There are (as far as I know) only two ways to teach the factors that affect solubility. You either tell them, and they remember it, or you have them figure it out, and have them tell you. I’m really prefer to let them explore and find out for themselves. It makes for a great inquiry activity. Students work to dissolve samples of sugar under different conditions and compare dissolving rates. (I’ll make a note that this lab IS NOT about reaction rates.)
Materials Needed
- Graduated cylinders
- Beakers
- Stirring rods
- Sugar cubes
- Pre-measured sugar samples (2.5 grams each)
Procedure
Students will do trials for each of the following.
- Surface Area:
- Place equal amounts of water in two beakers.
- Add a sugar cube to one beaker and granulated sugar to the other. (They love the sugar cubes for some reason.)
- Observe which dissolves more readily, discussing how surface area impacts solubility.
- Temperature:
- Prepare warm water (20-30°C above tap temperature).
- Add equal amounts of water and sugar to two beakers.
- Compare the dissolution rates, emphasizing temperature’s role in solubility.
- Agitation:
- Using tap water, add sugar to two beakers.
- Stir one solution and leave the other unstirred.
- Discuss how agitation affects the rate of dissolving.
- Concentration
- Add equal amounts of water to two beakers
- Add 2.5 grams of sugar to one beaker and 10 grams to the other
- After a few minutes, compare the amount of sugar dissolved in each beaker
Lab Set Up – Solubility Factors
I’ve done the set up a few different ways. I initially did this lab as a stations lab simply because I didn’t have enough stirring rods for each group of students to have their own, but once I got a full lab that wasn’t a problem.
So I give the kids graduated cylinders, 2 beakers, a stirring rod, a sugar cube and 5 pre-measured samples of sugar, weighing in at 2.5 grams. There aren’t enough balances for me to give one to every pair of students (I’d need 13 of them). This is especially hard when the other science teachers in the department are looking for the balances. It’s just easier for me to pre-measure the samples. The kids measure out the water in the graduated cylinders. We have the proper materials for this, and to be honest, my kids could use the practice.
Quick Tips
The Sugar Cube
I always try to get the sugar cube out of the way quickly. I find the students are absolutely fascinated with the sugar cube. Apparently it’s the little things in life.
Types of Data
While I prefer the qualitative data in this lab you can get quantitative data if you prefer. You could add in stopwatches to evaluate how much time it takes for a sample to dissolve. (But be prepared to have a max amount of time allotted since some of these samples can sit a long time before full dissolution.
Warming the Water
Any time I can skip the hotplate or Bunsen burner, I’m usually going to do it. In any lab I’ve had, I can only get hot water to run out of one sink. For that reason, I find it’s easier to heat water in my electrical kettle. I only warm the water 20 to 30 degrees warmer than the tap water to see the difference in dissolving rates. No ned to come to a full boil.
Student Led Teaching
My favorite part of this lab is having a kid “be the teacher.” This kid will get up in front of the room, makes sure everyone calls them Ms. or Mr. Whomever and teaches the factors that affect solubility. I like to pick a kid that needs a little extra love or attention. I’ve also been known to pick a trouble maker. It gets them to realize what it feels like to be a teacher.
One of the reasons this lab is so successful is because it’s pretty intuitive. The kids kind of know what the answers are supposed to be. The lab is really just to get them to solidify their preconceptions. It can also correct a few kids who may have something backwards.
Aside from supervising the lab and making sure nobody is getting hurt or doing the wrong thing, this is a pretty easy day for me. It’s a green chemistry lab. So I don’t have to worry much about the chemicals (just contamination from the equipment, really). You can read more about my green chemistry labs here.
You can get the specific lab form I use here. I hope this gives you an idea on how you can morph your factors that affect solubility lab or activity so that it’s easier on you! You can also read more about how my students write lab reports here, or skip the reading and just get a copy of the free lab rubric I use instead.
