Sunday, October 10, 2010

Sweet Science

Tim and I usually try to do an activity in the morning before school.  He tends to pick a holiday craft but lately I've been promoting science experiments.  No, he's not looking for a cure for cancer or solving global warming.  I just try to find easy but educational activities that stretch his current understanding of the natural world.
This mason jar contains a ghoulishly purple syrup for rock candy.
Initially when I asked him if he wanted to make rock candy, he asked me when he could eat it.  When I told him it would be a week, he said "skip it."  Undeterred, I decided to start making the sugar syrup to see if I could grab his attention.  Sure enough, he was asking me what I was doing while I was rounding up ingredients.

Most recipes for rock candy have you boiling water in a pan and then adding sugar little by little.  I decided that we would make ours in the microwave.  The only challenge would be to not let the syrup boil over while it was in the oven.  I avoided that by heating the sugar water in minute increments.

While I was heating the cup of water before adding the sugar, I had Tim cut string in twelve inch lengths.  He did an outstanding job using the ruler and clipping the string into the desired length.  We decided to use butcher's twine because of the rough surface which would give our sugar crystals a place to grow.

Once Tim cut six pieces of string, we tied them onto a pencil and let the twelve tails dangle into a quart mason jar.  Meanwhile, I heated the cup of water in the microwave until it was almost boiling.  Then Tim added a cup of sugar to the water and stirred it until dissolved.  It was interesting listening to his dialogue about the syrup.  He like seeing the bubbles in the syrup and enjoyed watching the sugar change from white to clear.  Tim has considerable observational skills and is wonderful at describing his experiences.

Next, I added another cup of water to the mixture and heated the syrup till almost boiling.  Then Tim added a second cup of sugar.  He kept asking me "I wonder what this will taste like?"  I appreciated the fact that he was curious and was thinking ahead to the end product.  After the sugar was dissolved, I cautiously heated the syrup (one minute at a time on high power) because I didn't want the mixture to froth over.

For me, the fascinating part of the activity is making a saturated solution.  The syrup needs a longer time to heat up after you add the third cup of sugar.  The sucrose molecules are occupying close quarters and have less water around themselves to stay dissolved.  Tim noticed by the fourth cup of sugar, that the mixture was thick, more opaque and full of bubbles.

Tim's favorite part of the recipe was adding the food coloring.  He kept flip-flopping between orange and purple (probably because of Halloween this month).  When he chose purple, the sugar syrup ended up looking more like royal blue than a true purple.

Once the syrup was colored we poured it carefully into the quart mason jar without letting the syrup touch the pencil or strings.  Unfortunately, the light weight of the strings caused them to float rather than stay submerged in the syrup.  If we had weighted down the twine, the strings might have remained immersed in the sugar water.  I tried to poke them down with a knife unsuccessfully.

Needless to say, I put a sign on the jar to discourage curious persons from picking it up and shaking the contents.  Saturated sugar solutions will crystalize with any possible disturbance (change in heat, change in movement) so quality rock candy needs to sit for about a week.  This gives the sucrose molecules the opportunity to join together and form monclinic crystals.

The chunky confection takes about a week to form.
It was challenging for Tim to wait the full week for his rock candy.  Although, each day he would look at it and wonder what was happening inside that jar.  I thought it was a great exercise in using his reasoning skills.  When the seventh day came, Tim was thrilled to taste his confection.

It took me a while to get the strings of candy separated from the block of sugar that formed on the bottom of the jar.  Once I did, Tim gobbled up the candy on the first string within seconds.  I think next time we make this recipe, we're going to add some flavoring.  Pure sugar, to me is too cloying.  Sugar needs a little enhancement like cinnamon or the traditional anise.

Our experiment was a sweet success.  Tim got to see some authentic science with sucrose crystals.  He was able to observe and ask thought provoking questions. Yet, most of all, his patience was rewarded with a scrumptious sugary delight.

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