I found this experiment online where students add vinegar to different solids. I remember doing this as a child and finding it fascinating. Actually I used to enjoy anything involving mixing, combining and observing. I have fond memories of my sister and I using various bathroom products to make concoctions in our sink, similar to George in Georges's Magic Medicine, although we never fed it to our grandmother.
We did this experiment on Monday and I will have pictures to follow, but if you want to do this with your class, feel free to use the experiment template I created to go with it.