Coping with Chemistry-7th Grade
By Barbara Benson
In Donna’s From Nature Stories to Natural Science (104-106), she suggests organizing the Chemistry main lesson for grade 7 around the traditional elements of Fire, Water Earth and Air, with Fire (combustion) being the natural starting point. Since I found this main lesson somewhat challenging as a homeschooling parent, I thought it would be helpful to share what I did with my daughters in this three week main lesson.
RESOURCES: Aside from Donna’s science book, my other main text (which she mentioned in her resources) was A Demonstration Manual for Use in Waldorf School Seventh Grade Chemistry Main Lesson by Mikko Bojarsky ( available at waldorfbooks.com). For lab materials I purchased everything from Home Science Tools ( homesciencetools.com) which included their basic chemistry lab equipment kit, a pair of lab aprons, gloves, safety goggles, and some extra chemicals (hydrochloric acid, sodium hydroxide and calcium carbonate).
CORE CONCEPT: The main point of this block was to engage my daughter in working with these four classic elements, doing experiments with observation, sleeping on the experience, and then working towards a scientific “concept” the next day, writing up and illustrating her experiments. With certain experiments, we asked key questions to guide our observations and then answered them the next day. Sometimes it will be necessary to repeat the experiment the next day to frame the concepts learned. We observed in our experiments, as Donna notes, that the water in chemistry is” the catalyst, the diluent, the carrier of other substances…(which)can be studied in its various forms :solid, liquid and gas”. ( 106)
COMBUSTION (Fire, secondarily Air and Earth and Water)
We began with the study of combustion, and our first experiment (What are the components of fire?) was to burn a large number of natural objects we collected using a candle. They included: white pine cone and needles, cypress pine cone, dried oak, maple and sycamore leaves, the leaf and root of fresh weed, hemp, raffia, wool, a paper towel, newspaper, drawing paper, cardboard, string and human hair. By burning at least a dozen materials, one observes that each item burns uniquely.
On day one she carefully observed the different burning styles of each material and the production of heat, light, smoke and ash in the various examples. One thing that was particularly effective was to notice the difference between burning leaves and burning the root. It explained graphically how the more fleshy root, not exposed to light, did not ignite well. The next day, my daughter picked six of these materials to illustrate in her drawing with the candle flame and she wrote up her observations. One interesting conclusion is to note that the only component of combustion that falls back to earth is ash with its weight of minerals, the other components are released into the air.
Our second experiment ( What are the zones of the flame?) was to simply examine a burning candle and work to understand the role of air in the burning process. We explored the several colors of the flame, blew on it with a glass straw, and carefully bserved the hottest blue section and the yellow white tip that gives off the most light. If we quickly swiped a finger sideways through the flame, it would not be burned. When the candle itself is moved from side to side, the flame drags along behind it but when it is moved up and down the flame shrinks going up and stretches more going down. The glass straw was used to blow lightly on the flame, causing it to flicker making the top yellow part reduced and producing a moving wind sound.
We observed and the next day conceptualized that the heated wax vapor ( gas) travels up the wick to be ignited. My daughter especially enjoyed testing this by relighting an extinguished candle from the rising wax vapor without the lit match touching the wick. We also took a “cold” candle and observed that it could not be relit immediately since not enough wax had melted. In our write up we answered the question of why air was necessary for combustion and what exactly ignites when lighting a candle ( the wax). We could “relight” the candle that had been extinguished because the wax vapor particles in the smoke form in cooler air. The heat from the match ignites the vapor smoke and the fire burns down the smoke trail to relight the candle.
Our third experiment ( How does burning consume air?) was to cut off the air supply to the lit candles by placing them under jars. We counted how long it took before the flame expired and tried different sizes of jars. This was a good way to demonstrated the role of oxygen in combustion. It is also interesting to note in this experiment that water vapor occurs on the jar sides covering a lit candle.
We conceptualized later that water vapor condenses on the walls because the walls are cooler and in the bigger jar with more oxygen, the flame burns longer, causing the walls to warm more and producing less condensation.
Our fourth experiment ( Why was the water drawn up from the plate after the flame burned out?) was to put the lit candle on a plate or small bowl of water with the glass jar over the candle. We observed that the water was sucked up inside the jar, creating a real suction effect when she went to remove the jar. This is a simple experiment that effectively demonstrated the concept of the partial vacuum created when the air supply is used up. The flame seeks air and sucks up the water, creating a partial vacuum. The vacuum is also caused by air pressure.(As the warm air in the jar cools and contracts the outside air pressure pushes the water up until the atmospheric pressure inside and outside the jar are equalized and stabilized).
