Home School Life Journal

Home School Life Journal
"Let us strive to make each moment beautiful."
Saint Francis DeSales
painting by Katie Bergenholtz

Science Investigations that all students should do Before High School, #2: Acid and Base Explorations

#2: Acid and Base Explorations
If you take half a head of purple cabbage and simmer it a few minutes in enough water to fully cover it, you can get a two-liter bottle of acid/base indicator liquid. You can use this liquid directly in clear cups or you can soak absorbent paper in it and then let it dry to make test strips which can be dipped in test liquids. The absorbent paper can be paper towels or coffee filters.Because this provides so much indicator liquid, you can feel free to do lots of things with it without running out. I like to begin with letting my younger boys experiment on their own with it. I give them a container of water with baking soda mixed in, a small bottle of vinegar and a container of cabbage indicator. I tell them that they can do whatever experimenting they want with it except they cannot eat any of these materials. I know they are all non-toxic, but they are not particular good just to drink and it sets a good precedent for the chemicals they will use later on in chemistry.

We had cups of lemon juice, vinegar, water with baking soda dissolved in it, water with crushed Tums mixed in and milk. We talked about each of these liquids and whether they tasted sour or not.

Then we used our indicator to determine whether the liquid was an acid or a base. They could easily see that all the ingredients that were sour also turned pink, indicating that they were acids.The liquids that were slippery when you rubbed them between your fingers turned green and were bases.
I encouraged them to experiment with the liquids and indicator, pouring the contents of one cup into another and they discovered that after much experimentation that all of the cups turned a purple, and indicated that they had neutralized and were not either base nor acid.
And so they mixed and poured...

and experimented.

and exclaimed over the color changes...

and bubbles.

It captivated their attention for quite some time.



 Now that they have experimented on their own, I can now tell them about how the indicator works. I have them mix the indicator with a known acid (white vinegar) and a known base (ammonia) and a known neutral liquid (milk) so that they could have color coding to refer to as they tested other unknown liquids. 
They were eager to find out what colors meant what about the pH of the liquids because they had already experimented until they were satisfied. They were ready to find out what it all meant now.

 So we tested some unknown liquids and put them in the correct categories.
Reading Real Science 4 Kids Chemistry, Level I.
 Now that we had enough data, we could look at what made the acids similar, what made the bases similar and what were the differences between the two. They came up with the ideas and I helped them put it in more scientific language. Quentin started first with the tastes, the textures. James added what he had remembered from what we read about pH and covalent compounds. Sam added additional information of precipitates and how acids and bases turn into salts and water when combined. They all talked about how acids contained hydrogen atoms (H), and bases have a oxygen and hydrogen atom combination (OH).



Using a funnel fill a large balloon with baking soda (about 2 Tablespoons).
Put about 3/4 cup of white vinegar in an empty 2-liter bottle.
Pour about 1/2 cup of the cooled "red" cabbage juice in the 2-liter bottle with the vinegar (leave the leaves out). The vinegar should change the color of the cabbage juice from purple to pink or red.

Slip the balloon's neck over the 2-liter's neck without dropping in the baking soda as much as you can.
When you are ready, dump the baking soda into the bottle by lifting the balloon. The chemical reaction between the baking soda and the vinegar creates carbon dioxide and water. The carbon dioxide inflates the balloon and the neutralizing of the vinegar's acid changes the cabbage juice's color from pink back to purple...

and then to blue. The photo makes it look more purple than it did in real life.
The baking soda then turns the liquid to a base, and turns the cabbage juice to a blue color.
The anthocyanin in the cabbage makes it an acid/base indicator.

6 comments:

  1. We are continually on the same page :)

    ReplyDelete
  2. Oh my goodness, now I really want to do that..... Maybe I'll add a head of cabbage to my grocery list this week.

    ReplyDelete
  3. Happy, happy birthday Phyllis.

    ReplyDelete
  4. The red cabbage PH is on my list to do, but Leah's pomegranate one sounds interesting too. I wonder which one is stronger...

    ReplyDelete
  5. I didn't know about the slipperiness. I just love the way you do and share about science.

    ReplyDelete
  6. Acid and base explorations are great science investigations - I'm looking forward to the rest of this series!

    ReplyDelete

Thank you so much for taking the time to comment. It means so much.