Wednesday, March 6, 2013

pH Cabbage indicator tutorial and labs

Cabbage Juice as a pH indicator: Tutorial and tips for pH labs from STEM Mom

Although pH paper won't break the bank, it is easy to make a pH indicator solution (or paper) from supplies you can get at your local grocery. What you need:

  • red cabbage
  • filter paper or coffee filters 
  • boiling water
  • pot
  • strainer

I've taken a lot of photos, because red cabbage is absolutely beautiful! But really, making the solution as easy as boiling a cabbage and using the water as the indicator! 

Steps to Make Cabbage Indicator Solution


Cut cabbage into small pieces: pH indicator lab from STEM Mom.or


  1. Dice 1/2-3/4 of a cabbage into small pieces and enjoy the beautiful color.  
Cut cabbage into small pieces: pH indicator lab from STEM Mom.or


2.  Boil water in the microwave or on the stove.
3.  Pour boiling water over the cut cabbage and allow to steep until room temperature.

Steep cabbage in boiling water to make pH indicator solution: STEM mom.org

Steep cabbage in boiling water to make pH indicator solution: STEM mom.org



4.  Strain cabbage through a strainer so only the purple liquid remains. You may chose to filter the cabbage/water solution through a coffee filter in addition to straining. 

Strain cabbage to isolate purple indicator water; from STEMmom.org


Strain cabbage to isolate purple indicator water; from STEMmom.org


5. Reserve the purple liquid for experimentation. I store my excess cabbage juice in an empty plastic peanut butter container with a tight lid. 


Labs Using Cabbage pH Indicator 


Its best to set students up to experience the whole pH spectrum. While you could TELL them about the differences between acids and bases, I believe its best to let them experience the color changes in an inquiry-based lab, and allow them ask questions naturally, so they actually want to know why there are differences. 

Therefore, I suggest providing students with the following materials to test and record:

  • lemon juice
  • white distilled vinegar
  • water
  • baking soda
  • washing soda (or ammonia) 

Boy testing pH of lemon using cabbage indicator; STEMmom.org

Start the laboratory experience by determining the scope of the pH scale. You do this by using the materials listed above.  

Pour the cooled cabbage indicator solution into test tubes or small jars. We used glass baby food jars which worked great because they don't tip easily, and any color change is easily noticeable. So we poured cabbage juice (which does have an odor you will notice) into each of the 5 jars. Then we created a data table that looked like this. However, I provide a free student lab sheet at the bottom of this post if you want something quick.

Entering data for pH lab using cabbage indicator: STEMmom.org

 
Since I am working with a five-year old, I made the table, and had colored pencils and crayons  available for him to use to record data.  He poured, squeezed, and dabbled the lemon juice, vinegar, water, baking soda, and washing soda, into the baby food jars one at a time and got amazingly different results; visible by stark color differences. 


Washing soda for pH cabbage lab: from STEMmom.org

FYI: crayons were great to use, Caleb, my 5-year old could look at the solution, and search for a crayon that matched, and use that to fill in his data table. The goal here was to create a scale on which we could base all of the miscellaneous tests we wanted to do. 

Boy mixing baking soda; pH indicator lab from STEM Mom.org

Here is what our baseline comparison tests look like: 
  • Lemon Juice = pink
  • Vinegar = red
  • Water = no change, purple
  • Baking soda = blue
  • Washing soda = green 
  • Bleach or drain cleaner = yellow/white


pH Baseline comparison using cabbage indicator

We had all our baby food jars all lined up in order from lowest (acid) to highest (base) and then began our own testing sessions. I had Caleb choose items and then predict whether he thought it would be acidic like lemon juice, neural like water, or basic like washing soda. That made it a game and kept us moving through the activity (Disclaimer: I've cropped out the Lego Minifigures that were a constant distraction throughout the lab...) 

Data recording for pH lab: STEMmom.org

Baseline of colors for pH lab using cabbage indicator: from STEMmom.org

Once we had our baseline pH jars set up, we picked items from the refrigerator, cabinet, and bathroom to compare. I poured the sample solutions we wanted to test into the test tubes, and had my son use a dropper to add the cabbage indicator solution. We were not picky about how many drops etc...but if you teach older kids, keeping volumes constant is a good idea.    

