Since we’re all doing public service and keeping each other safe against COVID by staying home, we thought we should launch a series of at-home experiments you can do with items you can find on your weekly resupply trip to the store. While we have done these experiments at our events, we challenge you to kick it up a notch, add your own unique *pizzazz*, and share your spin on these experiments with the community. Science – but make it fancy.
To kick things off, we are going to explore the chemistry of acidity using everyone’s favorite vegetable, *checks notes…* red cabbage. Some would argue it’s best served sauteed, while others would argue it’s better served cold. We think it’s best served as a pH indicator after you run out of on-demand content.
Red cabbages, like blueberries and many other red or blue fruits and veggies, contain a class of pigments called anthocyanins. The anthocyanins in red cabbages are interesting because they can change color in the presence of an acid or a base. Adding acidity to a slurry of red cabbage anthocyanins makes the pigment turn red. In contrast, adding a base to the same solution turns it blue, green, or yellow depending on the strength of the base. This is because the pigment breaks down at higher pH, or less acidity (see figure below), which causes it to change color. An increase in acidity, or lower pH, stabilizes the pigment again. You can try this at home by boiling or blending some red cabbage and adding the resulting liquid to different household items that you might consider acidic or basic. What happens when you add it to vinegar? Lemon juice? Dish soap? The color change will tell you whether it’s an acid or base!
Let’s break this down even further. What even is an acid or a base? Scientists actually classify acids and bases in several different ways, so let’s focus on just one. You may remember from high school science, potentially in a dusty corner in your brain you haven’t used in years, that molecules are made up of positively charged protons, chargeless neutrons, and negatively charged electrons. Acids, in this definition, are molecules dissolved in water that give away protons, while bases accept new protons. Because strong acids really want to give away a proton, they easily react with the materials around them, like cloth, a table, or human flesh (ouch!). The opposite is true for strong bases, with similarly damaging consequences. In practical use, this explains why strong acids and strong bases tend to be extremely corrosive. (But don’t worry, none of the materials we work with today are that harsh.) We use the measurement scale we mentioned earlier, pH (or “power of hydrogen”), to describe the strength of an acid or base. Low numbers on the scale are more acidic, and high numbers are basic, with a neutral value of 7. It’s also a logarithmic scale, which means that every integer decrease on the scale is actually a ten-fold increase in concentration of protons in solution. So, sulfuric (or battery) acid with a pH of 1 is 10,000,000, or 10^7, times as acidic as water with a neutral pH of 7!
**PIZZAZZ TIME** Let’s take this concept, jazz it up a bit, and use it to make–a lava lamp! To do this you’ll need the following scientific protocol.
Ingredients needed:
- That red cabbage you bought (for science!)
- Alka-Seltzer tablets (for post-holiday meal ease)
- A clear jar or bottle
- Cooking oil
- Water
- (Optional) We would recommend some glitter if it weren’t for microplastic pollution, so maybe shiny biodegradable confetti?
Pizzazz protocol:
- Make a purple-ish blue cabbage juice by boiling cabbage leaves or blending and straining them.
- Fill your jar or bottle a third of the way full with cabbage juice (delicious).
- Fill another third of the way up with water.
- Fill the rest of the way up with oil. Due to the hydrophobic nature of the oil, it will not mix well with the water. Add not-glitter if desired.
- Finally, drop in an Alka-Seltzer tablet.
Watch the oil move around due to the fizzing of the Alka-Seltzer and also watch the lamp change color! We added an acid, so it will turn red or pink! (Alka-Seltzer is a combination of sodium bicarbonate, which can act as an acid or a base, citric acid, and aspirin–also known as acetylsalicylic acid.)
Let’s also think about the implications of acid-base chemistry in biology. A lot of biological and environmental processes are sensitive to changes in acidity. Many plants, for example, grow best in a specific pH range. Our planet’s oceans are also rapidly becoming more acidic due to increased carbon dioxide dissolution, which has disastrous effects on coral reefs and other marine ecosystems. We must have ways to measure pH to quantify these problems, and although they’re a bit more sophisticated than cabbage juice, they operate on the same principles.
There you have it! Have fun with your color-changing lava lamp and stay tuned for more home experiments! If you try out your own cabbage pH indicator, share a video with us in the comments or on social media and tag us @ChiTownBio!