With the new BC curriculum, grade 5 science now involves an introduction to mixtures. Our grade 5 teachers, having never taught chemistry, came to me looking for support in how to plan out their unit. After walking them through a few hands-on lessons that would excite their students, we agreed that it might be fun for their grade 5s to come to the middle school science lab for a guest lecture (me!) and experiment. The students came about 3 weeks into their unit with a good understanding of solutions. They had experimented with evaporation as a means of separating out a salt water solution, and were here to learn another form of separation – crystallization.
Because the students were young, a lot of preparation had to go into this experiment. I boiled water on hot plates, using 2L beakers and dissolved about 10 tablespoons of borax into each. By adding heat, you are creating a supersaturated solution, which, when cooled, will more easily crystallize back out again.
While the borax water solution was being made, the students were crumpling up a pipe cleaner into the shape of their choice. Using a small piece of string and a popsicle stick, the students suspended their pipe cleaner from the popsicle stick in such a way that the pipe cleaner did not touch the sides or the bottom of a 250mL beaker. Some students needed one-on-one support for this.
Once the borax was dissolved, the students came over in small groups with their beaker and pipe cleaner set-up. They put a few drops of food colouring into the bottom of the beaker before I filled it about three-quarters of the way with borax water solution. The students suspended their pipe cleaner in the beaker and then left these by the back of the class where they would not be disturbed.
To ensure the water did not evaporate before the borax could crystallize, I covered the beakers with paper towel. They sat out over the weekend, but within as little as an hour, you’ll begin to see crystallization. One overnight is often enough for the crystals to form.
The students were so excited to come back on Monday and check on their crystals. Even though I am not their teacher, and this was not their classroom, they came knocking at my door first thing Monday morning to see if they could check on them! Needless to say, when they did get them back in the afternoon, they were thrilled with the results! It always makes me so happy to see faces light up from a science experiment.