Oceanic Acidification & Seashells

Birds and their eggs aren't the only animals for whom an increasingly acidic environment would cause great harm.  This simple activity demonstrates the effect of acid on shellfish.

You'll need a couple of shells (large or small, any variety, but for the sake of comparison, it's good to have two of the same), two cups or beakers, vinegar and water.

Place each shell in a cup/beaker.

Cover one shell with water.  You might want to use salt water, as these organisms live in the ocean, but I didn't think of that as I was setting things up. You could also do three shells at a time - one in vinegar, one in water and one in salt water.

Cover the other shell with vinegar. 

You'll notice that the shell in the vinegar immediately begins to form bubbles and fizz.  The vinegar is breaking down the calcium carbonate that composes the shell. 

Within 24 hours, you'll notice the shell that was in vinegar has holes in it.  If there was still a creature living in the shell, this could obviously be detrimental.

Vinegar, while a weak acid, is quite a bit stronger than acidified ocean water.  The stronger acid speeds up the process, making it visible within a short period of time - perfect for students to grasp an understanding of the process.  Shells in an acid ocean environment would be subject to the same chemistry, it would just take place at a slower rate.  

You can learn more about the chemistry taking place, as well as ocean acidification here.  

You may wish to continue to leave the shell in the vinegar for an extended time to observe further.  If so, it may be necessary to replace or replenish the vinegar.  (I used a small enough amount of vinegar that the chemical reaction came to a halt within a day or so).

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Rate of Reaction: How Does Surface Area Affect the Rate of Reaction?

 The combination of Alka-Seltzer and water produce a chemical reaction.

To see how surface area affects the rate at which this reaction takes place, you'll need two Alka-Seltzer tablets and two glasses of water. 

 Keep one of the tablets intact and crush the other tablet (crushing it into an actual powder would be even better than the pieces I've shown here - good chance to break out the mortar and pestle if you've got them).

Drop the whole tablet and the crushed tablet into the water (each tablet into its own glass of water) and observe the length of time it takes each reaction to finish. 

End of School: Playing with Polymers

Tracy from The Science Spot has come through once again with a fantastic unit, Playing with Polymers, in which students make four different polymers - Gloop, Boogers, Goobers, and Super Slime.

Tracy does this as part of curriculum, as part of a study on petrochemicals.  I did it at the end of the school year, and the one drawback to doing it then is that this activity does require quite a few supplies and pieces of equipment.  But, the students LOVE it - I'll take the mess if I can have engaged students right up until school's out! 

And, Tracy does make it fairly painless for the teacher; she includes lists of materials (in quantities for 100 students), recipes, set-up instructions and so on.  If you keep the materials well-organized and labeled, things will go smoothly.  And your students will love you!

Homemade Indicator Papers

If you've made some cabbage juice indicator and are looking for another way to save it for longer use, try making your own indicator papers.

Cut paper (I used coffee filters) into strips about 1/2" wide and a 2-3" long.

Submerge the strips in cabbage juice until they are fully soaked.

Remove the strips and place them in a warm spot to dry.

Store the dried strips in a resealable bag.

To use, place a drop of the liquid to be tested on the paper.  If it's a base, it will turn pink.  If it's a base, it will turn green.  And if it's neutral, there will be no color change.

The color change isn't as drastic as you'd see with litmus paper, but it's there. 

Cabbage Juice Indicator

Red cabbage juice is a great indicator - it turns pink in an acid, green in a base, and stays blue in a neutral substance.  And while it takes a little time to make, it's a whole lot cheaper than other indicators. 

To make some: 
Chop up a head of red cabbage and place it in a large pan.  Cover the cabbage with water.  Simmer for about 20 minutes (your house will smell like cabbage).

Let the contents cool before you remove the cabbage.  Store the water (now cabbage juice) in a jar*.

To test your cabbage juice:
Set up three glasses:
Pour a little vinegar in the first, some baking soda dissolved in water in the second, and tap water in the third.

Add a few drops of cabbage juice to each glass and observe.

*You can freeze the cabbage juice for longer storage.  Pour it into ice cube trays and freeze.  Then place the cubes in a freezer bag or box.  Pull out individual cubes as you need them.

Rate of Reaction: Glow Sticks

Background:
*Glow sticks work because of a chemical reaction.
Glow sticks contain two substances - one housed in the plastic casing and another inside a thin glass tube within the plastic. When the stick is bent, the glass breaks, allowing the two substances to react with one another. More information can be found here.

*The speed at which a chemical reaction occurs is dependent upon the temperature at which the reaction is occurring.
This is not the only factor that influences rate of reaction, just the only one we'll be talking about here.

For today's experiment:
You'll need two glow sticks* (two of the same color is best - makes it easier to compare), 2 glasses, hot water and cold water.

The water can come from the tap. I usually stick the glass of cold water in the freezer for a minute or two while I'm getting everything else ready, just to make it extra cold. I get as hot of water as I can from the tap. I suppose you could boil some water, but this works just fine and reduces the prep work.

Put your two glasses next to each other. Activate both glow sticks at the same time and place one in each glass.

Left side = hot water, Right side = cold water

After a minute or two, you'll notice that the stick in the hot water is glowing much brighter** than the one in the cold water. In fact, the one in the cold water will barely appear to be glowing.

Left side = cold water, Right side = hot water

The reaction that causes the glowing is occurring at a much more rapid pace in the hot water, thus the stronger glow.

Your students may have heard that they can save their glow sticks by placing them in the freezer. Doing so will slow down the rate of reaction, so the glow stick will last longer; but it doesn't stop the reaction, once the glow stick has been activated, it won't last forever, even in the freezer.
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*Keep your eyes on the dollar section of stores such as Target - you can occasionally find 12 sticks for a dollar there - makes it affordable enough to consider doing in the classroom.

**There really is a drastic difference in the 'amount' of glow being emitted from the two tubes, I promise. It doesn't photograph very well, at least not with my limited photography skills. So try it for yourself.