaller(see pictures below).  Once it is too difficult to roll the straw up any more, continue to pinch tightly and hold the straw steady for Student 2 to flick.
  2. Student 2:  Flick the straw with your finger quickly and with force so that the straw pops.  

IMG_1770IMG_1771

      

What to illustrate/discuss with this demo:

  1. As Student 1 is rolling up the straw, the volume of the gas in the straw is decreasing even though no gas escapes.  As the volume decreases and the gas particles get pushed closer together, the pressure (gas collisions per time with walls) increases.
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Demo #23 – Red Cabbage Juice pH Indicator

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Red Cabbage Juice

A Natural pH Indicator

Useful in Units: Acids & Bases

Background and Uses

The juice that can be made from Red Cabbage is a natural pH indicator.  Although it will make your house (or prep room) a little stinky, I find the rewards well worth the smell.  It is a universal indicator and changes to many different colors – see below.  

Red Cabbage Juice

Image Link

I use the indicator to have the students test the pH of many household products. These include many cleaners, ammonia, Liquid Plumber, bleach, lemon juice, milk, orange juice, and anything else I can find in the house.  In general, foods often test in the acidic range and cleaners test in the basic range.

One point you could make to the kids is that red cabbage is sometimes more red and sometimes more purple at the grocery store.  This is due to the pH of the soil in which the cabbage was grown.

Alterations to try and pitfalls to avoid for this demo:  

  1. Make sure that Ammonia and Bleach based products are not mixed.  The reaction between these compounds is a chlorine-based gas that is poisonous.
  2. I put my cabbage juice in a big jug that has a spout on the bottom.  This makes it easy for students to get a little of the juice out of a big container.
  3. Milk may not indicate too well.  

Safety Considerations: (This list is NOT all inclusive – see all disposal laws and use your professional judgement)

  • Make sure that Ammonia and Bleach based products are not mixed.  The reaction between these compounds is a chlorine-based gas that is poisonous.

Concepts the Demo Illustrates:

Indicators, Acids, Bases, pH

Where I found this demonstration:

I first learned about this demonstration as a MAT student at Union College from another student – most likely my chemistry partner Lisa Saccochia.  

Procedure (Red Cabbage Juice pH Indicator)

Making Cabbage Juice

  1. Chop up a head of red cabbage.
  2. Put cabbage in a large pot and fill with water.
  3. Heat mixture on stove to a boil and allow it to simmer for a half hour or so.
  4. Allow the mixture to cool.
  5. Strain cabbage out of mixture – collect dark purple cabbage juice.
  6. Put cabbage juice in container.  It can be diluted greatly so add as much water as you like to make the volume of juice you desire.  

Household Products to try

  • cleaners
  • ammonia
  • drain cleaner
  • bleach
  • lemon juice
  • milk
  • orange juice
  • dishwasher detergent
  • colorless soda

Demo #33 – What is your radiation dosage?

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Calculate Your Personal Radiation Exposure

Useful in Units: Nuclear

Background and Uses

While discussing Solution Equilibrium in class, I try to make a point of describing Global Warming and how the CO2 dissolved in the oceans may play a role.  We then discuss how we can reduce the amount of carbon from fossil fuels that is being put into the atmosphere as CO2.  My feeling is that the electric car is the future – but how do we make more electricity without using more fossil fuels.  Nuclear power plants seem to be the answer.  They do not create any air or water pollution (on good days and almost all days are good days) and seem to be sustainable if the recycling of the waste is as possible as is currently being stated.

Later in the year, during my Nuclear Unit, I show the “Back to Chernobyl” and “Chernobyl Heart” videos to my students.  They see the immediate effect of a meltdown and the effects that are still occurring in Russia.  We discuss Global Warming again and whether the students still feel as strongly about Nuclear Power being the answer.  It is a tough call for many of them.

As part of that class I pass out the “Estimate Your Personal Radiation Dosage” from the American Nuclear Society that can be found on the next page.  The students always seem to like to find out if they receive a high dosage and where their dosage comes from.

Alterations to try and pitfalls to avoid for this demo:

  1. You might be surprised by students who have had large doses.  I once had a student that had to have many X-Rays in one year due to kidney problems.  Her dosage for the year was far above normal.

Concepts the Demo Illustrates:

Radiation

Where I found this demonstration:

The American Nuclear Society offers guides for teachers.  This is a worksheet that was enclosed in one of these guides and is used with permission from the American Nuclear Society.

Link to worksheet:

American Nuclear Society: Annual Radiation Dosage Worksheet