Acid Rain Vs. Chalk

Our last experiment from the Geology Rocks! book was on acid rain:

acid rain 1 In just skimming the picture, I thought we were going to somehow sculpt a person to use as our guinea pig, but in reading the actual items needed, this was a piece of chalk…I don’t know about you, but my chalk-carving skills are not such that I could make such a 3D, sculpture-in-the-round version of a person, especially wearing a hat! Plus, this was obviously made from a chunky piece of sidewalk chalk and all we had on hand are the small pieces of colored chalk I use to write grocery reminders on our kitchen chalk board. So here is my masterpiece of paper clip carving:

chalk dummy See the face?? I scratched in some stick figure arms and legs, too, but you can’t see them from this view. The book said to use “any” chalk from your local hardware store, as long as it was made from gypsum. Well, I looked but there was no ingredient list on our box of chalk, so I figured we were good to go.

We mixed a little water with some vinegar to simulate the acid of acid rain. Once again, we were without a medicine dropper, so we improvised with a drinking straw:

and now for the acid rain

readying the acid rain

After watching the chalk for a few minutes and seeing that nothing was happening, we poured the rest of the acid rain solution on the plate and waited.

Nothing. Apparently our chalk was not made from gypsum after all. Based on this experiment combined with trying to make our own chalk, I am making a mental note to stay away from chalk-based activities from here on out.


DIY Play Dough, Candy Caves, and Volcanoes

In my last post about DIY Chalk, the article also includes a recipe for DIY play dough, but I used a different one that I found on Pinterest. Of course, I need to start actually pinning things and not just writing them down…I scribbled a note to myself with the ingredients for homemade, no-cook play dough, but when I went back to Pinterest to find it a few days later, of course I couldn’t! So my apologies for not giving the pinner his or her due props, but this is the recipe I used:

  • 1/2 cup cold water
  • 1/2 cup salt
  • 1 teaspoon vegetable oil
  • 1 cup flour
  • 1 tablespoon cornstarch
  • food coloring
  1. Mix water, salt, oil, and food coloring.
  2. Mix flour and corn starch and add a spoonful at a time to the wet ingredients, stirring constantly until you get the consistency of pizza dough (or, duh, play dough–this is my comment, not part of original recipe)

When I searched play dough recipes on Pinterest again, I couldn’t find one specifying corn starch…most used cream of tartar instead. But I’m here to say that the above recipe worked just fine, with the following caveats: I was out of vegetable oil so I used olive oil…no problems there (I guess if you are not planning to eat the recipe, oil is oil). My box of corn starch was all but empty from the great chalk-making extravaganza (see above link) , but on the bright side, I found the tablespoon that had been missing since that debacle…it was in the box, which is probably why I put a virtually empty box back in the pantry, as the added weight of the tablespoon inside made me think it had corn starch in it!

The recipe says to mix the food coloring in with the wet stuff, which I did, but then decided I wanted it more red and tried adding additional food coloring after I had mixed the dough and it really didn’t make any difference, so if you’re like me and tend to skip a step or think you can just combine stuff randomly because you are super lazy, be sure to at least adhere to that particular instruction.

The reason we made play dough wasn’t to actually play with it in the usual sense, but rather to use it for two different science experiments from the book Geology Rocks. The first one was Candy Caves, whereby using sugar cubes, play dough, and a a few other household items, you can replicate how water in the earth seeps into tiny cracks in rocks and dissolves them slowly over time:

candy caves

First, we gathered our supplies: sugar cubes, a clear glass, play dough, a toothpick, and some water. The book called for a medicine dropper to drip the water, but we improvised with a drinking straw and the bonus physics lesson of how you can put your finger over one end and suspend the water:

candy cave supplies

quality control First you stack the sugar cubes around the bottom of your glass. Jack had never seen or tasted a sugar cube, so naturally he had to perform some quality control maneuvers prior to working with them. Once they are stacked, you cover them with play dough and then poke holes in the play dough with a toothpick:

aerating the play dough

After that, you use your dropper or straw to slowly add water and watch as it works its way through the holes in the play dough to the sugar beneath:

candy cave 2 You can still make out the spaces between the play dough and the sugar cubes to the left and right but below the sugar cubes were all dissolving into one big slab:

candy cave view from below

So there you have it, Candy Caves was easy to pull together and the lesson about the power of water erosion was readily observed and applicable to other daily observations about rain, tides, etc. And the best take away is that Jack uses the “straw trick” to entertain himself whenever we go out to eat now!

The second experiment calling for play dough was a Volcano (something I have yearned to do since I was a child and watched Peter on the Brady Bunch make one erupt on Marcia and her snooty friends):

Once again, we gathered our supplies (yes, this is a different tablecloth than the above pics–thanks for noticing!):

volcano supplies

The book suggested an empty salad dressing bottle, but we improvised, substituting a small, empty water bottle, placed in the center of a baking pan and then covered with the play dough:

volcano instructions theirs vs ours:

volcano aerial view

Once your volcano is finished, use a funnel to pour in 1/4 cup baking soda. I used a chop stick to help get it through the funnel faster, we always seem to have a random supply of those around the house. Add a squirt of dish detergent on top of the baking soda. Then mix 1/4 cup vinegar with a few drops of food coloring, add to the volcano and…

making the volcano

….and…you get a little vinegar reacting with the baking soda and fizzing up in the funnel. No big explosion, nothing foaming down the sides of the mountain, plenty of time for the people below to evacuate their homes, nothing like the cool picture in the book. Perhaps the fact that the baking soda in question has been in my freezer for, oh, I am going to go out on a limb here and guess at least several years now (I think I read somewhere that it lasts longer if you keep it there vs the ‘fridge?) was the problem? I may need to refine my scientific methods…

So there you have it: surprisingly enough, Candy Caves were way cooler…I guess slow erosion beats not-really-explode-y stuff every now and then…plus they have candy in their name, so there’s that.