Lab Set Up for pH cabbage lab: from STEMmom.org

Additional Materials to have on hand:
  • Test tubes (not essential, but cool)
  • droppers
  • lab notebook and pencil

Boy with test tube; pH indicator lab from STEM Mom.org

We tested:
  • milk = purple = neutral
  • canned mandarin orange syrup = pink = acid
  • bleach = white = base (off our scale, completely removed the purple)
  • window cleaner = green = base
  • liquid soap = pink = acid 


Boy with dropper and pH lab: STEMmom.org

Other ideas of items to test (but allow your kids make the final decision):
  • cream of tartar 
  • ammonia
  • antacids
  • soapy water
  • salty water
  • rain
  • oven cleaner
  • cleaning solutions
  • soda (pops) clear is better
  • oranges/orange juice

NOTE: Some of these suggested materials are dangerous. Make sure the children know the dangers of the chemicals, and handle them with care.  


Compare tests to cabbage baseline pH scale; from STEMmom.org



Boy smiling with colored solutions in 2 test tubes; pH lab from STEMmom.org

I'm not usually about going out and buying items you'll only use once or twice, but I couldn't believe the difference it made to have test tubes for this lab! We've used baby food jars before, and I guess they aren't that impressive to a 5 year old. But when he saw the test tubes, in a holder, with rubber stoppers, he was "all about" the science experiment. (He even tried to make a white lab coat by taping together computer paper...cute right?) He couldn't wait to pour liquids into and out of these narrow tubes. He also was super excited about the droppers (that I got for free). So I guess what I am saying, is that you would consider having these "science-y" things around so kids feel more like a real scientist.   

Colored solutions in test tubes for pH test with cabbage; from STEMmom.org

 Storage of Cabbage pH Indicator

I have poured the excess cabbage juice pH indicator solution into an empty plastic peanut butter container. I will update you as to how well the indicator does over time. (You need to read my update, because storing the cabbage solution in plastic does NOT work.) And the DIY pH papers can be stored in a paper envelope, as long as the envelope is kept dry and out of light. I have posted a tutorial on how to make the pH papers, which will make storage a bit easier. 

Storing cabbage pH indicator solution and DIY pH paper: from STEMmom.org



DIY Cabbage Indicator solution: via STEMmom.org

I've made a student worksheet to accompany this lab. It would work for elementary and middle level. 


Free download of student worksheet for a cabbage pH indicator lab: from STEMmom.org

 Resources for Cabbage pH Lab


I believe this YouTube video Using Cabbage as a pH indicator was done by a couple of college kids, and does a good job of showing how to make the indicator, as provide in real-time examples of the purple changing colors along the entire pH spectrum.

Science Buddies: Describes how to use cabbage (and other plant materials) as indicators.

You can even make pH filter paper that function like the pH papers you would buy at a science supply store.

If you like this post on pH: you'll like the posts I've done since:

DIY pH Paper using Cabbage Juice and Coffee Filters
Baseline pH Scale to Use on the Field  


Enjoy
Darci the STEM Mom




3 comments:

  1. Hi, found your site through Adventures in Mommydom's Science Sunday linky. Love it! We did this experiment as well (I have two boys, 4 and 7). I adjusted it to show both their school classes, preschool and second grade. I love your website, and definitely will be checking out your book! :) (here's our experiment and results: http://blog.anportraits.com/2013/03/02/learning-about-acids-and-bases-seattle-area-lifestyle-photographer/)

    ReplyDelete
    Replies
    1. So great to connect with you. Your photos of this lab are beautiful, and so are your kids. Doesn't the love of photography blend so nicely with blogging? Thanks so much for commenting.

      Darci

      Delete
  2. I was gonna comment that a friend of mine used to always use the coffee filter she strained it with for ph paper, but then I saw your link further down........

    Thanks for linking up to Science Sunday!

    ReplyDelete

I love comments! Would love to know you were here! :)

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