Acids and bases are one of my favorite units to teach. I think that’s because I really love solutions and find that bonding is a fairly easy unit for my students. (That’s taken years, by the way. It didn’t start out super easy.). And getting them to distinguish acids and bases has kind of been super fun for me. And I’ve found it to be even more fun to teach to my physical science students that are mostly new to chemistry concepts.
My Acid Base Back Story
Now, I’m not totally sure where this resource came from, but I know I got it from Teachers Pay Teachers. And I found that it had a major error. It was a set of slides that I bought, probably during my first year. It taught that acids and bases were both ionic. Because they dissociate in water. But really, that’s not true.
And me, being the first year teacher that was kind of drowning, slash kind of looking for shortcuts to make my life easier, taught it wrong. I just went with the slides really without looking at them. And those angel babies in my first year were kind enough to politely question me. And then I felt like an idiot.
Think of HCl for example: that’s obviously a covalent bond. Granted, chlorine is highly electronegative. But that doesn’t convert this into an ionic bond. Water doesn’t actually get this compound to dissociate. Instead, the compound is ionized by water. Mainly a difference in name, considering the result is the same.
Lucky(?) for me, I had the chance to teach this lesson again in my first year. (My first round of chemistry was VERY accelerated and squished into one semester.) And I looked to see if the resource was updated on TPT. And unfortunately it wasn’t. The slides were still wrong. So instead, I taught it myself with something I took the time to sit and create.
Distinguish Acids and Bases from Bond Type
With my kids having a good background in bonding, it was easy for me to lean into that for distinguishing acids and bases. Acids have covalent bonds and bases have ionic bonds. And that’s always where I have started. I’ll even take some time to break out the Ionic vs. Covalent card sort to give them a refresher on types of chemical bonds.
Then because they’ve already learned solutions, I talk about the very slight difference between dissociation and ionization. In dissociatiation, the molecule falls apart because it is attracted to charges on water molecules. In ionization, the molecule is attacked by water due to attraction from water molecules. Either way, the result is the same. An electrolyte!
Truly we start with acids and bases as formulas. And we’ll do my acid-base card sort. But at this point, they sort them based on the chemical formula ONLY.
Properties of Acids and Bases Comes Second
AND THEN I’ll teach them the properties of acids and bases. Like acids taste sour and bases are bitter. I’ve found that my kids are REALLY great with distinguishing acids and bases when I teach it in this way. Relying on their chemistry knowledge to guide them, works better for me than their real life knowledge.
Yeah, bleach is a base, and if you get it on your hands it can feel soapy. But not enough of my kids have been in this situation to make the connection. Bleach will burn a paper cut the same way lemon juice will. Plenty of kids have gotten soap in their eyes in the shower, but very few have had a squirt of lemon juice in their eye. I love pulling in real life knowledge and applications when I can, but I’ve found it’s really hard with acids and bases.
Plus the kids always think that acids are somehow more dangerous than bases. With the “formula first” method, it’s a lot easier to debunk those thoughts.
So for the properties, we will do another card sort. I actually prefer to teach this lesson with my chrome books and do it digitally. There’s a lot of cards and pieces otherwise. But considering I have class sets of these activities, it’s not so bad with physical cards either. Plus that allows a greater opportunity for kids to work together.
If you try the formula first method, let me know how it works out for you! I find it’s a great way to integrate some spiral review. Especially as we get closer to the final exam time. Click below to have me email you my list of spiral review strategies.