ACIDS and BASES ( Earth)
Our first demonstration experiment was a simple experiment mixing baking soda and vinegar in a glass jar. My daughter lit a match and put it into the fizzing, bubbling mixture of the two ingredients and the match was immediately extinguished. We observed the smell and smoke and tasted the resulting mixture- salty! We conceptualized the next day that the carbon dioxide being released was heavier than air and trapped a lot of the smoke in the jar. Also, the byproduct of the chemical reaction of acids and basses is the formation of some kind of salt.
The second experiment was to take an E flask with a rubber cork and short and long tubes, a glass straw and three votive candles. My daughter mixed the baking soda and vinegar in the flask and then hovered the long tube from the corked flask over the lit votives. When she held down the short tube on the cork with one finger, the flames in the tea lights were extinguished.
We conceptualized later that when carbon dioxide was being released in the flask , it was channeled through the tube and smothered and extinguished the votives.
Our third experiment explored the nature of acids and bases more carefully. We talked about their tastes and smells and noted that they were polar opposites, which combined created salt. We also discussed “indicators” that show the presence of an acid or base by color. We used the ph litmus test strips and put one in vinegar, and the other in baking soda mixed with water. We observed the difference in colors and numbers on the test strips.
Our fourth experiment was a multiday one ( 3 days) with a raw and hard-boiled egg placed in a beakers with vinegar. We observed changes over three days. By day three the hard- boiled egg shell had flaked off and the egg was bigger. The raw egg floated and sometimes spinned in the vinegar but by day three it was a lot bigger than the hard- boiled egg and was very bouncy. The hard -boiled egg was not at all bouncy. Our later conclusions were that the acid in the vinegar dissolved the calcium shell ( base) and since the raw egg was more easily penetrated by the vinegar, it swelled more dramatically, absorbing about 2/3rds of the vinegar. The inner section of the raw egg absorbed so much that its texture was changed completely and became bouncy.
Stronger Acids and Bases and Crystallizing (earth/air/water)
These experiments were all done outside on our picnic table with full safety gear on. Our first experiment was to add hydrochloric acid to calcium carbonate chips (marble chips). Hydrochloric acid is number 1 on the ph scale and quite dangerous. We put a few marble chips in the flask and covered the chips with water which created a little cloudiness. Then we poured about the same amount of hydrochloric acid in to the flask which created condensation bubbles and fumes. The acid began dissolving the marble chips. Our later concept was to understand that the acid chlorine in hydrochloric acid replaces the carbon dioxide in calcium carbonate. The reaction heats up and the hydrochloric drives the weaker acid out and calcium chloride (salt), with released carbon dioxide and water as the result. It was interesting to see those marble chips dissolved and salt created as a result. We learned that this type of reaction is called a replacement reaction.
The second experiment involved the even more dangerous experiment of adding hydrochloric acid directly to sodium hydroxide ( please practice this yourself first for full safety ). Lye pebbles were placed at the bottom of the beaker and then we carefully poured in a few drops of acid. Immediately the mix violently bubbled, steamed and fumed impressively. We were careful to avoid the noxious fumes but observed the heat of the reaction and noticed that after not more than a minute and a half, all the lye pebbles were dissolved and common table salt, sodium chloride, lay at the bottom. We flooded our experiment with water and noticed that all cloudiness and the salt completely dissolved in the water, becoming quite clear. We then very carefully washed up and stored our chemicals safely away.
The third experiment involved experiencing the dissolving and reforming of salt crystals. We boiled 500 ml of water in a beaker on top of an alcohol burner and stirred in small amounts of sea salt with a glass stirring stick into the hot water. After about a total of 1/4 cup of salt being added, the solution could not dissolve any more salt- we had achieved saturation. We then let it heat for five more minutes and then “painted” with the saturated solution on black construction paper with a paintbrush. When it cooled, small salt crystals formed. Our conclusions the next day were that the salt that is dissolved is called a solute and the liquid dissolving it is a solent. The solubility of a salt is generally in proportion to its temperature. The solute “precipitates” (falls out of solution into solid form) and forms crystals. The dried black paper was full of the tiny crystals in the form of a square. A fourth experiment can be done using a small test tube and Epsom salts. Pour about 2 teaspoons of the salt into about 35 milliliters of hot water. When the tube is held above the alcohol burner with a pair of tongs, there will be vigorous vibrations as the solution boils and dissolves the Epsom salts in about 5 minutes. When the burner is extinguished, the contents of the tube can then be poured into a brownish pyrex pan and watched for precipitation. When the liquid cools, one can see the distinctive crystalline form of Epsom salts- like quartz crystals.
Many seventh grade texts also work with the lime cycle but since we had only three weeks to cover this main lesson, the experiments above were about all we could accomplish. Donna also suggests working with photosynthesis in plants to join the Four Elements together. We did not do this in 7th but we did do it in the very beginning of our first lesson in 8th grade organic chemistry where we explored and drew the cycle carefully to explore this amazing process in plants.
Christopherus Homeschool Consultant