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The pH scale is used to measure how acidic or basic a solution is. Acids have a pH below 7; bases have a pH above. Neutral solutions (like distilled water) with a balanced number of H+ and OH- ions have a pH of 7. Do the following projects to explore the cool effects of pH.
Make ordinary water turn bright pink and then back to clear! This makes a great "magic trick" to impress your friends - just be careful no one mistakes it for fruit punch and drinks any!
>> Check out our project video to see this trick in action!
What to do:
Phenolphthalein is a pH indicator, but it only turns colors in reaction to bases. When you poured the four glasses back into the pitcher, the phenolphthalein reacted to the sodium carbonate, a base, and turned the solution to bright pink "kool-aid." To change it back to "water," all you had to do was add the acidic vinegar, which turned the phenolphthalein colorless again.
Rainbow Reaction Tube
Amaze your friends by mixing two solutions to make a rainbow! Watch as purple sinks to the bottom and red floats to the top, and they mix together to form every color in between.
What to do:
Universal indicator changes colors to show the pH level of a substance. In this case, when you mixed an acidic solution (vinegar) with a basic one (sodium carbonate), the indicator made a colorful spectrum – from dark blue to red. Interestingly, if you had added the solutions in the opposite order, you would not have seen a rainbow. To get the rainbow effect, another scientific principle is at work—density. The sodium carbonate solution you made is denser than the indicator solution, so it sinks to the bottom. As the sodium carbonate solution makes its way to the bottom, some of its molecules mix with vinegar molecules, making a new solution, which shows up as a color of the pH scale.
If you don’t turn the graduated cylinder upside down, the rainbow will last several days. Over time the colors will mix together through the process of diffusion. The molecules of each solution will mix throughout the graduated cylinder, rather than staying concentrated at the top or bottom. Once you mix the acid and base solutions together, the solution will be pH neutral, and look yellow or slightly green.
To make a different kind of rainbow tube, try making this rainbow density column with all household materials.
More Chemistry pH Projects:
Even though both hurt, bee stings and wasp stings are different! A bee sting is acidic, but a wasp sting is basic.
Most shampoos are acidic, to make hair smoother. Baby shampoos, though, have a neutral pH of around 7, so they are safe for babies and won't sting their eyes.
Visit Chem4Kids to learn more about the science behind pH.
Learn to make your own pH indicator out of red cabbage juice!
Play around with pH when you serve drinks to aliens in this fun online game.
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