Indicator Sponge – A Discrepant Event Demonstration from Flinn Scientific

The discrepant event of placing a red sponge in a red solution and having it turn blue is sure to capture your students’ attention and stimulate a lively discussion of possible explanations.

The indicator sponge is saturated with congo red solution. Congo red is a dye, a biological stain, and a pH indicator. It has been used as a direct fabric dye for cotton to produce a bright red fabric. Biologists use Congo red as a general contrast stain for cellulose. Congo red is also used as a pH indicator. The colour transition is between pH 3.0 and 5.0. Below a pH of 3.0 (very acidic solutions), the indicator is blue. Above pH 5.0, the indicator is red. When a cellulose sponge is soaked in a Congo red solution, the dye becomes permanently bonded to the cellulose fibers. The active acid/base sites on Congo red are still available and the sponge now becomes an indicator sponge for acids. It can also be used to check for acid spills on counters after students have used acids.

Click here to download the entire activity…

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The strengths and weaknesses of acids and bases – George Zaidan and Charles Morton

Vinegar may have a powerful smell, but did you know it’s actually a weak acid? In the chemical economy, acids actively give away their protons while bases actively collect them — but some more aggressively than others. George Zaidan and Charles Morton use the currency of subatomic particles to explain this unseen exchange.

Lesson by George Zaidan and Charles Morton, animation by Karrot Animation

Ted ED. The strengths and weaknesses of acids and bases – George Zaidan and Charles Morton

Vinegar may have a powerful smell, but did you know it’s actually a weak acid? In the chemical economy, acids actively give away their protons while bases actively collect them — but some more aggressively than others. George Zaidan and Charles Morton use the currency of subatomic particles to explain this unseen exchange.

Lesson by George Zaidan and Charles Morton, animation by Karrot Animation

pH Rainbow Tube Demonstration

The lesson here is a good one and it applies to all your favorite demonstrations—they make terrific inquiry labs for your students!

This video is part of the Flinn Scientific Best Practices for Teaching Chemistry Video Series, a collection of over 125 hours of free professional development training for chemistry teachers –http://elearning.flinnsci.com

ATTENTION: This demonstration is intended for and should only be performed by certified science instructors in a safe laboratory/classroom setting.