experiential science: solutions and crystallization

We’re studying science through Bernard Nebel’s Building Foundations of Scientific Understanding (often simply referred to as BFSU), which is a delightful program.  We’re still working through the first book, intended for grades K-2.  Nebel walks through each topic, explaining concepts and terminology to the instructor, giving guidelines for sharing the material with students (mostly through Socratic discussion), and providing a list of useful books.  Lessons are not strictly linear, but weave between the branches of science and can be arranged as best suits the learners–though Nebel explains that certain concepts must be understood before others can be introduced. The only lack in Nebel’s material, in my opinion, is its minimal use of hands-on exploration.  While most concepts are introduced with a demonstration, they are often developed verbally.

My kids LOVE science, but when they think science, they think messy and playful. So instead of trying to look elsewhere for curriculum, I decided to build on the awesome foundation provided by BFSU by doing quick searches for hands-on ways for my kids to experience the concepts.  I thought I’d share my results here.

Though I’ve been doing this for a while, it just now occurred to me to share my work, so I’ll start with one of our recent units: solutions and crystallization.  The activities and our discussions were based on Lesson A-9 in the first BFSU book.  You can read for yourself to glean discussion points, but I’ve listed my activities below.

mixorsolutionActivity 1: Mixture or Solution?

First we had to determine the difference between a simple mixture (which we’d already discussed) and a solution.  I’ll list my supplies below, but don’t feel bound by what I used–I just chose what I had on hand.  Nebel describes a simpler form of this activity in his book.

  • Supplies: clear containers, water, stirrers, various substances for mixing
  • Gather a variety of similar-looking substances.  I chose sugar, salt, flour, bread crumbs, vanilla, and sand.  (I also had oil on hand for the oil/water/soap experiment that Nebel describes.  I won’t bother to replicate it here, since it’s in the book.)
  • Assemble one small container of water (preferably a clear container) and a stirring implement (I used toothpicks) for each of your substances.
  • Have your kids stir a small amount of each substance into one of the containers.  What do they notice? Do some behave differently than others?

Activity 2: Crystallization

We did two separate crystallization activities in one fell swoop: Borax and rock candy.

  • Designer Crystals (Requires pipe cleaner, Borax, water, jar, string, stick)
    • Using a pipe cleaner (or two!) let your children form a design on which to grow crystals.  They can make a letter, their name in cursive, or simply some squiggles, but be sure the design can be lowered into your chosen jar (and lifted out again!) without touching the sides or the mouth of the jar.  You’ll need a bit of extra room to get it out once it’s laden with crystals.
    • Tie your pipe cleaner to a string and your string to a stick.  You’ll balance the stick across the mouth of the jar and the string will dangle your design into the water.  Be sure your design will be completely submerged but NOT touching the bottom or sides of the jar–leave at least a half-inch clearance, if not more.
    • Measure how much water it will take to fill your jar, and heat that amount of water.  You can do this via the stovetop or a microwave.
    • Once your water is hot, stir in a generous helping of Borax powder.  Different people recommend different amounts, but this experiment doesn’t seem too fussy.  I accidentally got two batches with different amounts, and both worked fine.  The idea is to super-saturate your liquid.
    • At this point you can add food coloring if you’d like, but the color of your pipe cleaner seems to be more powerful than the color of the crystals.  Wait for your solution to cool before pouring it into the jar (or before handling the jar, if you opted to microwave it).
    • Dangle your design in the jar of Borax water and set it aside where it won’t be disturbed.  Our designs were heavily covered with crystals within hours, to the point where I had to pry them from the bottom with a knife.  The results were pretty exciting!
  • Edible Crystals (Requires skewer, sugar, water, jar, springy clothespin, rulers)
    crystals

    Borax (foreground, already finished) and rock candy (background, looking like nothing yet)

    • Measure your skewer and clip a clothespin on it so it will balance on the mouth of your jar and dangle inside without touching the sides or bottom of the jar.  If you need to, use rulers to make the mouth of your jar more narrow so the clothespin can balance.
    • Measure how much water you need to fill your jar.  Pour this into a saucepan and heat it.  Keeping your water just below boiling, begin to add sugar at a rate of about a half-cup at a time.  I’ve read that you need about 3 times as much sugar as water; I forgot to measure, but I know I used waaay more sugar than I thought I would and had to stir way longer that I thought I should to see if it would dissolve.  (The kids got bored and wandered off.)  By the time my liquid was super-saturated, the top seemed to get cloudy and not clear up even after I stopped stirring and let it settle some.
    • Let your liquid cool until it’s easy to handle.  (Otherwise at the very least you risk burning your hand while handling your jar!)  Pour it into your jar, being careful not to pour any undissolved crystals of sugar into the jar.  (Rock candy is easiest to eat on a stick, not stuck to the bottom of a jar.)  You can add food coloring if you’d like.
    • Balance your skewers atop the jar and be prepared to wait at least a day before seeing any difference at all and a week or more before you have something worth chewing on.  Some people say this process can be sped up by dipping the skewers into the solution, rolling them in sugar, and letting that coating dry before dangling them.

Activity 3: Solar Still

I like to have a “so now what” type of moment about the things we learn.  So how can we use our knowledge of solutions?  I posed a real question to my kids: Suppose you were stuck on a boat in the ocean and you ran out of water.  You know that salt water will kill you.  How can you get fresh water other than waiting for rain?  I could have let them develop the whole thing on their own, but once they had the concept I put together a solar still and had them figure out how it worked.

  • Supplies: salt, water, large bowl, glass or heavy container that fits inside bowl and is shorter, plastic wrap, rock
  • Mix some saltwater in the bottom of your large bowl.  Taste it if you’d like.
  • Place your glass in the middle of the saltwater.  It has to be a glass or something heavy, otherwise it’ll float around or tip and ruin the experiment.
  • Cover the bowl with plastic wrap, ensuring that it is tightly sealed around the edges.
  • Place the rock on top of the plastic wrap, centering it over your empty glass and making sure it slightly depresses the wrap.
  • Put your still in a warm place and wait for the results.  Alternately, you could speed up the natural process by using warm water that will already be evaporating reasonably fast.
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