Gather a large collection of household substances; cleaning products, health and beauty products, beverages, etc. (See below for a more detailed list).
To perform this experiment in a classroom, place a small amount of each substance into a small beaker. Label the substance, either with a label on the beaker or an index card next to the beaker. Place a stirring rod (or comparable tool) in each beaker.
Students will touch the stirring rod to a piece of pH paper. They will then consult the key that comes with the pH paper to determine the substance's pH (I have laminated several of the keys and try to tape one to the end of each lab table, so there's always one nearby and all students are crowded around one or two small pieces of paper).
By touching the stirring rod to the paper (as opposed to dipping the paper into the substance) students will be able to test 3 or 4 substances on each piece of pH paper.
After testing each substance and recording the pH, students can create a pH scale of household items.
Have your students look for patterns... foods, skin care products, cleaning products, etc.
What are the commonly used numbers on the pH scale? Are there any numbers that weren't used at all?
What results surprised your students?
Some substances you might* want your students to test:
toilet bowl cleaner
tea (regular and herbal)
plant acidifier (MirAcid)**
soap scum remover
saline solution (for contacts)
*Always use your best judgement and keep your school's policies in mind.
**Dissolve in water.