Unit 4 Reflections: Worksheet 1 and Electrolysis of Water

Going by the modeling "book" is not working for me lately.

Friday: I expected pure substances vs. mixtures to be a review for my students, especially after the feedback I was receiving in our post-lab discussion.  The topics are covered heavily in physical science. The students usually blow right through it in years past.  I thought it would be a great chance to squeeze in some much needed textbook reading/writing practice, with it being a familiar topic that is not all that difficult to grasp from reading.

Um... no.  That's not how it went with these students.

Friday, in class, they were assigned to read the (very short) unit out of the textbook on classification of matter.  They were then to write me a paragraph classifying the stuff we saw in the lab (salt, sand, iron, salt/sand/iron together, water, sulfur, iron, iron sulfide) as a pure substance or a mixture using vocabulary they read in the text.  I figured after they read about the topic, we'd jump right into Worksheet 1 on Monday.

What they actually did instead of reading-- sit with the book in front of them without flipping a page, then turned in a list of garbage that showed they didn't even as much look at the headings on the pages.  Not cool.  I know it was Friday, but COME ON.

So, I got to spend all of Monday reteaching what they didn't read in the book.  I did it in a PowerPoint that I've used in the past, then finally gave them Woksheet 1.

I've never understood why this is so hard for students:

I used to assign a similar worksheet in years past and my students went into panic mode when they saw it.  After my Modeling Workshop, it occurred to me that I was assuming that students had a conceptual picture of particles when it was something I truly never taught.  This year, since we have been explicitly working in conceptual "particle" mode all year, I didn't anticipate it being nearly as panic inducing.  Wrong again.  *head desk*

So we wasted more time today slooooowly correcting the very wrong answers on Worksheet 1 until it finally seemed like my students had some idea of the difference between elements, compounds, and mixtures.

Onward ho-- next we were supposed to start building towards the Law of Definite Proportions with a demonstration using a Hoffman Apparatus.  My Modeling Workshop was generous enough to provide us all with our very own Hoffman Apparatus!  Unfortunately, they didn't give us a power source.  Never fear, they told us, you can just use a 6V or 9V battery.  Ha.  Hahaha.  Ha. Of course, I procrastinated until the last minute to try this idea and found that while a battery will cause some decomposition, I could not get the reaction to go nearly fast enough to be visually impressive.  Maybe it was just me.

I needed a backup plan.  My first thought was to do the 9V battery/pencil lead electrolysis of water-- but a single set up is way too small for an effective demo.  Plus, I really wanted them to see that it was twice as much hydrogen than oxygen, and actually prove it was hydrogen/oxygen and not just bubbles.

Thanks to Google and YouTube, at the 11th hour I was able to rig up some of these setups using materials I had on hand:

Small plastic container with two push pins through the bottom, 2 test tubes, a 9V battery, and a solution of water with a small amount of sodium biocarbonate

The containers were a little cumbersome to manipulate, but the setup worked well overall.  Between weak batteries and time constraints, we didn't see a perfect 2:1 ratio, but the students clearly saw more gas being formed on the cathode side than on the anode side.  I was able to come around with a flaming splint and demonstrate the hydrogen "pop" to each group.  There wasn't quite enough oxygen to re-ignite a hot splint, but it was enough to at least make the flame visually grow.  We discussed how water vapor would not cause a flame to grow or pop-- too much water vapor may even extinguish a flame.  We also discussed that the container did not feel hot enough to be boiling, so it couldn't be "boiling" water.

I told them that scientists have found that a compound of a substance always has the same ratio of elements.  Water is always 2H:1O.  We then hypothesized the ratios of elements in other familiar compounds, like sodium chloride and glucose.

We were going to watch "Gases and How They Combine," as suggested by the lesson plan.  I watched the video myself on YouTube and it is BORING and dated.  While the demonstrations and explanations are great, I don't see my students paying enough attention to get anything out of it.  I think we'll jump right into Worksheet 2 tomorrow... then on to Dalton's Playhouse.

Despite being dreadfully far behind and feeling like 50% of my students are shut down... I do hope that by the time we get to balancing equations, it should be a non-issue.  That's basically all they are doing in Worksheet 2.