cript it shows the quantity of atoms of the element it immediately follows. When a number is written in front of a molecule it applies to all the atoms in the molecule. For example: H2 shows 1 molecule of 2 hydrogens bonded together, while 2NaCl shows 2 separate molecules of Na bonded to Cl, or 2 Na atoms and 2 Cl atoms in total.
Next, we talked about how we would begin to solve the equations. My son solved the first 5 or so equations entirely using the Lego bricks. He began by assembling one molecule of each reactant and then breaking them down to form the molecules of the products. He quickly observed that sometimes more molecules of reactants would need to be present in order to form the different molecules of product and sometimes there would be leftover atoms that would need to find a home in the equation, perhaps by increasing the number of molecules of product. Using the Lego bricks he was able to visualize where all the atoms were going and where they came from.
Starting with the 6th equation, he decided he wanted to try to balance the equation using math and then check it with the Lego bricks. If you are unfamiliar with solving chemical equations, the easiest way is to start by counting the number of atoms in the reactant(s) (the left side of the equation) and then counting the number of atoms in the product(s) (the right side of the equation). Compare the number of atoms of each element in the reactant(s) to the number of atoms of each element in the product(s). If the number of atoms are unequal, you next must find the simplest way to equalize them on both sides of the equation. If you have more than one element to balance, solve for the element that only appears in one molecule of reactant and one molecule of product first. Add coefficients as needed based on this element and then recalculate the other elements in the other molecules of the equation. Continue this process until you have balanced your equation. I was surprised how quickly my son was able to figure out the math of this process and I was impressed when he began to see patterns forming that helped him solve the equations even more quickly. He gave up checking the equations with Lego bricks about 10 equations into our exercise.
After finishing the 20 equations I had written out for him, he expressed an interest in balancing equations using real chemical symbols that make up real molecules. I made a short list of 5 equations just for him to try out. He was able to transfer the knowledge he used with our made up chemical equations to real world equations very easily. And as a bonus, this gave us a chance to practice identifying elements by their chemical symbol and also the nomenclature of molecules.
After spending so much time doing math and worksheets, I thought it might be fun to see a chemical equation in action! I wrote the equation for the reaction of baking soda and vinegar and asked my son if he recognized any of the molecules and asked him if it was a balanced equation as written.
NaHCO3 + CH3COOH → CO2 + Na+ + H2O + CH3COO-
Note: Vinegar is a mixture of many different chemicals. It is typically 5% acetic acid dissolved in water, so the molecular formula for acetic acid is used in this equation.
This equation is balanced as written, but we wondered how we could prove that the equation is an accurate description of what took place. Usually we play with baking soda and vinegar in a way that will result in an uncontrolled eruption, but this time we wanted a smaller reaction that we could observe more closely. We combined a small amount baking soda and vinegar in resealable sandwich bag, and sealed it up to watch the bubbling reaction. What happens to the bag as the reaction takes place? How could you test the contents of the bag to validate the chemical equation? (Hint: O2 is necessary for flame, H2 causes an explosive pop of flame, CO2 will extinguish a flame)
We really enjoyed this activity. I initially worried that it might be a little advanced for my 8 year old son, but he surprised me with his enthusiasm and quick comprehension. A few day