Glimpse Into The Classroom: Seventh Grade Chemistry
By Jeanette Voss, Long-time Main Lesson Teacher
Science at WSL is taught in (ascending) blocks by class teachers. The natural sciences of physics and chemistry begin in 6th and 7th grade respectively and end in 8th grade. We practice the phenomenological approach to doing science and all students have in their books a motto, first written by Michael Faraday, as a reminder:
We come here to be philosophers, and I hope you will always remember that when a result happens, especially if it is new, you should say “What is the cause? Why does it occur?” And you will in the course of time find out the answer.
Over the course of the block, we discussed the use and value of making a hypothesis vs. coming to a conclusion and the fact that if the outcome of an experiment is other than predicted, this is not a “mess-up” but rather a scientific observation and a possibility to explore variables.
The current main lesson block of Inorganic Chemistry in 7th grade began with a high-level overview of the history as well as the origin of the word and practice of chemistry. I spoke about the discoveries and achievements of scholars in Egypt, India, and China long before this knowledge of the transformation of substances through human manipulation was brought to the shores of Europe. Metallurgy, the study of properties of metals, as well as their usage and means of extraction from sands or ores, was practiced all around the world in indigenous populations long before European contact. The discovery of gold and silver in the Americas for instance became a driving force behind the incentive to claim other peoples’ lands for European kings and queens.
In the chemistry lessons, however, we based our investigations and experiments loosely on Aristotle’s theory of the four primary elements of matter (fire, water, air, and earth). The 7th graders began their experiments with the study of fire, specifically with combustion. Careful observations of fire, flame, smoke, charcoal, and ash provided a re-introduction to the scientific, phenomenological, process first practiced in our physics block on simple machines, shortly before the Winter break. As New Englanders, many of you most likely enjoy fires while camping or in a fireplace, and most are familiar with a lit candle. Yet, how many of us have really looked at the shape, color, or movement of a flame? How many of us pay attention to the appearance of a trail or cloud of smoke? The students practiced careful observation skills by lighting and monitoring a “campfire” outside. They learned to “read” it by identifying the footprint of a fire by the ash and charcoal it left behind. They heard about scholars in Ancient India who knew that certain substances produced different colors of flame (long before Bunsen and Kirchhoff created their flame test about 200 years ago). We discussed the role of oxygen and witnessed the power of carbon dioxide to quicken or extinguish a flame, respectively.
The study of the element of water began with a generalized presentation of water as a human right. Students conducted a personal water usage research project at home, which they then compared to the UN regulations of how much clean and safe water each person on Earth should have for personal use (between 50 – 100 gallons/day). The recall of last year’s study of the Natural Water Cycle was expanded by a discussion of the Human Water Cycle (impact of humans on the environment in terms of water), before we looked at other properties of water such as the ability to dissolve some substances, or to act as a catalyst to reactions with others. The use of heat allowed us to make super-saturated salt solutions and we observed how salts can precipitate out of the solution and lead to the formation of crystals in the right conditions.
When possible, I allowed the students to do simple hands-on labs to teach them proper laboratory skills - including safety procedures - and the writing of simple lab reports all following a prescribed template.
When the weather cooperated, we set up a limekiln outside and the students witnessed the steps necessary for burning limestone. Once the limestone had been baked and cooled, we slaked it the next day and everyone now knows why the resulting substance is called quicklime. The lime cycle is one of the key experiences in the study of chemistry in grade 7. We were able to decompose an inert salt and break it into two substances: an acid (carbon dioxide, carbonic acid in water) and a base (quicklime). Because opposites attract, the acid and the base will form a salt (calcium carbonate) again.
The remaining ten days of Inorganic Chemistry were spent investigating the properties of acids and bases as well as the pH scale. Purple cabbage juice served as our indicator fluid and the resulting rainbow of colors in test tubes will serve as a memory to build upon in future years. The block ended with an introduction to the seven archetypal metals, and the class observed an impressive replacement reaction with silver nitrate and copper wire by the end of the block.
This block ended with a formal chemistry test, and we discussed test taking skills that hopefully served to allay potential test taking fears and build confidence.
