Sunday, September 13, 2015

Apologia Chemistry Conservation of Mass.

C16 is working through module 3 at the moment, and she did a really cool experiment.

Chemistry experiment from Apologia Chemistry on the conservation of mass.   The first question might be, what the heck is conservation of mass?  It is a fancy way of saying that matter cannot be created or destroyed; it can only change forms-i.e. when matter goes through a change, the total mass remains the same.  Got it?

Look at it this way.  Trying to figure out if the mass of matter is the same before and after a chemical change has occurred is what you are trying to accomplish.  So everything has to be weighed before any changes are made.

What you need:
~A few beakers or glass containers.  We do not have fancy glass beakers so we opted to use my beloved Mason jars.  We filled one up with water and marked off what would be 250 mL and 100 mL as you can see by the Post-it notes.  We also marked off 50 mL, 60 mL, and 10 mL so we could mark where to stop filling the jars up when those amounts were called for.
~White vinegar
~red (purple) cabbage leaves (we used four).
~lye (sodium hydroxide).  This is tricky to find, we actually ended up using drain cleaner that contained sodium hydroxide instead, and it worked just fine.
~a stirring rod (we just used a wooden dowel).
~2 cups of water
~a glass plate/saucer
~a mass scale

Put two cups of water into a pot and then add the cabbage leaves.  We used four.  Then boil the leaves for five minutes.  While you wait for the leaves to boil for five minutes, measure the mass of the 100 mL beaker, and then add 60 mL of vinegar.  Carefully measure out a teaspoon of lye and put it on the watch glass.  Allowed the cabbage to cool for a few minutes.  Then pour about 50 mL of the cabbage/water liquid into the 250-mL beaker.  You may want to let it cool just a bit and then pour about 10 mL of the solution into the 100-mL beaker.  The vinegar should have turned pink. That was the first chemical change.  The cabbage has anthocyanins-i.e. water-soluble pigments.  Next, place the stirring rod in the beaker.  Cover that beaker with your glass plate and measure the mass of the items combined.  Once you get your new total mass, dump the lye from the glass plate into the vinegar and stir with the stirring rod.  If you did this all correctly, the liquid in the beaker should have changed colors but the mass should have stayed the same.  Here are the pics of our results.  
The supplies are ready to go.

60 mL of vinegar in the first jar and 10 mL in the second jar.

Once you add the cabbage water, the vinegar turns pink -i.e. the first chemical change.  You need to reweigh this jar and then add in your lye from the watch plate.  This is when the nice pink color will turn into a cloudy solution.  The mass should have remained the same during this second chemical change.  All done!  We were just messing around in the next pics to try and catch the solutions changing color as more lye was poured in.  You may notice that the level of the solution in the jar stays about the same even though a lot of lye is being poured in.  

The most interesting part of this for me was that no matter how much lye we added, the solution level stayed relatively the same.

Happy homeschooling...............

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