Last week I posted asking for votes on if you’d like to have instructions for doing the Cabbage Juice Lab at home and overwhelmingly y’all said YES! So here it is! The cabbage juice lab is a way to test solutions that you have around the house for their pH level! The science is so cool as a natural way to determine if something is an acid or a base! Kids love this demonstration/activity because of the WOW effect of solutions changing colors from clear to pink, green, blue or yellow! Simple to do at home and you’ll have a lot of fun! Read below for the science behind this activity and how to do it safely!
You know what they say… safety first! So here is the low down when doing this activity/demonstration at home with kids. Working with any strong chemical, especially a liquid and especially an acidic solution or a basic solution comes with hazards. It’s always a good idea to protect your eyes and your hands/skin. If you have any type of safety goggles, I suggest wearing them, or be cautious when pouring and handling these substances. While they are all “find at home” chemicals and solutions, they shouldn’t be played with. Additionally, I wouldn’t mix anything hastily as you can never be too sure how it will react. If you plan on doing this at home with younger children, I’d do it as a demonstration and let them participate by making predictions, choosing what to test and/or let them pour the cabbage juice (which is very safe). Let’s leave the pouring of the tested chemical solutions to adults or older children. I did this lab with 7th and 8th graders and would totally trust them to handle everything carefully. You know your kids at home and what they can handle with supervision so make the best choice for you. 🙂
All this being said, this activity is very safe as long as materials are handled carefully, not drank, inhaled or poured over your body and into your eyes ;). Common sense – I hope!
What in the world is this about!? Lessons for you and your kids:
Solutions have a physical property called pH or “Potential of Hydrogen” which measures the amount/concentration of hydrogen ions in the solution. The concentration of hydrogen ions in the solution will determine how acidic it is. Additionally, if there is a presence of hydroxide ions (OH-) then the solution will be more alkaline or “basic”. The pH scale measures how acidic or basic a solution is with distilled water being perfectly in the middle at neutral. Acids and Bases are on opposite sides of the scale and range in intensity from a numerical pH value of 0 – 14. (See below)
WHY is water (distilled) perfectly neutral?! Well if you take a hydrogen ion (H+) (acid) and combine it with a hydroxide ion (OH-) (base) then you have two hydrogen atoms bonded with one oxygen atom. Famously known as H2O or water! You’ll notice that the positive and negative ions cancel out and form a neutral compound which is neither acidic or basic and has a pH of 7!
But back to Acids and Bases. Acids and Bases are opposite of each other on the pH scale and have very different properties. Acids often times are corrosive and eat away at materials (especially metals). Bases are commonly used in cleaning materials but don’t be fooled, strong bases are just as dangerous as strong acids. When you combine the two they go through a “Neutralization Reaction” that produces water and a byproduct of salt. To learn even more you can check out my old slideshow on acids and bases here.
Here are some examples of Acids and Bases and where they lie on the pH scale. Remember the further away from neutral they are the more powerful and potentially dangerous they are.
SO WHAT’S THIS HAVE TO DO WITH CABBAGES?! Well! Cabbages (red cabbages) have a chemical in them that when extracted can act as a NATURAL INDICATOR! Meaning it can determine if something is an acid or a base! HOW you may ask!? Well, it changes the color depending on the solution! THIS is where the fun is for you at home!
Depending on if the solution is an acid, a base or neutral it will change colors according to this chart below:
That’s right! IF your solution is acidic it will change into a pink or red color (depending on how acidic). It is it more alkaline or basic then it will change to either blue, teal green or bright yellow (depending on how strong of a base it is).
SO LET’S GET STARTED AT HOME!
- Red (purple) cabbage
- Water & large pot for boiling
- Knife for cutting cabbage
- Spoons (at least two)
- Plastic Cups
- Large pitcher
- Acid and Base solutions found at home. Consider using testing the following:
- Lemon Juice
- Apple Juice
- Soda (sprite or clear may be best)
- Baking soda: Take a cup of warm water and stir a fair amount into the water. It may settle to the bottom, just stir well before combining with cabbage juice.
- Powdered laundry detergent: same directions as above
- Ammonia: Handle with CARE!
- Bleach: Handle with CARE!
- Sugar Solution: Mix similarly to baking soda
- Hand sanitizer
- Dish Soap
STEP ONE: Make Cabbage Juice!
Note: This will smell! BUT the smell will go away quickly, just open some windows 🙂
Take your red (purple) cabbage and chop it into chunks. No need to be precise here but I wouldn’t chop too small because it’s annoying to strain out. You can also peel the leaves and rip it into pieces. See the image below.
Next put the chopped cabbage into a pot and fill with enough water to cover the cabbage. Set stove-top to high and allow the water to boil. Boil the cabbage until the liquid is dark purple and the leaves look very pale and have lost their purple color (they will look pale purple to gray).
Now take the cabbage mixture off the heat and turn off the stove. Allow to cool a bit and then strain out the cabbage leaves. Pour your cabbage juice into a large pitcher or container and place in the fridge until cool.
STEP TWO: Prepare the solutions
In separate cups or containers prepare the solutions you wish to test. I like to use solo cups and then mark the cups with Sharpie so I remember which solution is which. Remember that if you choose to test Ammonia and/or Bleach, they have a very strong odor and should be carefully handled. DO NOT directly inhale these fumes or ingest and be careful when handling to avoid skin contact.
STEP THREE: Prepare the space and brains!
Before doing this demonstration I’d put something down on the table to protect it. A plastic table cloth or even some trash bags will work just fine. :).
If you are doing this with kids prepare them for what they are going to see by teaching them a little about acids and bases! Tell them that acids will turn pink or red and bases will turn blue, green or yellow. You can have them look at the solutions you’re going to test and predict what they think each will be!
If you feel it necessary and have these materials available, go ahead and put on your safety gear! Eye goggles and gloves are always a good idea and teach kids that we don’t “play” with chemicals, we treat them carefully because they can be dangerous.
STEP FOUR: Test your solutions!
In separate cups or glasses pour in some of your chilled cabbage juice. (One cup of cabbage juice for each solution your testing)
Now test each solution separately by pouring it into the separate cup of cabbage juice and watch the colors change! Keep track of each result! You could also try and to line them up and determine where they are on the pH scale! Which solution is the most acidic? Which solution is the most basic?
EXTENSION: Neutralization Reaction!
Now that you’ve test all of your solutions you can try to mix an acid and a base! A safe way to do this is to mix the baking soda solution and the vinegar. Grab a large clear bowl or a larger clear cup/glass. Ask yourself or your kids what will happen when you mix an acid and a base together?! What color would the mixture be? The green/blue baking soda and the pink vinegar will not only create a gas and bubble up in a dramatic fashion but because the product is NEUTRAL the color will turn back to PURPLE!
The good news about clean up is that it’s easy! Just dispose of the solutions the way you normally would. So if you don’t normally pour bleach down the drain then don’t pour the bleach solution down the drain. :). The reason I use plastic cups versus glasses is very simply that I like how easy it is to clean up.